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Question 38

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


Atomic number of Phosphorous is 15.

The Ground state configuration is

& the excited state configuration is

The 5 electrons present in valence shell form bond pairs with the electrons of five chlorine atoms. Phosphorus atom is sp3d hybridized in the excited state.


The geometry of PCl5 is trigonal bipyramidal .The P atom lies in the centre of an equatorial triangle & three P-Cl bonds (equatorial bonds) are directed towards its three corners with 120° bond angle. The remaining two P-Cl bonds (axial bonds) lie above & below the plane of the triangle at bond angle 90° .


The axial bonds are longer than equatorial bonds because the axial Cl atoms suffer from more repulsion then the equatorial Cl atoms,as a result the axial Cl atoms tries to reside far away from the equatorial Cl atoms, & hence axial bond are longer than equatorial bonds.

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