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Phosphorus Oxides P4O6 (oxidation state of P is +3) and P4O10 (oxidation state of P is +5) are known: they both have tetrahedral cage structures, the difference being that the terminal cage positions are occupied in P4O10 whereas they are not in P4O6.
Group 15 forms binary halides with the elements in two oxidation states: tri-halides with the oxidation state of +3, and penta-halides with the oxidation state of +5.
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 60o), and black phosphorus which is made up of extended layers of trigonal pyramidal coordinated P atoms. Structure of P4 in white phosphorus: The small bond angle in the tetrahedron means this is a highly strained, and therefore very