Is SiBr4 Polar or Nonpolar? (And Why?)

SiBr4 is a NONPOLAR molecule.

But why? 

And how can you say that SiBr4 is a nonpolar molecule?

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

SiBr4 is a NONPOLAR molecule because all the four bonds (Si-Br bonds) are identical and SiBr4 has symmetrical geometry which cancels out the bond polarity.

Let me explain this in detail with the help of SiBr4 lewis structure and its 3D geometry.

Why is SiBr4 a Nonpolar molecule? (Explained in 3 Steps)

SiBr4 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 SiBr4 lewis structure and it contains four Si-Br bonds.

(Note: If you want to know the steps of drawing the SiBr4 lewis dot structure, then visit this article: SiBr4 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the SiBr4 molecule has four Si-Br bonds.

Now in the next step we have to check whether these four Si-Br 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 SiBr4 molecule. It has four Si-Br bonds.

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

From the above image;

• Electronegativity of Silicon (Si) = 1.9 ^[5]
• Electronegativity of Bromine (Br) = 2.96 ^[6]

Now let’s see the polarity of each bond.

For Si-Br bond;
The electronegativity difference (ΔEN) = 2.96 – 1.9 = 1.06
This value lies between 0.4 to 1.7, which indicates that the bond between Silicon (Si) and Bromine (Br) is polar.
Hence, each Si-Br 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 Bromine atoms (Br).

But wait, this alone won’t tell you whether the entire SiBr4 molecule is polar or nonpolar.

So let’s proceed to the next step to check the symmetry of the SiBr4 molecule.

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

Have a look at this 3D structure of SiBr4. You can see that the structure of SiBr4 is symmetrical. 

The silicon atom is at the center and it is surrounded by 4 bromine atoms which are equidistant as well as at equal angles.

As all the four bonds (Si-Br) are symmetrical and the SiBr4 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 SiBr4.

Hence, the SiBr4 molecule is a nonpolar molecule.

I hope you have understood the reason behind the nonpolar nature of SiBr4 molecule.

See the polarity of other molecules to make your concepts clear:
Is CHBr3 Polar or Nonpolar?
Is ICl4- Polar or Nonpolar?
Is XeCl2 Polar or Nonpolar?
Is AsF3 Polar or Nonpolar?
Is SCl4 Polar or Nonpolar?