Question

Pcl5 is known but ncl5 is not known.Why?

Answer 1

The covalency of nitrogen its only 3 so nitrogen from ncl3 but due to vacant Orbit covalency of phosphorus is 3 and 5 so Phosphorus from both pcl3 and PCL5

Answer 2

Phosphorous has d-orbitals & hence

can accommodate the electrons

from Cl into them,in case of N the

d-orbitals are absent & electrons can be

accommodated only in p-orbitals.Hence

PC15 exists.