Question

Explain the following: The bond angle in PH₃ molecule is less than in NH₃.

Answer 1

In NH3, there are 4 electron pairs (3 bonding pairs & 1 lone pair) in the outer most shell of N. The repulsion between lone pair and a bond pair of electrons always exceeds to that of two bond pairs. Thus the bond angles are reduced from 109.27' to 107.48'.

Considering that PH3 would be expected to be similar. But, the bond pairs of electrons are much further away from the central atom due to its larger size than they are in NH3. Thus the lone pair causes even greater distortion in PH3. So the bond angle decrease to 91.18'

Thus, the bond angle of PH3 molecule is lesser than that in NH3 molecule.