Which metal has the most negative electron affinity and why?

Why does Cl have a higher electron affinity than Fluorine even though it's below Fluorine in the halogen group?

• Electron affinity is the amount of energy released when an electron is added to an atom. Electron affinity increases from left to right in a period and decreases down the ...show more

• Answer:

  Because of the proximity of the electrons in fluorine. Because of its small size, the fluorine atom exerts a significant pull on its electrons. However, its small size also causes the electrons to approach each other very closely, meaning they start to repel each other due to their like charge. To insert another electron in the highly repelling environment of fluorine would take a certain amount of energy. Chlorine is larger in size. Because of this, it is less reactive, since the nucleus does not exert such a great pull on electrons. However, inserting an electron in a shell where there is much more space will not take as much energy, because the repulsion to be overcome is lower. This means that it is more energy efficient than for the fluorine atom. Hence, chlorine has a higher electron affinity than fluorine.