Is HNO3 Polar or Nonpolar? (And Why?)

HNO3 is a POLAR molecule.

But why? 

And how can you say that HNO3 is a polar molecule?

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

HNO3 is a POLAR molecule because the O-H bond present in the molecule is polar, 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 HNO3 molecule polar.

Let me explain this in detail with the help of HNO3 lewis structure and its 3D geometry.

Why is HNO3 a Polar molecule? (Explained in 2 Steps)

HNO3 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 2 steps!

Step #1: Draw the lewis structure

Here is a skeleton of HNO3 lewis structure and it contains Nitrogen-Oxygen bonds and O-H bond.

(Note: If you want to know the steps of drawing the HNO3 lewis dot structure, then visit this article: HNO3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the HNO3 molecule has Nitrogen-Oxygen bonds and O-H bond.

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 HNO3.

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] [5]}

Now let’s come to the example of HNO3 molecule. It has Nitrogen-Oxygen bonds and O-H bond.

You can see the electronegativity values of Hydrogen (H), Nitrogen (N) and Oxygen (O) atoms from the periodic table given below.

From the above image;

• Electronegativity of Hydrogen (H) = 2.2 ^[6]
• Electronegativity of Nitrogen (N) = 3.04 ^[7]
• Electronegativity of Oxygen (O) = 3.44 ^[8]

Now let’s see the polarity of each bond.

For Nitrogen-Oxygen bond;
The electronegativity difference (ΔEN) = 3.44 – 3.04 = 0.4
Now this value is exactly between the range of polar and nonpolar bonds, so we cannot perfectly say whether the Nitrogen-Oxygen bonds are polar or nonpolar.
In some textbooks, you may find some different range of ΔEN, but if we consider the above mentioned range for ΔEN, then we can say that the Nitrogen-Oxygen bonds can be either highly nonpolar or very less polar.

For O-H bond;
The electronegativity difference (ΔEN) = 3.44 – 2.2 = 1.24
This value lies between 0.4 to 1.7, which indicates that the bond between Oxygen (O) and Hydrogen (H) is polar.
Hence, the O-H bond is a polar covalent bond.

You can see in the above image that because of higher electronegativity of Oxygen atom (of O-H bond), the partial positive charge (ẟ+) appears on the Hydrogen atom (H) and partial negative charge (ẟ-) appears on the Oxygen atom (O).

From this, you can easily get the idea that the HNO3 molecule is a polar molecule.

But let’s also see its 3D molecular geometry for better understanding.

Have a look at this 3D structure of HNO3. The more electronegative oxygen atom (O) has a tendency to pull the shared electron pair towards itself, which results in partial positive charge on the hydrogen atom (H) and partial negative charge on oxygen atom (O).

Because of this, there are positive and negative poles of charges on the overall molecule of HNO3.

Hence, the HNO3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of HNO3 molecule.

See the polarity of other molecules to make your concepts clear:
Is IBr3 Polar or Nonpolar?
Is NH2- Polar or Nonpolar?
Is KrF2 Polar or Nonpolar?
Is BrCl5 Polar or Nonpolar?
Is ClO2- Polar or Nonpolar?