Question

why Ncl5 is known while Pcl5 is known

Answer 1

NCl5 is not known as nitrogen has very small size and cannot bear 5 large chlorine atoms. Hence NCl5 is not known as Pcl5 is known as it can easily hold 5 cl atoms.

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.