What would be the valence electron configuration of Ga2+?

[curlz]

I'm a bit confused as to what the valence electron configuration would be because I know that in the 11th group they have s and d valence electrons. So I thought the valence configuration would be 4s2 3d9, but apparently that's wrong. I'm not really sure how to do this one.

[michelleunicorn]

jL9++

[j_sun]

The correct answer is: [Ar] 4s1 3d10

Explanation: The reason for this is that cations are not quite as simple as anions in their configurations. You CANNOT merely subtract 2 electrons by going back 2 spaces on the periodic table as you did. Instead, you must subtract or take away the atoms from highest energy level first, which here would be n=4. The fourth energy level contains 3 electrons in Ga. Ga 2+ signifies to take away two of these electrons from the fourth energy level. Which would give the configuration of [Ar] 4s1 3d10. Now if the question asked for, let's say, Ga 5+, then the answer would be [Ar] 3d8 because you have used up the electrons on the highest energy level (4) so you must up down to the third to take away the remaining two electrons.

Hopefully that explanation makes sense of the whole deal with cations and their electron configurations. Anions are merely just about adding electrons.