Chemical Bonding: SO₂ Lewis Structure

Drawing the Lewis Structure for SO₂

Viewing Notes:

• The Lewis structure for SO₂ requires you to place more than 8 valence electrons on Sulfur (S).
• You might think you've got the correct Lewis structure for SO₂ 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 SO₂. SO₂ is a good example to help understand how to calculate formal charges.

Transcript: Hi, this is Dr. B. Let's do the SO2 Lewis structure. On the periodic table: Sulfur, 6 valence electrons. Oxygen has 6. We have two Oxygens, though, for a total of 18 valence electrons. We'll put the Sulfur in the middle; it's the least electronegative. Oxygens on the outside, and then we'll use our valence electrons. Two between atoms to form chemical bonds, and then let's go around the Oxygens here. Two, 4, 6, 8, 10, 12, 14, 16, we'll put two here, 18, and we've used all our valence electrons. You can see the Oxygens both have an octet; eight valence electrons.

The Sulfur, however, only has 6. So we can move two valence electrons from here and share them with the Sulfur. Now Sulfur has 8, and the Oxygens both have 8 as well. You might think we're done at this point; however, Sulfur can hold more than 8. It's in period 3 of the periodic table, the third row, so we'll want to check our formal charges on this. For Oxygen, on the periodic table, it's in group 6, it has 6 valence electrons. Nonbonding, we have these right here, 6. And then bonding, there are two, which we'll divide by 2. Six minus 6 minus 1 gives you negative 1. For the Sulfur, we have 6, because it's in group 6 on the periodic table. Two nonbonding, and then 2, 4, 6 bonding divided by 2. Six minus 2 minus 3 gives us a positive 1. For the last Oxygen, 6 valence electrons, 2, 4 which are nonbonding, and then 4 right here which are bonding, divided by two. Six minus 4 minus 2 is zero.

So looking at our formal charges here, we have nonzero formal charges. This may not be the best structure. So we're going to want to try to change something to see if we can get these to zero. When I see this +1 here, it makes me think that I should move 2 electrons to the center here. So let's get rid of these and put them right here. Sulfur has more than 10 now, but I think that's going to solve our problem. Let's check and see. So for the Oxygen, still 6; now we have 4 nonbonding and 4 bonding, we'll divide by 2. Six minus 4 minus 2: zero. For the Sulfur, 6 minus 2 nonbonding; and now we have a total of 8 bonding, divided by 2. Six minus 2 minus 4 is zero. And then this last Oxygen over here, 6 minus 4 nonbonding; 4 bonding divided by 2: that gives us zero, as well. So these are all zero now, which is a much more reasonable structure for us to have for SO2.

So this would be the best structure for SO2, sulfur dioxide. This is Dr. B., and thanks for watching.