Oxidation States of Phosphorus Compounds

The difference in oxidation states between nitrogen and phosphorus is less pronounced than between oxygen and sulfur. Organophosphorus compounds having phosphorus oxidation states ranging from –3 to +5, as shown in the following table, are well known (some simple inorganic compounds are displayed in green). As in the case of sulfur, the P=O double bonds drawn in some of the formulas do not consist of the customary sigma & pi-orbitals found in carbon double bonds. Phosphorus is a third row element, and has five empty 2d-orbitals that may be used for p-d bonding in a fashion similar to p-p (π) bonding. In this way phosphorus may expand an argon-like valence shell octet by two electrons (e.g. phosphine oxides).