Oxygen
Uploaded by xxbritishgalxx on Mar 01, 2005
Atomic Number: 8
Atomic Radius: 66 pm
Atomic Symbol: O
Melting Point: -218.79 ºC
Atomic Weight: 15.9994
Boiling Point: -182.95 ºC
Electron Configuration: [He]2s22p4
Oxidation States: -2
History
(Gr. oxys: acid, and genes: forming) For many centuries, workers occasionally realized air was composed of more than one component. The behavior of oxygen and nitrogen as components of air led to the advancement of the phlogiston theory of combustion, which captured the minds of chemists for a century. Oxygen was prepared by several workers, including Bayen and Borch, but they did not know how to collect it, did not study its properties, and did not recognize it as an elementary substance.
Priestley is generally credited with its discovery, although Scheele also discovered it independently.
Its atomic weight was used as a standard of comparison for each of the other elements until 1961 when the International Union of Pure and Applied Chemistry adopted carbon 12 as the new basis.
Sources
Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, the process once thought to give the sun and stars their energy. Oxygen under excited conditions is responsible for the bright red and yellow-green colors of the Aurora Borealis.
A gaseous element, oxygen forms 21% of the atmosphere by volume and is obtained by liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15% oxygen. The element and its compounds make up 49.2%, by weight, of the earth's crust. About two thirds of the human body and nine tenths of water is oxygen.
In the laboratory it can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst.
Properties
The gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are strongly paramagnetic.
Forms
Ozone (O3), a highly active compound, is formed by the action of an electrical discharge or ultraviolet light on oxygen.
Ozone's presence in the atmosphere (amounting to the equivalent of a layer 3 mm thick under ordinary pressures and temperatures) helps prevent harmful ultraviolet rays of the sun from reaching the earth's surface. Pollutants in the atmosphere may have a detrimental effect on this ozone layer. Ozone is toxic and exposure should not exceed 0.2 mg/m# (8-hour time-weighted average - 40-hour...