How the SO2 lewis structure is formed
Lewis structure of SO2
The SO2 Lewis structure contains a sulphur atom (S) and two oxygen atoms (O), with the sulphur atom as the central atom (S) and two oxygen atoms (O) surrounding the sulphur atom (S) at a bond angle of 119 degrees. There are 2 double bonds between the sulfur atom (S) and each oxygen atom (O). There are 2 lone pairs on the two oxygen atoms (O) and 1 lone pair on the sulphur atom (S). This is shown in the diagram below:
Steps for drawing the SO2 Lewis structure
Step 1 Calculate the number of valence electrons for S and O
Sulphur and oxygen are both elements of group 16 on the periodic table. Therefore, there are 6 valence electrons in both sulphur and oxygen atoms, so the total valence electrons in the SO2 molecule = valence electrons given by 1 sulphur atom + valence electrons given by 2 oxygen atoms = 6 + 6(2) = 18.
Step 2 Identify the central atom
The central atom is required to have a high valence, or minimal electronegativity. For the sulphur dioxide molecule, sulphur has a lower electronegativity value than oxygen, so sulphur is the central atom and oxygen is the external atom.
Step 3 Labelling the electron lone pairs between atoms
Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells, total electron pairs are determined by dividing the number total valence electrons by two. For, SO2 molecule, Total number of pairs of electrons are 9.
The sulphur atom is connected to each of the two oxygen atoms by a σ-bond (one σ-bond equals one electron pair), and the remaining seven electron pairs are distributed as follows: one electron pair on the sulphur atom and three electron pairs on the oxygen atom (2).
Step 4 Stability of structure and minimize charges on atoms by converting lone pairs to bonds
When there are positive and negative charges on lot of atoms or higher charges (like +2, +3, -2, -3) on atoms in an ion or molecule, that structure is not stable. Therefore, We should try to reduce charges on atoms if it is a possible.
In order to check the stability of the central sulphur (S) atom we have to check if it is forming an octet, if it does not have an octet then the lone pair of electrons is moved in order to form a double or triple bond, in order for this sulphur atom to be stable the pairs of electrons have to be shifted away from the outer oxygen atoms so that the sulphur atom can have 8 electrons (i.e octet). After the move, each of the two oxygen atoms forms a double bond with the sulphur atom, retaining one lone pair of electrons on the sulphur atom and two lone pairs of electrons on each of the two oxygen atoms. See the diagram below.
