11. 2073 Set D Q. No. 1 Ammonia molecule has got trigonal pyramidal geometry even though nitrogen of ammonia gets
sp3 hybridization. Give reason.
[2]

See explanation

Explanation:

I know that we usually associate the sp3 hybridization to the tetrahedral shape. This is common in molecules such as CH4. So it may sound somewhat strange that NH3 molecule has an sp3 hybridized nitrogen atom and a trigonal pyramidal geometry.

Let us recall that the central nitrogen atom in NH3 has a lone pair of electrons. These lone pairs causes more repulsion than bond pairs. As a result of the presence of this lone pair, the bond angle in the NH3 molecule is distorted away from the expected 109.7 degrees in tetrahedral geometry and the bonding groups are now arranged in a trigonal pyramidal geometry(with bond angle less than 109.7 degrees) to minimize electron pair repulsions.