Question

Explain the following observation giving appropriate reasons:
The $HEH$ bond angle of then hydrides of group $15$ elements decreases as we move down the group.

Answer 1

As we move from $N{H}_3$ to $Bi{H}_3$, the size of the central atom goes on increasing and its electronegativity goes on decreasing. Due to this, the bond pair of electrons tend to lie away from the central atom. As a result, the repulsion between the pairs decreases as we move from $N{H}_3$ to $Bi{H}_3$. Consequently the bond angle decreases as we go down the group from $N{H}_3$ to $Bi{H}_3$.