Atomic Number: 8
Atomic Symbol: O
Atomic Weight: 15.9994
Electron Configuration: [He]2s22p4
History(Gr. oxys, sharp, acid, and genes, forming; acid former) 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.
SourcesOxygen 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.
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.
PropertiesThe gas is colorless, odorless, and tasteless. The liquid and solid
forms are a pale blue color and are strongly paramagnetic.
FormsOzone (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/m3 (8-hour
time-weighted average - 40-hour work week). Undiluted ozone has a bluish
color. Liquid ozone is bluish black and solid ozone is violet-black.
CompoundsOxygen, which is very reactive, is a component of hundreds of
thousands of organic compounds and combines with most elements.
UsesPlants and animals rely on oxygen for respiration. Hospitals
frequently prescribe oxygen for patients with respiratory ailments.
IsotopesOxygen has nine isotopes. Natural oxygen is a mixture of three
Natural occurring oxygen 18 is stable and available
commercially, as is water (H2O with 15% 18O). Commercial oxygen
consumption in the U.S. is estimated at 20 million short tons per year and the
demand is expected to increase substantially.
Oxygen enrichment of steel blast furnaces accounts for the
greatest use of the gas. Large quantities are also used in making synthesis
gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding.
Air separation plants produce about 99% of the gas, while
electrolysis plants produce about 1%.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.