Is SeO2 Polar or Nonpolar? (And Why?)

SeO2 is a POLAR molecule.

But why? 

And how can you say that SeO2 is a polar molecule?

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

SeO2 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 SeO2 molecule polar.

Let me explain this in detail with the help of SeO2 lewis structure and its 3D geometry.

Why is SeO2 a Polar molecule? (Explained in 3 Steps)

SeO2 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 SeO2 lewis structure and it contains two Se=O bonds.

(Note: If you want to know the steps of drawing the SeO2 lewis dot structure, then visit this article: SeO2 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the SeO2 molecule has two Se=O bonds.

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

And we also have to check the molecular geometry of SeO2.

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] [5]}

Now let’s come to the example of SeO2 molecule. It has two Se=O bonds.

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

From the above image;

• Electronegativity of Selenium (Se) = 2.55 ^[6]
• Electronegativity of Oxygen (O) = 3.44 ^[7]

Now let’s see the polarity of each bond.

For Se=O bond;
The electronegativity difference (ΔEN) = 3.44 – 2.55 = 0.89
This value lies between 0.4 to 1.7, which indicates that the bond between Selenium (Se) and Oxygen (O) is polar.
Hence, the Se=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 Selenium atom (Se) and partial negative charge (ẟ-) appears on the Oxygen atom (O).

But wait, we also have to look at the molecular geometry of SeO2 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 SeO2. The Selenium atom (Se) is at the center and it is surrounded by 2 Oxygen atoms (O).

It also has one lone pair on the Selenium atom (Se).

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

Because of this, there are positive and negative poles of charges on the overall molecule of SeO2.

Hence, the SeO2 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of SeO2 molecule.

See the polarity of other molecules to make your concepts clear:
Is OH- Polar or Nonpolar?
Is SeF6 Polar or Nonpolar?
Is ICl3 Polar or Nonpolar?
Is XeO3 Polar or Nonpolar?
Is XeO4 Polar or Nonpolar?