Phosphorus

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The chemical element Phosphorus has the symbol P and atomic number 15.

Phosphorus had been used as the generic name for substances that shine in the dark without burning - the name coming from the Greek, meaning light-bearing. In the 1670s, the German alchemist Brand of Hamburg attempted the distillation of the salts prepared by the evaporation of urine, and produced a white material that glowed in the dark, and burned brilliantly.

Pure phosphorus exists in several forms. The most common are red, and yellow (or white phosphorus), both of which are groups of tetrahedral groups of four atoms.

White phosphorus burns on contact with air and on exposure to heat or light can transform to red phosphorus. White phosphorus is used in military incendiaries and smoke pots. Early matches used white phosphorus in their composition, which had considerable dangers due to its toxicity: murders, suicides and accidental poisonings resulting from its use.(an apocryphal tale tells of a woman attempting to murder her husband with white phosphorus in his food, which was detected by the stew giving off luminous steam). In addition, exposure to the vapours gave match workers a necrosis of the bones of the jaw, the infamous `phossy jaw'.

When red phosphorus was discovered, with its far lower flammability and toxicity, it was adopted as a safer alternative for match manufacture. Red phosphorus is stable at room temperature but burns from impact or frictional heating. A black phosphorus allotrope exists which has a structure similar to graphite - the atoms are arranged in heaxagonal sheet layers and will conduct electricity.

In compounds phosphorus can have the oxidation numbers -3, 3 and 5. Phosphorous compounds form an essential part of the functions of living things, from the adenosine phosphates in cellular energy reactions, to the calcium phosphate salts that are a component of animal bones.