The electron gain enthalpy with negative sign is less for oxygen for sulphur. Explain.

Explanation

The size of O-atom is smaller than that of S-atom. When an electron is added to neutral gaseous atom, the electron- electron repulsions experienced by the small-sized 2p - subshell of O-atom are relatively larger than those encountered in the big-sized 3p -subshell of S-atom. As a result, more energy is released in the case of S-atom than in the case of O-atom. Hence, the negative electron gain enthalpy of S is higher than that of O.
`O(g)+etoO^(-)(g),Delta_(eg)H=-141kJ.mol^(-1)`
`S(g)+etoS^(-)(g),Delta_(eg)H=-200kj.mol^(-1)`