First and second electrons gains enthalpies of oxygen and `-141 and +702 kJ mol^(-1)` . How is large number of oxides accounted for ?

Explanation

`O(g) + e^(-) to O^(-)(g), DeltaH = -141 kJ mol^(-1)`
`O^(-)(g) + e^- + O^(2-) (g) , Delta H = + 702 kJ mol^(-1)`
Formation of `O^(-)` is exothermic and `O^(-2)` is endothermic. However, oxygen is divalent and forms oxide with stable `ns^2np^6` configuration. Further , the lattice energies of oxides are very high on account of greater electrostatic forces of attraction.