Let’s take the example of SO₂, here the central S atom has 6 valence electrons. S uses 1 pair of electron to form a double bond with each O atom. So, S in total uses four of its valence electrons to form two double bonds with two O atoms. Now after bond formation two electrons are still left on S, thus S has a lone pair of electron. In the absence of a lone pair of electron on S, SO₂ would have a linear structure, O=S=O. However, the lone pair-bond pair repulsion causes SO₂ to have a bent structure.
