page_title: Phosphorus
section_title: Phosphorus(V)
hierarchical_section_title: Phosphorus / Compounds / Phosphorus(V)
context_page_description: Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth. It has a concentration in the Earth's crust of about one gram per kilogram. In minerals, phosphorus generally occurs as phosphate.
  Elemental phosphorus was first isolated as white phosphorus in 1669. White phosphorus emits a faint glow when exposed to oxygen – hence the name, taken from Greek mythology, Φωσφόρος meaning "light-bearer", referring to the "Morning Star", the planet Venus. The term "phosphorescence", meaning glow after illumination, derives from this property of phosphorus, although the word has since been used for a different physical process that produces a glow. The glow of phosphorus is caused by oxidation of the white phosphorus — a process now called chemiluminescence. Together with nitrogen, arsenic, antimony, and bismuth, phosphorus is classified as a pnictogen.
  Phosphorus is essential for life. Phosphates are a component of DNA, RNA, ATP, and phospholipids.
context_section_description: The most prevalent compounds of phosphorus are derivatives of phosphate (PO₄³⁻), a tetrahedral anion. Phosphate is the conjugate base of phosphoric acid, which is produced on a massive scale for use in fertilisers. Being triprotic, phosphoric acid converts stepwise to three conjugate bases:
  H₃PO₄ + H₂O ⇌ H₃O⁺ + H₂PO₄⁻       Kₐ₁= 7.25×10⁻³
  H₂PO₄⁻ + H₂O ⇌ H₃O⁺ + HPO₄²⁻       Kₐ₂= 6.31×10⁻⁸
  HPO₄²⁻ + H₂O ⇌ H₃O⁺ +  PO₄³⁻        Kₐ₃= 3.98×10⁻¹³
  Phosphate exhibits a tendency to form chains and rings containing P-O-P bonds. Many polyphosphates are known, including ATP. Polyphosphates arise by dehydration of hydrogen phosphates such as HPO₄²⁻ and H₂PO₄⁻. For example, the industrially important pentasodium triphosphate (also known as sodium tripolyphosphate, STPP) is produced industrially on by the megatonne by this condensation reaction:
  2 Na₂[(HO)PO₃] + Na[(HO)₂PO₂] → Na₅[O₃P-O-P(O)₂-O-PO₃] + 2 H₂O
  Phosphorus pentoxide (P₄O₁₀) is the acid anhydride of phosphoric acid, but several intermediates between the two are known. This waxy white solid reacts vigorously with water.
  With metal cations, phosphate forms a variety of salts. These solids are polymeric, featuring P-O-M linkages. When the metal cation has a charge of 2+ or 3+, the salts are generally insoluble, hence they exist as common minerals. Many phosphate salts are derived from hydrogen phosphate (HPO₄²⁻).
  PCl₅ and PF₅ are common compounds. PF₅ is a colourless gas and the molecules have trigonal bipyramidal geometry. PCl₅ is a colourless solid which has an ionic formulation of PCl₄⁺ PCl₆⁻, but adopts the trigonal bipyramidal geometry when molten or in the vapour phase. PBr₅ is an unstable solid formulated as PBr₄⁺Br⁻and PI₅ is not known. The pentachloride and pentafluoride are Lewis acids. With fluoride, PF₅ forms PF₆⁻, an anion that is isoelectronic with SF₆. The most important oxyhalide is phosphorus oxychloride, (POCl₃), which is approximately tetrahedral.
  Before extensive computer calculations were feasible, it was thought that bonding in phosphorus(V) compounds involved d orbitals. Computer modeling of molecular orbital theory indicates that this bonding involves only s- and p-orbitals.
caption: The tetrahedral structure of P4O10 and P4S10.
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