Phosphorus
. Phosphorus, symbol P, reactive nonmetallic element that is important to living organisms and has many industrial uses. The atomic number of phosphorus is 15, and its atomic weight is 30.974. Phosphorus is in group 15 (or Va) of the periodic table . Phosphorus was discovered about 1669 by the German alchemist Hennig Brand in the course of experiments in which he attempted to prepare gold from silver. PROPERTIES AND OCCURRENCE Phosphorus exists in three main allotropic (distinctly different) forms: ordinary (or white) phosphorus, red phosphorus, and black phosphorus. Of these, only white and red phosphorus are of commercial importance. When freshly prepared, ordinary phosphorus is white, but it turns light yellow when exposed to sunlight. It is a crystalline, translucent, waxy solid, which glows faintly in moist air and is extremely poisonous. It ignites spontaneously in air at 34° C (93° F) and must be stored under water. It is insoluble in water, slightly soluble in organic solvents,