So for example, if we were going to do O2 minus,
we would begin with oxygen, okay, so, electron configuration of oxygen.
You're going to want to look at the periodic table and
verify that this is what you would have come up with, helium 2s2, 2p4.
Now you see here, that it has six valence electrons, and
if you look at oxygen's group number, it has got a six associated with it.
So we know that it matches up.
So now where are you going to put the next electrons?
Well, there's still two spots available, in the p orbital.
So those two electrons can go into the oxygen, in,
into the 2p subshell there, and be up to 2p6.
Now you can't get any bigger than six, but that fills up that valence shell.
And that gives oxygen, with a two minus charge,
the same electron configuration as neon.
So you could also write, for the configuration of O2 minus,
you could write neon and that would be correct as well.
Look at your periodic table.
See how neon is two to the right of oxygen?