(i) Why all the bonds of $PC{{l}_{5}}$ are not equivalent?
(ii) Why does nitrogen show catenation property less than phosphorus?
Or
Unlike phosphorus, nitrogen shows little tendency for catenation. Why?
(i) In $PC{{l}_{5}}$, P is sp3 hybridised and thus, possesses trigonal bipyramidal geometry. It has three equatorial P—Cl bonds and two axial P—Cl bonds. Since, two axial P—Cl bonds are repelled by three bond pairs while three equatorial P—Cl bonds are repelled by two bond pairs. Therefore, axial bonds are longer than equatorial bonds. Thus, all the five P—Cl bonds in PC15 are not equivalent.
(ii) The property of catenation depends upon the strength of the element-element bond. Since, the N—N bond strength (159 kj ${{mol}^{-1}}$) is much weaker than P—P bond strength (213 kj ${{mol}^{-1}}$), therefore, nitrogen shows less catenation property than phosphorus.