Question

Discuss the structure of NH₃ and explain why does it possess a shorter bond angle than the expected one.

Answer 1

1. The structure of NH₃ (ammonia) is trigonal pyramidal due to sp³ hybridisation of the nitrogen atom, which forms three \[\ce{N - H}\] bonds and holds one lone pair of electrons.
2. The ideal tetrahedral bond angle is 109°28', but in NH₃, the \[\ce{H - N - H}\] bond angle is 107.8°.
3. This smaller bond angle is because the lone pair on nitrogen repels the bonding pairs more strongly than bond pairs repel each other.
4. This greater lone pair-bond pair repulsion compresses the bond angle, making it less than the ideal tetrahedral angle.

Thus, NH₃ has a distorted tetrahedral shape with a compressed bond angle of 107.8° due to the presence of the lone electron pair on nitrogen.