Predict the ground‑state electron configuration of each ion. Use the abbreviated noble gas notation.

Question

Cr^2+

Cu^2+

Co^2+

Answer 1

Cr: [Ar] 3d5 4s1, so Cr2+= [Ar] 3d⁴

Cu:[Ar] 3d10 4s1, so Cu2+= [Ar] 3d⁹

Co:[Ar] 3d7 4s2, so Co2+=[Ar] 3d⁷ 

Since these metals are becoming cations (+), it means that they are losing electrons, thus you would pull them off the outer most orbital.

Cr and Cu have unique configurations because they steal electrons from the 4s because they prefer to be half-full or full orbitals. So if you have 4 electrons in the 3d, like in Cr, it is more energetically favorable to have 5 electrons in the 3d and have a half-filled subshell since the 3d has 5 orbitals, so you would pull an electron from the 4s.