The bond angle of a sulphur dioxide, or SO2, molecule is 120 degrees. Two oxygen atoms are covalently bonded to an atom of sulphur by one double covalent bond and one single covalent bond. The electron cloud on the oxygen atoms causes repulsion and this forms the angle.
A molecule of sulphur dioxide is coplanar. There are two electron pairs on the two oxygen atoms that are not involved in bond formation. These electrons carry the same negative charge. The electrostatic force of repulsion between them causes the oxygen atoms to pull away from each other. As a result, the angle between O-S-O atoms increases to 120 degrees.