Properties of phosphorus

Phosphorus is a highly reactive element, and its most important chemical properties are as follows. Reaction with oxygen: yellow (white) phosphorus catches fire readily in air, giving dense white fumes of phosphorus pentoxide, P4O10, whereas red phosphorus is less reactive and only reacts with oxygen on heating, giving either phosphorus trioxide, P4O6, or phosphorus pentoxide, P4O10, depending on conditions (P4 + 3O2 -> P4O6; P4 + 5O2 -> P4O10). Reaction with chlorine: phosphorus forms both a trichloride and a pentachloride with chlorine; yellow phosphorus reacts violently even at room temperature, while red phosphorus needs heating (P4 + 6Cl2 -> 4PCl3; P4 + 10Cl2 -> 4PCl5). Reaction with alkali: on boiling in an inert atmosphere, yellow phosphorus reacts with sodium hydroxide solution to liberate phosphine gas, with phosphorus itself acting as the reducing agent (and simultaneously being oxidised to hypophosphite) — P4 + 3NaOH + 3H2O -> 3NaH2PO2 (sodium hypophosphite) + PH3. Reaction with nitric acid: treatment with concentrated nitric acid, catalysed by traces of iodine, oxidises phosphorus all the way to orthophosphoric acid (P4 + 20HNO3 -> 4H3PO4 + 20NO2 + 4H2O). Reaction with metals: phosphorus reacts with metals such as calcium and magnesium to give ionic phosphides (P4 + 6Mg -> 2Mg3P2, magnesium phosphide; P4 + 6Ca -> 2Ca3P2, calcium phosphide), while more electropositive metals such as sodium and potassium react with it vigo …