Is POCl3 Polar or Nonpolar? (And Why?)

POCl3 is a POLAR molecule.

But why? 

And how can you say that POCl3 is a polar molecule?

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

POCl3 is a POLAR molecule because the P=O bond and P-Cl bonds present in the molecule are polar and it has asymmetric geometry 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 POCl3 molecule polar.

Let me explain this in detail with the help of POCl3 lewis structure and its 3D geometry.

Why is POCl3 a Polar molecule? (Explained in 3 Steps)

POCl3 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 POCl3 lewis structure and it contains one P=O bond and three P-Cl bonds.

(Note: If you want to know the steps of drawing the POCl3 lewis dot structure, then visit this article: POCl3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the POCl3 molecule has one P=O bond and three P-Cl bonds.

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

And we also have to check the molecular geometry of POCl3.

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 POCl3 molecule. It has one P=O bond and three P-Cl bonds.

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

From the above image;

• Electronegativity of Phosphorus (P) = 2.19 ^[6]
• Electronegativity of Oxygen (O) = 3.44 ^[7]
• Electronegativity of Chlorine (Cl) = 3.16 ^[8]

Now let’s see the polarity of each bond.

For P=O bond;
The electronegativity difference (ΔEN) = 3.44 – 2.19 = 1.25
This value lies between 0.4 to 1.7, which indicates that the bond between Phosphorus (P) and Oxygen (O) is polar.
Hence, the P=O bond is a polar covalent 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, each P-Cl bond is a polar covalent bond.

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

(Note: There is more negative charge on oxygen atom as compared to chlorine atoms, because oxygen is more electronegative than chlorine.)

But wait, we also have to look at the molecular geometry of POCl3 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 POCl3. The Phosphorus atom (P) is at the center and it is surrounded by 1 Oxygen atom (O) and 3 Chlorine atoms (Cl).

It has asymmetric geometry because of different bond lengths and difference in electronegativity of P=O bond and P-Cl bonds.

Because of this, there are positive and negative poles of charges on the overall molecule of POCl3.

Hence, the POCl3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of POCl3 molecule.

See the polarity of other molecules to make your concepts clear:
Is H2Se Polar or Nonpolar?
Is AlCl3 Polar or Nonpolar?
Is COCl2 Polar or Nonpolar?
Is C3H8 (Propane) Polar or Nonpolar?
Is SiBr4 Polar or Nonpolar?