The formation of the oxide ion O^2–(g) requires first an exothermic and then an endothermic step as shown below.
The formation of the oxide ion O2–(g) requires first an exothermic and then an endothermic step as shown below.
O(g) + e– = O–(g) ; ΔH° = –142kJ mol–1
O–(g) + e– = O2–(g) ; ΔH° = 844kJ mol–1
This is because
(a) oxygen is more electronegative
(b) oxygen has high electron affinity
(c) O– ion will tend to resist the addition of another electron
(d) O– ion has comparatively larger size than oxygen atom.
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