Electron gain enthalpy of Cl is more negative than F though electronegativity of F is greater than 'Cl'- Explain.

Explanation

There are six, valency electrons in oxygen and it requires two electrons to complete its octet. So, O-atom accepts one electrons to complete its octet. So, O-atom accepts one electron to convert into `O^(-)` ion and in the process liberates energy. Thus, first electron-gain enthalpy of oxygen is negative.
`O(g)+e to O^(-)(g) +141kJ mol^(-1)(Delta_(i)H_(1)=-ve)`.
However, when another electron is added to `O^(-)` to form `O^(2-)` ion, energy is absorbed to overcome the strong electrostatic repulsion between negatively charged `O^(-)` ion and the secon incoming electron. thus, second electron gain enthalpy of oxygen is positive.
`O^(-)(g)+e to O^(2-)(g) -(780kJ*mol^(-1))(Delta_(i)H_(2)=+ve)`.