FACTOID # 26: Delaware is the latchkey kid capital of America, with 71.8% of households having both parents in the labor force.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "Helium" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Helium
hydrogenheliumlithium
-

He

Ne
Appearance
Colorless gas, exhibiting a purple glow when placed in a high voltage electric field
General properties
Name, symbol, number helium, He, 2
Pronunciation /ˈhiːliəm/, HEE-lee-əm
Element category noble gases
Group, period, block 181, s
Standard atomic weight 4.002602(2) g·mol−1
Electron configuration 1s2
Electrons per shell 2 (Image)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
0.1786 g/L
Melting point (at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Boiling point 4.22 K, −268.93 °C, −452.07 °F
Critical point 5.19 K, 0.227 MPa
Heat of fusion 0.0138 kJ·mol−1
Heat of vaporization 0.0829 kJ·mol−1
Specific heat capacity (25 °C) 20.786 J·mol−1·K−1
Vapor pressure (defined by ITS-90)
P/Pa 1 10 100 1 k 10 k 100 k
at T/K     1.23 1.67 2.48 4.21
Atomic properties
Electronegativity no data (Pauling scale)
Ionization energies 1st: 2372.3 kJ·mol−1
2nd: 5250.5 kJ·mol−1
Covalent radius 28 pm
Van der Waals radius 140 pm
Miscellanea
Crystal structure hexagonal close-packed
Magnetic ordering diamagnetic[1]
Thermal conductivity (300 K) 0.1513 W·m−1·K−1
Speed of sound 972 m/s
CAS registry number 7440-59-7
Most stable isotopes
Main article: Isotopes of helium
iso NA half-life DM DE (MeV) DP
3He 0.000137%* 3He is stable with 1 neutron
4He 99.999863%* 4He is stable with 2 neutrons
*Atmospheric value, abundance may differ elsewhere.

Helium is the chemical element with atomic number 2 and an atomic weight of 4.0026, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Next to hydrogen, it is the second most abundant element in universe, and accounts for 24% of the elemental mass of our galaxy. Helium may refer to: Helium, the chemical element Helium-3, an isotope of helium Helium-4, an isotope of helium Helium (band), a rock band See also Helium dating, a method of age determination Helium flash, a stage of stellar evolution Helium fusion, a type of nuclear fusion Category: ... This article is about the chemistry of hydrogen. ... This article is about the chemical element. ... For other uses, see Neon (disambiguation). ... This article is about the chemistry of hydrogen. ... This article is about the chemical element. ... General Name, symbol, number beryllium, Be, 4 Chemical series alkaline earth metals Group, period, block 2, 2, s Appearance white-gray metallic Standard atomic weight 9. ... For other uses, see Boron (disambiguation). ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... This article is about the chemical element and its most stable form, or dioxygen. ... Distinguished from fluorene and fluorone. ... For other uses, see Neon (disambiguation). ... For sodium in the diet, see Salt. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, symbol, number aluminium, Al, 13 Chemical series poor metals Group, period, block 13, 3, p Appearance silvery Standard atomic weight 26. ... Not to be confused with Silicone. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... This article is about the chemical element. ... General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... For other uses, see Calcium (disambiguation). ... General Name, symbol, number scandium, Sc, 21 Chemical series transition metals Group, period, block 3, 4, d Appearance silvery white Standard atomic weight 44. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery grey-white metallic Standard atomic weight 47. ... General Name, symbol, number vanadium, V, 23 Chemical series transition metals Group, period, block 5, 4, d Appearance silver-grey metal Standard atomic weight 50. ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... Fe redirects here. ... For other uses, see Cobalt (disambiguation). ... For other uses, see Nickel (disambiguation). ... For other uses, see Copper (disambiguation). ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... Not to be confused with Galium. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Standard atomic weight 72. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... For other uses, see Selenium (disambiguation). ... Bromo redirects here. ... For other uses, see Krypton (disambiguation). ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Standard atomic weight 85. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... General Name, Symbol, Number yttrium, Y, 39 Chemical series transition metals Group, Period, Block 3, 5, d Appearance silvery white Standard atomic weight 88. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... General Name, Symbol, Number niobium, Nb, 41 Chemical series transition metals Group, Period, Block 5, 5, d Appearance gray metallic Standard atomic weight 92. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Standard atomic weight 95. ... General Name, Symbol, Number technetium, Tc, 43 Chemical series transition metals Group, Period, Block 7, 5, d Appearance silvery gray metal Standard atomic weight [98](0) g·mol−1 Electron configuration [Kr] 4d5 5s2 Electrons per shell 2, 8, 18, 13, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number Ruthenium, Ru, 44 Chemical series transition metals Group, Period, Block 8, 5, d Appearance silvery white metallic Standard atomic weight 101. ... General Name, Symbol, Number rhodium, Rh, 45 Chemical series transition metals Group, Period, Block 9, 5, d Appearance silvery white metallic Standard atomic weight 102. ... For other uses, see Palladium (disambiguation). ... This article is about the chemical element. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ... General Name, Symbol, Number indium, In, 49 Chemical series poor metals Group, Period, Block 13, 5, p Appearance silvery lustrous gray Standard atomic weight 114. ... This article is about the metallic chemical element. ... This article is about the element. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ... For other uses, see Iodine (disambiguation). ... General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... For other uses, see Barium (disambiguation). ... General Name, Symbol, Number lanthanum, La, 57 Chemical series lanthanides Group, Period, Block 3, 6, f Appearance silvery white Atomic mass 138. ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 140. ... General Name, Symbol, Number praseodymium, Pr, 59 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance grayish white Standard atomic weight 140. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Standard atomic weight 144. ... General Name, Symbol, Number promethium, Pm, 61 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance metallic Atomic mass [145](0) g/mol Electron configuration [Xe] 4f5 6s2 Electrons per shell 2, 8, 18, 23, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number samarium, Sm, 62 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 150. ... General Name, Symbol, Number europium, Eu, 63 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 151. ... General Name, Symbol, Number gadolinium, Gd, 64 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 157. ... General Name, Symbol, Number terbium, Tb, 65 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 158. ... General Name, Symbol, Number dysprosium, Dy, 66 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 162. ... General Name, Symbol, Number erbium, Er, 68 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 167. ... General Name, Symbol, Number thulium, Tm, 69 Chemical series lanthanides Group, Period, Block ?, 6, f Appearance silvery gray Atomic mass 168. ... Yb redirects here; for the unit of information see Yottabit General Name, Symbol, Number ytterbium, Yb, 70 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 173. ... General Name, Symbol, Number lutetium, Lu, 71 Chemical series lanthanides Group, Period, Block n/a, 6, d Appearance silvery white Standard atomic weight 174. ... General Name, Symbol, Number hafnium, Hf, 72 Chemical series transition metals Group, Period, Block 4, 6, d Appearance grey steel Standard atomic weight 178. ... General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Standard atomic weight 180. ... For other uses, see Tungsten (disambiguation). ... General Name, Symbol, Number rhenium, Re, 75 Chemical series transition metals Group, Period, Block 7, 6, d Appearance grayish white Standard atomic weight 186. ... General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Standard atomic weight 190. ... This article is about the chemical element. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... This article is about the element. ... General Name, Symbol, Number thallium, Tl, 81 Chemical series poor metals Group, Period, Block 13, 6, p Appearance silvery white Standard atomic weight 204. ... General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous pink Standard atomic weight 208. ... General Name, Symbol, Number polonium, Po, 84 Chemical series metalloids Group, Period, Block 16, 6, p Appearance silvery Standard atomic weight (209) g·mol−1 Electron configuration [Xe] 6s2 4f14 5d10 6p4 Electrons per shell 2, 8, 18, 32, 18, 6 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number astatine, At, 85 Chemical series halogens Group, Period, Block 17, 6, p Appearance metallic (presumed) Standard atomic weight (210) g·mol−1 Electron configuration [Xe] 4f14 5d10 6s2 6p5 Electrons per shell 2, 8, 18, 32, 18, 7 Physical properties Phase solid Melting point 575 K... For other uses, see Radon (disambiguation). ... General Name, Symbol, Number francium, Fr, 87 Chemical series alkali metals Group, Period, Block 1, 7, s Appearance metallic Standard atomic weight (223) g·mol−1 Electron configuration [Rn] 7s1 Electrons per shell 2, 8, 18, 32, 18, 8, 1 Physical properties Phase  ? solid Density (near r. ... For other uses, see Radium (disambiguation). ... General Name, Symbol, Number actinium, Ac, 89 Chemical series actinides Group, Period, Block 3, 7, f Appearance silvery Standard atomic weight (227) g·mol−1 Electron configuration [Rn] 6d1 7s2 Electrons per shell 2, 8, 18, 32, 18, 9, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... General Name, Symbol, Number protactinium, Pa, 91 Chemical series actinides Group, Period, Block n/a, 7, f Appearance bright, silvery metallic luster Standard atomic weight 231. ... This article is about the chemical element. ... General Name, Symbol, Number neptunium, Np, 93 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery metallic Standard atomic weight (237) g·mol−1 Electron configuration [Rn] 5f4 6d1 7s2 Electrons per shell 2, 8, 18, 32, 22, 9, 2 Physical properties Phase solid Density (near r. ... This article is about the radioactive element. ... General Name, Symbol, Number americium, Am, 95 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white sometimes yellow Standard atomic weight (243) g·mol−1 Electron configuration [Rn] 5f7 7s2 Electrons per shell 2, 8, 18, 32, 25, 8, 2 Physical properties Phase solid Density (near... General Name, Symbol, Number curium, Cm, 96 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery Atomic mass (247) g/mol Electron configuration [Rn] 5f7 6d1 7s2 Electrons per shell 2, 8, 18, 32, 25, 9, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number berkelium, Bk, 97 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (247) g·mol−1 Electron configuration [Rn] 5f9 7s2 Electrons per shell 2, 8, 18, 32, 27, 8, 2 Physical properties Phase solid... General Name, Symbol, Number californium, Cf, 98 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery Standard atomic weight (251) g·mol−1 Electron configuration [Rn] 5f10 7s2 Electrons per shell 2, 8, 18, 32, 28, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number einsteinium, Es, 99 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Standard atomic weight (252) g·mol−1 Electron configuration [Rn] 5f11 7s2 Electrons per shell 2, 8, 18, 32, 29, 8, 2 Physical properties Phase... General Name, Symbol, Number fermium, Fm, 100 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (257) g·mol−1 Electron configuration [Rn] 5f12 7s2 Electrons per shell 2, 8, 18, 32, 30, 8, 2 Physical properties Phase solid... General Name, Symbol, Number mendelevium, Md, 101 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (258) g·mol−1 Electron configuration [Rn] 5f13 7s2 Electrons per shell 2, 8, 18, 32, 31, 8, 2 Physical properties Phase solid... General Name, Symbol, Number nobelium, No, 102 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (259) g/mol Electron configuration [Rn] 5f14 7s2 Electrons per shell 2, 8, 18, 32, 32, 8, 2 Physical properties Phase solid Melting... General Name, Symbol, Number lawrencium, Lr, 103 Chemical series transition metals Group, Period, Block n/a, 7, d Appearance unknown, probably silvery white or metallic gray Standard atomic weight [262] g·mol−1 Electron configuration [Rn] 5f14 6d1 7s2 Electrons per shell 2, 8, 18, 32, 32, 9, 2 Physical... General Name, Symbol, Number rutherfordium, Rf, 104 Chemical series transition metals Group, Period, Block 4, 7, d Standard atomic weight (265) g·mol−1 Electron configuration probably [Rn] 5f14 6d2 7s2 Electrons per shell 2, 8, 18, 32, 32, 10, 2 Physical properties Phase presumably a solid Density (near r. ... General Name, Symbol, Number dubnium, Db, 105 Chemical series transition metals Group, Period, Block 5, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (262) g/mol Electron configuration perhaps [Rn] 5f14 6d3 7s2 (guess based on tantalum) Electrons per shell 2, 8, 18, 32, 32, 11... General Name, Symbol, Number seaborgium, Sg, 106 Chemical series transition metals Group, Period, Block 6, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (266) g/mol Electron configuration perhaps [Rn] 5f14 6d4 7s2 (guess based on tungsten) Electrons per shell 2, 8, 18, 32, 32, 12... General Name, Symbol, Number bohrium, Bh, 107 Chemical series transition metals Group, Period, Block 7, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (264) g/mol Electron configuration perhaps [Rn] 5f14 6d5 7s2 (guess based on rhenium) Electrons per shell 2, 8, 18, 32, 32, 13... General Name, Symbol, Number hassium, Hs, 108 Chemical series transition metals Group, Period, Block 8, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (269) g/mol Electron configuration perhaps [Rn] 5f14 6d6 7s2 (guess based on osmium) Electrons per shell 2, 8, 18, 32, 32, 14... General Name, Symbol, Number meitnerium, Mt, 109 Chemical series transition metals Group, Period, Block 9, 7, d Appearance unknown, probably silvery white or metallic gray Standard atomic weight [276] g·mol−1 Electron configuration perhaps [Rn] 5f14 6d7 7s2 (guess based on iridium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number darmstadtium, Ds, 110 Chemical series transition metals Group, Period, Block 10, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (281) g/mol Electron configuration perhaps [Rn] 5f14 6d9 7s1 (guess based on platinum) Electrons per shell 2, 8, 18, 32, 32, 17... General Name, Symbol, Number roentgenium, Rg, 111 Chemical series transition metals Group, Period, Block 11, 7, d Appearance unknown, probably yellow or orange metallic Atomic mass (284) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s1 (guess based on gold) Electrons per shell 2, 8, 18, 32, 32, 18, 1... General Name, Symbol, Number ununtrium, Uut, 113 Chemical series presumably poor metals Group, Period, Block 13, 7, p Appearance unknown, probably silvery white or metallic gray Atomic mass (284) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p1 (guess based on thallium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number ununquadium, Uuq, 114 Chemical series presumably poor metals Group, Period, Block 14, 7, p Appearance unknown, probably silvery white or metallic gray Standard atomic weight [289] g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p2 (guess based on lead) Electrons per shell 2, 8... General Name, Symbol, Number ununpentium, Uup, 115 Group, Period, Block 15, 7, p Atomic mass (299) g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p3 (guess based on bismuth) Electrons per shell 2, 8, 18, 32, 32, 18, 5 CAS registry number 54085-64-2 Selected isotopes References... General Name, Symbol, Number ununhexium, Uuh, 116 Chemical series presumably poor metals Group, Period, Block 16, 7, p Appearance unknown, probably silvery white or metallic gray Atomic mass (302) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p4 (guess based on polonium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number ununseptium, Uus, 117 Chemical series presumably halogens Group, Period, Block 17, 7, p Appearance unknown, probably dark metallic Standard atomic weight predicted, (310) g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p5 (guess based on astatine) Electrons per shell 2, 8, 18, 32, 32... General Name, Symbol, Number ununoctium, Uuo, 118 Chemical series noble gases Group, Period, Block 18, 7, p Appearance unknown, probably colorless Atomic mass predicted, (314) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p6 (guess based on radon) Electrons per shell 2, 8, 18, 32, 32, 18, 8 Phase... The Periodic Table redirects here. ... This is a list of chemical elements, sorted by name and color coded according to type of element. ... Categories: Chemical elements ... Look up pronunciation in Wiktionary, the free dictionary. ... This article is about the chemical series. ... A group, also known as a family, is a vertical column in the periodic table of the chemical elements. ... In the periodic table of the elements, a period is a horizontal row of the table. ... A block of the periodic table of elements is a set of adjacent groups. ... The noble gases are a chemical series. ... A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the elements. ... The s-block of the periodic table of elements consists of the first two groups: the alkali metals and alkaline earth metals, plus hydrogen. ... ... To help compare different orders of magnitude, the following list describes various mass levels between 10−36 kg and 1053 kg. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... Electron atomic and molecular orbitals In atomic physics and quantum chemistry, the electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (, a crystal). ... For other uses, see Electron (disambiguation). ... Example of a sodium electron shell model An electron shell, also known as a main energy level, is a group of atomic orbitals with the same value of the principal quantum number n. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... For other uses, see Gas (disambiguation). ... For other uses, see Density (disambiguation). ... The melting point of a solid is the temperature range at which it changes state from solid to liquid. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... Italic text This article is about the boiling point of liquids. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ... For other uses, see Kelvin (disambiguation). ... Standard enthalpy change of fusion of period three. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... The heat of vaporization is a physical property of substances. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval. ... Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard for making measurements on the kelvin and Celsius temperature scales. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ... Kilojoule per mole are an SI derived unit of energy per amount of material, where energy is measured in units of 1000 joules, and the amount of material is measured in mole units. ... Atomic radius: Ionic radius Covalent radius Metallic radius van der Waals radius edit The covalent radius, rcov, is a measure of the size of atom which forms part of a covalent bond. ... To help compare different orders of magnitude this page lists lengths between 10 pm and 100 pm (10-11 m and 10-12 m). ... The van der Waals radius of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. ... You have big harry skanky balls ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... For other senses of this word, see magnetism (disambiguation). ... Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ... K value redirects here. ... For other uses, see Speed of sound (disambiguation). ... Metre per second (U.S. spelling: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector), defined by distance in metres divided by time in seconds. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Although there are eight known isotopes of helium (He) (standard atomic mass: 4. ... For other uses, see Isotope (disambiguation). ... Natural abundance refers to the prevalence of different isotopes of an element as found in nature. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... In physics, the decay mode describes a particular way a particle decays. ... The decay energy is the energy released by a nuclear decay. ... The electronvolt (symbol eV) is a unit of energy. ... In nuclear physics, a decay product, also known as a daughter product, is a nuclide resulting from the radioactive decay of a parent or precursor nuclide. ... Stable isotopes are chemical isotopes that are not radioactive. ... This article or section does not adequately cite its references or sources. ... Stable isotopes are chemical isotopes that are not radioactive. ... This article or section does not adequately cite its references or sources. ... The periodic table of the chemical elements A chemical element is a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. ... See also: List of elements by atomic number In chemistry and physics, the atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom. ... In English, to be inert is to be in a state of doing little or nothing. ... In physics and chemistry, monatomic is a combination of the words mono and atomic, and means single atom. ... For other uses, see Gas (disambiguation). ... This article is about the chemical series. ... The Periodic Table redirects here. ... Italic text This article is about the boiling point of liquids. ... The melting point of a solid is the temperature range at which it changes state from solid to liquid. ... This article is about the chemistry of hydrogen. ...


