${MgO} \Rightarrow {Mg}^{2+}\quad {O}^{2-}$

${CaO} \quad \Rightarrow {Ca}^{2+} \quad {O}^{2-}$

${K}_{2} {O} \Rightarrow 2 {~K}^{+} \quad{O}^{2-}$

${Na}_{2} {O}_{2} \Rightarrow 2 {Na}^{+} \quad {O}_{2}^{2-}$

${KO}_{2} \quad \Rightarrow {K}^{+} \quad {O}_{2}^{-}$

${O}_{2}^{-} \Rightarrow$ Complete octet, diamagnetic

${O}^{2} \Rightarrow \sigma_{1 {~s}}^{2} \sigma_{1 {~s}}^{* 2} \sigma_{2 {~s}}^{2} \sigma_{2 {~s}}^{*_{2}} \sigma_{2 {px}}^{2} \pi_{2 {py}}^{2} \simeq \pi_{2 {pz}}^{2} \pi_{2 {py}}^{*_{2}} \simeq \pi_{2 {pz}}^{*_{2}}({dia})$

${O}_{2}^{-} \Rightarrow \sigma_{1 {~s}}^{2} \sigma_{1 {~s}}^{*_{2}} \sigma_{2 {~s}}^{2} \sigma_{2 {~s}}^{* 2} \sigma_{2 {px}}^{2} \pi_{2 {py}}^{2} \simeq \pi_{2 {p} z}^{2} \pi_{2 {py}}^{*} \simeq \pi_{2 {pz}}^{* 1}({para})$