Which of the following pairs of elements would have a more negative electron gain enthalpy?

Question

CASE_STUDIESTrends in Electron Gain Enthalpy Across Periodic Table2 sub-questions

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

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