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.

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.