Why `PCl_(5)` exists but `NCl_(5)` does not ?

Explanation

Electron configuration of `""_(15)P` is `1s^(2) 2sp^(2) 2sp^(2) 2p^(6) 3s^(2) 3p_(x)^(1) 3p_(y)^(1) 3p_(z)^(1)` .
Thus, the 3d orbitals of the valence shell are empty . Hence , an electron from 3s can jump to 3d , giving the
configuration `1s^(2) 2sp^(2) 2p^(6) 3s^(1) 3p_(x)^(1) 3p_(y)^(1) 3p_(z)^(1)3d^(1)` . Thus , it can extend its covalency to 5. in case of `""_(7)N` , elec-
tronic configuration `1s^(2) 2s^(2) 2p_(x)^(1) 2p_(y)^(1)2p_(z)^(1)` . As there is no 2d orbital , it connot extend its covalency to 5.