Electron Configurations for 3.9

[Alex Nguyen 3I]

Is there any particular reason why the ground state configuration of both are designated at [Ar] 3d7 and [3d6] respectively? Is it appropriate to leave out the 4s orbital?

[Reine Nakamura 1C]

Because Co2+ and Fe2+ are ions with a positive charge, you start with the electron configuration of the neutral atom and remove 2 electrons. When electrons fill the 4s subshell and begin to occupy the 3d subshell, the 3d subshell has a lower energy than the 4s. Therefore, when you go to remove 2 electrons, they will come from the highest energy/outermost subshell, which is the 4s in this case. It's appropriate to leave out the 4s subshell when writing the electron configurations to acknowledge that those 2 electrons have been removed.

[Alex Nguyen 3I]

So does the 3d state a higher energy level than 4s until it is "occupied" or does the 4s state always have more energy?

[Christopher Ansay 1C]

I believe a 4s state is lower in energy than a 3d orbital until the 4s orbital is fully occupied.