Phosphorus occurs in two forms: white phosphorus is made up of pyramidal P₄ units, and is very reactive due to the bond strain in the cage (the P-P-P bond angle is 60^o), and black phosphorus which is made up of extended layers of trigonal pyramidal coordinated P atoms.

Phosphorus forms binary compounds with virtually every metallic element, and many MP compounds have the ZnS (zinc blende) structure. However, compounds containing formally P^3- are metallic and not ionic.

Phosphorus Hydrides

Phosphorus forms hydrides of the same stoichiometry as nitrogen, but the properties are very different.(see here for a comparison of nitrogen and phosphorus.)

Phosphine (PH₃): This has the same pyramidal structure as ammonia, and burns in air after ignition. However, it is only sparingly soluble in water, unlike ammonia, and gives a solution which is neither basic nor acidic.

Diphosphine (P₂H₄): again, this has no basic properties, unlike hydrazine, N₂H₄.

Other Group 15 Hydrides

The stability of MH₃ falls rapidly down the group, and SbH₃ and BiH₃ are very thermally unstable. This reflects the decreasing strength of the M-H bond strength down the group.

AsH₃ and SbH₃ are poisonous.