An unknown yellow spectral line signature in sunlight was first observed from a solar eclipse in 1868 by French astronomer Pierre Janssen. Janssen is jointly credited with the discovery of the element with Norman Lockyer, who observed the same eclipse and was the first to propose that the line was due to a new element which he named helium. In 1903, large reserves of helium were found in the natural gas fields of the United States, which is by far the largest supplier of the gas. Animation of the dispersion of light as it travels through a triangular prism. ... Pierre Janssen Pierre Jules César Janssen (February 22, 1824–December 23, 1907) was a French astronomer who along with the English scientist Sir Joseph Norman Lockyer is credited with discovering the gas helium. ... This article or section should be merged with Timeline of chemical element discovery The story of the discoveries of the chemical elements is presented here in chronological order. ... Sir Joseph Norman Lockyer or Norman Lockyer (May 17, 1836 – August 16, 1920) was an English scientist and astronomer. ... Natural gas rig Oil and natural gas are produced by the same geological process: anaerobic decay of organic matter deep under the Earths surface. ...


Helium is used in cryogenics (its largest single use, accounting for about a quarter of production), mostly the cooling of superconducting magnets, particularly the main commercial application in MRI scanners. Helium's other industrial uses as a pressurizing and purge gas, and a protective atmosphere for arc welding and processes (such as growing crystals to make silicon wafers), account for half of its use. Economically minor uses, such as lifting gas in balloons and airships are popularly known.[2]. Inhaling a small volume of the gas temporarily changes the timbre and quality of the human voice. In scientific research, the behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying quantum mechanics (in particular the phenomenon of superfluidity) and to those looking at the effects that temperatures near absolute zero have on matter (such as superconductivity). In physics or engineering, cryogenics is the study of the production of very low temperatures (below –150 °C, –238 °F or 123 K) and the behavior of materials at those temperatures. ... Superconducting magnets are electromagnets that are built using superconducting coils. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... Manual Metal Arc welding, also known as stick or MMA welding is one of the most common forms of welding. ... An etched silicon wafer In microelectronics, a wafer is a thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed by doping (for example, diffusion or ion implantation), etching, and deposition of various materials. ... USS Akron (ZRS-4) in flight, November 2, 1931 An airship or dirigible is a buoyant lighter-than-air aircraft that can be steered and propelled through the air. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... Superfluidity is a phase of matter characterised by the complete absence of viscosity. ... For other uses, see Absolute Zero (disambiguation). ... This article is about matter in physics and chemistry. ... A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. ...


Helium is the second lightest element and is the second most abundant in the observable universe, being present in the universe in masses more than 12 times those of all the heavier elements combined. Helium's abundance is also similar to this in our own Sun and Jupiter. This high abundance is due to the very high binding energy (per nucleon) of helium-4 with respect to the next three elements after helium (lithium, beryllium, and boron). This helium-4 binding energy also accounts for its commonality as a product in both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and was formed during the Big Bang. Some new helium is being created presently as a result of the nuclear fusion of hydrogen, in all but the very heaviest stars, which fuse helium into heavier elements at the extreme ends of their lives. Natural abundance refers to the prevalence of different isotopes of an element as found in nature. ... For other uses, see Universe (disambiguation). ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... For other uses, see Big Bang (disambiguation). ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... This article is about the astronomical object. ...


On Earth, the lightness of helium has caused its evaporation from the gas and dust cloud from which the planet condensed, and it is thus relatively rare—0.00052% by volume in the atmosphere. What helium is present today has been mostly created by the natural radioactive decay of heavy radioactive elements (thorium and uranium), as the alpha particles that are emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations up to seven percent by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... This article is about the chemical element. ... An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... For other uses, see Natural gas (disambiguation). ... Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. ...

Contents

History

Scientific discoveries

The first evidence of helium was observed on August 18, 1868 as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Pierre Janssen during a total solar eclipse in Guntur, India.[3][4] This line was initially assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D3 Fraunhofer line because it was near the known D1 and D2 lines of sodium.[5] He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος (helios)."[6][7][8] For other uses, see Wavelength (disambiguation). ... An elements emission spectrum is the relative intensity of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited). ... The chromosphere (literally, color sphere) is a thin layer of the Suns atmosphere just above the photosphere, roughly 10,000 kilometers deep (approximating to, if a little less than, the diameter of the Earth). ... Sol redirects here. ... Pierre Janssen Pierre Jules César Janssen (February 22, 1824–December 23, 1907) was a French astronomer who along with the English scientist Sir Joseph Norman Lockyer is credited with discovering the gas helium. ... Photo taken during the 1999 eclipse. ... This article is about a city in India. ... For sodium in the diet, see Salt. ... Sir Joseph Norman Lockyer or Norman Lockyer (May 17, 1836 – August 16, 1920) was an English scientist and astronomer. ... Solar Fraunhofer lines In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer (1787--1826). ... Sir Edward Frankland (January 18, 1825 – August 9, 1899) was an English chemist. ...

Picture of visible spectrum with superimposed sharp yellow and blue and violet lines.
Spectral lines of helium

In 1882, Italian physicist Luigi Palmieri detected helium on Earth, for the first time, through its D3 spectral line, when he analyzed the lava of Mount Vesuvius.[9] Luigi Palmieri (April 22, 1807 - September 9, 1896) was an Italian physicist and meteorologist. ... This article is about Earth as a planet. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... This article is about the mountain in Italy. ...


On March 26, 1895 British chemist Sir William Ramsay isolated helium on Earth by treating the mineral cleveite (a variety of uraninite with at least 10% rare earth elements) with mineral acids. Ramsay was looking for argon but, after separating nitrogen and oxygen from the gas liberated by sulfuric acid, he noticed a bright yellow line that matched the D3 line observed in the spectrum of the Sun.[5][10][11][12] These samples were identified as helium by Lockyer and British physicist William Crookes. It was independently isolated from cleveite in the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight.[4][13][14] Helium was also isolated by the American geochemist William Francis Hillebrand prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen. His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science.[15] For other uses, see William Ramsay (disambiguation). ... Cleveite is a radioactive mineral containing uranium and found in Norway. ... For the band, see Pitchblende (band). ... de;Metalle der Seltenen Erden Categories: Stub | Chemical element groups ... For other uses, see acid (disambiguation). ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... This article is about the chemical element and its most stable form, or dioxygen. ... Sulfuric acid, (also known as sulphuric acid) H2SO4, is a strong mineral acid. ... Sir William Crookes, OM, FRS (17 June 1832 – 4 April 1919) was an English chemist and physicist. ... Per Teodor Cleve (Stockholm February 10, 1840 – Uppsala June 18, 1905) was a Swedish chemist and geologist. ... Nils Abraham Langlet (July 9, 1868 - March 30, 1936; known by his second given name) was a Swedish chemist. ... This article is about the modern city of Uppsala. ... ...


In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside. In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin.[16] He tried to solidify it by further reducing the temperature but failed because helium does not have a triple point temperature at which the solid, liquid, and gas phases are at equilibrium. Onnes' student Willem Hendrik Keesom was eventually able to solidify 1 cm3 of helium in 1926.[17] Ernest Rutherford, 1st Baron Rutherford of Nelson OM PC FRS (30 August 1871 – 19 October 1937), widely referred to as Lord Rutherford, was a chemist (B.Sc. ... An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... For other uses, see Kelvin (disambiguation). ... In physics, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. ... Willem Hendrik Keesom (1876-1956) was a Dutch scientist who, in 1926, invented a method to solidify helium. ...


In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no viscosity at temperatures near absolute zero, a phenomenon now called superfluidity.[18] This phenomenon is related to Bose-Einstein condensation. In 1972, the same phenomenon was observed in helium-3, but at temperatures much closer to absolute zero, by American physicists Douglas D. Osheroff, David M. Lee, and Robert C. Richardson. The phenomenon in helium-3 is thought to be related to pairing of helium-3 fermions to make bosons, in analogy to Cooper pairs of electrons producing superconductivity.[19] Semenov (on the right) and Kapitsa (on the left), portrait by Boris Kustodiev, 1921 Pyotr Leonidovich Kapitsa (Russian Пётр Леонидович Капица) (July 9, 1894 – April 8, 1984) was a Soviet/Russian physicist who discovered superfluidity with some contribution from John F. Allen and Don Misener in 1937. ... For other uses, see Viscosity (disambiguation). ... For other uses, see Absolute Zero (disambiguation). ... Superfluidity is a phase of matter characterised by the complete absence of viscosity. ... A Bose–Einstein condensate is a phase of matter formed by bosons cooled to temperatures very near to absolute zero. ... Douglas Dean Osheroff (born August 1, 1945) is a American physicist. ... This article needs to be wikified. ... Robert Coleman Richardson (born June 26, 1937 in Washington D.C.) is an American physicist. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... In particle physics, bosons are particles with an integer spin, as opposed to fermions which have half-integer spin. ... BCS theory successfully explains conventional superconductivity, the ability of certain metals at low temperatures to conduct electricity without resistance. ... A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. ...

Extraction and use

After an oil drilling operation in 1903 in Dexter, Kansas produced a gas geyser that would not burn, Kansas state geologist Erasmus Haworth collected samples of the escaping gas and took them back to the University of Kansas at Lawrence where, with the help of chemists Hamilton Cady and David McFarland, he discovered that the gas consisted of, by volume, 72% nitrogen, 15% methane (a combustible percentage only with sufficient oxygen), 1% hydrogen, and 12% an unidentifiable gas.[4][20] With further analysis, Cady and McFarland discovered that 1.84% of the gas sample was helium.[21][22] This showed that despite its overall rarity on Earth, helium was concentrated in large quantities under the American Great Plains, available for extraction as a byproduct of natural gas.[23] The greatest reserves of helium were in the Hugoton and nearby gas fields in southwest Kansas and the panhandles of Texas and Oklahoma. Dexter is a city located in Cowley County, Kansas. ... This article is about the U.S. state. ... Erasmus Haworth, Ph. ... The University of Kansas (often referred to as KU or just Kansas) is an institution of higher learning in Lawrence, Kansas. ... Hamilton Perkins Cady, (May 2, 1874 - May 26, 1943), was an American chemist who in 1907 in collaboration with David McFarland discovered that helium could be extracted from natural gas. ... Methane is a chemical compound with the molecular formula . ... For other uses see fire (disambiguation). ... This article is about the chemistry of hydrogen. ... The Great Plains states. ... Hugoton Natural Gas Area is a combination of large natural gas fields in the U.S. State of Kansas, the largest of which is the Hugoton Field. ...


