Is SeO3 Polar or Nonpolar? (And Why?)

SeO3 is a NONPOLAR molecule.

But why? 

And how can you say that SeO3 is a nonpolar molecule?

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

SeO3 is a NONPOLAR molecule because all the three bonds (Se=O bonds) are identical and SeO3 has symmetrical geometry which cancels out the bond polarity.

Let me explain this in detail with the help of SeO3 lewis structure and its 3D geometry.

Why is SeO3 a Nonpolar molecule? (Explained in 3 Steps)

SeO3 is a nonpolar molecule because it does not have any pole of positive charge and negative charge on it.

Let me explain this to you in 3 steps!

Step #1: Draw the lewis structure

Here is a skeleton of SeO3 lewis structure and it contains three Se=O bonds.

(Note: If you want to know the steps of drawing the SeO3 lewis dot structure, then visit this article: SeO3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the SeO3 molecule has three Se=O bonds.

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

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 SeO3 molecule. It has three 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 Selenium-Oxygen 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, each Selenium-Oxygen bond is a polar covalent bond.

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

But wait, this alone won’t tell you whether the entire SeO3 molecule is polar or nonpolar.

So let’s proceed to the next step to check the symmetry of the SeO3 molecule.

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

Have a look at this 3D structure of SeO3. You can see that the structure of SeO3 is symmetrical. 

The selenium atom is at the center and it is surrounded by 3 oxygen atoms which are equidistant as well as at equal angles.

As the bonds (Se=O) are symmetrical and the SeO3 molecule has a symmetrical geometry, their bond polarity gets canceled with each other.

Because of this, there are no positive and negative poles of charges on the overall molecule of SeO3.

Hence, the SeO3 molecule is a nonpolar molecule.

I hope you have understood the reason behind the nonpolar nature of SeO3 molecule.

See the polarity of other molecules to make your concepts clear:
Is Acetic acid (CH3COOH) Polar or Nonpolar?
Is H3O+ Polar or Nonpolar?
Is BBr3 Polar or Nonpolar?
Is BeH2 Polar or Nonpolar?
Is Cyclohexane (C6H12) Polar or Nonpolar?