Question

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

Answer 1

Atomic number of P in PCI₅ = 15 = 1s³ , 2s³ , 2p⁶ , 3s² , 2p³ , ground state

Here one 3s, three 3p and one 3d [3d² ] atomic orbitals undergo hybridisation giving to sp³d hybridisation.

1,2,3 are inclined at angle of 120º,4,5 are inclined ⊥ plane of paper.

Shape of PCl₅ is Trigonal bipyramidal

a : axial bonds

e : equatorial bonds

The P-CI equatorial bond length is 2.04 Å whereas P-Cl axial bond length is 2.10 Å . The reason for the longer axial bond length is that the three P-C1 equatorial bonds are repelled only by two electron pairs. 

Thus, the repulsion exerted on the axial bond pairs is more and hence bond length is longer.