Lewis Structure of CH3COOH (Acetic acid) (In 6 Simple Steps)

Ready to learn how to draw the lewis structure of CH3COOH (acetic acid)?

Awesome!

Here, I have explained 6 simple steps to draw the lewis dot structure of CH3COOH (along with images).

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of CH3COOH (or Acetic acid) contains three C-H bonds, and a COOH functional group attached to carbon. The Carbon atom (C) is at the center and it is surrounded by three Hydrogen atoms (H) and one COOH group. Both the oxygen atoms have 2 lone pairs.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of CH3COOH).

6 Steps to Draw the Lewis Structure of CH3COOH

Step #1: Calculate the total number of valence electrons

Here, the given molecule is CH3COOH (acetic acid). In order to draw the lewis structure of CH3COOH, first of all you have to find the total number of valence electrons present in the CH3COOH molecule.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in CH3COOH

• For Carbon:

Carbon is a group 14 element on the periodic table. ^[1]

Hence, the valence electrons present in carbon is 4 (see below image).

• For Hydrogen: 

Hydrogen is a group 1 element on the periodic table. ^[2]

Hence, the valence electron present in hydrogen is 1 (see below image).

• For Oxygen:

Oxygen is a group 16 element on the periodic table. ^[3]

Hence, the valence electron present in oxygen is 6 (see below image).

Hence in a CH3COOH molecule, 

Valence electrons given by each Carbon (C) atom = 4
Valence electron given by each Hydrogen (H) atom = 1
Valence electrons given by each Oxygen (O) atom = 6
So, total number of Valence electrons in CH3COOH molecule = 4 + 1(3) + 4 + 6 +6 + 1 = 24

Step #2: Select the center atom (H is always outside)

While selecting the center atom, always put the least electronegative atom at the center.

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[4]

Here in the CH3COOH molecule, if we compare the carbon atom (C), oxygen atom (O) and hydrogen atom (H), then hydrogen is less electronegative than oxygen and carbon. But as per the rule, we have to keep hydrogen outside.

So, carbon (which is less electronegative than oxygen) should be placed in the center and the remaining hydrogen atoms as well as COOH group will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of CH3COOH molecule, put the two electrons (i.e electron pair) between the carbon atom, oxygen atom and hydrogen atom to represent a chemical bond between them.

These pairs of electrons present between the Carbon (C), Oxygen (O) and Hydrogen (H) atoms form a chemical bond, which bonds these atoms with each other in a CH3COOH molecule.

Step #4: Complete the octet (or duplet) on outside atoms

Don’t worry, I’ll explain!

In the Lewis structure of CH3COOH, the outer atoms are hydrogen atoms as well as oxygen atom.

Hydrogen already has a duplet (see below image).

So now, you have to complete the octet on oxygen atom (because oxygen requires 8 electrons to have a complete outer shell).

Now, you can see in the above image that the oxygen atom forms an octet.

Also, all the 24 valence electrons of CH3COOH molecule (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of CH3COOH.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e carbon) has an octet or not. 

In simple words, we have to check whether the central Carbon (C) atom has 8 electrons or not.

As you can see from the above image, the central atom (i.e carbon) has only 6 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of carbon atom, we have to move the electron pair from the outer atom (i.e oxygen atom) to form a double bond.

Now you can see from the above image that the carbon atom is having 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on carbon atom (C), oxygen atom (O) as well as each hydrogen atom (H).

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

• For Carbon:
  Valence electrons = 4 (as it is in group 14)
  Nonbonding electrons = 0
  Bonding electrons = 8
• For Hydrogen:
  Valence electron = 1 (as it is in group 1)
  Nonbonding electrons = 0
  Bonding electrons = 2
• For Oxygen:
  Valence electron = 6 (as it is in group 16)
  Nonbonding electrons = 4
  Bonding electrons = 4

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
C	=	4	–	0	–	8/2	=	0
H	=	1	–	0	–	2/2	=	0
O	=	6	–	4	–	4/2	=	0

So you can see above that the formal charges on carbon, hydrogen as well as oxygen are “zero”.

Hence, there will not be any change in the above structure and the above lewis structure of CH3COOH is the final stable structure only.

Each electron pair (:) in the lewis dot structure of CH3COOH represents the single bond ( | ). So the above lewis dot structure of CH3COOH (acetic acid) can also be represented as shown below.

Related lewis structures for your practice:
Lewis structure of SiCl4
Lewis structure of BrO3-
Lewis structure of CBr4
Lewis structure of OCN-
Lewis structure of ICl4-

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