264.

Descibe the hybridisation in case of PCl₅. Why are the axial bonds longer as compared to equatorial bonds?

Hybridization is the phenomenon of intermixing of atomic orbitals of slightly different energies of the atoms by redistributing their energies to form a new set of orbitals of equivalent energies and identical shape.
Atomic number of phosphorus P=15.
Electronic configuration of P
Ground state 1s² 2s² 3s² 3p³ 3d⁰

Electronic configuration of P
excited state 1s² 2s² 3s¹ 3p³ 3d¹


Now phosphorus has five empty shells, five Cl hybridised to form an equal set of equivalent five sp3d hybrid orbitals. These 5 sp3d orbitals are directed towards the five corners of a trigonal bipyramidal geometry.

In PCl₅, out of the five hybrid orbitals, three orbitals form a P-Cl bond in one plane making and angle (P-Cl-P) 120 with each other. This plane is represented as equatorial plane and the bonds formed are equatorial bonds. Out of the remaining two hybrid orbitals, one lie perpendicularly above and the other lie perpendicularly above and the other lie perpendicularly below the equatorial plane, making an angle 90 with the plane and forms P-Cl bonds. These two bonds are called axial bonds. Since the axial bonds suffer more repulsive interaction from the equatorial bond pairs, they are found to be slightly longer and hence, slightly weaker than the equatorial bonds.