1. Tardigrade
  2. Question
  3. Chemistry
  4. 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° = −142kJmol−1 O− (g) + e-O2− (g)ΔH° = 844kJmol−1

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Q. The formation of the oxide ion $O^{2-}(g)$ requires first an exothermic and then an endothermic step as shown below
$O\left(g\right) + e^{−}O^{−} \left(g\right)ΔH^{\circ} = −142kJmol^{−1}$
$O^{−} \left(g\right) + e^{-}O^{2−} \left(g\right)ΔH^{\circ} = 844kJmol^{−1}$

AIEEEAIEEE 2004Classification of Elements and Periodicity in Properties

Solution:

$O^{-1}\left(g\right) + e \longrightarrow O^{-2}\left(g\right)$
Due to the electronic repulsion, amount of the energy is needed to add electron