Bond energies nitrogen-phosphorus

The bond energy of the P=P bond is 493kI/mol and the P-P bond energy is 209kJ/mol. Use these values to show that form of elemental phosphorus is expected to be different from that of elemental nitrogen. 

The stable form of nitrogen at room temperature is N2, which has an extraordinarily strong (946 kJ mol-1) triple bond In contrast, white phosphorus consists of P4 molecules (see Chapter 16), and the thermodynamically stable form is black phosphorus, a polymer. At temperatures above 800 °C dissociation to P> molecules does take place, but these are considerably less stable than N2 with a bond energy of488 kJ mol 1. In this case. too. in the heavier element several single bonds arc more effective than the multiple bond. 

A quantum-mechanical study of the model compounds TiCl3N=PH3 and Re03N=PH3 reveals that the metal-ligand bond dissociates homolytically. Variation of the metal-nitrogen-phosphorus angle influences the potential energy surface only to a small extent." ... 

Apparently, the particulate organic matter is oxidized, even in deep waters, but at a very slow rate. This modification of organic matter tends to the formation of very inert substances, more aliphatic molecules, refractory to further decomposition. The organic matter first loses nitrogen, phosphorus and oxygen since the activation energies for cleav e of the C—C and C—H bonds are several kcal mole" higher than those of the C—N, C—P or C—O bonds (Toth and Lerman, 1977). 

It has already been pointed out that in the case of phosphorus the magnitude of the tt-bonding energy is much less in relation to the o-bonding energy than is the case with nitrogen (Table 3.12). 

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