Acetic acid (CH3COOH) lewis structure, molecular structure, hybridization, polarity
Acetic acid is a simple organic or monocarboxylic acid made up of two carbon, two oxygen, and four hydrogens with the chemical formula CH3COOH. It is a weak acid also known as ethanoic acid appears as a colorless liquid and odor like heavy vinegar. It is corrosive to metals and tissue.
In this article, we will discuss Acetic acid (CH3COOH) lewis structure or electron dot structure, hybridization, polar or nonpolar, geometry, etc.
Long-term exposure to acetic acid can cause severe irritation in the eyes, skin, nose, throat, etc, and in other body parts as well. Acetic acid becomes flammable and explosive over the temperature of 40ºC. Acetic acid exists as a polar or protic solvent in its liquid form.
Properties of Acetic acid
- It is soluble in water and has a dipole moment of 1.74D.
- It has a boiling point of 118 to 119 °C and a melting point of 16 to 17 °C.
- It has a pungent smell and appears as a colorless liquid in nature.
- The molar mass of ethanoic acid is 60.052 g·mol−1.
- Acetic acid is the conjugate acid of acetate.
|Name of Molecule||Acetic acid or ethanoic acid|
|Hybridization||Sp³ – Sp2|
|Total Valence electron for CH3COOH||24|
|Dipole moment||1.74 D|
How to draw lewis structure for CH3COOH (Acetic acid)
Lewis structure of CH3COOH is not much difficult to draw as you might think. We only need a good approach to draw the lewis diagram of any molecule, it doesn’t matter whether the molecule simple or complex.
CH3COOH Lewis structure contains one double bond in the functional group(COOH), 4 total lone pairs on surrounding atoms, and 8 bonded pairs attached one atom to another.
Now we will draw the lewis structure of acetic acid step by step with all possible explanations.
Follow some steps for drawing the lewis dot structure of CH3COOH (Acetic acid)
1. Count total valence electrons in CH3COOH
As we know, Lewis structure or electron dot structure helps us to know, how atoms or valence electrons are arranged in a molecule. So, the first step of drawing the lewis diagram of any molecule is to determine the valence electron present within a molecule.
Valence electrons are the electrons that are present in the outermost shell of the atom. To find the valence electron in the CH3COOH molecule, just look at their periodic group of atoms.
As carbon belongs to the 14th periodic group, oxygen to the 16th, and hydrogen present in the 1st group of the periodic table. Hence, the valence electron for carbon is 4, for oxygen, it is 6, and for hydrogen, it is 1.
⇒ Total number of the valence electrons in carbon = 4
⇒ Total number of the valence electrons in oxygen = 6
⇒ Total number of the valence electrons in hydrogen = 1
∴ Total number of valence electron available for the lewis structure of CH3COOH = 4(2) + 6(2) + 1(4) = 24 valence electrons [∴CH3COOH molecule contains two carbon, two oxygen, and 4 hydrogen]
2. Find the least electronegative atom and placed it at center
As less electronegative atoms are more prone to share more electrons with surrounding atoms, hence in lewis’s diagram, the least electronegative atom always holds the place of the central position.
In the CH3COOH molecule, three types of atoms are present – hydrogen, oxygen, and carbon. It should be noted that in the lewis diagram, hydrogen atoms always go outside means they always hold the place of the surrounding position, no matter what’s the situation is.
This is because hydrogen can only hold two valence electrons in their outermost shells.
From carbon and oxygen, the carbon atom(2.55) is less electronegative than the oxygen atom(3.44), hence carbon holds the place of a central position in the lewis diagram.
Are you wondering how we place these atoms in random positions in the above structure? CH3COOH molecule contains a functional group that is also called the carboxylic group(COOH). This group is always working together in a structure.
A functional group in organic chemistry is a collection of atoms within molecules which bind together to react in predictable ways.
Therefore, in the above structure, the COOH group atoms are placed together whereas hydrogen always goes outside in the lewis diagram.
3. Connect outer atoms to central atom with a single bond
Here’s we connect all surrounding atoms with the central atom by a single bond. So, just connect all outside atoms(hydrogen and oxygen) with the central atom(carbon) using a single bond.
Note – COOH functional group will work together.
Now just start to count the valence electron we used in the above structure. A single bond means two valence electrons. In the above structure, 7 single bonds are used for connecting surrounding atoms to the central position.
Hence, 7 × 2 = 14 valence electrons are used in the above structure from a total of 24 valence electrons available for CH3COOH.
∴ (24 – 14) = 10 valence electrons
Therefore, we are left with 10 valence electrons more.
4. Place remaining valence electrons starting from outer atom first
In this step, we need to complete the octet of outer atoms(hydrogen and oxygen) by putting the remaining valence electron we have. “An octet means having 8 valence electrons in the outermost shell of an atom”.
