Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.
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 O2- 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.
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