Question

What is the O – S – O bond angle in a $S{{O}_{3}}$molecule?

Answer 1

Hint: Bond angle is the angle between the adjacent atoms in the molecule. The bond angle in any molecule varies with the presence of the bond pair of electrons and the lone pair of electrons according to VSEPR theory. The $S{{O}_{3}}$ molecule is called sulfur trioxide whose geometry is trigonal planar.

Complete answer:
The shapes of molecules tell us the bond angles between them. These shapes are identified using VSEPR theory that stands for valence shell electron pair repulsion theory. This theory suggests that a shape of a molecule is dependent on the valence pair of electrons in the atoms of that molecule. These valence electrons are distributed in the form of bond pair and lone pairs. The interactions of these pairs are in the order, lone pair – lone pair > lone pair – bond pair > bond pair – bond pair. This states that lone pair lone pair interaction is more due to which the shape of the molecule distorts and the bond angle changes.
We have been given a $S{{O}_{3}}$ molecule that has sulfur and oxygen. The total valence electrons in sulfur and oxygen are 6, so the total valence electrons on the molecule will be $4\times 6=24$ valence electrons. These electrons are distributed in such a way that they form 3 electron pairs. Each pair of electrons is distributed in a way that it completes its octet, so there is no lone pair of electrons. Therefore due to 3 oxygen atoms, the shape of the molecule becomes trigonal planar. The bond angle in trigonal planar molecule is $120{}^\circ $, as the following structure suggests:

Hence, the bond angle of O – S – O bond in a $S{{O}_{3}}$ molecule is $120{}^\circ $.

Note:
$S{{O}_{3}}$ molecule is an example where the central atom is surrounded by only bond pairs and has a regular geometry. There are various molecules that are surrounded by both lone pairs and bond pairs explained in the VSEPR theory. In VSEPR theory the multiple bond like that in carbon and oxygen, $C=O$ is considered as a single electron pair, so 3 bond pairs in $S{{O}_{3}}$ molecule.