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Question

On a periodic table it shows that Zn and Cd and Hg all have 0 electron affinity. Why is that?

What I've noticed

I've noticed that these three elements are the end of the D orbital and they are completely full, i think that it has to do something with that But i am not entirely sure

Part two of question

Why is electron affinity expressed in negative numbers? Ex: Cs=-45.5kj/mol

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They all have 2 electrons in their highest occupied s sublevel and 10 electrons in their highest occupied d sublevel (both sublevels are full). As a result, they can not complete any orbitals by adding an electron and they can not put an electron in a sublevel that is occupied. All of the other transition metals will either add an electron to complete the highest s sublevel, or into an already occupied d sublevel, or (in the case of palladium) add one to an s sublevel that is empty.

Cd, Hg and Zn thus are unique in that they will all have to put an unpaired electron alone into a p sublevel.

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