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Encyclopedia > Selenium dioxide
Selenium dioxide
Selenium dioxide
Other names Selenium(IV) oxide
Selenium dioxide
Molecular formula SeO2
Molar mass 110.96 g/mol
Appearance White crystalline solid
CAS number [7446-08-4]
Density and phase 3.95 g/cm3, solid
Solubility in water 3.950 g/100 ml (25 °C)
Boiling point 315 °C sublimes
Acidity (pKa) 2.62 (H2SeO3 HSeO3 + H+)
8.32 (HSeO3 SeO32− + H+)
Crystal structure chain structure
EU classification Toxic (T)
Dangerous for
the environment (N)
NFPA 704
Image:nfpa h3.png Image:nfpa f0.png Image:nfpa r0.png
R-phrases R23/25, R33, R50/53
S-phrases S1/2, S20/21, S28
S45, S60, S61
U.S. Permissible
Exposure Limit
5 ppm
IDLH (NIOSH) 100 ppm
Flash point non-flammable
RTECS number WS4550000
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other cations Sulfur dioxide
Tellurium dioxide
Related compounds Selenium trioxide
Selenous acid
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Selenium dioxide is one of the more frequently encountered compounds of selenium. Image File history File links Download high resolution version (3241x1345, 20 KB) Summary Description: Solid state structure of selenium dioxide. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... General Name, Symbol, Number selenium, Se, 34 Chemical series nonmetals Group, Period, Block 16, 4, p Appearance gray, metallic luster Atomic mass 78. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... 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. ... It has been suggested that this article or section be merged with Solution. ... Water has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. ... The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid. ... In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant (Ka) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... The coordination geometry of an atom is the geometrical pattern formed by its neighbors in a molecule or a crystal. ... Rose des Sables (Sand Rose), formed of gypsum crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (as amended) is the main source of European Union law concerning chemical safety. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... The Permissible Exposure Limit (PEL or OSHA PEL) is a legal limit in the United States for personal exposure to a substance, usually expressed in parts per million (ppm). ... Immediately Dangerous to Life and Health (IDLH or NIOSH IDLH) is a limit for personal exposure to a substance defined by the United States National Institute for Occupational Safety and Health (NIOSH), normally expressed in parts per million (ppm). ... The National Institute for Occupational Safety and Health (NIOSH) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. ... The flash point of a fuel is the lowest temperature at which it can form an ignitable mix with air. ... RTECS, also known as Registry of Toxic Effects of Chemical Substances, is a database of toxicity information compiled from the open scientific literature that is available for charge. ... The refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ... The dielectric constant εr (represented as or K in some cases) is defined as the ratio: where εs is the static permittivity of the material in question, and ε0 is the vacuum permittivity. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... IR spectrum of a thin film of liquid ethanol. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ... Mass spectrometry is an analytical technique to measure the mass-to-charge ratio (m/q) of ions. ... // An ion is an atom or group of atoms with a net electric charge. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... Tellurium dioxide (TeO2 or paratellurite) is a solid oxide of tellurium. ... Selenous acid, H2SeO3, is an oxygen acid of selenium. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... General Name, Symbol, Number selenium, Se, 34 Chemical series nonmetals Group, Period, Block 16, 4, p Appearance gray, metallic luster Atomic mass 78. ...



Selenium dioxide may be prepared from selenium by burning in air or by reaction with hydrogen peroxide, but perhaps the most convenient preparation is by the dehydration of selenous acid. Hydrogen peroxide (H2O2) is a clear liquid, slightly more viscous than water, that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant, as an oxidizer, and in rocketry (particularly in high concentrations as high-test peroxide (HTP) as a monopropellant), and... Selenous acid, H2SeO3, is an oxygen acid of selenium. ...

3Se + 4HNO3 + H2O → 3H2SeO3 + 4NO
H2SeO3 → SeO2 + H2O


Solid selenium dioxide is colorless. Structurally, the solid consists of a polymeric chain of alternating selenium and oxygen atoms. Each Se atom, which are pyramidal, bears a terminal oxide group. Polymer is a generic term used to describe a very long molecule consisting of structural units and repeating units connected by covalent chemical bonds. ...

SeO2 is considered an acidic oxide dissolving in water to form selenous acid and reacting with base to form selenite SeO32-. An Acidic oxide (sometimes known as an acidic anhydride, but not to be confused with an acid anhydride) is an oxide that either reacts with water to form an acid; or reacts with a base to form a salt. ...


Selenium dioxide imparts a red colour to glass: it is used in small quantities to counteract the blue colour due to cobalt impurities and so to create (apparently) colourless glass. In larger quanties, it give a deep ruby red colour. This article refers to the material. ... General Name, Symbol, Number cobalt, Co, 27 Chemical series transition metals Group, Period, Block 9, 4, d Appearance metallic with gray tinge Atomic mass 58. ...

It is also used as a toner in photographic developing.



  • Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn.) New York:Wiley-Interscience. ISBN 0-471-19957-5.
  • Lide, D. R. (Ed.) (2002). CRC Handbook of Chemistry and Physics (83rd Edn.), Boca Raton (FL):CRC Press. ISBN 0-8493-0483-0.

Sir Geoffrey Wilkinson was an English chemist He was born 14 July 1921 in the village of Springside, near Todmorden in Yorkshire. ...

External links

  • International Chemical Safety Card 0946
  • European Chemicals Bureau

  Results from FactBites:
Selenium - Wikipedia, the free encyclopedia (1492 words)
Selenium also occurs in organic compounds such as dimethyl selenide, selenomethionine and selenocysteine, all of which have high bioavailability and are toxic in large doses.
Selenium poisoning as a result of agricultural runoff was also found to have caused birth defects in birds.
Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown that selenium deficiency does strongly corelate with the progression of the disease and the risk of death[25][26][27].
ATSDR - ToxFAQs™: Selenium (1057 words)
Selenium is a trace mineral needed in small amounts for good health, but exposure to much higher levels can result in neurological effects and brittle hair and deformed nails.
Selenium is a naturally occurring mineral element that is distributed widely in nature in most rocks and soils.
Selenium sulfide is not present in foods and is a very different chemical from the organic and inorganic selenium compounds found in foods and in the environment.
  More results at FactBites »



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