Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks. Elemental phosphorus exists in two major forms – white phosphorus and red phosphorus, but due to its high reactivity, phosphorus is never found as a free element on Earth.
The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen – hence its name given from Greek mythology, meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus. Although the term "phosphorescence", meaning glow after illumination, derives from this property of phosphorus, the glow of phosphorus originates from oxidation of the white (but not red) phosphorus and should be called chemiluminescence.
Phosphorus compounds are used in explosives, nerve agents, friction matches, fireworks, pesticides, toothpastes, and detergents.
Phosphorus is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. It is thus an essential element for all living cells, and organisms tend to accumulate and concentrate it. For example, elemental phosphorus was historically first isolated from the sedement in human urine, and bone ash was an important early phosphate source. Low phosphate levels are an important limit to growth in some aquatic systems. Today, the most important commercial use of phosphorus-based chemicals is the production of fertilizers, to replace the phosphorus that plants remove from the soil.
