Is PH3 Polar or Nonpolar? (And Why?)

PH3 is a POLAR molecule.

But why? 

And how can you say that PH3 is a polar molecule?

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

PH3 is a POLAR molecule because it has a lone pair of electrons on the Phosphorus atom (P) which causes the entire molecule to bend.
This bending of PH3 molecule results in asymmetric geometry, which makes the molecule polar.

Let me explain this in detail with the help of PH3 lewis structure and its 3D geometry.

Why is PH3 a Polar molecule? (Explained in 2 Steps)

To understand the polar nature of PH3 molecule, first of all you should know its lewis structure as well as its molecular geometry.

So let’s see this in the steps below.

Step #1: Draw the lewis structure

Here is a skeleton of PH3 lewis structure and it contains three P-H bonds.

(Note: If you want to know the steps of drawing the PH3 lewis dot structure, then visit this article: PH3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the PH3 molecule has three P-H bonds.

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

And we also have to check the molecular geometry of PH3.

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 PH3 molecule. It has three P-H bonds.

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

From the above image;

• Electronegativity of Phosphorus (P) = 2.19 ^[5]
• Electronegativity of Hydrogen (H) = 2.2 ^[6]

Now let’s see the polarity of each bond.

For P-H bond;
The electronegativity difference (ΔEN) = 2.2 – 2.19 = 0.01
This value is less than 0.4, which indicates that the bond between Phosphorus (P) and Hydrogen (H) is nonpolar.
Hence, each P-H bond is a nonpolar covalent bond.

But wait, we also have to look at the molecular geometry of PH3 to know whether it has a symmetric shape or not.

Have a look at this 3D structure of PH3. The Phosphorus atom (P) is at the center and it is surrounded by 3 Hydrogen atoms (H).

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 PH3.

Hence, the PH3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of PH3 molecule.

See the polarity of other molecules to make your concepts clear:
Is NO2 Polar or Nonpolar?
Is BH3 Polar or Nonpolar?
Is CO Polar or Nonpolar?
Is CH3F Polar or Nonpolar?
Is NOCl Polar or Nonpolar?