Question

What is the H - S - H bond angle in ${{H}_{2}}S$?
(A) \[{{104.5}^{0}}\]
(B) ${{92.1}^{0}}$
(C) ${{91}^{0}}$
(D) ${{90}^{0}}$

Answer 1

Hint: Draw the expanded structure of ${{H}_{2}}S$. Try to identify the number of lone pairs on the central atom i.e. sulphur in this case. Now find the hybridisation of the sulphur atom. The hybridisation will help to determine the shape of the compound and hence the bond angle of H - S - H.

Complete step by step solution:
Valence bond theory is one of the two theories along with the molecular orbital theory that was developed for the sole purpose of devising a mechanism to explain quantum mechanics of chemical bonding. According to the valence bond theory, a covalent bond is formed between two atoms by the overlap of half-filled valence atomic orbitals of the two atoms containing an unpaired electron each.
We will now draw the expanded structure of ${{H}_{2}}S$:

In the above structure, we observe that,
Number of bond pairs = 2
Number of lone pair of electrons = 2
The coordination number becomes 4. The hybridization is $\text{s}{{\text{p}}^{\text{3}}}$ and the shape of the molecule is bent.
Since the shape of the molecule is bent, the bond angle of H - S - H is ${{92.1}^{0}}$.

Therefore, the correct answer is option (B).

Note: Although the valence bond theory helps in predicting the shape and hybridisation of the molecule it has some drawbacks as well. Some of the limitations are mentioned below:
-Failure to explain the tetravalency exhibited by carbon
-No information regarding the energy possessed by electrons
-No clear distinction between weak and strong ligands
-No explanation regarding the colour of metal complexes