Is Acetic acid (CH3COOH) Polar or Nonpolar? (And Why?)

Acetic acid (CH3COOH) is a POLAR molecule.

But why? 

And how can you say that acetic acid is a polar molecule?

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

Acetic acid (CH3COOH) is a POLAR molecule because the Oxygen (O) 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 CH3COOH molecule polar.

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

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

Acetic acid (CH3COOH) 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 CH3COOH lewis structure and it contains C-H bonds, C-O bond, C-C bond and O-H bond.

(Note: If you want to know the steps of drawing the CH3COOH lewis dot structure, then visit this article: CH3COOH lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the CH3COOH molecule has C-H bonds, C-C bond, C-O bond and O-H bond.

Now in the next step we have to check whether these C-H bonds, C-C bond, C-O bond and O-H bond are polar or nonpolar.

And we also have to check the molecular geometry of CH3COOH.

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 CH3COOH molecule. It has C-H bonds, C-C bond, C-O bond and O-H bond.

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

From the above image;

• Electronegativity of Carbon (C) = 2.55 ^[5]
• Electronegativity of Hydrogen (H) = 2.2 ^[6]
• Electronegativity of Oxygen (O) = 3.44 ^[7]

Now let’s see the polarity of each bond.

For C-H bond;
The electronegativity difference (ΔEN) = 2.55 – 2.2 = 0.35 
This value is less than 0.4, which indicates that the bond between Carbon (C) and Hydrogen (H) is nonpolar.
Hence, each C-H bond is a nonpolar covalent bond.

For C-C bond;
The electronegativity difference (ΔEN) = 2.55 – 2.55 = 0 
This value is less than 0.4, which indicates that the Carbon-Carbon is nonpolar.
Hence, each C-C bond is a nonpolar covalent bond.

For Carbon-Oxygen bond;
The electronegativity difference (ΔEN) = 3.44 – 2.55 = 0.89
This value lies between 0.4 to 1.7, which indicates that the bond between Carbon (C) and Oxygen (O) is polar.
Hence, each Carbon-Oxygen bond is a polar covalent bond.

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, the partial positive charge (ẟ+) appears on the Carbon atom (C) as well as Hydrogen atoms (H) and partial negative charge (ẟ-) appears on the Oxygen atoms (O).

From this, you can easily get the idea that the CH3COOH 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 CH3COOH. The more electronegative oxygen atom (O) has a tendency to pull the shared electron pair towards itself, which results in partial positive charge on carbon atom (C) & 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 CH3COOH.

Hence, the CH3COOH molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of acetic acid (CH3COOH) molecule.

See the polarity of other molecules to make your concepts clear:
Is H3O+ Polar or Nonpolar?
Is BBr3 Polar or Nonpolar?
Is BeH2 Polar or Nonpolar?
Is Cyclohexane (C6H12) Polar or Nonpolar?
Is IOF5 Polar or Nonpolar?