Phosphorus

Phosphorus has five valence electrons ([Ne]3s2 3p3), sitting below nitrogen in group 15. Unlike nitrogen, it does not form strong multiple bonds, so instead of a diatomic gas, elemental phosphorus forms single-bonded structures. White phosphorus consists of P4 tetrahedra whose 60° bond angles are badly strained, so it is highly reactive: it ignites in air at about 30 °C and glows in the dark as it slowly oxidizes. Heating it converts it to red phosphorus, a much more stable polymer, and high pressure gives black phosphorus, which is layered like graphite.

In nature, phosphorus is found almost entirely as phosphate, PO4 3-, and it is essential to life: phosphate groups form the backbone of DNA and RNA, carry energy in ATP and make up the membranes around every cell. Bones and teeth are largely calcium phosphate. Because crops remove phosphorus from soil, most mined phosphate rock goes into fertilizers, and about 70% of known reserves lie in Morocco and Western Sahara. Phosphate washing off farmland into lakes can feed algal blooms that starve the water of oxygen.

Discovery

In 1669 Hennig Brand, a Hamburg merchant and alchemist searching for the philosopher's stone, boiled down large quantities of urine and heated the residue. He obtained a white, waxy substance that glowed in the dark. Brand is the first person known by name to have discovered an element. The name comes from the Greek phosphoros, 'light-bearer', which was also an ancient name for Venus as the morning star.