SO2 Lewis Structure

SO₂ (sulfur dioxide) has one sulfur atom and two oxygen atoms.

In the lewis structure of SO₂, there are two double bonds around the sulfur atom, with two oxygen atoms attached to it. On each oxygen atom, there are two lone pairs, and on the sulfur atom, there is one lone pair.

Contents

Steps

Here’s how you can draw the SO₂ lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)

Let’s break down each step in detail.

#1 Draw Sketch

First, determine the total number of valence electrons

In the periodic table, both sulfur and oxygen lie in group 16.

Hence, both sulfur and oxygen have six valence electrons.

Since SO₂ has one sulfur atom and two oxygen atoms, so…

Valence electrons of one sulfur atom = 6 × 1 = 6
Valence electrons of two oxygen atoms = 6 × 2 = 12

And the total valence electrons = 6 + 12 = 18

Learn how to find: Sulfur Valence Electrons and Oxygen Valence Electrons

Second, find the total electron pairs

We have a total of 18 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 18 ÷ 2 = 9

Third, determine the central atom

We have to place the least electronegative atom at the center.

Since sulfur is less electronegative than oxygen, assume that the central atom is sulfur.

Therefore, place sulfur in the center and oxygens on either side.

And finally, draw the rough sketch

#2 Mark Lone Pairs

Here, we have a total of 9 electron pairs. And two S — O bonds are already marked. So we have to only mark the remaining seven electron pairs as lone pairs on the sketch.

Also remember that sulfur is a period 3 element, so it can keep more than 8 electrons in its last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygens.

So for each oxygen, there are three lone pairs, and for sulfur, there is one lone pair.

Mark the lone pairs on the sketch as follows:

Lone pairs marked on SO₂ lewis structure

#3 Mark Charges

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For sulfur atom, formal charge = 6 – 2 – ½ (4) = +2

For each oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

Here, both sulfur and oxygen atoms have charges, so mark them on the sketch as follows:

Formal charges marked on SO₂ lewis structure

The above structure is not a stable lewis structure because both sulfur and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

#4 Minimize Charges

Convert a lone pair of the oxygen atom to make a new S — O bond with the sulfur atom as follows:

Lone pair of left oxygen is converted, but still there are charges

#5 Minimize Charges Again

Since there are charges on sulfur and oxygen atoms, again convert a lone pair of the oxygen atom to make a new S — O bond with the sulfur atom as follows:

Lone pair of right oxygen is converted, and got the stable lewis structure of SO₂

In the above structure, you can see that the central atom (sulfur) forms an octet. And the outside atoms (oxygens) also form an octet. Hence, the octet rule is satisfied.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of SO₂.

Next: NO₂ Lewis Structure

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