The formation of the oxide ion, O2−(g) from oxygen atom requires first an exothermic and then an endothermic step as shown below: O(g)+e−→O−(g);ΔfH∘=−141 kJ mol−1O−(g)+e−→O2−(g);ΔfH∘=+780 kJ mol−1 Thus, process of formation of O2− in gas phase is unfavourable even though O2− is isoelectronic with neon. It is due to the fact that,

The formation of the oxide ion, O2−(g) from oxygen atom requires fir

1.	The formation of the oxide ion, O2−(g) from oxygen atom requires first an exothermic and then an endothermic step as shown below: O(g)+e−→O−(g);ΔfH∘=−141 kJ mol−1O−(g)+e−→O2−(g);ΔfH∘=+780 kJ mol−1 Thus, process of formation of O2− in gas phase is unfavourable even though O2− is isoelectronic with neon. It is due to the fact that,
Answer» The formation of the oxide ion, $O_{(g)}^{2 -}$ from oxygen atom requires first an exothermic and then an endothermic step as shown below: $O_{(g)} + e^{-} \to O_{(g)}^{-}; Δ_{f} H^{\circ} = - 141 k J m o l^{- 1} O_{(g)}^{-} + e^{-} \to O_{(g)}^{2 -}; Δ_{f} H^{\circ} = + 780 k J m o l^{- 1}$ Thus, process of formation of $O^{2 -}$ in gas phase is unfavourable even though $O^{2 -}$ is isoelectronic with neon. It is due to the fact that,