Is SiO2 Polar or Nonpolar? (And Why?)

SiO2 is a NONPOLAR molecule.

But why? 

And how can you say that SiO2 is a nonpolar molecule?

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

SiO2 is a NONPOLAR molecule because both the bonds (Si=O bonds) are identical and SiO2 has symmetrical geometry which cancels out the bond polarity.

Let me explain this in detail with the help of SiO2 lewis structure and its 3D geometry.

Why is SiO2 a Nonpolar molecule? (Explained in 3 Steps)

SiO2 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 SiO2 lewis structure and it contains two Si=O bonds.

(Note: If you want to know the steps of drawing the SiO2 lewis dot structure, then visit this article: SiO2 lewis structure).

So from the above diagram we have come to know that the SiO2 molecule has two Si=O bonds.

Now in the next step we have to check whether these two Si=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]}

Now let’s come to the example of SiO2 molecule. It has two Si=O bonds.

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

From the above image;

• Electronegativity of Silicon (Si) = 1.9 ^[5]
• Electronegativity of Oxygen (O) = 3.44 ^[6]

Now let’s see the polarity of each bond.

For Silicon-Oxygen bond;
The electronegativity difference (ΔEN) = 3.44 – 1.9 = 1.54
This value lies between 0.4 to 1.7, which indicates that the bond between Silicon (Si) and Oxygen (O) is polar.
Hence, each Silicon-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 Silicon atom (Si) and partial negative charge (ẟ-) appears on the Oxygen atoms (O).

But wait, this alone won’t tell you whether the entire SiO2 molecule is polar or nonpolar.

So let’s proceed to the next step to check the symmetry of the SiO2 molecule.

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

Have a look at this 3D structure of SiO2. You can see that the structure of SiO2 is symmetrical. 

The silicon atom is at the center and it is surrounded by 2 oxygen atoms which are equidistant as well as at equal angles.

As both the bonds (Si=O) are symmetrical and the SiO2 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 SiO2.

Hence, the SiO2 molecule is a nonpolar molecule.

I hope you have understood the reason behind the nonpolar nature of SiO2 molecule.

See the polarity of other molecules to make your concepts clear:
Is SBr2 Polar or Nonpolar?
Is CHF3 Polar or Nonpolar?
Is SeF4 Polar or Nonpolar?
Is CH2Br2 Polar or Nonpolar?
Is Ammonium ion (NH4+) Polar or Nonpolar?