Question

Give reason that phosphorous forms PCI5 While nitrogen cannot form NCI5 why

Answer 1

we know that Nitrogen belongs to the 2nd period and phosphorus belongs to the 3rd.

when we see further about their electronic configuration then we find that nitrogen does not have vacant d orbitals because 2D does not exist but in case of phosphorus it has vacant D orbital because 3D can exist.

since nitrogen does not have any vacant D orbital, the electron cannot be excited from it and the maximum covalency of the nitrogen remains 3. but in case of phosphorus as it has vacant D orbital the electrons can be excited and the maximum Valency of Phosphorus can become 5. therefore Phosphorus can combined with 5 chlorine but nitrogen cannot.

I hope you will understand.