Which of the following will have the most negative electron gain enthalpy and which the least negative? `P, S, Cl, F`. Explain your answer.

Explanation

Electron gain enthalpy generally becomes more negative across a period as we move from left to right within a group, electron to the 2p-orbital leads to greater repulsion than adding an electron to the larger 3-p orbital. Hence, the most negative electron gain enthalpy is of chlorine and the least negative electron gain enthalpy is of phosphorus.