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# Knowing the electron gain enthalpy values for O ® O–^-and O ® O^2- as –141 and 702 kJ mol–1 respectively,

7.19     Knowing the electron gain enthalpy values for $O\rightarrow O^{-}$ and $O\rightarrow O^{2-}$ as $-141$ and $702 kJ mol^{-1}$ respectively,  how can you account for the formation of a large number of oxides having $O^{2-}$species and not $O^{-}$?

Lattice energy directly depends on the charge carried by an ion. More the lattice energy, more stable the compound will be. When metal and oxygen combine, the lattice energy of the oxide, which involves $O^{2-}$ion is much more than the oxide which involves $O^{-}$ion. Ionic compound stability depends on the lattice energy of the compound. Thus the oxides of  $O^{2-}$ is more stable than oxides having  $O^{-}$.