Electron configuration of Co(II) ion??

i would have thought it was ------4s2 3d5

But mark scheme says ------3d7

I dont understand?? Im always getting these wrong so any advice appreciated

Reply 1

bl0bf1sh

Original post by uhhhh6678987654

i would have thought it was ------4s2 3d5

But mark scheme says ------3d7

I dont understand?? Im always getting these wrong so any advice appreciated

When d-block elements form ions, the 4s electrons are lost first.

Chemguide gives some good explanations:
https://chemguide.co.uk/inorganic/transition/features.html
https://chemguide.co.uk/atoms/properties/3d4sproblem.html

Reply 2

NG05

So from what I understand the electronic configuration of Co is [Ar]3d7 4s2
the electrons are always removed from the s orbital first so Co2+ is [Ar] 3d7

sorry if this doesn’t make sense or i’m wrong!