Question

Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.

Answer 1

When an electron is added to O atom to form $O^{–}$ ion, energy is released. Thus, the first electron gain enthalpy of O is negative.


On the other hand, when an electron is added to O– ion to form $O^{2–}$ ion, energy has to be given out in order to overcome the strong electronic repulsions. Thus, the second electron gain enthalpy of O is positive.