1. Tardigrade
  2. Question
  3. Chemistry
  4. The formation of the oxide ion O(g)2- requires first an exothermic and then an endothermic step as shown below: beginmatrixO(g)+e- arrow O(g)-;&Δ H=-142 kJ mol-1 O(g)+e arrow O(g)2-;&Δ H=844 KJ mol-1 endmatrix This is because:

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Q. The formation of the oxide ion $O_{\left(g\right)}^{2-}$ requires first an exothermic and then an endothermic step as shown below:
$\begin{matrix}O_{\left(g\right)+e^{-} \rightarrow O_{\left(g\right)}^{-};}&\Delta H=-142\,kJ \,mol^{-1}\\ O\left(g\right)+e \rightarrow O_{\left(g\right)}^{2-};&\Delta H=844\,KJ \,mol^{-1}\end{matrix}$
This is because:

Classification of Elements and Periodicity in Properties

Solution:

$O^{-}$ acquires negative charge and thus shows repulsion for another electron