the configuration of Co is [Ar] 4s2 3d7

why when Co forms an ion at Co3+ does it become [Ar]3d6...

I dont see why the electronics are removed from the s-orbital before the d here... can anyone explain this to me real quick?

When transition metals form ions, they lose electrons from the subshell with the highest principle quantum number first. That's why the 2 4s electrons are not present.

i'll assume thats a general rule then

thank you.

Interesting, I would have assumed it to be 4s1 3d5, since this way the d shell would be half full thus more stable.

yeah

thats what i thought as well... half full being more stable but apparenylt this is a general rule for transition metals