This enabled the United States to become the world's leading supplier of helium. Following a suggestion by Sir Richard Threlfall, the United States Navy sponsored three small experimental helium production plants during World War I. The goal was to supply barrage balloons with the non-flammable, lighter-than-air gas. A total of 5,700 m3 (200,000 cubic feet) of 92% helium was produced in the program even though less than a cubic meter of the gas had previously been obtained.[5] Some of this gas was used in the world's first helium-filled airship, the U.S. Navy's C-7, which flew its maiden voyage from Hampton Roads, Virginia to Bolling Field in Washington, D.C. on December 1, 1921.[24] Sir Richard Threlfall (August 14, 1861 - July 10, 1932) was an English chemist and engineer, he established the School of Physics at the University of Sydney and made important contributiosn to military scince during World War I. Threlfall was a son of Richard Threlfall of Hollowforth, near Preston, Lancashire. ... USN redirects here. ... “The Great War ” redirects here. ... US Marine Corps barrage balloon, Parris Island, May 1942 A barrage balloon is a large balloon tethered with metal cables, used to defend against bombardment by aircraft by damaging the aircraft on collision with the cables. ... Hampton Roads, Virginia 1858 Hampton Roads is the name of both a body of water and the land areas which surround it in southeastern Virginia in the United States. ... This article is about the U.S. state. ... Bolling Air Force Base, in Southwest Washington, DC, is named for Col. ... For other uses, see Washington, D.C. (disambiguation). ...


Although the extraction process, using low-temperature gas liquefaction, was not developed in time to be significant during World War I, production continued. Helium was primarily used as a lifting gas in lighter-than-air craft. This use increased demand during World War II, as well as demands for shielded arc welding. The helium mass spectrometer was also vital in the atomic bomb Manhattan Project.[25] This page is a candidate to be moved to Wiktionary. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... A Helium mass spectrometer (often called a leak detector) or sniffer, is a scientific instrument, used to detect very small leaks, typically using a vacuum and injecting helium around a chamber or cavity. ... This article is about the World War II nuclear project. ...


The government of the United States set up the National Helium Reserve in 1925 at Amarillo, Texas with the goal of supplying military airships in time of war and commercial airships in peacetime.[5] Due to a US military embargo against Germany that restricted helium supplies, the Hindenburg was forced to use hydrogen as the lift gas. Helium use following World War II was depressed but the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant to create oxygen/hydrogen rocket fuel (among other uses) during the Space Race and Cold War. Helium use in the United States in 1965 was more than eight times the peak wartime consumption.[26] ... The National Helium Reserve is an American strategic reserve of over a billion cubic feet of Helium gas, stored at the Cliffside Storage Facility about 12 miles northwest of Amarillo, Texas in a natural geologic gas storage formation. ... Amarillo redirects here. ... For other uses, see Texas (disambiguation). ... USS Akron (ZRS-4) in flight, November 2, 1931 An airship or dirigible is a buoyant lighter-than-air aircraft that can be steered and propelled through the air. ... The Hindenburg redirects here. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... Rocket fuel is a propellant that reacts with an oxidizing agent to produce thrust in a rocket. ... For a list of key events, see Timeline of space exploration. ... For other uses, see Cold War (disambiguation). ...


After the "Helium Acts Amendments of 1960" (Public Law 86–777), the U.S. Bureau of Mines arranged for five private plants to recover helium from natural gas. For this helium conservation program, the Bureau built a 425-mile (684 km) pipeline from Bushton, Kansas to connect those plants with the government's partially depleted Cliffside gas field, near Amarillo, Texas. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, when it then was further purified.[27] For most of the 20th century, the U.S. Bureau of Mines (USBM) was the primary United States Government agency conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral resources. ... Bushton is a city located in Rice County, Kansas. ... This article is about the U.S. state. ...


By 1995, a billion cubic meters of the gas had been collected and the reserve was US$1.4 billion in debt, prompting the Congress of the United States in 1996 to phase out the reserve.[4][28] The resulting "Helium Privatization Act of 1996"[29] (Public Law 104–273) directed the United States Department of the Interior to start emptying the reserve by 2005.[30] Congress in Joint Session. ... The United States Department of the Interior (DOI) is a Cabinet department of the United States government that manages and conserves most federally owned land. ...


Helium produced between 1930 and 1945 was about 98.3% pure (2% nitrogen), which was adequate for airships. In 1945, a small amount of 99.9% helium was produced for welding use. By 1949, commercial quantities of Grade A 99.95% helium were available.[31]


For many years the United States produced over 90% of commercially usable helium in the world, while extraction plants in Canada, Poland, Russia, and other nations produced the remainder. In the mid-1990s, a new plant in Arzew, Algeria producing 17 million cubic meters (600 million cubic feet) began operation, with enough production to cover all of Europe's demand. Meanwhile, by 2000, the consumption of helium within the US had risen to above 15 million kg per year.[32] In 2004–2006, two additional plants, one in Ras Laffen, Qatar and the other in Skikda, Algeria were built, but as of early 2007, Ras Laffen is functioning at 50%, and Skikda has yet to start up. Algeria quickly became the second leading producer of helium.[33] Through this time, both helium consumption and the costs of producing helium increased.[34] In the 2002 to 2007 period helium prices doubled,[35] and during 2008 alone the major suppliers raised prices about 50%.[citation needed] Arzew is a town and seaport in Algeria, 22 miles from Oran. ... Skikda (Arabic: ولاية سكيكدة ) is a city in north eastern Algeria and a port on the Gulf of Stora, the ancient Sinus Numidicus. ...

Characteristics

The helium atom

Helium atom
Picture of a diffuse gray sphere with grayscale density decreasing from the center. Length scale about 1 Angstrom. An inset outlines the structure of the core, with two red and two blue atoms at the length scale of 1 femtometer.
An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one angstrom, equal to 10−10 m or 100,000 fm.

Helium in quantum mechanics

Helium is the next simplest atom to solve using the rules of quantum mechanics, after the hydrogen atom. Helium is composed of two electrons in orbit around a nucleus containing two protons along with some neutrons. However, as in Newtonian mechanics, no system consisting of more than two particles can be solved with an exact analytical mathematical approach (see 3-body problem) and helium is no exception. Thus, numerical mathematical methods are required, even to solve the system of one nucleus and two electrons. However, such computational chemistry methods have been used to create a quantum mechanical picture of helium electron binding which is accurate to within < 2% of the correct value, in a few computational steps.[36] In such models it is found that each electron in helium partly screens the nucleus from the other, so that the effective nuclear charge Z which each electron sees, is about 1.69 units, not the 2 charges of a classic "bare" helium nucleus. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... Electron cloud is a term used- if not originally coined- by the nobelaurate and acclaimed educator Richard Feynman in The Feynman Lectures on Physics, for discussing exactly what is an electron?. This intuitive model provides a simplified way of visualizing an electron as a solution of the Schrödinger equation. ... An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ... This article is about the unit of length. ... Femtometre (American spelling: femtometer) is an SI measure of length that is equal to 10−15 (femto) of a metre. ... For other uses, see Atom (disambiguation). ... Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. ... The n-body problem is the problem of finding, given the initial positions, masses, and velocities of n bodies, their subsequent motions as determined by classical mechanics, i. ... Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to complement the information obtained by actual chemical experiments, predict hitherto unobserved chemical phenomena, and solve related problems. ...

The related stability of the helium-4 nucleus and electron shell

The nucleus of the helium-4 atom, which is identical with an alpha particle is particularly interesting, inasmuch as high energy electron-scattering experiments show its charge to decrease exponentially from a maximum at a central point, exactly as does the charge density of helium's own electron cloud. This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons (although the nuclear particles are subject to a different nuclear binding potential), so that all these fermions fully occupy 1s1s orbitals in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin. Adding another of any of these particles would require angular momentum and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature. An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ... Electron cloud is a term used- if not originally coined- by the nobelaurate and acclaimed educator Richard Feynman in The Feynman Lectures on Physics, for discussing exactly what is an electron?. This intuitive model provides a simplified way of visualizing an electron as a solution of the Schrödinger equation. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ...


For example, the stability and low energy of the electron cloud state in helium accounts for the element's chemical inertness (the most extreme of all the elements), and also the lack of interaction of helium atoms with themselves, producing the lowest melting and boiling points of all the elements.


In a similar way, the particular energetic stability of the helium-4 nucleus, produced by similar effects, accounts for the ease of helium-4 production in atomic reactions involving both heavy-particle emission, and fusion. Some stable helium-3 is produced in fusion reactions from hydrogen, but it is a very small fraction, compared with the highly favorable helium-4. The stability of helium-4 is the reason hydrogen is converted to helium-4 (not deuterium or helium-3 or heavier elements) in the Sun. It is also partly responsible for the fact that the alpha particle is by far the most common type of baryonic particle to be ejected from atomic nuclei; in other words, alpha decay is far more common than cluster decay. Alpha decay Alpha decay is a type of radioactive decay in which an atom emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or decays) into an atom with a mass number 4 less and atomic number 2... Cluster decay is the nuclear process in which a radioactive atom emits a cluster of neutrons and protons. ...

Binding energy per nucleon of common isotopes. The binding energy per particle of helium-4 is significantly larger than all nearby nuclides.

The unusual stability of the helium-4 nucleus is also important cosmologically: it explains the fact that in the first few minutes after the Big Bang, as the "soup" of free protons and neutrons which had initially been created in about 6:1 ratio cooled to the point that nuclear binding was possible, almost all first compound atomic nuclei to form were helium-4 nuclei. So tight was helium-4 binding, in fact, than helium-4 production consumed nearly all of the free neutrons in a few mintues, before they could beta-decay, and also leaving very few left to form any lithium, beryllium, or boron. Helium-4 nuclear binding per nucleon is stronger than in any of these elements (see nucleogenesis and binding energy) and thus no energetic drive was available, once helium had been formed, to make elements 3, 4 and 5. It was barely energetically favorable for helium to fuse into the next element with a lower energy per nucleon, carbon. However, due to lack of intermediate elements, this process requires three helium nuclei striking each other nearly simultaneously (see triple alpha process). There was thus no time for significant carbon to be formed in the Big Bang, before the early expanding universe cooled, in a matter of a few minutes, to the temperature and pressure point where helium fusion to carbon was no longer possible. This left the early universe with a very similar ratio of hydrogen/helium as is observed today (3 parts hydrogen to 1 part helium-4 by mass), with nearly all the neutrons in the universe (even as it exists today) trapped in helium-4. For other uses, see Big Bang (disambiguation). ... Physics In physics, nucleogenesis is the process that occurred a few minutes after the Big Bang when the atomic nuclei were created. ... Binding energy is the energy required to disassemble a whole into separate parts. ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... The triple alpha process is the process by which three helium nuclei (alpha particles) are transformed into carbon. ...


All heavier elements (including those necessary for rocky planets like the Earth, and for carbon-based or other life), have thus had to be created since the Big Bang, in stars which were hot enough to burn not just hydrogen (for this produces only more helium), but hot enough to burn helium itself. Such stars are massive and therefore rare, and this fact accounts for the fact that all other chemical elements after hydrogen and helium today account for only 2% of the mass of atomic matter in the universe. Helium-4, by contrast, makes up about 23% of the universe's ordinary matter—nearly all the ordinary matter which isn't hydrogen.

Gas and plasma phases

gas discarge tube filled with pure helium

Helium is the least reactive noble gas after neon and thus the second least reactive of all elements; it is inert and monatomic in all standard conditions. Due to helium's relatively low molar (atomic) mass, in the gas phase its thermal conductivity, specific heat, and sound speed are all greater than any other gas except hydrogen. For similar reasons, and also due to the small size of helium atoms, helium's diffusion rate through solids is three times that of air and around 65% that of hydrogen.[5] This article is about the chemical series. ... For other uses, see Neon (disambiguation). ... In English, to be inert is to be in a state of doing little or nothing. ... In physics and chemistry, monatomic is a combination of the words mono and atomic, and means single atom. ... K value redirects here. ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... For other uses, see Speed of sound (disambiguation). ... This article is about the chemistry of hydrogen. ... diffusion (disambiguation). ...

Illuminated light red gas discharge tubes shaped as letters H and e.
Helium discharge tube shaped like the element's atomic symbol.

Helium is less water soluble than any other gas known,[37] and helium's index of refraction is closer to unity than that of any other gas.[38] Helium has a negative Joule-Thomson coefficient at normal ambient temperatures, meaning it heats up when allowed to freely expand. Only below its Joule-Thomson inversion temperature (of about 32 to 50 K at 1 atmosphere) does it cool upon free expansion.[5] Once precooled below this temperature, helium can be liquefied through expansion cooling. Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... The Joule-Thomson effect is a physical process in which the temperature of a gas is decreased by letting the gas expand adiabatically. ... The Joule-Thomson effect is a physical process in which the temperature of a gas is decreased by letting the gas expand adiabatically. ...


Most extraterrestrial helium is found in a plasma state, with properties quite different from those of atomic helium. In a plasma, helium's electrons are not bound to its nucleus, resulting in very high electrical conductivity, even when the gas is only partially ionized. The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind together with ionized hydrogen, the particles interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora.[39] For other uses, see Plasma. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... The aurora on Jupiter, powered by Jovian Birkeland currents [Ref. ... Aurora borealis Aurora borealis The aurora is a glow observed in the night sky, usually in the polar zone. ...

