Difference between revisions of "Oxygen"
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The preparation was first carried out by Swedish chemist [[Carl Wilhelm Scheele]] on several occasions during the period 1771–73. Scheele heated various compounds such as [[Potassium nitrate|KNO<sub>3</sub>]], [[Magnesium nitrate|Mg(NO<sub>3</sub>)<sub>2</sub>]] and [[Mercury(II) oxide|HgO]] and found that they gave off a gas that he named "vitriol air", which supported combustion better than normal air.<ref name="G&E">{{Greenwood&Earnshaw1st|pages=698–756}}.</ref> Scheele's results, however, were not published until 1777.<ref>{{citation | first = Carl Wilhelm | last = Scheele | authorlink = Carl Wilhelm Scheele | title = Chemische Abhandlung von der Luft und dem Feuer | url = http://books.google.co.uk/books?id=beoTAAAAQAAJ | location = Uppsala and Leipzig | publisher = Siverderus | year = 1777}}; [http://web.lemoyne.edu/~giunta/scheele77.html Translated extracts].</ref> In the meantime, Priestley had isolated the gas given off by heating HgO and named it "dephlogisticated air", and published his results in 1775 after proving that the gas was different from [[nitrous oxide]].<ref>{{citation | title = Experiments and Observations on Different Kinds of Air. Volume II | edition = 2nd | year = 1775 | location = London | url = http://books.google.co.uk/books?id=gB0UAAAAQAAJ | first = Joseph | last = Priestley | authorlink = Joseph Priestley | publisher = J. Johnson}}.</ref> | The preparation was first carried out by Swedish chemist [[Carl Wilhelm Scheele]] on several occasions during the period 1771–73. Scheele heated various compounds such as [[Potassium nitrate|KNO<sub>3</sub>]], [[Magnesium nitrate|Mg(NO<sub>3</sub>)<sub>2</sub>]] and [[Mercury(II) oxide|HgO]] and found that they gave off a gas that he named "vitriol air", which supported combustion better than normal air.<ref name="G&E">{{Greenwood&Earnshaw1st|pages=698–756}}.</ref> Scheele's results, however, were not published until 1777.<ref>{{citation | first = Carl Wilhelm | last = Scheele | authorlink = Carl Wilhelm Scheele | title = Chemische Abhandlung von der Luft und dem Feuer | url = http://books.google.co.uk/books?id=beoTAAAAQAAJ | location = Uppsala and Leipzig | publisher = Siverderus | year = 1777}}; [http://web.lemoyne.edu/~giunta/scheele77.html Translated extracts].</ref> In the meantime, Priestley had isolated the gas given off by heating HgO and named it "dephlogisticated air", and published his results in 1775 after proving that the gas was different from [[nitrous oxide]].<ref>{{citation | title = Experiments and Observations on Different Kinds of Air. Volume II | edition = 2nd | year = 1775 | location = London | url = http://books.google.co.uk/books?id=gB0UAAAAQAAJ | first = Joseph | last = Priestley | authorlink = Joseph Priestley | publisher = J. Johnson}}.</ref> | ||
− | Priestley's work certainly had the greater impact, as he was able to discuss it with French chemist [[Antoine Lavoisier]] in October 1774 during a visit to Paris with his mentor and employer the Earl of Shelbourne. | + | Priestley's work certainly had the greater impact, as he was able to discuss it with French chemist [[Antoine Lavoisier]] in October 1774 during a visit to Paris with his mentor and employer the Earl of Shelbourne. Lavoisier repeated and extended Priestley's work, and published his results in 1777 as ''Mémoire sur la combustion en général''<ref>{{citation | first = Antoine | last = Lavoisier | authorlink = Antoine Lavoisier | title = Mémoire sur la combustion en général | url = http://www.lavoisier.cnrs.fr/ice/modules/ice2pdf/pdf/extraitPDF06-04-2010_9-53-25.pdf | journal = Mem. Acad. Sci. Paris | year = 1777 | pages = 592}}.</ref> and ''Considérations générales sur la nature des acides et sur les principes dont ils sont composés''.<ref>{{citation | first = Antoine | last = Lavoisier | authorlink = Antoine Lavoisier | title = Considérations générales sur la nature des acides et sur les principes dont ils sont composés | url = http://books.google.co.uk/books?id=qbc-AAAAcAAJ&hl=en&pg=PA248#v=onepage | journal = Mem. Acad. Sci. Paris | year = 1778}}.</ref> |
+ | It was Lavoisier who proposed the name "oxygen" for the new gas. | ||
==Occurance and production== | ==Occurance and production== |
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Oxygen (ˈɒksɨdʒɨn) is a colourless gas which makes up about one fifth of the Earth's atmosphere. Its name comes from the Greek ὀξύς (oxys; acid, literally "sharp", from the taste of acids) and -γενής (-genēs; producer, literally "begetter").
