Question

The formation of the oxide ion, $O_{(g)}^{2 -},$ from oxygen atom requires first an exothermic and then an endothermic step as shown below:

(1) $O_{(g)} + e^{-} \rightarrow O_{(g)}^{-};\Delta H^{o} = - 141kJmol^{- 1}$

(2) $O_{(g)}^{-} + e^{-} \rightarrow O_{(g);}^{2 -}\Delta H^{o} = + 780kJmol^{- 1}$

Thus, process of formation $O^{2 -}$ in gas phase is unfavovurable even though $O^{2 -}$ is isoelectronic with neon. It is due to the fact that,

• A. Oxygen is more electronegative
• B. Addition of electron in oxygen results in larger size of the ion
• C. Electron repulsion outweighs the stability gained by achieving noble gas configuration
• D. $O^{-}$ ion has comparatively smaller size than oxygen atom.

Answer 1

Answer: (C)

Electron repulsion outweighs the stability gained by achieving noble gas configuration

Answer 2

: Due to small size of O atom, electron repulsion outweighs the stability gained by achieving noble gas configuration.