Is PBr3 Polar or Nonpolar? (And Why?)

PBr3 is a POLAR molecule.

But why? 

And how can you say that PBr3 is a polar molecule?

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

PBr3 is a POLAR molecule because the Bromine (Br) present in the molecule is more electronegative, 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 PBr3 molecule polar.

Let me explain this in detail with the help of PBr3 lewis structure and its 3D geometry.

Why is PBr3 a Polar molecule? (Explained in 3 Steps)

PBr3 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 3 steps!

Step #1: Draw the lewis structure

Here is a skeleton of PBr3 lewis structure and it contains three P-Br bonds.

(Note: If you want to know the steps of drawing the PBr3 lewis dot structure, then visit this article: PBr3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the PBr3 molecule has three P-Br bonds.

Now in the next step we have to check whether these P-Br bonds are polar or nonpolar.

And we also have to check the molecular geometry of PBr3.

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 PBr3 molecule. It has three P-Br bonds.

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

From the above image;

• Electronegativity of Phosphorus (P) = 2.19 ^[6]
• Electronegativity of Bromine (Br) = 2.96 ^[7]

Now let’s see the polarity of each bond.

For P-Br bond;
The electronegativity difference (ΔEN) = 2.96 – 2.19 = 0.77
This value lies between 0.4 to 1.7, which indicates that the bond between Phosphorus (P) and Bromine (Br) is polar.
Hence, the P-Br bond is a polar covalent bond.

You can see in the above image that because of higher electronegativity of Bromine atom, the partial positive charge (ẟ+) appears on the Phosphorus atom (P) and partial negative charge (ẟ-) appears on the Bromine atoms (Br).

But wait, we also have to look at the molecular geometry of PBr3 to know whether it has a symmetric shape or not.

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

Have a look at this 3D structure of PBr3. The Phosphorus atom (P) is at the center and it is surrounded by 3 Bromine atoms (Br).

It also has one lone pair on the Phosphorus atom (P).

Due to the lone pair on the phosphorus atom (P), its molecular geometry becomes asymmetric.

Because of this, there are positive and negative poles of charges on the overall molecule of PBr3.

Hence, the PBr3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of PBr3 molecule.

See the polarity of other molecules to make your concepts clear:
Is CF2Cl2 Polar or Nonpolar?
Is C2H6 Polar or Nonpolar?
Is OCl2 Polar or Nonpolar?
Is OCS Polar or Nonpolar?
Is Benzene (C6H6) Polar or Nonpolar?