Why is the bond angle of other hydride in group 15 so less compare to any

All these hydrides are covalent in nature and have pyramidal structure. These involve sp³ hybridization of the central atom and one of the tetrahedral position is occupied by a lone pair.

Shape of NH₃ molecule

Due to the presence of lone pair, the bond angle in NH₃ is less than the normal tetrahedral angle. It has been found to be 107^o. Down the group the bond angle decreases as:

 Explanation:

In all these hydrides, four electron pairs, three bond pairs and one lone pair surround the central atom. Now, as we move down the group from N to Bi, the size of the atom goes on increasing and its electronegativity decreases. Consequently, the position of bond pair shifts more and more away from the central atom in moving from NH3 to BiH3. For e.g., the bond pair in NH3 is close to N in N-H bond than the bond pair in P-H bond in PH3. As a result, the force of repulsion between the bonded pair of electrons in NH3 is more than in PH3. In general, the force of repulsion between bonded pairs of electrons decreases as we move from NH3 to BiH3 and therefore, the bond angle also decreases in the same order.

Regards

Arun (askIITians forum expert)