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Oxygen's key role in combustion make it necessary for smelting steel and in oxy acetylene welding. |
Oxygen
| Atomic Number: | 8 | Atomic Radius: | 152 pm (Van der Waals) |
| Atomic Symbol: | O | Melting Point: | -218.79 °C |
| Atomic Weight: | 16.00 | Boiling Point: | -182.96 °C |
| Electron Configuration: | [He]2s22p4 | Oxidation States: | 2, 1, −1, −2 |
History
From the Greek word oxys, acid, and genes, forming. 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.
Joseph 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 work week). Undiluted ozone has a bluish color. Liquid ozone is bluish black and solid ozone is violet-black.
Compounds
Oxygen, which is very reactive, is a component of hundreds of thousands of organic compounds and combines with most elements.
Uses
Plants and animals rely on oxygen for respiration. Hospitals frequently prescribe oxygen for patients with respiratory ailments.
Isotopes
Oxygen has nine isotopes. Natural oxygen is a mixture of three isotopes.
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%.