Allotropes of oxygen

Allotropes of oxygen


There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others include:

  • Atomic oxygen (O1, a free radical)
  • Singlet oxygen (O2), either of two metastable states of molecular oxygen
  • Tetraoxygen (O4), another metastable form
  • Solid oxygen, existing in six variously colored phases, of which one is O8 and another one metallic

Atomic oxygen

Atomic oxygen is very reactive; on Earth's surface it doesn't exist naturally for very long, though in space, the presence of plenty of ultraviolet radiation results in a low Earth orbit atmosphere of about 96% atomic oxygen.[1]


The common allotrope of elemental oxygen on Earth, O2, is known as dioxygen. Elemental oxygen is most commonly encountered in this form, as about 21% (by volume) of Earth's atmosphere. O2 has a bond length of 121 pm and a bond energy of 498 kJ/mol.[2]

Oxygen itself is a colourless gas with a boiling point of -183°C.[3] It can be condensed out of air by cooling with liquid nitrogen, which has a boiling point of -196°C. Liquid oxygen is pale blue in colour, and is quite markedly paramagnetic—liquid oxygen contained in a flask suspended by a string is attracted to a magnet.

Singlet oxygen

Singlet oxygen is the common name used for the two metastable states of molecular oxygen (O2) with higher energy than the ground state triplet oxygen. Because of the differences in their electron shells, singlet oxygen has different chemical properties than triplet oxygen, including Diels-Alder reaction, or absorbing and emitting light at different wavelengths. It can be generated in a photosensitized process by energy transfer from dye molecules such as rose bengal, methylene blue or porphyrins, or by chemical processes such as spontaneous decomposition of hydrogen trioxide in water or the reaction of hydrogen peroxide with hypochlorite


Triatomic oxygen (Ozone, O3), is a very reactive allotrope of oxygen that is destructive to materials like rubber and fabrics and is also damaging to lung tissue.[4] Traces of it can be detected as a sharp, chlorine-like smell,[3] coming from electric motors, laser printers, and photocopiers. It was named "ozone" by Christian Friedrich Schönbein, in 1840, from the Greek word ὠζώ (ozo) for smell.[5]

Ozone is thermodynamically unstable toward the more common dioxygen form, and is formed by reaction of O2 with atomic oxygen produced by splitting of O2 by UV radiation in the upper atmosphere.[5] Ozone absorbs strongly in the ultraviolet and functions as a shield for the biosphere against the mutagenic and other damaging effects of solar UV radiation (see ozone layer).[5] Ozone is formed near the Earth's surface by the photochemical disintegration of nitrogen dioxide from the exhaust of automobiles.[6] Ground-level ozone is an air pollutant that is especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma.[7] The immune system produces ozone as an antimicrobial (see below).[8] Liquid and solid O3 have a deeper-blue color than ordinary oxygen and they are unstable and explosive.[5][9]

Ozone is a pale blue gas condensable to a dark blue liquid. It is formed whenever air is subjected to an electrical discharge, and has the characteristic pungent odour of new-mown hay, or for those living in urban environments, of subways - the so-called 'electrical odour'.


Tetraoxygen had been suspected to exist since the early 1900s, when it was known as oxozone, and was identified in 2001 by a team led by F. Cacace at the University of Rome. The molecule O4 was thought to be in one of the phases of solid oxygen later identified as O8. Cacace's team think that O4 probably consists of two dumbbell-like O2 molecules loosely held together by induced dipole dispersion forces.

Phases of solid oxygen

There are 6 known distinct phases of solid oxygen. One of them is a dark-red O8 cluster. When oxygen is subjected to a pressure of 96 GPa, it becomes metallic, in a similar manner as hydrogen,[10] and becomes more similar to the heavier chalcogens, such as tellurium and polonium, both of which show significant metallic character. At very low temperatures, this phase also becomes superconducting.


  1. ^ Out of Thin Air, a February 17, 2011 article from the NASA website
  2. ^ Chieh, Chung. "Bond Lengths and Energies". University of Waterloo. Retrieved 2007-12-16. 
  3. ^ a b Chemistry Tutorial : Allotropes from
  4. ^ Stwertka 1998, p.48
  5. ^ a b c d Mellor 1939
  6. ^ Stwertka 1998, p.49
  7. ^ "Who is most at risk from ozone?". Retrieved 2008-01-06. 
  8. ^ Paul Wentworth Jr., Jonathan E. McDunn, Anita D. Wentworth, Cindy Takeuchi, Jorge Nieva, Teresa Jones, Cristina Bautista, Julie M. Ruedi, Abel Gutierrez, Kim D. Janda, Bernard M. Babior, Albert Eschenmoser, Richard A. Lerner (2002-12-13). "Evidence for Antibody-Catalyzed Ozone Formation in Bacterial Killing and Inflammation". Science 298 (5601): 2195–2199. Bibcode 2002Sci...298.2195W. doi:10.1126/science.1077642. PMID 12434011. 
  9. ^ Cotton, F. Albert and Wilkinson, Geoffrey (1972). Advanced Inorganic Chemistry: A comprehensive Text. (3rd Edition). New York, London, Sydney, Toronto: Interscience Publications. ISBN 0-471-17560-9.
  10. ^ Peter P. Edwards and Friedrich Hensel (2002-01-14). "Metallic Oxygen". ChemPhysChem 3 (1): 53–56. doi:10.1002/1439-7641(20020118)3:1<53::AID-CPHC53>3.0.CO;2-2. PMID 12465476. Retrieved 2007-12-16. 

Further reading

  • Parks, G. D.; Mellor, J. W. (1939). Mellor's Modern Inorganic Chemistry (6th ed.). London: Longmans, Green and Co. 
  • Stwertka, Albert (1998). Guide to the Elements (Revised ed.). Oxford University Press. ISBN 0-19-508083-1. 

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Oxygen — This article is about the chemical element and its most stable form, O2 or dioxygen. For other forms of this element, see Allotropes of oxygen. For other uses, see Oxygen (disambiguation). nitrogen ← oxygen → fluorine ↑ O ↓ …   Wikipedia

  • Allotropes of carbon — Eight allotropes of carbon: a) Diamond, b) Graphite, c) Lonsdaleite, d) C60 (Buckminsterfullerene or buckyball), e) C540, f) C70, g) Amorphous carbon, and h) single walled carbon nanotube or buckytube. This is a list of the allotropes of carb …   Wikipedia

  • Allotropes of phosphorus — Elemental phosphorus can exist in several allotropes; the most common of which are white and red. There are also violet and black phosphorus, and gaseous diphosphorus.White phosphorus White phosphorus , or yellow phosphorus , or simply… …   Wikipedia

  • Compounds of oxygen — Water (H2O) is the most familiar oxygen compound The oxidation state f oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides. Compounds containing oxygen in other oxidation… …   Wikipedia

  • Solid oxygen — is also used colloquially to refer to oxidizers such as perchlorates, chlorates, or iodine pentoxide from which oxygen can be produced. Solid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K (−218.79 °C, −361.82 °F).… …   Wikipedia

  • Allotropy — (Gr. allos , other, and tropos , manner) is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each different allotrope, the element s atoms are… …   Wikipedia

  • Ozone — For other uses, see Ozone (disambiguation). Ozone …   Wikipedia

  • Ozone depletion — Image of the largest Antarctic ozone hole ever recorded (September 2006) Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth s… …   Wikipedia

  • Sulfur — This article is about the chemical element. For other uses, see Sulfur (disambiguation). phosphorus ← sulfur → chlorine …   Wikipedia

  • Chemical element — The periodic table of the chemical elements A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus.[1] Familiar examples of …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”