In comparing phosphorus to nitrogen, some basic differences must be remem-bered. Phosphorus is much less electronegative than nitrogen (2.2 vs. 3.0 ),and its greater size causes bond lengths to be considerably larger (P-C, 1.84 in phosphines; N-C 1.70 in amines). This creates a difference in the steric environment around these these atoms. A more profound difference is in ability of phosphorus to participate in a form of multiple bonding to oxygen that is absent in nitrogen chemistry; this leads to a great variety of structural types (e.g. ,phosphoric, phosphonic, and phosphinic acids and derivatives ) that are quite unknown for nitrogen.