Phosphorous can form PCl_(5) molecule in the excited state of phosphorous atom. But the formation of PH_(5) is not possible in the same state. How do you account for this?

Phosphorous can form PCl_(5) molecule in the excited state of phosphor

1.	Phosphorous can form PCl_(5) molecule in the excited state of phosphorous atom. But the formation of PH_(5) is not possible in the same state. How do you account for this?
Answer» Solution :The valence electronic configuration of phosphorous is `3s^(2)3p^(3)`. THOUGH there are only three half-filled orbitals for bonding, in the excited state five half-filled orbitals are AVAILABLE for bond formation. Among these five orbitals, three are 'p-' orbitals and two are 'd-' orbitals. These orbitals overlap with the half-filled '3p'orbitals of five chlorine atoms forming `PCl_(5)` molecule. Such a situation is not POSSIBLE with hydrogen atoms SINCE there is wide VARIATION in energies between '3d' orbitals of phosphorous and '1s' orbitals of hydrogen.