Question

Choose the correct order of negative electron gain enthalpy.

• A. Cl < K < Br < Ca
• B. Cl < Br < K < Ca
• C. K < Ca < Br < Cl
• D. Ca < K < Br < Cl

Answer 1

The correct option is D Ca < K < Br < Cl

Put differently, we are looking at the electron affinity $E_{ea}$ values. The electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

Generally as we move down the group, electron affinity goes on decreasing. But due to small size of $F$ atom, there is more repulsion between existing electron and incoming electron. So, the electron affinity becomes less than $Cl$ atom.
Hence, the correct order is $I<Br<F<Cl$