Is SiH3Br Polar or Nonpolar? (And Why?)

SiH3Br is a POLAR molecule.

But why? 

And how can you say that SiH3Br is a polar molecule?

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

SiH3Br is a POLAR molecule because the Si-Br bond present in the molecule is polar, 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 SiH3Br molecule polar.

Let me explain this in detail with the help of SiH3Br lewis structure and its 3D geometry.

Why is SiH3Br a Polar molecule? (Explained in 2 Steps)

SiH3Br 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 2 steps!

Step #1: Draw the lewis structure

Here is a skeleton of SiH3Br lewis structure and it contains three Si-H bonds and one Si-Br bond.

So from the above diagram we have come to know that the SiH3Br molecule has three Si-H bonds and one Si-Br bond.

Now in the next step we have to check whether these three Si-H bonds and one Si-Br bond are polar or nonpolar.

And we also have to check the molecular geometry of SiH3Br.

Step #2: Check the bond polarity and molecular geometry

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 SiH3Br molecule. It has three Si-H bonds and one Si-Br bond.

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

From the above image;

• Electronegativity of Silicon (Si) = 1.9 ^[5]
• Electronegativity of Hydrogen (H) = 2.2 ^[6]
• Electronegativity of Bromine (Br) = 2.96 ^[7]

Now let’s see the polarity of each bond.

For Si-H bond;
The electronegativity difference (ΔEN) = 2.2 – 1.9 = 0.3 
This value is less than 0.4, which indicates that the bond between Silicon (Si) and Hydrogen (H) is nonpolar.
Hence, each Si-H bond is a nonpolar covalent 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, the Si-Br bond is a polar covalent bond.

You can see in the above image that because of large electronegativity difference of Silicon and Bromine atom, the partial positive charge (ẟ+) appears on the Silicon atom (Si) and partial negative charge (ẟ-) appears on the Bromine atom (Br).

From this, you can easily get the idea that the SiH3Br molecule is a polar molecule.

But let’s also see its 3D molecular geometry for better understanding.

Have a look at this 3D structure of SiH3Br. The more electronegative bromine atom (Br) has a tendency to pull the shared electron pair towards itself, which results in partial positive charge on silicon atom (Si) and partial negative charge on bromine atom (Br).

Because of this, there are positive and negative poles of charges on the overall molecule of SiH3Br.

Hence, the SiH3Br molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of SiH3Br molecule.

See the polarity of other molecules to make your concepts clear:
Is SeCl4 Polar or Nonpolar?
Is H2Te Polar or Nonpolar?
Is NH3 (Ammonia) Polar or Nonpolar?
Is CO2 Polar or Nonpolar?
Is CCl4 Polar or Nonpolar?