Is PCl3 Polar or Nonpolar? (And Why?)

PCl3 is a POLAR molecule.

But why? 

And how can you say that PCl3 is a polar molecule?

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

PCl3 is a POLAR molecule because the Chlorine (Cl) 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 PCl3 molecule polar.

Let me explain this in detail with the help of PCl3 lewis structure and its 3D geometry.

Why is PCl3 a Polar molecule? (Explained in 3 Steps)

PCl3 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 PCl3 lewis structure and it contains three P-Cl bonds.

(Note: If you want to know the steps of drawing the PCl3 lewis dot structure, then visit this article: PCl3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the PCl3 molecule has three P-Cl bonds.

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

And we also have to check the molecular geometry of PCl3.

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 PCl3 molecule. It has three P-Cl bonds.

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

From the above image;

• Electronegativity of Phosphorus (P) = 2.19 ^[5]
• Electronegativity of Chlorine (Cl) = 3.16 ^[6]

Now let’s see the polarity of each bond.

For P-Cl bond;
The electronegativity difference (ΔEN) = 3.16 – 2.19 = 0.97
This value lies between 0.4 to 1.7, which indicates that the bond between Phosphorus (P) and Chlorine (Cl) is polar.
Hence, the P-Cl bond is a polar covalent bond.

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

But wait, we also have to look at the molecular geometry of PCl3 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 PCl3. The Phosphorus atom (P) is at the center and it is surrounded by 3 Chlorine atoms (Cl).

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 PCl3.

Hence, the PCl3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of PCl3 molecule.

See the polarity of other molecules to make your concepts clear:
Is HCN Polar or Nonpolar?
Is CH2O Polar or Nonpolar?
Is XeF4 Polar or Nonpolar?
Is SF6 Polar or Nonpolar?
Is BCl3 Polar or Nonpolar?