Is SO2 Polar or Nonpolar? (And Why?)

SO2 is a POLAR molecule.

But why? 

And how can you say that SO2 is a polar molecule?

Want to know the reason?
Let’s dive into it!

SO2 is a POLAR molecule because the Oxygen (O) present in the molecule is more electronegative, which causes the partial positive (ẟ+) and partial negative (ẟ-) charge to appear on the molecule. These ẟ+ and ẟ- charges are responsible to make the entire SO2 molecule polar.

Let me explain this in detail with the help of SO2 lewis structure and its 3D geometry.

Why is SO2 a Polar molecule? (Explained in 3 Steps)

SO2 is a polar molecule because it has poles of partial positive charge (ẟ+) and partial negative charge (ẟ-) on it.

Let me explain this to you in 3 steps!

Step #1: Draw the lewis structure

Here is a skeleton of SO2 lewis structure and it contains two S=O bonds.

(Note: If you want to know the steps of drawing the SO2 lewis dot structure, then visit this article: SO2 lewis structure, Or you can also watch this short 3 minute video).

So from the above diagram we have come to know that the SO2 molecule has two S=O bonds.

Now in the next step we have to check whether these S=O bonds are polar or nonpolar.

And we also have to check the molecular geometry of SO2.

Step #2: Check whether individual bonds are polar or nonpolar

The chemical bonds can be either nonpolar, polar or ionic depending on the difference of the electronegativity values (ΔEN) between the two atoms.

Have a look at the above image.

• If the electronegativity difference (ΔEN) is less than 0.4, then the bond is nonpolar covalent bond.
• If the electronegativity difference (ΔEN) is between 0.4 to 1.7, then the bond is polar covalent bond. 
• If the electronegativity difference (ΔEN) is greater than 1.7, then the bond is an ionic bond. ^{[1] [2] [3] [4]}

Now let’s come to the example of SO2 molecule. It has two S=O bonds.

You can see the electronegativity values of Sulfur (S) and Oxygen (O) atoms from the periodic table given below.

From the above image;

• Electronegativity of Sulfur (S) = 2.58 ^[5]
• Electronegativity of Oxygen (O) = 3.44 ^[6]

Now let’s see the polarity of each bond.

For S=O bond;
The electronegativity difference (ΔEN) = 3.44 – 2.58 = 0.86
This value lies between 0.4 to 1.7, which indicates that the bond between Sulfur (S) and Oxygen (O) is polar.
Hence, the S=O bond is a polar covalent bond.

You can see in the above image that because of higher electronegativity of Oxygen atom, the partial positive charge (ẟ+) appears on the Sulfur atom (S) and partial negative charge (ẟ-) appears on the Oxygen atoms (O).

But wait, we also have to look at the molecular geometry of SO2 to know whether it has a symmetric shape or not.

Step #3: Check whether the molecule is symmetric or not

Have a look at this 3D structure of SO2. The Sulfur atom (S) is at the center and it is surrounded by 2 Oxygen atoms (O).

It also has one lone pair on the Sulfur atom (S).

Due to the lone pair on the sulfur atom (S), its molecular geometry becomes asymmetric.

Because of this, there are positive and negative poles of charges on the overall molecule of SO2.

Hence, the SO2 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of SO2 molecule.

See the polarity of other molecules to make your concepts clear:
Is CS2 Polar or Nonpolar?
Is Hydrogen Chloride (HCl) Polar or Nonpolar?
Is BF3 Polar or Nonpolar?
Is H2S Polar or Nonpolar?
Is CH3Cl Polar or Nonpolar?