Hi, this is Dr. B. Let's do the SOCl2 Lewis
structure.
Sulfur has 6 valence electrons.
Oxygen has 6.
Chlorine has 7, we have two Chlorines.
And that equals 26 valence electrons.
Sulfur's the least electronegative, it can
go at the center.
Let's put a Chlorine on either side and then
the Oxygen right there.
We have 26 valence electrons.
We'll put two electrons between each of the
atoms, form chemical bonds.
There's six; and then around the outside,
8, and 26.
At this point, you might think you're done.
Everything has eight valence electrons, you've
used only the 26 that you were given.
Looks like a pretty good structure.
The problem is, we really need to check the
formal charges.
Sulfur is in period 3 and that means it can
hold more than eight valence electrons.
So let's check the formal charges for SOCl2,
just to be sure.
OK, so let's look at the Chlorine.
Chlorine is in group 7 or 17 on the periodic
table, so it has 7 valence electrons.
Nonbonding, these electrons right here are
not involved in chemical bonds, there are
six of them.
and then we have two forming the bond with
the Sulfur, and we'll divide that by two.
Seven minus 6 minus 1 is zero.
Because the Chlorines are symmetrical, they'll
both be zero.
For the Sulfur, 6 on the periodic table.
We have two nonbonding, and then we have a
total of 6 involved in chemical bonds, and
we'll divide that 6 by 2.
Six minus 2 minus 3 is plus 1.
Finally, for the Oyxgen, in group 6, six valence
electrons.
We have six not involved in chemical bonds.
Two bonding, which we divide by two.
Six minus 6 minus 1 is minus 1.
So when I look at this structure and the formal
charges, I see I have a +1, -1; this might
not be the best structure.
I should probably investigate another structure.
And because I see a plus 1, I think there's
probably going to be a double bond in the
next structure I'll try.
Chlorines don't really form double bonds.
I'm thinking it might be on the Oxygen.
So let's try that, see what it looks like.
So I've moved the two electrons that were
up here to right here to form a double bond.
Still have the same number of valence electrons
in the entire molecule.
Let's check our formal charges for Chlorine.
Really, nothing's changed with Chlorine.
We have 7 valence electrons minus the 6 here
that are nonbonding and the 2 that are bonding,
so it's still zero.
For Sulfur, 6 valence electrons, two nonbonding.
And now we have four plus (2, 6, 8) eight
total bonding, divided by 2.
Six minus 2 minus 4 is zero.
And then for Oxygen, 6 minus the four nonbonding.
We have 4 bonding here, divided by 2...also
equals zero.
Because my formal charges are all zero now,
I know that this is the best structure for
SOCl2.
So when you're drawing the Lewis structure
for SOCl2, make sure you check your formal
charges.
This is Dr. B., and thanks for watching.
