To calculate formal charges we're going to work with the Lewis structure here
And what we're trying to do is figure out if this Lewis structure and the way we've arranged the electrons
Makes the most sense if it's the most favorable or likely structure for the co 3 to - polyatomic
Ion so let's calculate formal charges for each atom in the CO3 2-  , the carbonate, ion
We'll start with this oxygen right here first
We write the number of valence electrons for the oxygen we get that from the periodic table
Oxygen is in group 6 or 16
It has 6 valence electrons, and we're gonna subtract the nonbonding valence electrons
These are the electrons that aren't involved in bonds. We have 2
4 6
of those and
Then we'll subtract the bonding electrons
These are the valence electrons between atoms they're formed in the chemical bond in this case they're shared. We have 2
which will divide by 2, so 6 minus 6 is 0
Minus 1 is minus 1 and that's the formal charge on this oxygen, and we'll put that one right here in parentheses
What's nice is this oxygen here is
the same as this one right here their orientation of electrons is the same, and we don't need to do that one again
We'll just put the negative 1 there showing that its formal charge is negative 1
Let's do the outside oxygen on the right in oxygen is 6 on the periodic table
We can check that - nonbonding these are those outside valence electrons not involved in bonds 2 4
- the bonding electrons, and we have 2 4 of those which will divide by 2
6 minus 4 is 2 minus 2 is 0
So the formal charge here is
0 now let's do the carbon in the center of the molecule carbon has 4 valence electrons
We put the 4 here we subtract the nonbonding
All of these electrons are between atoms they're involved in the chemical bonds
So we have a 0 for nonbonding and the bonding electrons. I have 2 4 6
8
Which I will divide by -
4 - 0 minus 4 is 0 so the formal charge on the carbon in the center
That is zero at this point
we've calculated the formal charges for the CO3 2-
polyatomic ion the carbonate, ion.
And we found that they are overall 0 plus 0 plus negative 1 plus negative 1
We have a negative 2 overall charge which isn't surprising because CO3 2- .
This is Dr. B with the formal charges for CO3 2-  and thanks for watching