Contents
History
The discovery of oxygen is often credited to English chemist Joseph Priestley, although the full story is somewhat more involved. That there is a component of air which is necessary for combustion and respiration was recognized by Leonardo da Vinci in the fifteenth century, and confirmed by English chemist John Mayow in the mid-seventeenth century.[10] However, the interpretation of these results was hampered by the rise of phlogiston theory, which stated that substances gave off phlogiston during combustion: air that was no longer capable of supporting combustion was said to be saturated with phlogiston. The unequivocal identification of oxygen as a chemical substance would have to wait for its preparation by chemical means.
The preparation was first carried out by Swedish chemist Carl Wilhelm Scheele on several occasions during the period 1771–73. Scheele heated various compounds such as KNO3, Mg(NO3)2 and HgO and found that they gave off a gas that he named "vitriol air", which supported combustion better than normal air.[11] Scheele's results, however, were not published until 1777.[12] In the meantime, Priestley had isolated the gas given off by heating HgO and named it "dephlogisticated air", and published his results in 1775 after proving that the gas was different from nitrous oxide.[13]
Priestley's work certainly had the greater impact, as he was able to discuss it with French chemist Antoine Lavoisier in October 1774 during a visit to Paris with his mentor and employer the Earl of Shelbourne. Lavoisier repeated and extended Priestley's work, and published his results in 1777 as Mémoire sur la combustion en général[14] and Considérations générales sur la nature des acides et sur les principes dont ils sont composés.[15] It was Lavoisier who proposed the name "oxygen" for the new gas.
Occurance and production
Oxygen is almost ubiquitous at the surface of the Earth. The approximate mass fractions of oxygen are: crustal rocks 46%; the human body 61%; sea water 86%. The amount fraction of oxygen in the Earth's atmosphere (at sea level) is 20.9476%,[16] amounting to some 1015 tonnes. Apart from the atmosphere, the vast majority of this oxygen is chemically combined in a wide variety of inorganic and organic compounds: in the atmosphere, oxygen exists almost entirely as dioxygen (O2) molecules, its normal elemental state, with a small (but very important) amount of ozone (O3).
While it is difficult to obtain precise statistics, oxygen is believed to be the third most important bulk industrial chemical, after sulfuric acid and lime but ahead of ammonia and nitrogen, with production of at least 100 million tonnes per year. It is produced by the fractional distillation of liquid air. As the transport costs for the raw material (air) are zero, it is often economic to locate the oxygen plant close to the consumer, even for relatively small consumers such as hospitals.
Use
The majority of oxygen produced (ca. 70%) is used in the basic oxygen process for steelmaking.[11] A streem of pure oxygen is blown into the molton iron, where it burns off the residual carbon to produce low-carbon (0.1–1.0%) steel. Another large scale use is in oil refining, particularly in fluid catalytic cracking (FCC) units that treat roughly one-third of the total crude oil. The oxygen does not play a direct role in the cracking process, but is used to regenerate the catalyst, which rapidly gets contaminated with byproduct coke. The oxygen is mixed with air to give a mixture of around 28% O2,[2] and this is used to burn the coke off the catalyst: the heat released from the combustion of the coke compensates for the heat lost in the endothermic cracking reactions, hence the need for a strict control of the rate of combustion.
Oxygen is also used in other bulk chemical processes, such as the manufactire of ethylene oxide, propylene oxide, ethylene dichloride, vinyl chloride, vinyl acetate, titanium dioxide and ferric sulfate. It can also be used to enrich the air stream in processes that normally use air, such as the production of acrylonitrile and terephthalic acid, and is used in the production of synthesis gas (CO/H2).[2][11]
Allotropes
Oxygen forms two allotropes: dioxygen (O2) and ozone (O3). Dioxygen is by far the commonest form. It is a colourless and odourless gas at ambient temperature and pressure, and condenses to a pale blue liquid at −183.0 °C. Unusually for a diatomic molecule, it is paramagnetic, with two unpaired electrons occupying π* orbitals.
Ozone (trioxygen) is an unstable, toxic gas with a characteristic odour. It is formed from dioxygen by the action of an electric discharge (e.g., during lighteneing storms) or ultraviolet light (e.g., in photochemical smog). The O3 molecule is bent, with an angle of 116.8(5)° at the central oxygen and bond lengths of 127.8(3) pm.