Solid and liquid phases

Unlike any other element, helium will remain liquid down to absolute zero at normal pressures. This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. Solid helium requires a temperature of 1–1.5 K (about –272 °C or –457 °F) and about 25 bar (2.5 MPa) of pressure.[40] It is often hard to distinguish solid from liquid helium since the refractive index of the two phases are nearly the same. The solid has a sharp melting point and has a crystalline structure, but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30%.[41] With a bulk modulus on the order of 50 MPa[42] it is 50 times more compressible than water. Solid helium has a density of 0.214 ± 0.006 g/ml at 1.15 K and 66 atm; the projected density at 0 K and 25 bar (2.5 MPa) is 0.187 ± 0.009 g/ml.[43] Helium exists in liquid form only at very low temperatures. ... For other uses, see Absolute Zero (disambiguation). ... In a quantum mechanical system such as the particle in a box or the quantum harmonic oscillator, the lowest possible energy is called the zero-point energy. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... The melting point of a solid is the temperature range at which it changes state from solid to liquid. ... For other uses, see Crystal (disambiguation). ... Fluid Dynamics Compressibility (physics) is a measure of the relative volume change of fluid or solid as a response to a pressure (or mean stress) change: . For a gas the magnitude of the compressibility depends strongly on whether the process is adiabatic or isothermal, while this difference is small in... The bulk modulus (K) of a substance essentially measures the substances resistance to uniform compression. ... The megapascal, symbol MPa is an SI unit of pressure. ...

Helium I state

Below its boiling point of 4.22 kelvins and above the lambda point of 2.1768 kelvins, the isotope helium-4 exists in a normal colorless liquid state, called helium I.[5] Like other cryogenic liquids, helium I boils when it is heated and contracts when its temperature is lowered. Below the lambda point, however, helium doesn't boil, and it expands as the temperature is lowered further. Italic text This article is about the boiling point of liquids. ... Lambda point is the temperature (approximately 2. ... For other uses, see Isotope (disambiguation). ... Cryogenics is the study of very low temperatures or the production of the same, and is often confused with cryobiology, the study of the effect of low temperatures on organisms, or the study of cryopreservation. ...


Helium I has a gas-like index of refraction of 1.026 which makes its surface so hard to see that floats of styrofoam are often used to show where the surface is.[5] This colorless liquid has a very low viscosity and a density of 0.145 g/mL, which is only one-fourth the value expected from classical physics.[5] Quantum mechanics is needed to explain this property and thus both types of liquid helium are called quantum fluids, meaning they display atomic properties on a macroscopic scale. This may be an effect of its boiling point being so close to absolute zero, preventing random molecular motion (thermal energy) from masking the atomic properties.[5] The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... Styrofoam is a trademark name for polystyrene thermal insulation material, manufactured by Dow Chemical Company. ... For other uses, see Viscosity (disambiguation). ... Classical physics is physics based on principles developed before the rise of quantum theory, usually including the special theory of relativity and general theory of relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. ...

Helium II state

Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called helium II. Boiling of helium II is not possible due to its high thermal conductivity; heat input instead causes evaporation of the liquid directly to gas. The isotope helium-3 also has a superfluid phase, but only at much lower temperatures; as a result, less is known about such properties in the isotope helium-3.[5] K value redirects here. ... Vaporization redirects here. ... Helium II will creep along surfaces in order to find its own level - after a short while, the levels in the two containers will equalize. ...

A cross-sectional drawing showing one vessel inside another. There is a liquid in the outer vessel, and it tends to flow into the inner vessel over its walls.
Unlike ordinary liquids, helium II will creep along surfaces in order to reach an equal level; after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.[5]

Helium II is a superfluid, a quantum-mechanical state of matter with strange properties. For example, when it flows through capillaries as thin as 10−7 to 10−8 m it has no measurable viscosity.[4] However, when measurements were done between two moving discs, a viscosity comparable to that of gaseous helium was observed. Current theory explains this using the two-fluid model for helium II. In this model, liquid helium below the lambda point is viewed as containing a proportion of helium atoms in a ground state, which are superfluid and flow with exactly zero viscosity, and a proportion of helium atoms in an excited state, which behave more like an ordinary fluid.[44] A Rollin film is a 30 nm thick liquid film of Helium in the Helium II state. ... For other uses, see Viscosity (disambiguation). ... In physics, the ground state of a quantum mechanical system is its lowest-energy state. ...


In the fountain effect, a chamber is constructed which is connected to a reservoir of helium II by a sintered disc through which superfluid helium leaks easily but through which non-superfluid helium cannot pass. If the interior of the container is heated, the superfluid helium changes to non-superfluid helium. In order to maintain the equilibrium fraction of superfluid helium, superfluid helium leaks through and increases the pressure, causing liquid to fountain out of the container.[45] This article or section does not cite its references or sources. ...


The thermal conductivity of helium II is greater than that of any other known substance, a million times that of helium I and several hundred times that of copper.[5] This is because heat conduction occurs by an exceptional quantum mechanism. Most materials that conduct heat well have a valence band of free electrons which serve to transfer the heat. Helium II has no such valence band but nevertheless conducts heat well. The flow of heat is governed by equations that are similar to the wave equation used to characterize sound propagation in air. When heat is introduced, it moves at 20 meters per second at 1.8 K through helium II as waves in a phenomenon known as second sound.[5] For other uses, see Copper (disambiguation). ... In solids, the valence band is the highest range of electron energies where electrons are normally present at zero temperature. ... The wave equation is an important partial differential equation that describes the propagation of a variety of waves, such as sound waves, light waves and water waves. ... Second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. ...


Helium II also exhibits a creeping effect. When a surface extends past the level of helium II, the helium II moves along the surface, against the force of gravity. Helium II will escape from a vessel that is not sealed by creeping along the sides until it reaches a warmer region where it evaporates. It moves in a 30 nm-thick film regardless of surface material. This film is called a Rollin film and is named after the man who first characterized this trait, Bernard V. Rollin.[5][46][47] As a result of this creeping behavior and helium II's ability to leak rapidly through tiny openings, it is very difficult to confine liquid helium. Unless the container is carefully constructed, the helium II will creep along the surfaces and through valves until it reaches somewhere warmer, where it will evaporate. Waves propagating across a Rollin film are governed by the same equation as gravity waves in shallow water, but rather than gravity, the restoring force is the van der Waals force.[48] These waves are known as third sound.[49] Gravity is a force of attraction that acts between bodies that have mass. ... A nanometre (American spelling: nanometer, symbol nm) (Greek: νάνος, nanos, dwarf; μετρώ, metrÏŒ, count) is a unit of length in the metric system, equal to one billionth of a metre (or one millionth of a millimetre), which is the current SI base unit of length. ... A Rollin film is a 30 nm thick liquid film of Helium in the Helium II state. ... Ocean wave Wave clouds over Theresa, Wisconsin, USA Atmospheric gravity waves as seen from space. ... In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer to intermolecular forces that deal with forces due to the polarization of molecules. ...

Isotopes

There are eight known isotopes of helium, but only helium-3 and helium-4 are stable. In the Earth's atmosphere, there is one 3He atom for every million 4He atoms.[4] Unlike most elements, helium's isotopic abundance varies greatly by origin, due to the different formation processes. The most common isotope, helium-4, is produced on Earth by alpha decay of heavier radioactive elements; the alpha particles that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its nucleons are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis.[50] Although there are eight known isotopes of helium (He) (standard atomic mass: 4. ... For other uses, see Isotope (disambiguation). ... Stable isotopes are chemical isotopes that are not radioactive. ... Alpha decay Alpha decay is a type of radioactive decay in which an atom emits an alpha particle (two protons and two neutrons bound together into a particle identical to a helium nucleus) and transforms (or decays) into an atom with a mass number 4 less and atomic number 2... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... In nuclear physics, the nuclear shell model is a model of the atomic nucleus. ... In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ...


Helium-3 is present on Earth only in trace amounts; most of it since Earth's formation, though some falls to Earth trapped in cosmic dust.[51] Trace amounts are also produced by the beta decay of tritium.[52] Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten, and these ratios can be used to investigate the origin of rocks and the composition of the Earth's mantle.[51] 3He is much more abundant in stars, as a product of nuclear fusion. Thus in the interstellar medium, the proportion of 3He to 4He is around 100 times higher than on Earth.[53] Extraplanetary material, such as lunar and asteroid regolith, have trace amounts of helium-3 from being bombarded by solar winds. The Moon's surface contains helium-3 at concentrations on the order of 0.01 ppm.[54][55] A number of people, starting with Gerald Kulcinski in 1986,[56] have proposed to explore the moon, mine lunar regolith and use the helium-3 for fusion. “Space dust” redirects here. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... Tritium (symbol T or ³H) is a radioactive isotope of hydrogen. ... Earth cutaway from core to exosphere. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... This article is about Earths moon. ... Parts per million (ppm) is a measure of concentration that is used where low levels of concentration are significant. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ...


Liquid helium-4 can be cooled to about 1 kelvin using evaporative cooling in a 1-K pot. Similar cooling of helium-3, which has a lower boiling point, can achieve about 0.2 kelvin in a helium-3 refrigerator. Equal mixtures of liquid 3He and 4He below 0.8 K separate into two immiscible phases due to their dissimilarity (they follow different quantum statistics: helium-4 atoms are bosons while helium-3 atoms are fermions).[5] Dilution refrigerators use this immiscibility to achieve temperatures of a few millikelvins. Evaporative cooling is a system in which latent heat of evaporation is used to carry heat away from an object to cool it. ... A 1-K pot (i. ... Statistics of interacting identical particles (=when their wave functions overlap). ... In particle physics, bosons are particles with an integer spin, as opposed to fermions which have half-integer spin. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... Helium Dilution Refrigerator A dilution refrigerator is a cryogenic device first proposed by Heinz London. ...


It is possible to produce exotic helium isotopes, which rapidly decay into other substances. The shortest-lived heavy helium isotope is helium-5 with a half-life of 7.6 × 10–22 seconds. Helium-6 decays by emitting a beta particle and has a half life of 0.8 second. Helium-7 also emits a beta particle as well as a gamma ray. Helium-7 and helium-8 are created in certain nuclear reactions.[5] Helium-6 and helium-8 are known to exhibit a nuclear halo. Helium-2 (two protons, no neutrons) is a radioisotope that decays by proton emission into protium (hydrogen), with a half-life of 3 × 10–27 second.[5] Exotic helium isotopes are the unstable isotopes of helium. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... Alpha radiation consists of helium nuclei and is readily stopped by a sheet of paper. ... This article is about electromagnetic radiation. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide to produce products different from the initial particles. ... In nuclear physics, an atomic nucleus is said to be a halo if its radius is appreciably larger than that predicted by the liquid drop model, wherein the nucleus is considered to be a sphere of constant density. ... A radionuclide is an atom with an unstable nucleus. ... Proton emission (also known as proton radioactivity) is a type of radioactive decay in which a proton is ejected from a nucleus. ... A hydrogen atom is an atom of the element hydrogen. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ...

Compounds

Helium has a valence of zero and is chemically unreactive under all normal conditions.[41] It is an electrical insulator unless ionized. As with the other noble gases, helium has metastable energy levels that allow it to remain ionized in an electrical discharge with a voltage below its ionization potential.[5] Helium can form unstable compounds, known as excimers, with tungsten, iodine, fluorine, sulfur and phosphorus when it is subjected to an electric glow discharge, to electron bombardment, or else is a plasma for another reason. The molecular compounds HeNe, HgHe10, and WHe2, and the molecular ions He+2, He2+2, HeH+, and HeD+ have been created this way.[57] This technique has also allowed the production of the neutral molecule He2, which has a large number of band systems, and HgHe, which is apparently only held together by polarization forces.[5] Theoretically, other true compounds may also be possible, such as helium fluorohydride (HHeF) which would be analogous to HArF, discovered in 2000.[58] Calculations show that two new compounds containing a helium-oxygen bond could be stable.[59] Two new molecular species, predicted using theory, CsFHeO and N(CH3)4FHeO, are derivatives of a metastable [F– HeO] anion first theorized in 2005 by a group from Taiwan. If confirmed by experiment, such compounds will end helium's chemical inertness, and the only remaining inert element will be neon.[60] Noble gas compounds are chemical compounds that include an element from column 18 of the periodic table, the noble gases. ... For other uses, see Valence. ... This article is about the electrically charged particle. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... The ionization potential, ionization energy or EI of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. ... Look up chemical compound in Wiktionary, the free dictionary. ... An excimer[1] (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. ... now. ... A Plasma lamp In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. ... Spectral bands are part of optical spectra of polyatomic systems, including condensed materials, large molecules etc. ... The discovery of this first argon compound is credited to as group of Finnish scientists, lead by Markku Rasanen. ... For other uses, see Neon (disambiguation). ...


Helium has been put inside the hollow carbon cage molecules (the fullerenes) by heating under high pressure. The endohedral fullerene molecules formed are stable up to high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside.[61] If helium-3 is used, it can be readily observed by helium nuclear magnetic resonance spectroscopy.[62] Many fullerenes containing helium-3 have been reported. Although the helium atoms are not attached by covalent or ionic bonds, these substances have distinct properties and a definite composition, like all stoichiometric chemical compounds. The Icosahedral Fullerene C540 The Fullerenes, discovered in 1985 by Robert Curl, Harold Kroto and Richard Smalley at the University of Sussex and Rice University, are a family of carbon allotropes named after Richard Buckminster Fuller and are sometimes called buckyballs. ... Endohedral fullerenes are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ...

Occurrence and production

Natural abundance

Helium is the second most abundant element in the known Universe (after hydrogen), constituting 23% of the baryonic mass of the Universe.[4] The vast majority of helium was formed by Big Bang nucleosynthesis one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. In stars, it is formed by the nuclear fusion of hydrogen in proton-proton chain reactions and the CNO cycle, part of stellar nucleosynthesis.[50] This article is about the chemistry of hydrogen. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ... This article is about the astronomical object. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... Overveiw of the proton-proton chain. ... This article does not cite its references or sources. ... Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ...


In the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million.[63][64] The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere escapes into space by several processes.[65][66] In the Earth's heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements. Air redirects here. ... There are several different processes that can lead to the escape of a planetary atmosphere. ... Earths atmosphere is the layer of gases surrounding the planet Earth and retained by the Earths gravity. ...


