Question

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

Answer 1

Oxygen belongs to group 16 of p block elements.It is the first member of group 16.It is a non metal & most abundant in earth crust.
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(superoxide ion), energy has to be given out in order to overcome the strong electronic repulsions between $O^{-}$ &$e^{-}$ . Thus, the second electron gain enthalpy of O is positive.