• question_answer 7) Which of the following will have the most negative electron gain enthalpy and which the least negative? $P,S,Cl,F$ Explain your answer.

Electron gain enthalpy generally becomes more negative across a period as we move from left to right. $\text{Cl S P}$ Within a group, electron gain enthalpy becomes less negative down a group. However, adding an electron to $2p$-orbital leads to greater repulsion due to high electron density than adding an electron to the larger $3p$-orbital. Hence, chlorine has more negative electron gain enthalpy than fluorine. Therefore, phosphorus has least negative electron gain enthalpy and chlorine has most negative electron gain enthalpy.