Question

In which of the following processes is energy liberated?

• A. Cl = $C{l}^{+}$ + $e^{-}$
• B. HCl =$H^{+}$ + $C{l}^{-}$
• C. Cl + $e^{-}$= $C{l}^{-}$
• D. $O^{-}$ + $e^{-}$ = $O^{-2}$

Answer 1

The correct option is C

Cl + $e^{-}$= $C{l}^{-}$

Generally, to determine whether energy is released or absorbed when an electron is added to a neutral gaseous atom, you need to look at the stability of the species.

If we add an electron to Cl atom, energy will be released because $C{l}^{-}$ is more stable than Cl atom.
If we add an electron to N atom, energy will be absorbed because N is more stable than $N^{-}$

In the case of anions, energy is always absorbed when an electron is added.

So, if an electron is added to $O^{-}$ ion a lot of energy is needed to make it $O^2-$