Question

Although geometries of $N{H}_3$ and $H_{2}O$ molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss :

Answer 1

The central atom in ammonia and water molecules have$1$ and $2$ lone pairs of electrons respectively.

Lone pairs distort the molecular geometry. Lone pair-bond pair repulsion is stronger than bond pair-bond pair repulsion. The bond angle of ammonia reduces from ${109.5}^o$ (tetrahedral) to ${107}^o$.

In the case of a water molecule, the bond angle decreases to ${105.4}^o$ as more number of lone pair-bond pair repulsions are present.