Drawing the Lewis Structure for SOCl2

Viewing Notes:

  • The Lewis structure for SOCl2 requires you to place more than 8 valence electrons on Sulfur (S).
  • You might think you've got the correct Lewis structure for SOCl2 at first. Remember, Sulfur is in Period 3 and can hold more than 8 valence electrons.
  • You'll want to calculate the formal charges on each atom to make sure you have the best Lewis structure for SOCl2. SOCl2 is a good example to help understand how to calculate formal charges.

Transcript: 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.