Is BH3 Polar or Nonpolar? (And Why?)

BH3 is a NONPOLAR molecule.

But why? 

And how can you say that BH3 is a nonpolar molecule?

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

BH3 is a NONPOLAR molecule because all the three bonds (B-H bonds) are identical and BH3 has symmetrical geometry.
Also the electronegativity difference of Boron atom (B = 2.04) and Hydrogen atom (H = 2.2) is 0.16 (i.e 2.2 – 2.o4 = 0.16), which is very less. Hence the BH3 molecule is a nonpolar molecule.

Let me explain this in detail with the help of BH3 lewis structure and its 3D geometry.

Why is BH3 a Nonpolar molecule? (Explained in 2 Steps)

BH3 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 just 2 steps!

Step #1: Draw the lewis structure

Here is a skeleton of BH3 lewis structure and it contains three B-H bonds.

(Note: If you want to know the steps of drawing the BH3 lewis dot structure, then visit this article: BH3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the BH3 molecule has three B-H bonds.

Now in the next step we have to check whether these three B-H bonds are polar or nonpolar.

And we also have to check the molecular geometry of BH3.

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 BH3 molecule. It has three B-H bonds.

You can see the electronegativity values of Boron (B) and Hydrogen (H) atoms from the periodic table given below.

From the above image;

• Electronegativity of Boron (B) = 2.04 ^[5]
• Electronegativity of Hydrogen (H) = 2.2 ^[6]

Now let’s see the polarity of each bond.

For B-H bond;
The electronegativity difference (ΔEN) = 2.2 – 2.04 = 0.16
This value is less than 0.4, which indicates that the bond between Boron (B) and Hydrogen (H) is nonpolar.
Hence, each B-H bond is a nonpolar covalent bond.

As each B-H bonds are nonpolar, there will not be any partial positive charge (ẟ+) or partial negative charge (ẟ-) on the boron and hydrogen atoms.

From this, you can easily get the idea that the BH3 molecule is a nonpolar molecule.

But let’s also see whether this BH3 molecule has a symmetric geometry or not.

Have a look at this 3D structure of BH3. You can see that the structure of BH3 is symmetrical. 

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

As all the three bonds (B-H) are nonpolar and the BH3 molecule has a symmetrical geometry, there are no positive and negative poles of charges on the overall molecule of BH3.

Hence, the BH3 molecule is a nonpolar molecule.

I hope you have understood the reason behind the nonpolar nature of BH3 molecule.

See the polarity of other molecules to make your concepts clear:
Is CO Polar or Nonpolar?
Is CH3F Polar or Nonpolar?
Is NOCl Polar or Nonpolar?
Is BrF5 Polar or Nonpolar?
Is C2H2 Polar or Nonpolar?