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. Red phosphorus is stable at room temperature but burns from impact or frictional heating. Red phosphorus is used in the tips of matches. 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.
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