Let's do the CO3 2- Lewis structure: the carbonate
ion.
Carbon has 4 valence electrons; Oxygen has
six, we have 3 Oxygens, and this negative
2 means we have an extra two valence electrons.
Add that all up: 4 plus 18 plus 2: 24 valence
electrons.
Carbon is the least electronegative, put that
at the center.
Three Oxygens go around the Carbon.
We'll put two electrons between the atoms
to form chemical bonds.
We've used six.
And then around the Oxygens: 8, 10, and 24.
So we've used all 24 valence electrons.
All have octets, 8 valence electrons.
The Carbon, however, only has 6 valence electrons.
Let's move two valence electrons from here
to form a double bond with the Carbon.
So this Oxygen still has 8 valence electrons
but now the Carbon has 8 valence electrons.
We're still using only 24 valence electrons.
So the formal charges do make sense here because
the black Oxygens here and here both have
a formal charge of negative 1 and the Carbon
and the other Oxygen are 0.
So -1 plus -1, that does match up with what
we have for the carbonate ion here.
Because of that, this is the best Lewis structure
for CO3 2-.
There's one last thing we need to do: because
the CO3 2- ion has a charge of negative 2,
we need to put brackets around our Lewis structure
and put that negative 2 outside so everyone
knows that it is an ion and it has a negative
2 charge.
That's it: that's the Lewis structure for
CO3 2-.
This is Dr. B., and thanks for watching.
