Formula from Chapter 4:Sum of oxidation number

\(\mathrm{Charge}_{\mathrm{species}} = \sum (N_{\mathrm{atom}} \cdot \mathrm{Ox}_{\mathrm{atom}})\)     

\(\ce{ SO4^2-}\)

\(\mathrm{Ox}_{\mathrm{\ce{S}}}\) \(= 6\)


\(N_{\mathrm{\ce{S}}}\) \(= 1\)


\(\mathrm{Ox}_{\mathrm{\ce{O}}}\) \(= -2\)


\(N_{\mathrm{\ce{O}}}\) \(= 4\)


\(\mathrm{Charge}_{\mathrm{\ce{SO4^2-}}}\) \(= N_{\mathrm{\ce{S}}} \cdot \mathrm{Ox}_{\mathrm{\ce{S}}} + N_{\mathrm{\ce{O}}} \cdot \mathrm{Ox}_{\mathrm{\ce{O}}}\)

\(\ \ \ =1 \cdot 6 + 4 \cdot (-2)\)

\(\ \ \ =6 + -8\)

\(\ \ \ =-2\)