Question

What is the electronic configuration of `"Co"` atom and a `"Co"^(2+)` ion ??

Answer 1

`Co^(2+)` would most likely be `1s^2 2s^2 2p^6 3s^2 3p^6 4s^0 3d^7`, and `Co` would have `4s^2` instead (the rest otherwise the same).

Explanation:

The two outermost electrons are the 4s electrons so these are the two electrons that most likely will be lost. As the number of protons in the nucleus increases across the fourth period, the energy levels of the 3d electrons tends to become lower than the energy levels of the 4s electrons. This makes the 3d electrons more stable than the 4s electrons in late transition metals, and less likely to be lost in a chemical reaction.

Losing the two 4s electrons leaves a positive charge of +2 and seven 3d electrons.