Question

the electron gain enthalpy of O or F is less than that of succeeding element in their respective groups​

Answer 1

Answer- The above question is from the chapter 'Periodic Classification of Elements'.

Given question: The electron gain enthalpy of O or F is less than that of succeeding element in their respective groups​. Why?

Answer: 1. We know that electron gain enthalpy becomes less negative as we go down a group.

2. But in case of O or F, the electron gain enthalpy of O or F is less than that of succeeding element in their respective groups​ i.e. the electron gain enthalpy of S and Cl is more than that of O or F.

3. This happens because upon addition of electron in the quantum level of  n = 2, there is a repulsion between the electrons present in this level.

4. But, in the quantum level of n = 3, the addition of electron gets a larger space to occupy which reduces the repulsion between the electrons.

5. So, the electron gain enthalpy of O or F is less than that of succeeding element in their respective groups​ due to their smaller atomic size and more electron - electron repulsions.