Phosphorus - P, 15

The melting point of phosphorus (white) is 44.1C, boiling point (white) is 280C, specific gravity (white) is 1.82, (red) 2.20, (black) 2.25-2.69, with a valence of 3 or 5. There are four allotropic forms of phosphorus: two forms of white (or yellow), red, and black (or violet). White phosphorus exhibits a and b modifications, with a transition temperature between the two forms at -3.8C. Ordinary phosphorus is a waxy white solid. It is colorless and transparent in its pure form. Phosphorus is insoluble in water, but soluble in carbon disulfide. Phosphorus burns spontaneously in air to its pentoxide. It is highly poisonous, with a lethal dose of ~50 mg. White phosphorus should be stored under water and handled with forceps. It causes severe burns when in contact with skin. White phosphorus is converted to red phosphorus when exposed to sunlight or heated in its own vapor to 250C. Unlike white phosphorus, red phosphorus does not phosphoresce in air, although it still requires careful handling.

Red phosphorus, which is relatively stable, is used to make safety matches, tracer bullets, incendiary devices, pesticides, pyrotechnic devices, and many other products. There is a high demand for phosphates for use as fertilizers. Phosphates are also used to make certain glasses (e.g., for sodium lamps). Trisodium phosphate is used as a cleaner, water softener, and scale/corrosion inhibitor. Bone ash (calcium phosphate) is used to make chinaware and to make monocalcium phosphate for baking powder. Phosphorus is used to make steels and phosphor bronze and is added to other alloys. There are many uses for organic phosphorus compounds. Phosphorus is an essential element in plant and animal cytoplasm. In humans, it is essential for proper skeletal and nervous system formation and function.