Discovered | Name | Characteristics | Prepared | Uses

Oxygen is the lightest nonmetal of Group VIA. Other members of the group are sulfur(S), selenium(Se), tellurium(Te), and polonium(Po).

Priestley is generally credited with its discovery in 1774. It was prepared by heating mercury(II) oxide.

2 HgO(s) + heat 2 Hg(liq) + O2(g)

The name is derived from the Greek words, oxys and genes, meaning acid-former. Lavoisier gave it this name on the belief that all acids contained this element. The symbol O is an abbreviation of the name.

Oxygen is the third most abundant element found in the universe. As a gaseous element, it forms 21% of the atmosphere by volume. The element and its compounds make up 49.2% by weight of the earth's crust (as sand and similar materials). About two thirds of the human body and 89% of water is oxygen.

The gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are magnetic, but much less so than iron.

Ozone, O3, a highly active allotropic form of oxygen, is formed by the action of an electrical discharge or ultraviolet light on oxygen.

3 O2+ hv 2 O3

Ozone's presence in the atmosphere (amounting to the equivalent of a layer 3 mm thick at ordinary pressures and temperatures) is of vital importance in preventing ultraviolet rays from the sun from reaching the earth's surface and destroying life on earth.

For many centuries, scientists, including Leonardo da Vinci, 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 recognize it as an elementary substance. Priestley is generally credited with its discovery in 1774. Scheele discovered it independently at about the same time, but publication of his findings was delayed until after that of Priestley's.

Oxygen is prepared for commercial use by the liquefaction and fractional distillation of air and more expensively by the electrolysis of water.

2 H2O(liq) + electricity 2 H2(g) + O2(g)

In the laboratory it can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst.

2 KClO3(s) + heat 2 KCl(s) + 3 O2(g)

Oxygen is very reactive and capable of combining with most elements. It is a component of hundreds of thousands of organic compounds. It is essential for respiration of all plants and animals and for practically all combustion.

Oxygen enrichment for basic-oxygen steelmaking furnaces is the greatest industrial use of the gas. Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding. Oxygen is utilized in medicine in the treatment of respiratory diseases and is used for respiration in marines, high-flying planes and spaceships. Liquid oxygen is used as an oxidizer in the fuel systems of large rockets.

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. In 1929 W.F. Giaque and H.L. Johnston announced the discovery of heavy oxygen, i.e., of two isotopes of oxygen of mass 17 and 18, respectively.