Oxygen is prepared for commercial use by the liquefaction and fractional distillation of air and more expensively by the electrolysis of water it is stored and transported under high pressure in steel cylinders. It is found in the sun, and has a role in the stellar carbon cycle (see nucleosynthesis). It makes up about 90% of water, two thirds of the human body and one fifth by volume of air. Most of this oxygen is combined in the form of silicates, oxides and water. Oxygen is the most abundant element on earth, constituting about half of the total material of its surface. The rusting of iron and the corrosion of many metals results from the action of the oxygen in the air. The respiration of animals and plants is a form of oxidation essential to the liberation of the energy stored in such food materials as carbohydrates and fats. The burning of substances in air is rapid oxidation or combustion. The common reaction in which it unites with another substance is called oxidation (see oxidation and reduction). It is a constituent of many acids and of hydroxides, carbohydrates, proteins, fats and oils, alcohols, cellulose, and numerous other compounds such as the carbonates, chlorates, nitrates and nitrites, phosphates and phosphites, and sulphates and sulphites. Oxygen unites directly with a number of other elements to form oxides. Oxygen is extremely active chemically, forming compounds with almost all of the elements except the inert gases. Although eight isotopes of oxygen are known, atmospheric oxygen is a mixture of the three isotopes with mass numbers 16, 17, and 18. Oxygen is paramagnetic in its solid, liquid, and gaseous forms. When cooled below its boiling point oxygen becomes a pale blue liquid when cooled still further the liquid solidifies, retaining its color. Ozone is a highly reactive triatomic (O 3) allotrope of oxygen (see allotropy). Normal atmospheric oxygen is a diatomic gas (O 2) with molecular weight 31.9988. A poor conductor of heat and electricity, oxygen supports combustion but does not burn. It is denser than air and only slightly soluble in water. Oxygen is a colorless, odorless, tasteless gas it is the first member of Group 16 of the periodic table. Johnston announced the discovery of two isotopes of oxygen, of mass numbers 17 and 18. The fact that the gas is a component of the atmosphere was finally and definitely established by Lavoisier a few years later. As a result, Priestley and Scheele are credited with the discovery of the element independently.

Scheele had also succeeded in preparing oxygen from a number of substances, but publication of his findings was delayed until after that of Priestley's. The existence and properties of oxygen had been noted by many scientists before the announcement of its isolation by Priestley in 1774. −182.962℃ density 1.429 grams per liter at STP valence −2. Oxygen, gaseous chemical element symbol O at.

Diatomic oxygen charge