Question

Why does \[\ce{H - M - H}\] bond angle in the hydrides of group 16 elements decrease on going down the group?

Answer 1

1. The central atom size increases as we go down the group (from O to Te).
2. Electronegativity of the central atom decreases down the group.
3. Oxygen, being the most electronegative, holds electron density tightly, causing strong repulsion between lone pairs and bond pairs in (H₂O).
4. This strong electron pair repulsion in (H₂O) results in the largest bond angle (~104.5°).
5. With larger atom size and lower electronegativity down the group, electron density on the central atom decreases.
6. Reduced lone pair-bond pair repulsion leads to smaller bond angles in (H₂S), (H₂Se), and (H₂Te).
7. Hence, the \[\ce{(H - M - H)}\] bond angle decreases down the group from 104.5° to about 90°.