Phosphorus, phosphoric acid and phosphates
Relate phosphorus allotropes to oxidation, acid–base chemistry, nutrition and environmental balance.
Learning goals: compare white, red and black phosphorus; explain common oxidation states; derive phosphoric acid and phosphate salts; perform mole-ratio calculations; evaluate safe use and nutrient cycling.
1. Element and allotropes
Phosphorus is a group 15 nonmetal with five valence electrons. Important oxidation states are −3, +3 and +5. Elemental phosphorus is 0. Different bonding patterns create allotropes with very different properties. White phosphorus consists of strained tetrahedral P4 molecules, so it is highly reactive, toxic and capable of ignition; it is never a substance for unsupervised handling. Red phosphorus has a polymeric network and is less volatile and less reactive. Black phosphorus has layered structures and is the most thermodynamically stable common allotrope.