CH3COOH (Acetic acid) Lewis Structure in 6 Steps

So you have seen the above image by now, right?

Let me explain the above image in short.

CH3COOH (Acetic acid) lewis structure has Carbon atom (C) at the center which is surrounded by three Hydrogen atoms (H) and one COOH group. There are three C-H bonds and one COOH functional group attached to the carbon. There are 2 lone pairs on both the Oxygen atoms (O).

If you haven’t understood anything from the above image of CH3COOH lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of CH3COOH (acetic acid).

So let’s move to the steps of drawing the lewis structure of CH3COOH (acetic acid).

Steps of drawing CH3COOH lewis structure

Step 1: Find the total valence electrons in CH3COOH molecule

In order to find the total valence electrons in a CH3COOH molecule, first of all you should know the valence electrons present in carbon atom, hydrogen atom as well as oxygen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)

Here, I’ll tell you how you can easily find the valence electrons of carbon, hydrogen as well as oxygen using a periodic table.

Total valence electrons in CH3COOH molecule

→ Valence electrons given by carbon atom:

Carbon is group 14 element on the periodic table. ^[1] Hence the valence electrons present in carbon is 4.

You can see the 4 valence electrons present in the carbon atom as shown in the above image.

→ Valence electrons given by hydrogen atom:

Hydrogen is group 1 element on the periodic table. ^[2] Hence the valence electron present in hydrogen is 1.

You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.

→ Valence electrons given by oxygen atom:

Oxygen is group 16 element on the periodic table. ^[3] Hence the valence electrons present in oxygen is 6.

You can see the 6 valence electrons present in the oxygen atom as shown in the above image.

Hence, 

Total valence electrons in CH3COOH molecule = valence electrons given by 2 carbon atoms + valence electrons given by 4 hydrogen atoms + valence electrons given by 2 oxygen atoms = 4(2) + 1(4) + 6(2) = 24.

Step 2: Select the central atom

For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.

(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)

Now here the given molecule is CH3COOH and it contains carbon atoms (C), hydrogen atoms (H) and oxygen atoms (O).

So as per the rule we have to keep hydrogen outside.

Now, you can see the electronegativity values of carbon atom (C) and oxygen atom (O) in the above periodic table.

If we compare the electronegativity values of carbon (C) and oxygen (O) then the carbon atom is less electronegative.

So here the carbon atoms (C) are the center atom and the oxygen atom (O) is the outside atom.

In other way you can also see that the carbon atom is surrounded with three hydrogen atoms and one COOH group.

Step 3: Connect each atoms by putting an electron pair between them

Now in the CH3COOH molecule, you have to put the electron pairs between the carbon (C) atom, oxygen (O) atom and hydrogen (H) atoms.

This indicates that these atoms are chemically bonded with each other in a CH3COOH molecule.

Step 4: Make the outer atoms stable

Now in this step, you have to check the stability of the outer atoms.

Here in the sketch of CH3COOH molecule, you can see that the outer atoms are hydrogen atoms and oxygen atom.

These hydrogen atoms and oxygen atom are forming a duplet and octet respectively and hence they are stable.

Also, in step 1 we have calculated the total number of valence electrons present in the CH3COOH molecule.

The CH3COOH molecule has a total 24 valence electrons and all these valence electrons are used in the above sketch of CH3COOH.

Hence there are no remaining electron pairs to be kept on the central atom. 

So now let’s proceed to the next step.

Step 5: Check the octet on the central atom. If it does not have octet, then shift the lone pair to form a double bond or triple bond.

In this step, you have to check whether the central carbon atoms (C) are stable or not.

In order to check the stability of the central carbon (C) atoms, we have to check whether they are forming an octet or not.

Unfortunately, one of the carbon atoms is not forming an octet here. It has only 6 electrons and it is unstable.

Now to make this carbon atom stable, you have to shift the electron pair from the outer oxygen atom so that the carbon atom can have 8 electrons (i.e octet).

After shifting this electron pair, the carbon atom will get 2 more electrons and thus its total electrons will become 8.

You can see from the above picture that the carbon atom is forming an octet as it has 8 electrons.

Now let’s proceed to the final step to check whether the lewis structure of CH3COOH is stable or not.

Step 6: Check the stability of lewis structure

Now you have come to the final step in which you have to check the stability of lewis structure of CH3COOH.

The stability of lewis structure can be checked by using a concept of formal charge.

In short, now you have to find the formal charge on carbon (C) atoms, hydrogen (H) atoms as well as oxygen (O) atoms present in the CH3COOH molecule.

For calculating the formal charge, you have to use the following formula;

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

You can see the number of bonding electrons and nonbonding electrons for each atom of CH3COOH molecule in the image given below.

For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 8
Nonbonding electrons = 0

For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0

For Oxygen (O) atom:
Valence electrons = 6 (because oxygen is in group 16)
Bonding electrons = 4
Nonbonding electrons = 4

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

From the above calculations of formal charge, you can see that the carbon (C) atoms, hydrogen (H) atoms as well as oxygen (O) atoms have a “zero” formal charge.

This indicates that the above lewis structure of CH3COOH is stable and there is no further change in the above structure of CH3COOH.

In the above lewis dot structure of CH3COOH, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of CH3COOH.

I hope you have completely understood all the above steps.

For more practice and better understanding, you can try other lewis structures listed below.

Try (or at least See) these lewis structures for better understanding:

BrO3- lewis structure	CBr4 lewis structure
OCN- lewis structure	ICl4- lewis structure
SiF4 lewis structure	CH3F lewis structure