Phosphorus, a nonmetallic chemical element. It is an abundant element and in nature is always found combined with other elements. Phosphorus compounds known as phosphates are essential to life; they are used in cellular metabolism and are found in cell protoplasm, nervous tissue, and bones.

Elemental phosphorus can exist in three forms, or allotropes—white, red, and black. (The white form is also known as yellow phosphorus; the black form, as violet phosphorus.) Only the white and red forms are important commercially. White phosphorus, the most common form, is a translucent, waxy solid. In contact with the air, white phosphorus glows and can ignite spontaneously. For this reason, it is usually kept underwater as a safety precaution. White phosphorus is very poisonous. Red phosphorus is not as reactive as the white form.

White phosphorus is used chiefly for producing phosphoric acid and other phosphorus compounds, primarily for use in fertilizers, detergents, and foods and beverages, and in treating metallic surfaces to prevent corrosion. Some white phosphorus is used in rat poisons and in metallurgy. Red phosphorus is used in the manufacture of safety matches and fertilizers.

Phosphorus was discovered in 1669 by Hennig Brand, a German alchemist. He gave the element its name after observing that it glows. (Phosphorus comes from the Greek word for light-bearing.) Most phosphorus is produced commercially from phosphate rock, which consists largely of calcium phosphate in the form of the mineral apatite. The southeastern United States, China, northern Africa, Kazakhstan, and Russia are the major sources of phosphate rock. White phosphorus of high purity is produced by heating phosphate rock in an electric furnace with silica and coke. Most white phosphorus is produced by treating phosphate rock with an acid such as sulfuric acid. Red phosphorus is produced by heating white phosphorus in an airtight container.

Symbol: P. Atomic number: 15. Atomic weight: 30.97376. Specific gravity: 1.82 (white), 2.20 (red). Melting point: 111.6 F. (44.2 C.) (white). Boiling point: 536 F. (280 C.) (white). Phosphorus has seven isotopes, of which only P-31 is stable. Phosphorus belongs to Group VA of the Periodic Table and has a valence of +3 or +5.