Question

The formation of the oxide ion $O^{2-}\left(g\right)$ requires first an exothermic and then an endothermic step as shown below.
$O\left(g\right)+e^{-}\to O^{-}\left(g\right);\Delta H^0=-142kJmo{l}^{-1}$
$O^{-}\left(g\right)+e^{-}\to O^{2-}\left(g\right);\Delta H^0=844kJmo{l}^{-1}$
The correct statement is?

• A. Oxygen is more electronegative
• B. $O^{-}$ion has comparatively larger size than oxygen atom
• C. $O^{-}$ion will tend to resist the addition of another electron
• D. Oxygen has high electron affinity

Answer 1

Answer: (A)

Oxygen is more electronegative

$O^{-}$ ion will tend to resist the addition of another electron

${O^{-}}_{\left(g\right)}+e^{-}⟶{O^{2-}}_{\left(g\right)};\Delta H=844kJ/mol$

The above process is unfavourable in the gas phase because the resulting ion increase in $e^{-}-e^{-}$ repulsion overweights the stability gained by achieving the noble gas configuration