Which among the following has smallest bond angle ?

Options

A. `H_2S`
B. `H_2O`
C. `NH_3`
D. `SO_2`

Answer

A

Explanation

In both `NH_3` and `SO_2`, the central atoms (N and S) carry only one lone pair of electrons while in `H_2S` and `H_2O`, the central atoms (S and O) carry two lone pairs. Due to lone pair-lone pair repulsion, the latter molecules will have smaller bond angles than the former molecules. In similar molecules (`H_2overset(..)S:` and `H_2overset(..)O:`), the bond angle decreases as the size of the central atom increases and its electronegativity decreases. Thus, `H_2S` has the smallest bond angle as sulphur is bigger than oxygen and less electronegative:
`H_2S(92.5^@) lt H_2O(104.5^@) lt NH_3(107.5^@) lt SO_2(119^@)`