Question

Which one of the following atoms has the most endothermic electron affinity?

A) Cl

B) Br

C) Na

D) Si

E) Mg

Answer 1

Using the grp VII as benchmark (usually EAs are associated w/ grp VII elements), the 1st EA is exothermic because energy is released due to formation of more stable ions e.g. Cl-, Br- etc.

As for the 2nd EA, it's basically adding electrons (-ve charge) to negative ions. Since like charges repel, it'll be a lot more difficult for the 2nd electron to be added to the atom. Therefore, a lot more energy is needed to be absorbed before the 2nd electron can be 'accepted', resulting in a net intake of energy rather than release.
Ans E
The subsequent EAs will also be endothermic, in fact even more so than the 2nd EA, cos it is increasingly difficult to add an electron to a more negatively charged ion.