Nearly all helium on Earth is a result of radioactive decay, and thus an Earthly helium balloon is essentially a bag of retired alpha particles. Helium is found in large amounts in minerals of uranium and thorium, including cleveite, pitchblende, carnotite and monazite, because they emit alpha particles (helium nuclei, He2+) to which electrons immediately combine as soon as the particle is stopped by the rock. In this way an estimated 3000 metric tons of helium are generated per year throughout the lithosphere.[67][68][69] In the Earth's crust, the concentration of helium is 8 parts per billion. In seawater, the concentration is only 4 parts per trillion. There are also small amounts in mineral springs, volcanic gas, and meteoric iron. Because helium is trapped in a similar way by non-permeable layer of rock like natural gas the greatest concentrations on the planet are found in natural gas, from which most commercial helium is derived. The concentration varies in a broad range from a few ppm up to over 7% in a small gas field in San Juan County, New Mexico.[70][71] Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays are a form of particle radiation which are highly ionizing and have low penetration. ... This article is about the chemical element. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... Cleveite is a radioactive mineral containing uranium and found in Norway. ... Uraninite is a uranium-rich mineral with a composition that is largely UO2 (uranium oxide), but which also contains UO3 and oxides of lead, thorium, and rare earths. ... Carnotite is a potassium uranium vanadate mineral with chemical formula: K2(UO2)2(VO4)2·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present. ... Monazite powder In geology, the mineral monazite is a reddish-brown phosphate containing rare earth metals and an important source of thorium, lanthanum, and cerium. ... The tectonic plates of the lithosphere on Earth. ... A natural spring on Mackinac Island in Michigan. ... For other uses, see Natural gas (disambiguation). ... San Juan County is a county located in the U.S. state of New Mexico. ...

Modern extraction

For large-scale use, helium is extracted by fractional distillation from natural gas, which contains up to 7% helium.[72] Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure Grade-A helium.[5] The principal impurity in Grade-A helium is neon. In a final production step, most of the helium that is produced is liquefied via a cryogenic process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers.[33][73] Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. ... Italic text This article is about the boiling point of liquids. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Methane is a chemical compound with the molecular formula . ... Activated carbon (also called activated charcoal) is the more general term which includes material mostly derived from charcoal. ... For other uses, see Neon (disambiguation). ... Cryogenics is the study of very low temperatures or the production of the same, and is often confused with cryobiology, the study of the effect of low temperatures on organisms, or the study of cryopreservation. ...


In 2008, approximately 169 million standard cubic meters (SCM) of helium were extracted from natural gas or withdrawn from helium reserves with approximately 78% from the United States, 10% from Algeria, and most of the remainder from Russia, Poland and Qatar.[74] In the United States, most helium is extracted from natural gas of the Hugoton and nearby gas fields in Kansas, Oklahoma, and Texas.[33] Diffusion of crude natural gas through special semipermeable membranes and other barriers is another method to recover and purify helium.[75] In 2000, The U.S. has proven helium reserves, in such gas well complexes, of about 147 billion standard cubic feet (4.2 billion SCM). This is enough helium for about 25 years of world use, or 35 years of U.S. use, although factors in saving and processing are expected to impact effective reserve numbers. It is estimated that the resourse base for yet-unproven helium in natural gas in the US is 31-53 trillion SCM, or roughly an order of magnitude more than the proven reserves. [76] Hugoton Natural Gas Area is a combination of large natural gas fields in the U.S. State of Kansas, the largest of which is the Hugoton Field. ... Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ...


Helium must be extracted from natural gas because it is present in air at only a fraction of that of neon, yet the demand for it is far higher. It is estimated that if all neon production production were retooled to save helium, that 0.1% of the world's helium demands would be satisfied. Similarly, only 1% of the world's helium demands could be satisfied by re-tooling all air distillation plants.[77] Helium can be synthesized by bombardment of lithium or boron with high-velocity protons, but this an economically completely non-viable method of production.[78] This article is about the chemical element. ... For other uses, see Boron (disambiguation). ...

Supply depletion

Current reserves of helium are being utilized much faster than they are being replenished. Given this situation, there are major concerns that the supply of helium may be depleted soon; the world's largest reserves, in Amarillo, Texas, are expected to run out within the next eight years. This might be preventable if current users capture and recycle the gas and if oil and gas companies make use of capture techniques when extracting gas.[79][80] Amarillo redirects here. ...

Applications

Estimated U.S. fractional helium use by category, by the U.S. Geological Survey, in 1996. Most of the cryogenic use is for superconducting MRI magnets. 71.9 million standard cubic meters is 13.8 million kg.

Of the 2008 world helium total production of about 32 million kg helium per year, the largest use (about 22% of the total in 2008) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners. [81] Other major uses (totalling to about 78% of use in 1996) were pressurizing and purging systems, maintainence of controlled atmospheres, and welding. Other uses by category were relatively minor fractions.[82] The United States Geological Survey (USGS) is a scientific agency of the United States government. ... Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ...


Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small containers called Dewars which hold up to 1,000 liters of helium, or in large ISO containers which have nominal capacities as large as 42 m3 (11,000 US gallons). In gaseous form, small quantities of helium are supplied in high pressure cylinders holding up to 8 m3 (300 standard cubic feet), while large quantities of high pressure gas are supplied in tube trailers which have capacities of up to 4,860 m3 (180,000 standard cubic feet). Italic text This article is about the boiling point of liquids. ... For other uses, see Density (disambiguation). ... Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. ... K value redirects here. ... In English, to be inert is to be in a state of doing little or nothing. ... A Dewar flask is a vessel designed to provide very good thermal insulation. ... A standard cubic foot is a measure of quantity of gas, equal to a cubic foot of volume at 60 degrees Fahrenheit and either 14. ...

Cigar-shaped blimp with "Good Year" written on its side.
Because of its low density and incombustibility, helium is the gas of choice to fill airships such as the Goodyear blimp.
Airships, balloons and rocketry

Because it is lighter than air, airships and balloons are inflated with helium for lift. While hydrogen gas is approximately 7% more buoyant, helium has the advantage of being non-flammable (in addition to being fire retardant).[28] In rocketry, helium is used as an ullage medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make rocket fuel. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in space vehicles. For example, the Saturn V booster used in the Apollo program needed about 370,000 m3 (13 million cubic feet) of helium to launch.[41] The Goodyear Blimp is the collective name for a fleet of blimps operated by Goodyear Tire and Rubber Company for advertising purposes and for use as a television camera platform for aerial views of sporting events. ... The expression lighter than air refers to objects, usually aircraft, that are buoyant in air because they have an average density that is less than that of air (usually because they contain gases that have a density that is lower than that of air). ... USS Akron (ZRS-4) in flight, November 2, 1931 An airship or dirigible is a buoyant lighter-than-air aircraft that can be steered and propelled through the air. ... A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust from within a rocket engine. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Rocket fuel is a propellant that reacts with an oxidizing agent to produce thrust in a rocket. ... Space exploration is the physical exploration of outer-Earth objects and generally anything that involves the technologies, science, and politics regarding space endeavors. ... For the moon designated Saturn V, see Rhea. ... The Apollo program was a human spaceflight program undertaken by NASA during the years 1961 – 1975 with the goal of conducting manned moon landing missions. ...

Commercial and recreational

Helium alone is less dense than atmospheric air, so it will change the timbre (not pitch[83]) of a person's voice when inhaled. However, inhaling it from a typical commercial source, such as that used to fill balloons, can be dangerous due to the risk of asphyxiation from lack of oxygen, and the number of contaminants that may be present. These could include trace amounts of other gases, in addition to aerosolized lubricating oil. In music, timbre, or sometimes timber, (from Fr. ... Pitch is the perceived fundamental frequency of a sound. ... Asphyxia is a condition of severely deficient supply of oxygen to the body. ...


For its low solubility in nervous tissue, helium mixtures such as trimix, heliox and heliair are used for deep diving to reduce the effects of narcosis.[84][85] At depths below 150 metres (490 ft) small amounts of hydrogen are added to a helium-oxygen mixture to counter the effects of high pressure nervous syndrome.[86] At these depths the low density of helium is found to considerably reduce the effort of breathing.[87] Nervous tissue is the fourth major class of vertebrate tissue. ... The meaning of term deep diving depends on the level of the divers diver training, diving equipment, breathing gas and surface support: in recreational diving, 30 metres / 100 feet may be a deep dive in technical diving, 60 metres / 200 feet may be a deep dive in surface supplied... Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in scuba divers at depth. ...


Helium-neon lasers have various applications, including barcode readers.[4] A typical handheld barcode scanner A barcode reader (or barcode scanner) is an electronic device for reading printed barcodes. ...

Industrial leak detection

One industrial application for helium is leak detection. Because it diffuses through solids at three times the rate of air, helium is used as a tracer gas to detect leaks in high-vacuum equipment and high-pressure containers.[88] diffusion (disambiguation). ...

Photo of a large, metal-framed device (about 3×1×1.5 m) standing in a room.
A dual chamber Helium Leak Detection Machine from KONTIKAB.

If one needs to know the total leak rate of the tested product (for example in a heat pumps or an air conditioning system), the object is placed in a test chamber, the air in the chamber is removed with vacuum pumps and the product is filled with helium under specific pressure. The helium that escapes through the leaks is detected by a sensitive device (mass spectrometer), even at the leak rates as small as 10−9 mbar·L/s (10−20 Pa·m3/s). The measurement procedure is normally automatic and is called Helium Integral Test. In a simpler test, the product is filled with helium and an operator is manually searching for the leak with a hand-held device called sniffer.[89] Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ...


For its inertness and high thermal conductivity, neutron transparency, and because it does not form radioactive isotopes under reactor conditions, helium is used as a heat-transfer medium in some gas-cooled nuclear reactors.[88] Helium is used as a shielding gas in arc welding processes on materials that are contaminated easily by air.[4] K value redirects here. ... Nuclear power station at Leibstadt, Switzerland. ... Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. ... Manual Metal Arc welding, also known as stick or MMA welding is one of the most common forms of welding. ...


Helium is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography,[41] because it is inert. Because of its inertness, thermally and calorically perfect nature, high speed of sound, and high value of the heat capacity ratio, it is also useful in supersonic wind tunnels[90] and impulse facilities[91]. Not to be confused with Silicone. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Standard atomic weight 72. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery grey-white metallic Standard atomic weight 47. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... Gas-liquid chromatography (GLC), or simply gas chromatography (GC) is a type of chromatography in which the mobile phase is a carrier gas, usually an inert gas such as helium or nitrogen, and the stationary phase is a microscopic layer of liquid on an inert solid support. ... An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces, where the constituent atoms or molecules undergo perfectly elastic collisions with the walls of the container and each other and are in constant random motion. ... For other uses, see Speed of sound (disambiguation). ... The heat capacity ratio is simply the ratio of the heat capacity at constant pressure to that at constant volume It should be noted that chemical engineers and many others commonly refer to the heat capacity ratio as rather than . ... NASA wind tunnel with the model of a plane A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects. ...


Helium, mixed with a heavier gas such as xenon, is useful for thermoacoustic refrigeration due to the resulting high heat capacity ratio and low Prandtl number.[92] The inertness of helium has environmental advantages over conventional refrigeration systems which contribute to ozone depletion or global warming.[93] Sonic or thermoacoustic refrigeration is a technology that uses high-amplitude sound waves in a pressurised gas to pump heat from one place to another. ... The heat capacity ratio is simply the ratio of the heat capacity at constant pressure to that at constant volume It should be noted that chemical engineers and many others commonly refer to the heat capacity ratio as rather than . ... The Prandtl Number is a dimensionless number approximating the ratio of momentum diffusivity and thermal diffusivity. ...

A large solid cylinder with a hole in its center and a rail attached to its side.
Liquid helium is used to cool the superconducting magnets in modern MRI scanners.
Scientific

The use of helium reduces the distorting effects of temperature variations in the space between lenses in some telescopes, due to its extremely low index of refraction.[5] This method is especially used in solar telescopes where a vacuum tight telescope tube would be too heavy.[94][95] This article is about the optical device. ... This article does not cite any references or sources. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ...


The age of rocks and minerals that contain uranium and thorium can be estimated by measuring the level of helium with a process known as helium dating.[4][5] This article is about the chemical element. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... Helium Dating (or He dating) is the method of age determination that depends on the production of helium during the decay of the radioactive isotopes uranium-235(U-235), uranium-238(U-238), and thorium-232(Th-232). ...


Liquid helium is used to cool certain metals to the extremely low temperatures required for superconductivity, such as in superconducting magnets for magnetic resonance imaging. The Large Hadron Collider at CERN uses 96 metric tons of liquid helium to maintain the temperature at 1.9 kelvins.[96] Helium at low temperatures is also used in cryogenics. A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. ... Superconducting magnets are electromagnets that are built using superconducting coils. ... MRI redirects here. ... , The Large Hadron Collider (LHC) is a particle accelerator and Hadron collider located at CERN, near Geneva, Switzerland. ... CERN logo The European Organization for Nuclear Research (French: ), commonly known as CERN (see Naming), pronounced (or in French), is the worlds largest particle physics laboratory, situated just northwest of Geneva on the border between France and Switzerland. ... In physics or engineering, cryogenics is the study of the production of very low temperatures (below –150 °C, –238 °F or 123 K) and the behavior of materials at those temperatures. ...


Helium is a commonly used carrier gas for gas chromatography. The leak rate of industrial vessels (typically vacuum chambers and cryogenic tanks) is measured using helium because of its small molecular diameter and because it is inert. No other inert substance will leak through micro-cracks or micro-pores in a vessel's wall at a greater rate than helium. A helium leak detector (see Helium mass spectrometer) is used to find leaks in vessels. Helium leaks through cracks should not be confused with gas permeation through a bulk material. While helium has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and syntheic materials, inert gasses such as helium will not permeate most bulk metals.[97] Gas-liquid chromatography (GLC), or simply gas chromatography (GC) is a type of chromatography in which the mobile phase is a carrier gas, usually an inert gas such as helium or nitrogen, and the stationary phase is a microscopic layer of liquid on an inert solid support. ... A Helium mass spectrometer (often called a leak detector) or sniffer, is a scientific instrument, used to detect very small leaks, typically using a vacuum and injecting helium around a chamber or cavity. ...

