PCI_(5) is known but NCI_(5) is not known. Or Nitrogen does not form pentahalide.

PCI_(5) is known but NCI_(5) is not known. Or Nitrogen does not form

1.	PCI_(5) is known but NCI_(5) is not known. Or Nitrogen does not form pentahalide.
Answer» Solution :ELECTRONIC configuration of P is `1 s^(2)2 s^(2) 2 s^(6) 3 s^(2)" "3 P_(x)^(1) 3P_(y)^(1)3P_(z)^(1)3d^(0)`. Thus, P has emptly 3d orbitals to which the 3S ELECTRON can be excited to have five half-filled orbitals needed for formation of `PCI_(5)`. Thus, `PCl_(5)`, is known. In contrast, electronic configuration of N is `1s^(2)2s^(2)2P_(x)^(1)2P_(y)^(1)2P_(z)^(1)`. Since the valence shell of nitrogen has n = 2, therefore, it cannot have d-orbitals. However, if one of the 2s electrons is excited to 3s orbital, five half-filled orbitals needed to form `NCI_(5)`can still be obtained. But such an excitation is thermodynamically not favourable since the energy needed for excitation is more than the energy expected to be generated during the formation of TWO additional P-CI bonds. Therefore, nitrogen doesnot form `NCI_(5)`. In other words, `NCI_(5)` is UNKNOWN.