Phosphorus is a chemical element; it has symbol P and atomic number 15. All elemental forms of phosphorus are highly reactive and are therefore never found in nature. Elemental phosphorus can be prepared artificially, the two most common allotropes being white phosphorus and red phosphorus. With 31P as its only stable isotope, phosphorus has an occurrence in Earth's crust of about 0.1%, generally as phosphate rock. A member of the pnictogen family, phosphorus readily forms a wide variety of organic and inorganic compounds, with as its main oxidation states +5, +3 and −3. The isolation of white phosphorus in 1669 by Hennig Brand marked the scientific community's first discovery of an element since antiquity. The name phosphorus is a reference to the god of the Morning star in Greek mythology, inspired by the faint glow of white phosphorus when exposed to oxygen. This property is also at the origin of the term phosphorescence, meaning glow after illumination, although white phosphorus itself does not exhibit phosphorescence, but chemiluminescence caused by its oxidation. Its high toxicity makes exposure to white phosphorus very dangerous, while its flammability and pyrophoricity can be weaponised in the form of incendiaries. Red phosphorus is less dangerous and is used in matches and fire retardants. Most industrial production of phosphorus is focused on the mining and transformation of phosphate rock into phosphoric acid for phosphate-based fertilisers. Phosphorus is an essential and often limiting nutrient for plants, and while natural levels are normally maintained over time by the phosphorus cycle, it is too slow for the regeneration of soil that undergoes intensive cultivation. As a consequence, these fertilisers are vital to modern agriculture. The leading producers of phosphate ore in 2024 were China, Morocco, the United States and Russia, with two-thirds of the estimated exploitable phosphate reserves worldwide in Morocco alone. Other applications of phosphorus compounds include pesticides, food additives, and detergents. Phosphorus is essential to all known forms of life, largely through organophosphates, organic compounds containing the phosphate ion PO3−4 as a functional group. These include DNA, RNA, ATP, and phospholipids, complex compounds fundamental to the functioning of all cells. The main component of bones and teeth, bone mineral, is a modified form of hydroxyapatite, itself a phosphorus mineral.
History
Phosphorus was the first element to be "discovered", in the sense that it was not known since ancient times. The discovery is credited to the Hamburg alchemist Hennig Brand in 1669, who was attempting to create the fabled philosopher's stone. To this end, he experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism. By letting the urine rot (a step later discovered to be unnecessary), boiling it down to a paste, then distilling it at a high temperature and leading the resulting vapours through water, he obtained a white, waxy substance that glowed in the dark and burned brilliantly. He named it in Latin: phosphorus mirabilis, lit. 'miraculous bearer of light'. The word phosphorus itself (Ancient Greek: Φωσφόρος, romanized: Phōsphoros, lit. 'light-bearer') originates from Greek mythology, where it references the god of the morning star, also known as the planet Venus. Brand at first tried to keep the method secret, but later sold the recipe for 200 thalers to Johann Daniel Kraft from Dresden. Kraft toured much of Europe with it, including London, where he met with Robert Boyle. The crucial fact that the substance was made from urine was eventually found out, and Johann Kunckel was able to reproduce it in Sweden in 1678. In 1680, Boyle also managed to make phosphorus and published the method of its manufacture. He was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of modern matches, and also improved the process by using sand in the reaction:
4 NaPO3 + 2 SiO2 + 10 C → 2 Na2SiO3 + 10 CO + P4 Boyle's assistant Ambrose Godfrey-Hanckwitz later made a business of the manufacture of phosphorus. In 1777, Antoine Lavoisier recognised phosphorus as an element after Johan Gottlieb Gahn and Carl Wilhelm Scheele showed in 1769 that calcium phosphate is found in bones by obtaining elemental phosphorus from bone ash. Bone ash subsequently became the primary industrial source of phosphorus and remained so until the 1840s. The process consisted of several steps. First, grinding up the bones into their constituent tricalcium phosphate and treating it with sulfuric acid:
Ca3(PO4)2 + 2 H2SO4 → Ca(H2PO4)2 + 2 CaSO4 Then, dehydrating the resulting monocalcium phosphate:
Ca(H2PO4)2 → Ca(PO3)2 + 2 H2O Finally, mixing the obtained calcium metaphosphate with ground coal or charcoal in an iron pot, and distilling phosphorus vapour out of a retort:
3 Ca(PO3)2 + 10 C → Ca3(PO4)2 + 10 CO + P4 This way, two-thirds of the phosphorus was turned into white phosphorus while one-third remained in the residue as calcium orthophosphate. The carbon monoxide produced during the reaction process was burnt off in a flare stack.
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