Safety

Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood. If enough helium is inhaled that oxygen needed for normal respiration is replaced asphyxia is possible. The safety issues for cryogenic helium are similar to those of liquid nitrogen; its extremely low temperatures can result in cold burns and the liquid to gas expansion ratio can cause explosions if no pressure-relief devices are installed. In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. ... Suffocation redirects here, for the band, see Suffocation (band). ... A tank of liquid nitrogen, used to supply a cryogenic freezer (for storing laboratory samples at a temperature of about -150 Celsius). ... This article is about a medical condition. ...


Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant thermal expansion that occurs when helium gas at less than 10 K is warmed to room temperature.[41] In physics, thermal expansion is the tendency of matter to change in volume in response to a change in temperature. ... For other uses, see Room temperature (disambiguation). ...

Biological effects

The speed of sound in helium is nearly three times the speed of sound in air. Because the fundamental frequency of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the pitches of the resonant frequencies of the vocal tract.[4][98] This causes a reedy, duck-like vocal quality which some people find amusing. (The opposite effect, lowering frequencies, can be obtained by inhaling a dense gas such as sulfur hexafluoride.) For other uses, see Speed of sound (disambiguation). ... Vibration and standing waves in a string, The fundamental and the first 6 overtones The fundamental tone, often referred to simply as the fundamental and abbreviated fo, is the lowest frequency in a harmonic series. ... In physics, resonance is an increase in the oscillatory energy absorbed by a system when the frequency of the oscillations matches the systems natural frequency of vibration (its resonant frequency). ... Sagittal section of human vocal tract The vocal tract is that cavity in animals and humans, where sound that is produced at the sound source (larynx in mammals; syrinx in birds) is filtered. ... Sulfur hexafluoride is an inorganic compound with the formula . ...


Inhaling helium can be dangerous if done to excess, since helium is a simple asphyxiant and so displaces oxygen needed for normal respiration.[4][99] Breathing pure helium continuously causes death by asphyxiation within minutes. Inhaling helium directly from pressurized cylinders is extremely dangerous, as the high flow rate can result in barotrauma, fatally rupturing lung tissue.[99][100] However, death caused by helium is quite rare, with only two fatalities reported between 2000 and 2004 in the United States.[100] Asphyxia is a condition of severely deficient supply of oxygen to the body. ... Asphyxia is a condition of severely deficient supply of oxygen to the body. ... Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding gas or liquid. ...


At high pressures (more than about 20 atm or two MPa), a mixture of helium and oxygen (heliox) can lead to high pressure nervous syndrome, a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem.[101][102] MPA is a TLA (three-letter acronym) that may mean: Macedonian Press Agency Marine Protected Area Maritime Patrol Aircraft Maryland and Pennsylvania Railroad (AAR reporting mark MPA) Master of Public Administration Master of Public Affairs Max Planck Institute for Astrophysics Metropolitan Police Authority Mid-atlantic Pagan Alliance Motion Picture Association...

