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Encyclopedia > Chemical Formula

A chemical formula is an easy way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs. For molecular compounds, it identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 19th-century books often used superscripts). For ionic compounds and other non-molecular substances, the subscripts indicate the ratio of elements in the empirical formula. For other uses, see Atom (disambiguation). ... Look up chemical compound in Wiktionary, the free dictionary. ... It has been suggested that Molecular compound be merged into this article or section. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... A chemical symbol is an abbreviation or short representation of the name of a chemical element. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A subscript is a number, figure, or indicator that appears below the normal line of type, typically used in a formula, mathematical expression, or description of a chemical compound. ... The crystal structure of sodium chloride, NaCl, a typical ionic compound. ... In chemistry, the empirical formula of a chemical compound is a simple expression of the relative number of each type of atom in it. ...


This system for writing chemical formulas was invented by the 19th-century Swedish chemist Jons Jakob Berzelius. Jöns Jacob Berzelius (August 20, 1779 - August 7, 1848) was a Swedish chemist, who invented modern chemical notation and is considered one of the fathers of modern chemistry (along with John Dalton and Antoine Lavoisier). ...

Contents

Molecular and structural formula

For example methane, a simple molecule consisting of one carbon atom bonded to four hydrogen atoms, has the chemical formula: Methane is a chemical compound with the molecular formula . ... For other uses, see Carbon (disambiguation). ... This article is about the chemistry of hydrogen. ...

CH4

and glucose with six carbon atoms, twelve hydrogen atoms and six oxygen atoms has the chemical formula: Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... This article is about the chemical element and its most stable form, or dioxygen. ...

C6H12O6.

A chemical formula supplies information about the types and spatial arrangement of bonds in the chemical, though it does not necessarily specify the exact isomer. For example ethane consists of two carbon atoms single-bonded to each other, with each carbon atom having three hydrogen atoms bonded to it. Its chemical formula can be rendered as CH3CH3. In ethylene there is a double bond between the carbon atoms (and thus each carbon only has two hydrogens), therefore the chemical formula may be written: CH2CH2, and the fact that there is a double bond between the carbons is implicit because carbon has a valence of four. However, a more explicit and correct method is to write H2C=CH2 or less commonly H2C::CH2. The two lines (or two pairs of dots) indicate that a double bond connects the atoms on either side of them. A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently (analogous to a chemical anagram). ... This article is about a chemical compound. ... Ethylene (or IUPAC name ethene) is the chemical compound with the formula C2H4. ...


A triple bond may be expressed with three lines or pairs of dots, and if there may be ambiguity, a single line or pair of dots may be used to indicate a single bond.


Molecules with multiple functional groups that are the same may be expressed in the following way: (CH3)3CH. However, this implies a different structure from other molecules that can be formed using the same atoms (isomers). The formula (CH3)3CH implies a chain of three carbon atoms, with the middle carbon atom bonded to another carbon (see image of 4 carbon "C" atoms), In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ...

and the remaining bonds on the carbons all leading to hydrogen atoms (hydrogen atoms are not shown in image). However, the same number of atoms (10 hydrogens and 4 carbons, or C4H10) may be used to make a straight chain: CH3CH2CH2CH3. This is an image for the chemical formula page. ...


The alkene but-2-ene has two isomers which the chemical formula CH3CH=CHCH3 does not identify. The relative position of the two methyl groups must be indicated by additional notation denoting whether the methyl groups are on the same side of the double bond (cis or Z) or on the opposite sides from each other (trans or E).


Polymers

For polymers, parentheses are placed around the repeating unit. For example, a hydrocarbon molecule that is described as: CH3(CH2)50CH3, is a molecule with 50 repeating units. If the number of repeating units is unknown or variable, the letter n may be used to indicate this: CH3(CH2)nCH3.
A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Look up Hydrocarbon in Wiktionary, the free dictionary. ...


Ions

For ions, the charge on a particular atom may be denoted with a right-hand superscript. For example Na+, or Cu2+. The total charge on a charged molecule or a polyatomic ion may also be shown in this way. For example: hydronium, H3O+ or sulfate, SO42-. This article is about the electrically charged particle. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas coloured yellow A polyatomic ion is a molecule that bears ionic groups, that is, a molecule with a charge. ...


For more complex ions, brackets [ ] are often used to enclose the ionic formula, as in [B12H12]2-. Parentheses ( ) can be nested inside brackets to indicate a repeating unit, as in [Co(NH3)6]3+. Here (NH3)6 indicates that the ion contains six NH3 groups, and [ ] encloses the entire formula of the ion with charge +3.


