Hi, this is Dr. B. Let's do the SO3 2- Lewis
structure.
For the SO3 2- compound, we have 26 total
valence electrons, and that includes these
two electrons up here--there are two extra
valence electrons.
So we have 26.
Let's put the Sulfur at the center and the
Oxygens around the outside.
Put two electrons between the atoms to form
chemical bonds.
We've used 6.
And then around the outside atoms.
So we have 6, 8, 10, and 24.
We have two left over.
We'll put them right here on the central atom.
So we've used all 26 valence electrons.
The structure looks pretty good.
Each of the atoms has an octet.
We've used the 26 valence electrons.
So this is a possible structure for the sulfite
ion, SO3 2-.
Since Sulfur is in the third period on the
periodic table, it can hold more than eight
valence electrons.
So we should check our formal charges here
to see if this is the best structure.
For the Sulfur, on the periodic table, it
has 6 valence electrons.
We have here, on the Lewis structure, 2 nonbonding;
and then these right here are all involved
in bonds, so 6 over 2.
Six minus 2 minus 6 over 2 is a positive 1
for the central Sulfur.
For the Oxygens; and they're all the same,
so we'll just do one; on the periodic table,
6 valence electrons.
Nonbonding, we have 6 nonbonding for each
of the Oxygens, and then 2 bonding.
Six minus 6 minus 1 gives us -1 for each of
the Oxygens.
So this makes sense.
I have a plus one here, and then three of
the minus ones, and that all adds up to negative
2.
So this makes sense as a structure.
I can put brackets around it and show that
it is, indeed, an ion.
I see this plus one here on the central Sulfur,
and I know if I pull a pair of electrons from
the Oxygen and form a double bond, that'll
go to zero.
So I'd like to try that and see what it looks
like.
So here, I've taken these two valence electrons
out here and I've moved them in to form a
double bond with the Sulfur.
That results in this Oxygen here and the Sulfur
now having zero for their formal charge.
These remain at a negative one, which makes
sense; we have a -1, -1, that keeps our -2
right here.
We've still used the number of valence electrons
that we were initially given.
So this may actually be a better Lewis structure
for SO3 2- because the formal charges, we
have more formal charges at zero than we did
in the previous structure.
So that's the SO3 2- Lewis structure.
This is Dr. B., and thanks for watching.