See also

Notes

  1. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
  2. ^ Helium: Up, Up and Away?Melinda Rose, Contributing Editor, Photonics Spectra, Oct. 2008. Accessed Feb 27, 2010. Entertaining and more up to day article on the helium industry. For a more authoritative but older 1996 pie chart showing US helium use by sector, showing much the same result, see the U.S. Geological Survey chart reproduced in the section on applications below.
  3. ^ Kochhar, R. K. (1991). "French astronomers in India during the 17th - 19th centuries". Journal of the British Astronomical Association 101 (2): 95–100. http://articles.adsabs.harvard.edu//full/1991JBAA..101...95K/0000100.000.html. Retrieved 2008-07-27. 
  4. ^ a b c d e f g h i j k l Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 175–179. ISBN 0-19-850341-5. 
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w Clifford A. Hampel (1968). The Encyclopedia of the Chemical Elements. New York: Van Nostrand Reinhold. pp. 256–268. ISBN 0442155980. 
  6. ^ Sir Norman Lockyer - discovery of the element that he named helium" Balloon Professional Magazine, 07 Aug 2009.
  7. ^ "Helium". Oxford English Dictionary. 2008. http://dictionary.oed.com/cgi/entry/50104457?. Retrieved 2008-07-20. 
  8. ^ Thomson, W. (1872). Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium. Rep. Brit. Assoc. xcix. 
  9. ^ Stewart, Alfred Walter (2008). Recent Advances in Physical and Inorganic Chemistry. BiblioBazaar, LLC. p. 201. ISBN 0554805138. http://books.google.com/books?id=pIqhPFfDMXwC&pg=PA201. 
  10. ^ Ramsay, William (1895). "On a Gas Showing the Spectrum of Helium, the Reputed Cause of D3 , One of the Lines in the Coronal Spectrum. Preliminary Note". Proceedings of the Royal Society of London 58: 65–67. doi:10.1098/rspl.1895.0006. 
  11. ^ Ramsay, William (1895). "Helium, a Gaseous Constituent of Certain Minerals. Part I". Proceedings of the Royal Society of London 58: 80–89. doi:10.1098/rspl.1895.0010. 
  12. ^ Ramsay, William (1895). "Helium, a Gaseous Constituent of Certain Minerals. Part II--". Proceedings of the Royal Society of London 59: 325–330. doi:10.1098/rspl.1895.0097. 
  13. ^ (German) Langlet, N. A. (1895). "Das Atomgewicht des Heliums" (in German). Zeitschrift für anorganische Chemie 10 (1): 289–292. doi:10.1002/zaac.18950100130. 
  14. ^ Weaver, E.R. (1919). "Bibliography of Helium Literature". Industrial & Engineering Chemistry. 
  15. ^ Munday, Pat (1999). John A. Garraty and Mark C. Carnes. ed. Biographical entry for W.F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator in American National Biography. 10-11. Oxford University Press. pp. 808–9; pp. 227–8. 
  16. ^ van Delft, Dirk (2008). "Little cup of Helium, big Science" (PDF). Physics today: 36–42. http://www-lorentz.leidenuniv.nl/history/cold/VanDelftHKO_PT.pdf. Retrieved 2008-07-20. 
  17. ^ "Coldest Cold". Time Inc.. 1929-06-10. http://www.time.com/time/magazine/article/0,9171,751945,00.html. Retrieved 2008-07-27. 
  18. ^ Kapitza, P. (1938). "Viscosity of Liquid Helium below the λ-Point". Nature 141: 74. doi:10.1038/141074a0. 
  19. ^ Osheroff, D. D.; Richardson, R. C.; Lee, D. M. (1972). "Evidence for a New Phase of Solid He3". Phys. Rev. Lett. 28 (14): 885–888. doi:10.1103/PhysRevLett.28.885. 
  20. ^ McFarland, D. F. (1903). "Composition of Gas from a Well at Dexter, Kan". Transactions of the Kansas Academy of Science 19: 60–62. doi:10.2307/3624173. http://www.jstor.org/stable/3624173. Retrieved 2008-07-22. 
  21. ^ "The Discovery of Helium in Natural Gas". American Chemical Society. 2004. http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html. Retrieved 2008-07-20. 
  22. ^ Cady, H.P.; McFarland, D. F. (1906). "Helium in Natural Gas". Science 24 (611): 344. doi:10.1126/science.24.611.344. PMID 17772798. 
  23. ^ Cady, H.P.; McFarland, D. F. (1906). "Helium in Kansas Natural Gas". Transactions of the Kansas Academy of Science 20: 80–81. doi:10.2307/3624645. http://mc1litvip.jstor.org/stable/3624645. Retrieved 2008-07-20. 
  24. ^ Emme, Eugene M. comp., ed (1961). "Aeronautics and Astronautics Chronology, 1920–1924". Aeronautics and Astronautics: An American Chronology of Science and Technology in the Exploration of Space, 1915–1960. Washington, D.C.: NASA. pp. 11–19. http://www.hq.nasa.gov/office/pao/History/Timeline/1920-24.html. Retrieved 2008-07-20. 
  25. ^ Hilleret, N. (1999). "Leak Detection". in S. Turner (PDF). CERN Accelerator School, vacuum technology: proceedings: Scanticon Conference Centre, Snekersten, Denmark, 28 May – 3 June 1999. Geneva, Switzerland: CERN. pp. 203–212. http://doc.cern.ch/yellowrep/1999/99-05/p203.pdf. "At the origin of the helium leak detection method was the Manhattan Project and the unprecedented leak-tightness requirements needed by the uranium enrichment plants. The required sensitivity needed for the leak checking led to the choice of a mass spectrometer designed by Dr. A.O.C. Nier tuned on the helium mass." 
  26. ^ Williamson, John G. (1968). "Energy for Kansas". Transactions of the Kansas Academy of Science (Kansas Academy of Science) 71 (4): 432–438. http://www.jstor.org/pss/3627447. Retrieved 2008-07-27. 
  27. ^ "Conservation Helium Sale" (PDF). Federal Register 70 (193): 58464. 2005-10-06. http://edocket.access.gpo.gov/2005/pdf/05-20084.pdf. Retrieved 2008-07-20. 
  28. ^ a b Stwertka, Albert (1998). Guide to the Elements: Revised Edition. New York; Oxford University Press, p. 24. ISBN 0-19-512708-0
  29. ^ Helium Privatization Act of 1996 Pub.L. 104-273
  30. ^ "Executive Summary". nap.edu. http://www.nap.edu/openbook/0309070384/html/index.html. Retrieved 2008-07-20. 
  31. ^ Mullins, P.V.; Goodling, R. M. (1951). Helium. Bureau of Mines / Minerals yearbook 1949. pp. 599–602. http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=div&did=ECONATRES.MINYB1949.PVMULLINS&isize=text. Retrieved 2008-07-20. 
  32. ^ "Helium End User Statistic" (PDF). U.S. Geological Survey. http://minerals.usgs.gov/ds/2005/140/helium-use.pdf. Retrieved 2008-07-20. 
  33. ^ a b c Smith, E.M.; Goodwin, T.W.; Schillinger, J. (2003). "Challenges to the Worldwide Supply of Helium in the Next Decade" (PDF). Advances in Cryogenic Engineering 49 A (710): 119–138. doi:10.1063/1.1774674. https://www.airproducts.com/NR/rdonlyres/E44F8293-1CEE-4D80-86EA-F9815927BE7E/0/ChallengestoHeliumSupply111003.pdf. Retrieved 2008-07-20. 
  34. ^ Kaplan, Karen H. (June 2007). "Helium shortage hampers research and industry". Physics Today (American Institute of Physics) 60 (6): pp. 31–32. doi:10.1063/1.2754594. http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_6/31_1.shtml. Retrieved 2008-07-20. 
  35. ^ Basu, Sourish (October 2007). "Updates: Into Thin Air". Scientific American (Scientific American, Inc.) 297 (4): pp. 18. http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=E0D18FB2-3048-8A5E-104115527CB01ADB. Retrieved 2008-08-04. 
  36. ^ Watkins, Thayer. San Jose State University. http://www.sjsu.edu/faculty/watkins/helium.htm. 
  37. ^ Weiss, Ray F. (1971). "Solubility of helium and neon in water and seawater". J. Chem. Eng. Data 16 (2): 235–241. doi:10.1021/je60049a019. 
  38. ^ Stone, Jack A.; Stejskal, Alois (2004). "Using helium as a standard of refractive". Metrologia 41: 189–197. doi:10.1088/0026-1394/41/3/012. 
  39. ^ Buhler, F.; Axford, W. I.; Chivers, H. J. A.; Martin, K. (1976). "Helium isotopes in an aurora". J. Geophys. Res. 81 (1): 111–115. doi:10.1029/JA081i001p00111. 
  40. ^ "Solid Helium". Department of Physics University of Alberta. 2005-10-05. http://www.phys.ualberta.ca/~therman/lowtemp/projects1.htm. Retrieved 2008-07-20. 
  41. ^ a b c d e Lide, D. R., ed. (2005), CRC Handbook of Chemistry and Physics (86th ed.), Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5 
  42. ^ Malinowska-Adamska, C.; Soma, P.; Tomaszewski, J. (2003). "Dynamic and thermodynamic properties of solid helium in the reduced all-neighbours approximation of the self-consistent phonon theory". Physica status solidi (b) 240 (1): 55–67. doi:10.1002/pssb.200301871. 
  43. ^ Henshaw, D. B. (1958). "Structure of Solid Helium by Neutron Diffraction". Physical Review Letters 109 (2): 328–330. doi:10.1103/PhysRev.109.328. 
  44. ^ Hohenberg, P. C.; Martin, P. C. (2000). "Microscopic Theory of Superfluid Helium". Annals of Physics 281 (1–2): 636–705 12091211. doi:10.1006/aphy.2000.6019. 
  45. ^ Warner, Brent. "Introduction to Liquid Helium". NASA. Archived from the original on 2005-09-01. http://web.archive.org/web/20050901062951/http://cryowwwebber.gsfc.nasa.gov/introduction/liquid_helium.html. Retrieved 2007-01-05. 
  46. ^ Fairbank, H. A.; Lane, C. T. (1949). "Rollin Film Rates in Liquid Helium". Physical Review 76 (8): 1209–1211. doi:10.1103/PhysRev.76.1209. 
  47. ^ Rollin, B. V.; Simon, F. (1939). "On the "film" phenomenon of liquid helium II". Physica 6 (2): 219–230. doi:10.1016/S0031-8914(39)80013-1. 
  48. ^ Ellis, Fred M. (2005). "Third sound". Wesleyan Quantum Fluids Laboratory. http://fellis.web.wesleyan.edu/research/thrdsnd.html. Retrieved 2008-07-23. 
  49. ^ Bergman, D. (1949). "Hydrodynamics and Third Sound in Thin He II Films". Physical Review 188 (1): 370–384. doi:10.1103/PhysRev.188.370. 
  50. ^ a b Weiss, Achim. "Elements of the past: Big Bang Nucleosynthesis and observation". Max Planck Institute for Gravitational Physics. http://www.einstein-online.info/en/spotlights/BBN_obs/index.html. Retrieved 2008-06-23. ; Coc, A. et al. (2004). "Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements". Astrophysical Journal 600: 544. doi:10.1086/380121. 
  51. ^ a b Anderson, Don L.; Foulger, G. R.; Meibom, A. (2006-09-02). "Helium Fundamentals". MantlePlumes.org. http://www.mantleplumes.org/HeliumFundamentals.html. Retrieved 2008-07-20. 
  52. ^ Novick, Aaron (1947). "Half-Life of Tritium". Physical Review 72: 972–972. doi:10.1103/PhysRev.72.972.2. 
  53. ^ Zastenker G. N. et al. (2002). "Isotopic Composition and Abundance of Interstellar Neutral Helium Based on Direct Measurements". Astrophysics 45 (2): 131–142. doi:10.1023/A:1016057812964. http://www.ingentaconnect.com/content/klu/asys/2002/00000045/00000002/00378626. Retrieved 2008-07-20. 
  54. ^ "Lunar Mining of Helium-3". Fusion Technology Institute of the University of Wisconsin-Madison. 2007-10-19. http://fti.neep.wisc.edu/Research/he3_pubs.html. Retrieved 2008-07-09. 
  55. ^ Slyuta, E. N.; Abdrakhimov, A. M.; Galimov, E. M. (2007). "The estimation of helium-3 probable reserves in lunar regolith" (PDF). Lunar and Planetary Science XXXVIII. http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf. Retrieved 2008-07-20. 
  56. ^ Hedman, Eric R. (2006-01-16). "A fascinating hour with Gerald Kulcinski". The Space Review. http://www.thespacereview.com/article/536/1. Retrieved 2008-07-20. 
  57. ^ Hiby, Julius W. (1939). "Massenspektrographische Untersuchungen an Wasserstoff- und Heliumkanalstrahlen (H+3, H2, HeH+, HeD+, He)". Annalen der Physik 426 (5): 473–487. doi:10.1002/andp.19394260506. 
  58. ^ Ming Wah Wong (2000). "Prediction of a Metastable Helium Compound: HHeF". Journal of the American Chemical Society 122 (26): 6289–6290. doi:10.1021/ja9938175. 
  59. ^ Grochala, W. (2009). "On Chemical Bonding Between Helium and Oxygen". Polish Journal of Chemistry 83: 87–122. 
  60. ^ "Collapse of helium’s chemical nobility predicted by Polish chemist". http://www.uw.edu.pl/en/strony/news/chemist.pdf. Retrieved 2009-05-15. 
  61. ^ Saunders, Martin Hugo; Jiménez-Vázquez, A.; Cross, R. James; Poreda; Robert J. (1993). "Stable Compounds of Helium and Neon: [email protected]60 and [email protected]60". Science 259 (5100): 1428–1430. doi:10.1126/science.259.5100.1428. PMID 17801275. 
  62. ^ Saunders, M. et al. (1994). "Probing the interior of fullerenes by 3He NMR spectroscopy of endohedral 3[email protected]60 and 3[email protected]70". Nature 367: 256–258. doi:10.1038/367256a0. 
  63. ^ Oliver, B. M.; Bradley, James G. (1984). "Helium concentration in the Earth's lower atmosphere". Geochimica et Cosmochimica Acta 48 (9): 1759–1767. doi:10.1016/0016-7037(84)90030-9. 
  64. ^ "The Atmosphere: Introduction". JetStream - Online School for Weather. National Weather Service. 2007-08-29. http://www.srh.weather.gov/jetstream/atmos/atmos_intro.htm. Retrieved 2008-07-12. 
  65. ^ Lie-Svendsen, Ø.; Rees, M. H. (1996). "Helium escape from the terrestrial atmosphere: The ion outflow mechanism". Journal of Geophysical Research 101 (A2): 2435–2444. doi:10.1029/95JA02208. 
  66. ^ Strobel, Nick (2007). "Nick Strobel's Astronomy Notes". http://www.astronomynotes.com/solarsys/s3.htm. Retrieved 2007-09-25. 
  67. ^ Cook, Melvine A. (1957). "Where is the Earth's Radiogenic Helium?". Nature 179: 213. doi:10.1038/179213a0. 
  68. ^ Aldrich, L. T.; Nier, Alfred O. (1948). "The Occurrence of He3 in Natural Sources of Helium". Phys. Rev. 74: 1590–1594. doi:10.1103/PhysRev.74.1590. 
  69. ^ Morrison, P.; Pine, J. (1955). "Radiogenic Origin of the Helium Isotopes in Rock". Annals of the New York Academy of Sciences 62 (3): 71–92. doi:10.1111/j.1749-6632.1955.tb35366.x. 
  70. ^ Zartman, R. E.; Wasserburg, G. J.; Reynolds, J. H. (1961). "Helium Argon and Carbon in Natural Gases". Journal of Geophysical Research 66 (1): 277–306. doi:10.1029/JZ066i001p00277. http://www.agu.org/journals/jz/v066/i001/JZ066i001p00277/. Retrieved 2008-07-21. 
  71. ^ Broadhead, Ronald F. (2005). "Helium in New Mexico – geology distribution resource demand and exploration possibilities" (PDF). New Mexico Geology 27 (4): 93–101. http://geoinfo.nmt.edu/publications/periodicals/nmg/27/n4/helium.pdf. Retrieved 2008-07-21. 
  72. ^ Winter, Mark (2008). "Helium: the essentials". University of Sheffield. http://www.webelements.com/helium/. Retrieved 2008-07-14. 
  73. ^ Cai, Z. et al. (2007). "Modelling Helium Markets" (PDF). University of Cambridge. http://www.jbs.cam.ac.uk/programmes/phd/downloads/conference_spring2007/papers/cai.pdf. Retrieved 2008-07-14. 
  74. ^ "Helium" (PDF). Mineral Commodity Summaries. U.S. Geological Survey. 2009. pp. 74–75. http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2009-heliu.pdf. Retrieved 2009-12-19. 
  75. ^ Belyakov, V.P.; Durgar'yan, S. G.; Mirzoyan, B. A. (1981). "Membrane technology—A new trend in industrial gas separation". Chemical and Petroleum Engineering 17 (1): 19–21. doi:10.1007/BF01245721. 
  76. ^ The Impact of Selling the Federal Helium Reserve Committee on the Impact of Selling the Federal Helium Reserve, Commission on Physical Sciences, Mathematics, and Applications, Commission on Engineering and Technical Systems, National Research Council. Publisher: The National Academies Press. Date: 2000. PAPERBACK ISBN-10: 0-309-07038-4;ISBN-13: 978-0-309-07038-6. Accessed March 2, 2010. For web PDF see [http://www.nap.edu/openbook.php?record_id=9860&page=44R See table 4.2 for the reserve estimate and page 47 for the unproven reserve estimate.
  77. ^ The Impact of Selling the Federal Helium Reserve, Op. cite, see page 40 for the estimate of total theoretical helium production by neon and liquid air plants
  78. ^ Dee, P. I.; Walton E. T. S. (1933). "A Photographic Investigation of the Transmutation of Lithium and Boron by Protons and of Lithium by Ions of the Heavy Isotope of Hydrogen". Proceedings of the Royal Society of London 141 (845): 733–742. doi:10.1098/rspa.1933.0151. 
  79. ^ "Helium Supplies Endangered, Threatening Science And Technology?". Science Daily. 2008. http://www.sciencedaily.com/releases/2008/01/080102093943.htm. Retrieved 2009-08-26. 
  80. ^ Jenkins, Emily (2000). "A Helium Shortage?". Wired. http://www.wired.com/wired/archive/8.08/helium.html. Retrieved 2009-08-26. 
  81. ^ Helium sell-off risks future supply. Michael Banks. Physics World. Jan. 27, 2010. accessed Feb. 27., 2010.
  82. ^ Pie chart showing estimated fractional categories of U.S. helium use, originally drawn in a U.S. Department of the Interior, U.S. Geological Survey. 1996. in: Mineral Industry Surveys: Helium. Reston, Va.: USGS. Taken from The Impact of Selling the Federal Helium Reserve. PAPERBACK ISBN-10: 0-309-07038-4;ISBN-13: 978-0-309-07038-6. Chapter 3, Figure 3.1, in [http://www.nap.edu/openbook.php?record_id=9860&page=27. This site. Accessed Feb. 27, 2010.
  83. ^ "Physics in speech". phys.unsw.edu.au.. http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html. Retrieved 2008-07-20. 
  84. ^ Fowler, B; Ackles KN, Porlier G (1985). "Effects of inert gas narcosis on behavior—a critical review". Undersea Biomedical Research Journal 12 (4): 369–402. PMID 4082343. http://archive.rubicon-foundation.org/3019. Retrieved 2008-06-27. 
  85. ^ Thomas, J. R. (1976). "Reversal of nitrogen narcosis in rats by helium pressure". Undersea Biomed Res. 3 (3): 249–59. PMID 969027. http://archive.rubicon-foundation.org/2771. Retrieved 2008-08-06. 
  86. ^ Rostain, J. C.; Gardette-Chauffour, M. C.; Lemaire, C.; Naquet, R. (1988). "Effects of a H2-He-O2 mixture on the HPNS up to 450 msw". Undersea Biomed. Res. 15 (4): 257–70. OCLC 2068005. PMID 3212843. http://archive.rubicon-foundation.org/2487. Retrieved 2008-06-24. 
  87. ^ Butcher, Scott J.; Jones, Richard L.; Mayne, Jonathan R.; Hartley, Timothy C.; Petersen, Stewart R. (2007). "Impaired exercise ventilatory mechanics with the self-contained breathing apparatus are improved with heliox". European Journal of Applied Physiology (Netherlands: Springer) 101 (6): 659. doi:10.1007/s00421-007-0541-5. PMID 17701048. 
  88. ^ a b Considine, Glenn D., ed (2005). "Helium". Van Nostrand's Encyclopedia of Chemistry. Wiley-Interscience. pp. 764–765. ISBN 0-471-61525-0. 
  89. ^ Hablanian, M. H. (1997). High-vacuum technology: a practical guide. CRC Press. p. 493. ISBN 0824798341. http://books.google.com/books?id=5L8uIAFm4SoC&pg=PA493. 
  90. ^ Beckwith, I.E.; Miller, C. G. (1990). "Aerothermodynamics and Transition in High-Speed Wind Tunnels at Nasa Langley". Annual Review of Fluid Mechanics 22: 419–439. doi:10.1146/annurev.fl.22.010190.002223. 
  91. ^ Morris, C.I. (2001) (PDF). Shock Induced Combustion in High Speed Wedge Flows. Stanford University Thesis. http://thermosciences.stanford.edu/pdf/TSD-143.pdf. 
  92. ^ Belcher, James R. et al (1999). "Working gases in thermoacoustic engines". The Journal of the Acoustical Society of America 105 (5): 2677–2684. doi:10.1121/1.426884. PMID 10335618. 
  93. ^ Makhijani, Arjun; Gurney, Kevin (1995). Mending the Ozone Hole: Science, Technology, and Policy. MIT Press. ISBN 0262133083. 
  94. ^ Jakobsson, H. (1997). "Simulations of the dynamics of the Large Earth-based Solar Telescope". Astronomical & Astrophysical Transactions 13 (1): 35–46. doi:10.1080/10556799708208113. 
  95. ^ Engvold, O.; Dunn, R.B.; Smartt, R. N.; Livingston, W. C. (1983). "Tests of vacuum VS helium in a solar telescope". Applied Optics 22: 10–12. doi:10.1364/AO.22.000010. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1983ApOpt..22...10E&db_key=AST. Retrieved 2008-07-27. 
  96. ^ LHC Guide booklet "CERN - LHC: Facts and Figures". CERN. http://visits.web.cern.ch/visits/guides/tools/presentation/LHC_booklet-2.pdf LHC Guide booklet. Retrieved 2008-04-30. 
  97. ^ Jack W. Ekin (2006). Experimental Techniques for Low-Temperature measurements. Oxford University Press. ISBN 0198570546. http://books.google.co.jp/books?id=Q9tmZQTDPiYC. 
  98. ^ Ackerman MJ, Maitland G (1975). "Calculation of the relative speed of sound in a gas mixture". Undersea Biomed Res 2 (4): 305–10. PMID 1226588. http://archive.rubicon-foundation.org/2738. Retrieved 2008-08-09. 
  99. ^ a b (German) Grassberger, Martin; Krauskopf, Astrid (2007). "Suicidal asphyxiation with helium: Report of three cases Suizid mit Helium Gas: Bericht über drei Fälle" (in German & English). Wiener Klinische Wochenschrift 119 (9–10): 323–325. doi:10.1007/s00508-007-0785-4. PMID 17571238. 
  100. ^ a b Engber, Daniel (2006-06-13). "Stay Out of That Balloon!". Slate.com. http://www.slate.com/id/2143631/. Retrieved 2008-07-14. 
  101. ^ Rostain JC, Lemaire C, Gardette-Chauffour MC, Doucet J, Naquet R (1983). "Estimation of human susceptibility to the high-pressure nervous syndrome". J Appl Physiol 54 (4): 1063–70. PMID 6853282. http://jap.physiology.org/cgi/pmidlookup?view=long&pmid=6853282. Retrieved 2008-08-09. 
  102. ^ Hunger Jr, W. L.; Bennett., P. B. (1974). "The causes, mechanisms and prevention of the high pressure nervous syndrome". Undersea Biomed. Res. 1 (1): 1–28. OCLC 2068005. PMID 4619860. http://archive.rubicon-foundation.org/2661. Retrieved 2008-08-09. 