Isotopes

Although isotopes are more relevant to nuclear chemistry or stable isotope chemistry than to conventional chemistry, different isotopes may be indicated with a left-hand superscript in a chemical formula. For example, the phosphate ion containing radioactive phosphorus-32 is 32PO43-. Also a study involving stable isotope ratios might include the molecule 18O16O. For other uses, see Isotope (disambiguation). ... Nuclear chemistry is a subfield of chemistry dealing with radioactivity, nuclear processes and nuclear properties. ... Stable isotopes are chemical isotopes that are not radioactive. ... This article is about the term superscript as used in typography. ...


A left-hand subscript is sometimes used to indicate redundantly the atomic number. For example, 8O2 for dioxygen, and 168O2 for the most abundant isotopic species of dioxygen. This is convenient when writing equations for nuclear reactions, in order to show the balance of charge more clearly. 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 nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. ...


Empirical formula

In chemistry, the empirical formula of a chemical is a simple expression of the relative number of each type of atom or ratio of the elements in the compound. Empirical formulas are the standard for ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative percent composition of a pure chemical substance by element. For other uses, see Chemistry (disambiguation). ... In chemistry, the empirical formula of a chemical compound is a simple expression of the relative number of each type of atom in it. ... In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently (analogous to a chemical anagram). ... Elemental analysis is a process where a sample of some material (eg. ... This article does not cite any references or sources. ...


For example hexane has a molecular formula of C6H14, or structurally CH3CH2CH2CH2CH2CH3, implying that it has a chain structure of 6 carbon atoms, and 14 hydrogen atoms. However, the empirical formula for hexane is C3H7. Likewise the empirical formula for hydrogen peroxide, H2O2, is simply HO expressing the 1:1 ratio of component elements. the 3rd ingredient in big mac ... For other uses, see Carbon (disambiguation). ... This article is about the chemistry of hydrogen. ... R-phrases , , , , S-phrases , , , , , , , , Flash point Non-flammable Related Compounds Related compounds Water Ozone Hydrazine Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colorless in...


Trapped atoms

The @ symbol ("at") indicates an atom or molecule trapped inside a cage but not chemically bound to it. This notation became popular in the 1990s with the discovery of fullerene cages, which can trap atoms such as La to form La@C60 or La@C82 for example. A non-fullerene example is [As@Ni12As20]3-, an ion in which one As atom is trapped in a cage formed by the other 32 atoms. The Icosahedral Fullerene C540 C60 and C-60 redirect here. ...


Non-stoichiometric formulas

Main article: Non-stoichiometric compound Non-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and are therefore in violation of the law of definite proportions. ...


Chemical formulas most often use integers for each element. However, there is a whole class of compounds, called non-stoichiometric compounds, that cannot be represented by small integers. Such a formula might be written using decimal fractions, as in Fe0.95O, or it might include a variable part represented by a letter, as in Fe1–xO, where x is normally much less than 1. The integers are commonly denoted by the above symbol. ... Non-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and are therefore in violation of the law of definite proportions. ... Decimal, or denary, notation is the most common way of writing the base 10 numeral system, which uses various symbols for ten distinct quantities (0, 1, 2, 3, 4, 5, 6, 7, 8 and 9, called digits) together with the decimal point and the sign symbols + (plus) and − (minus) to...


General forms for organic compounds

Chemical formula used for a series of compounds that differ from each other by a constant unit is called general formula. Such a series is called the homologous series, while its members are called homologs. The Hill system is a common convention for writing and sorting formulas. In chemistry, a homologous series is a series of organic compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass (see relative molecular mass). ... The Hill system is a system of writing chemical formulas such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other elements subsequently, in alphabetical order. ...


Hill System

Main article: Hill system

The Hill system is a system of writing chemical formulas such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other chemical elements subsequently, in alphabetical order. When the formula contains no carbon, all the elements, including hydrogen, are listed alphabetically. The Hill system is a system of writing chemical formulas such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other elements subsequently, in alphabetical order. ... For other uses, see Carbon (disambiguation). ... For other uses, see Atom (disambiguation). ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... This article is about the chemistry of hydrogen. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... This article needs cleanup. ...


References

Ralph S. Petrucci, William S. Harwood and F. Geoffrey Herring, General Chemistry, 8th Edition (Prentice-Hall 2002), chapter 3.


See also

The Periodic Table redirects here. ... A chemical symbol is an abbreviation or short representation of the name of a chemical element. ... The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. ...

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