Question

Explain electron gain enthalpy.

Answer 1

All alkali metals have negative electron gain enthalpy. Ionisation of sodium(or any atom) is endothermic process (495.8 KJ/mol), meaning, in isolated gaseous state, neutral atom is more stable. Electron gain process of $Na+$ is obviously an exothermic process (reverse of ionisation) due to the attraction of positively charged, $N{a}^{+}$ for a free electron. If an atom has spontaneous tendency, i.e., a positive tendency, to gain electron, then the electron-gain process is exothermic; hence, its electron gain enthalpy is said to be negative and if the atom is reluctant to gain an electron, i.e., it has a negative tendency to gain an electron and is forced to accept it, the electron-gain process is exothermic & hence its electron gain enthalpy value is positive.