Q. \[ \mathrm{SOCl}_2 \] formal charge.

Problem statement. Determine the formal charges on each atom in thionyl chloride, SOCl2. The usual Lewis structure has sulfur as the central atom, double bonded to oxygen, single bonded to two chlorine atoms, and bearing one lone pair.

Method. Formal charge is calculated with the formula: \( \text{FC} = V – N_{\text{nonbonding}} – \dfrac{N_{\text{bonding}}}{2} \). Here \(V\) is the number of valence electrons for the neutral atom, \(N_{\text{nonbonding}}\) is the number of electrons in lone pairs on that atom, and \(N_{\text{bonding}}\) is the total number of electrons in bonds to that atom.

Calculate the sulfur formal charge. Sulfur has \(V = 6\) valence electrons. In the Lewis structure it has one lone pair, so \(N_{\text{nonbonding}} = 2\). Sulfur is bonded to oxygen with a double bond and to two chlorines with single bonds, so the total bonding electrons on sulfur are \(N_{\text{bonding}} = 4\) from the S=O plus \(2 \times 2 = 4\) from the two S–Cl single bonds, giving \(N_{\text{bonding}} = 8\). Compute the formal charge:
\[
\text{FC}_{\text{S}} = 6 – 2 – \dfrac{8}{2} = 6 – 2 – 4 = 0.
\]

Calculate the oxygen formal charge. Oxygen has \(V = 6\) valence electrons. In the S=O double bond oxygen has two lone pairs, so \(N_{\text{nonbonding}} = 4\). The double bond contributes \(N_{\text{bonding}} = 4\) bonding electrons on oxygen. Compute the formal charge:
\[
\text{FC}_{\text{O}} = 6 – 4 – \dfrac{4}{2} = 6 – 4 – 2 = 0.
\]

Calculate the chlorine formal charges. Each chlorine atom has \(V = 7\) valence electrons. Each chlorine is bonded to sulfur by a single bond and has three lone pairs, so for each chlorine \(N_{\text{nonbonding}} = 6\) and \(N_{\text{bonding}} = 2\). Compute the formal charge for a chlorine:
\[
\text{FC}_{\text{Cl}} = 7 – 6 – \dfrac{2}{2} = 7 – 6 – 1 = 0.
\]

Conclusion. In the standard Lewis structure of SOCl2 with S=O double bond, S–Cl single bonds, and a lone pair on sulfur, the formal charges are zero on sulfur, zero on oxygen, and zero on each chlorine. Therefore all atoms have formal charge 0 in that structure.