Chemical properties
Water and hydrogen peroxide
Oxides
Oxygen forms binary compounds with all the elements except the noble gases (although xenon forms two well-defined oxides). Oxides cover the full range of bonding types from almost completely ionic (e.g., caesium oxide) to almost completely covalent (e.g., chlorine dioxide), and show a huge variety of structural types.
Oxygen fluorides
As fluorine is more electronegative than oxygen, their binary compounds are properly referred to as oxygen fluorides rather than fluorine oxides. The most stable is oxygen difluoride, OF2, first prepared in 1929, a colourless, toxic gas (bp = −145.3 °C) that is a powerful oxidizing and fluorinating agent. Dioxygen difluoride, O2F2, and other unstable species are also known.[11]
Dioxygen as a ligand
Organic compunds of oxygen
Biological role
Safety
Notes and references
Notes
References
- ↑ 1.0 1.1 Oxygen. In NIST Chemistry WebBook; National Institute for Standards and Technology, <http://webbook.nist.gov/cgi/inchi/InChI%3D1S/O2/c1-2>. (accessed 15 March 2010).
- ↑ 2.0 2.1 2.2 Oxygen. In Gas Encyclopedia; Air Liquide, <http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=48>. (accessed 3 April 2010).
- ↑ Allred, A. L. Electronegativity values from thermochemical data. J. Inorg. Nucl. Chem. 1961, 17 (3–4), 215–21. DOI: 10.1016/0022-1902(61)80142-5.
- ↑ 4.0 4.1 Oxygen, atomic. In NIST Chemistry WebBook; National Institute for Standards and Technology, <http://webbook.nist.gov/cgi/inchi/InChI%3D1S/O>. (accessed 15 March 2010).
- ↑ Mohr, Peter J.; Taylor, Barry N. CODATA recommended values of the fundamental physical constants: 2002. Rev. Mod. Phys. 2005, 77 (1), 1–107. DOI: 10.1103/RevModPhys.77.1.
- ↑ Cordero, Beatriz; Gómez, Verónica; Platero-Prats, Ana E.; Revés, Marc; Echeverría, Jorge; Cremades, Eduard; Barragán, Flavia; Alvarez, Santiago Covalent radii revisited. Dalton Trans. 2008 (5), 2832–38. DOI: 10.1039/b801115j.
- ↑ Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halids and chalcogenides. Acta Crystallogr. A 1976, 32 (5), 751–67. DOI: 10.1107/S0567739476001551.
- ↑ Bondi, A. van der Waals Volumes and Radii. J. Phys. Chem. 1964, 68 (3), 441–51. DOI: 10.1021/j100785a001.
- ↑ Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics; Hemisphere: New York, 1989. ISBN 0891167587, <http://www.codata.org/resources/databases/key1.html>.
- ↑ Mayow, John De sal-nitro et spiritu nitro-aereo. In Tractatus quinque medico-physici; Sheldonian: Oxford, 1674, summarized in Phil. Trans. R. Soc. London 1674, 9, 101–13, <http://gallica.bnf.fr/ark:/12148/bpt6k558143.image.f110.langEN>.
- ↑ 11.0 11.1 11.2 11.3 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 698–756. ISBN 0-08-022057-6.
- ↑ Scheele, Carl Wilhelm Chemische Abhandlung von der Luft und dem Feuer; Siverderus: Uppsala and Leipzig, 1777, <http://books.google.co.uk/books?id=beoTAAAAQAAJ>; Translated extracts.
- ↑ Priestley, Joseph Experiments and Observations on Different Kinds of Air. Volume II, 2nd ed.; J. Johnson: London, 1775, <http://books.google.co.uk/books?id=gB0UAAAAQAAJ>.
- ↑ Lavoisier, Antoine Mémoire sur la combustion en général. Mem. Acad. Sci. Paris 1777, 592, <http://www.lavoisier.cnrs.fr/ice/modules/ice2pdf/pdf/extraitPDF06-04-2010_9-53-25.pdf>.
- ↑ Lavoisier, Antoine Considérations générales sur la nature des acides et sur les principes dont ils sont composés. Mem. Acad. Sci. Paris 1778, <http://books.google.co.uk/books?id=qbc-AAAAcAAJ&hl=en&pg=PA248#v=onepage>.
- ↑ U.S. Standard Atmosphere, 1976; National Oceanic and Atmospheric Administration: Washington, D.C., 1976; p 3, <http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf>.
External links
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