References

External links

General
More detail
Miscellaneous

The Periodic Table redirects here. ... This article is about the chemistry of hydrogen. ... This article is about the chemical element. ... General Name, symbol, number beryllium, Be, 4 Chemical series alkaline earth metals Group, period, block 2, 2, s Appearance white-gray metallic Standard atomic weight 9. ... For other uses, see Boron (disambiguation). ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... This article is about the chemical element and its most stable form, or dioxygen. ... Distinguished from fluorene and fluorone. ... For other uses, see Neon (disambiguation). ... For sodium in the diet, see Salt. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, symbol, number aluminium, Al, 13 Chemical series poor metals Group, period, block 13, 3, p Appearance silvery Standard atomic weight 26. ... Not to be confused with Silicone. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... This article is about the chemical element. ... General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... For other uses, see Calcium (disambiguation). ... General Name, symbol, number scandium, Sc, 21 Chemical series transition metals Group, period, block 3, 4, d Appearance silvery white Standard atomic weight 44. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery grey-white metallic Standard atomic weight 47. ... General Name, symbol, number vanadium, V, 23 Chemical series transition metals Group, period, block 5, 4, d Appearance silver-grey metal Standard atomic weight 50. ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... General Name, symbol, number manganese, Mn, 25 Chemical series transition metals Group, period, block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... Fe redirects here. ... For other uses, see Cobalt (disambiguation). ... For other uses, see Nickel (disambiguation). ... For other uses, see Copper (disambiguation). ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... Not to be confused with Galium. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Standard atomic weight 72. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... For other uses, see Selenium (disambiguation). ... Bromo redirects here. ... For other uses, see Krypton (disambiguation). ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Standard atomic weight 85. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... General Name, Symbol, Number yttrium, Y, 39 Chemical series transition metals Group, Period, Block 3, 5, d Appearance silvery white Standard atomic weight 88. ... General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... General Name, Symbol, Number niobium, Nb, 41 Chemical series transition metals Group, Period, Block 5, 5, d Appearance gray metallic Standard atomic weight 92. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Standard atomic weight 95. ... General Name, Symbol, Number technetium, Tc, 43 Chemical series transition metals Group, Period, Block 7, 5, d Appearance silvery gray metal Standard atomic weight [98](0) g·mol−1 Electron configuration [Kr] 4d5 5s2 Electrons per shell 2, 8, 18, 13, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number Ruthenium, Ru, 44 Chemical series transition metals Group, Period, Block 8, 5, d Appearance silvery white metallic Standard atomic weight 101. ... General Name, Symbol, Number rhodium, Rh, 45 Chemical series transition metals Group, Period, Block 9, 5, d Appearance silvery white metallic Standard atomic weight 102. ... For other uses, see Palladium (disambiguation). ... This article is about the chemical element. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ... General Name, Symbol, Number indium, In, 49 Chemical series poor metals Group, Period, Block 13, 5, p Appearance silvery lustrous gray Standard atomic weight 114. ... This article is about the metallic chemical element. ... This article is about the element. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ... For other uses, see Iodine (disambiguation). ... General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... For other uses, see Barium (disambiguation). ... General Name, Symbol, Number lanthanum, La, 57 Chemical series lanthanides Group, Period, Block 3, 6, f Appearance silvery white Atomic mass 138. ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 140. ... General Name, Symbol, Number praseodymium, Pr, 59 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance grayish white Standard atomic weight 140. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Standard atomic weight 144. ... General Name, Symbol, Number promethium, Pm, 61 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance metallic Atomic mass [145](0) g/mol Electron configuration [Xe] 4f5 6s2 Electrons per shell 2, 8, 18, 23, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number samarium, Sm, 62 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 150. ... General Name, Symbol, Number gadolinium, Gd, 64 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 157. ... General Name, Symbol, Number terbium, Tb, 65 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 158. ... General Name, Symbol, Number dysprosium, Dy, 66 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 162. ... General Name, Symbol, Number erbium, Er, 68 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 167. ... General Name, Symbol, Number thulium, Tm, 69 Chemical series lanthanides Group, Period, Block ?, 6, f Appearance silvery gray Atomic mass 168. ... Yb redirects here; for the unit of information see Yottabit General Name, Symbol, Number ytterbium, Yb, 70 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 173. ... General Name, Symbol, Number lutetium, Lu, 71 Chemical series lanthanides Group, Period, Block n/a, 6, d Appearance silvery white Standard atomic weight 174. ... General Name, Symbol, Number hafnium, Hf, 72 Chemical series transition metals Group, Period, Block 4, 6, d Appearance grey steel Standard atomic weight 178. ... General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Standard atomic weight 180. ... For other uses, see Tungsten (disambiguation). ... General Name, Symbol, Number rhenium, Re, 75 Chemical series transition metals Group, Period, Block 7, 6, d Appearance grayish white Standard atomic weight 186. ... General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Standard atomic weight 190. ... This article is about the chemical element. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... This article is about the element. ... General Name, Symbol, Number thallium, Tl, 81 Chemical series poor metals Group, Period, Block 13, 6, p Appearance silvery white Standard atomic weight 204. ... General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous pink Standard atomic weight 208. ... General Name, Symbol, Number polonium, Po, 84 Chemical series metalloids Group, Period, Block 16, 6, p Appearance silvery Standard atomic weight (209) g·mol−1 Electron configuration [Xe] 6s2 4f14 5d10 6p4 Electrons per shell 2, 8, 18, 32, 18, 6 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number astatine, At, 85 Chemical series halogens Group, Period, Block 17, 6, p Appearance metallic (presumed) Standard atomic weight (210) g·mol−1 Electron configuration [Xe] 4f14 5d10 6s2 6p5 Electrons per shell 2, 8, 18, 32, 18, 7 Physical properties Phase solid Melting point 575 K... For other uses, see Radon (disambiguation). ... General Name, Symbol, Number francium, Fr, 87 Chemical series alkali metals Group, Period, Block 1, 7, s Appearance metallic Standard atomic weight (223) g·mol−1 Electron configuration [Rn] 7s1 Electrons per shell 2, 8, 18, 32, 18, 8, 1 Physical properties Phase  ? solid Density (near r. ... For other uses, see Radium (disambiguation). ... General Name, Symbol, Number actinium, Ac, 89 Chemical series actinides Group, Period, Block 3, 7, f Appearance silvery Standard atomic weight (227) g·mol−1 Electron configuration [Rn] 6d1 7s2 Electrons per shell 2, 8, 18, 32, 18, 9, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... General Name, Symbol, Number protactinium, Pa, 91 Chemical series actinides Group, Period, Block n/a, 7, f Appearance bright, silvery metallic luster Standard atomic weight 231. ... This article is about the chemical element. ... General Name, Symbol, Number neptunium, Np, 93 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery metallic Standard atomic weight (237) g·mol−1 Electron configuration [Rn] 5f4 6d1 7s2 Electrons per shell 2, 8, 18, 32, 22, 9, 2 Physical properties Phase solid Density (near r. ... This article is about the radioactive element. ... General Name, Symbol, Number americium, Am, 95 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white sometimes yellow Standard atomic weight (243) g·mol−1 Electron configuration [Rn] 5f7 7s2 Electrons per shell 2, 8, 18, 32, 25, 8, 2 Physical properties Phase solid Density (near... General Name, Symbol, Number curium, Cm, 96 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery Atomic mass (247) g/mol Electron configuration [Rn] 5f7 6d1 7s2 Electrons per shell 2, 8, 18, 32, 25, 9, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number berkelium, Bk, 97 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (247) g·mol−1 Electron configuration [Rn] 5f9 7s2 Electrons per shell 2, 8, 18, 32, 27, 8, 2 Physical properties Phase solid... General Name, Symbol, Number californium, Cf, 98 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery Standard atomic weight (251) g·mol−1 Electron configuration [Rn] 5f10 7s2 Electrons per shell 2, 8, 18, 32, 28, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number einsteinium, Es, 99 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Standard atomic weight (252) g·mol−1 Electron configuration [Rn] 5f11 7s2 Electrons per shell 2, 8, 18, 32, 29, 8, 2 Physical properties Phase... General Name, Symbol, Number fermium, Fm, 100 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (257) g·mol−1 Electron configuration [Rn] 5f12 7s2 Electrons per shell 2, 8, 18, 32, 30, 8, 2 Physical properties Phase solid... General Name, Symbol, Number mendelevium, Md, 101 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (258) g·mol−1 Electron configuration [Rn] 5f13 7s2 Electrons per shell 2, 8, 18, 32, 31, 8, 2 Physical properties Phase solid... General Name, Symbol, Number nobelium, No, 102 Chemical series actinides Group, Period, Block n/a, 7, f Appearance unknown, probably silvery white or metallic gray Atomic mass (259) g/mol Electron configuration [Rn] 5f14 7s2 Electrons per shell 2, 8, 18, 32, 32, 8, 2 Physical properties Phase solid Melting... General Name, Symbol, Number lawrencium, Lr, 103 Chemical series transition metals Group, Period, Block n/a, 7, d Appearance unknown, probably silvery white or metallic gray Standard atomic weight [262] g·mol−1 Electron configuration [Rn] 5f14 6d1 7s2 Electrons per shell 2, 8, 18, 32, 32, 9, 2 Physical... General Name, Symbol, Number rutherfordium, Rf, 104 Chemical series transition metals Group, Period, Block 4, 7, d Standard atomic weight (265) g·mol−1 Electron configuration probably [Rn] 5f14 6d2 7s2 Electrons per shell 2, 8, 18, 32, 32, 10, 2 Physical properties Phase presumably a solid Density (near r. ... General Name, Symbol, Number dubnium, Db, 105 Chemical series transition metals Group, Period, Block 5, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (262) g/mol Electron configuration perhaps [Rn] 5f14 6d3 7s2 (guess based on tantalum) Electrons per shell 2, 8, 18, 32, 32, 11... General Name, Symbol, Number seaborgium, Sg, 106 Chemical series transition metals Group, Period, Block 6, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (266) g/mol Electron configuration perhaps [Rn] 5f14 6d4 7s2 (guess based on tungsten) Electrons per shell 2, 8, 18, 32, 32, 12... General Name, Symbol, Number bohrium, Bh, 107 Chemical series transition metals Group, Period, Block 7, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (264) g/mol Electron configuration perhaps [Rn] 5f14 6d5 7s2 (guess based on rhenium) Electrons per shell 2, 8, 18, 32, 32, 13... General Name, Symbol, Number hassium, Hs, 108 Chemical series transition metals Group, Period, Block 8, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (269) g/mol Electron configuration perhaps [Rn] 5f14 6d6 7s2 (guess based on osmium) Electrons per shell 2, 8, 18, 32, 32, 14... General Name, Symbol, Number meitnerium, Mt, 109 Chemical series transition metals Group, Period, Block 9, 7, d Appearance unknown, probably silvery white or metallic gray Standard atomic weight [276] g·mol−1 Electron configuration perhaps [Rn] 5f14 6d7 7s2 (guess based on iridium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number darmstadtium, Ds, 110 Chemical series transition metals Group, Period, Block 10, 7, d Appearance unknown, probably silvery white or metallic gray Atomic mass (281) g/mol Electron configuration perhaps [Rn] 5f14 6d9 7s1 (guess based on platinum) Electrons per shell 2, 8, 18, 32, 32, 17... General Name, Symbol, Number roentgenium, Rg, 111 Chemical series transition metals Group, Period, Block 11, 7, d Appearance unknown, probably yellow or orange metallic Atomic mass (284) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s1 (guess based on gold) Electrons per shell 2, 8, 18, 32, 32, 18, 1... General Name, Symbol, Number ununtrium, Uut, 113 Chemical series presumably poor metals Group, Period, Block 13, 7, p Appearance unknown, probably silvery white or metallic gray Atomic mass (284) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p1 (guess based on thallium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number ununquadium, Uuq, 114 Chemical series presumably poor metals Group, Period, Block 14, 7, p Appearance unknown, probably silvery white or metallic gray Standard atomic weight [289] g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p2 (guess based on lead) Electrons per shell 2, 8... General Name, Symbol, Number ununpentium, Uup, 115 Group, Period, Block 15, 7, p Atomic mass (299) g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p3 (guess based on bismuth) Electrons per shell 2, 8, 18, 32, 32, 18, 5 CAS registry number 54085-64-2 Selected isotopes References... General Name, Symbol, Number ununhexium, Uuh, 116 Chemical series presumably poor metals Group, Period, Block 16, 7, p Appearance unknown, probably silvery white or metallic gray Atomic mass (302) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p4 (guess based on polonium) Electrons per shell 2, 8, 18, 32... General Name, Symbol, Number ununseptium, Uus, 117 Chemical series presumably halogens Group, Period, Block 17, 7, p Appearance unknown, probably dark metallic Standard atomic weight predicted, (310) g·mol−1 Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p5 (guess based on astatine) Electrons per shell 2, 8, 18, 32, 32... General Name, Symbol, Number ununoctium, Uuo, 118 Chemical series noble gases Group, Period, Block 18, 7, p Appearance unknown, probably colorless Atomic mass predicted, (314) g/mol Electron configuration perhaps [Rn] 5f14 6d10 7s2 7p6 (guess based on radon) Electrons per shell 2, 8, 18, 32, 32, 18, 8 Phase... The alkali metals are a series of elements comprising Group 1 (IUPAC style) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... The alkaline earth metals are a series of elements comprising Group 2 (IUPAC style) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). ... The lanthanide series comprises the 15 rare earth elements from lanthanum to lutetium on the periodic table, with atomic numbers 57 through 71. ... The actinide series encompasses the 14 chemical elements that lie between actinium and nobelium on the periodic table with atomic numbers 89 - 102 inclusive. ... In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... This article is about metallic materials. ... Metalloid is a term used in chemistry when classifying the chemical elements. ... Together with the metals and metalloids, a nonmetal is one of three categories of chemical elements as distinguished by ionization and bonding properties. ... This article is about the chemical series. ... This article is about the chemical series. ...


  Results from FactBites:
 
Helium - MSN Encarta (920 words)
Helium is used in inert-gas arc welding for light metals such as aluminum and magnesium alloys that might otherwise oxidize; the helium protects heated parts from attack by air.
Helium is used in place of nitrogen as part of the synthetic atmosphere breathed by deep-sea divers, caisson workers, and others, because it reduces susceptibility to the bends.
Helium, which may be essential to future advanced technologies, was not stockpiled by the U.S. government between 1973 and 1980, nor were private natural-gas producers required to recover helium from their wells.
Helium - Wikipedia, the free encyclopedia (4522 words)
Helium is used in cryogenics, as a deep-sea breathing gas, for inflating balloons and airships, and as a protective gas for many industrial purposes, such as arc welding.
Evidence of helium was first detected on August 18, 1868 as a bright yellow line with a wavelength of 587.49 nanometres in the spectrum of the chromosphere of the Sun, by French astronomer Pierre Janssen during a total solar eclipse in Guntur, India.
The principal impurity in Grade-A helium is neon.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m