The hydrogen atom is an exception to the octet rule as it only needs two electrons to fulfill the outermost shell.
As you see in the above structure, we had 10 remaining valence electrons and we put all these on oxygen outer atom to fulfill their octet, as all hydrogen atoms already have two electrons in their valence shell because of a single bond.
So, each oxygen atom has 8 valence electrons around them and each hydrogen has 2, hence, these atoms completed their octet comfortably.
Let’s move on to the next step to completing the octet of the central atom also.
5. Complete central atom octet and make covalent bond if necessary
As we already completed the octet of the outer atom in the above structure, now we need to complete the central atom(carbon) octet. Carbon needs 8 electrons in its outermost shell to achieve the octet.
If you see the 4th step structure, left side carbon already completed its octet as it is attached to 4 single bonds that share 8 electrons. But right side carbon has only 3 single bonds that contain 6 electrons.
Hence, we need two more electrons to fulfill the demand for right-side carbon. But we don’t have any remaining valence electron as we already used it all in the 4th step structure.
So, in these cases, we will convert the lone pair to a covalent bond without violating the octet of any atom.
As you see in the above structure, we convert the one lone pair of oxygen electrons to a covalent bond without violating any octet rule.
By looking at the above structure, we see our right side carbon completed the octet comfortably and the oxygen atom which we have taken one lone pair to convert into the covalent bond also achieved the octet.
Hence, all atoms in the above structure have their octet, so, we can say, we got our lewis structure of CH3COOH.
We completed the lewis structure of acetic acid but we needed to check its stability with the help of the formal charge concept.
6. Check the stability with the help of a formal charge concept
As we know, the lower the formal charges on the atom, the better is the stability of the lewis diagram.
We will calculate the formal charge on the 5th step structure.
⇒ Formal charge formula = (valence electrons – lone pair electrons – 1/2bonded pair electrons)
All hydrogen atoms in the CH3COOH Lewis diagram have zero formal charges, just count the F.C. on carbon and oxygen atoms.
Both carbon atoms have attached to 4 single bonds and zero lone pairs on it, hence, their formal charge will also be the same, so, just count F.C. for one carbon atom
For the carbon atom-
⇒ Valence electron of carbon = 4
⇒ Lone pair electrons on carbon = 0
⇒ Bonded pair electrons around carbon = 8 (4 single bond)
F.C. on carbon atom = (4 – 0 – 8/2) = 0
Both oxygen atoms have attached to 2 single bonds and both contain 2 lone pairs. Hence, their formal charge will also same. So, just count F.C. for one oxygen atom.
For oxygen atom-
⇒ Valence electron of oxygen = 6
⇒ Lone pair electrons on oxygen = 4
⇒ Bonded pair electrons around oxygen = 4
F.C. on oxygen atom = (6 – 4 – 4/2) = 0
So, all atoms in the CH3COOH lewis structure have zero formal charge-
Acetic acid (CH3COOH) lewis structure
So, the above lewis structure of Acetic acid is the best and stable as all atoms have formal charge zero.
I really hope you enjoyed the procedure of making a lewis diagram with all concepts and possible explanations.
⇒ Lewis structure of Acetate ion(CH3COO-) –
What is the molecular geometry of CH3COOH?
Using VSEPR theory and its chart, we can easily determine the shape or geometry of CH3COOH. “A molecular geometry is the three-dimensional arrangement of atoms within a molecule.”
Here’s the simple structure of CH3COOH –
We will found the molecular and electron geometry of CH3COOH around both carbon atoms(C1 and C2).
Carbon 1 is directly attached to the three hydrogens and one carbon atom on the right side, it contains no lone pair. Hence, as per VSEPR theory, this carbon 1 holds the electron and molecular geometry of tetrahedral. It has an AX4 generic formula.
Carbon 2 is only attached to the three atoms and it does also not contain any lone pair of electrons, hence, as per VSEPR theory, this atom holds the electron and molecular geometry of trigonal planar. It has an AX3 generic formula.
Hybridization of CH3COOH
According to hybridization, “two or more orbitals overlap each other and form two or more hybrid orbitals which have same energy and shape”.
To determine the hybridization of any molecule, we have to first determine the hybridization number or the steric number of the central atom.
In the case of the CH3COOH molecule, two carbon atoms(C1 and C2) undergo hybridization.
This first carbon atom is joined to the three hydrogen atoms and one right side carbon, so, the total number of attached atoms is four and it contains zero lone pairs.
Steric number of carbon(C1) = 4 + 0
∴ for the steric number of 4, we get Sp3 hybridization according to the VSEPR theory.
Carbon 2 belongs to the carboxylic functional group which is attached to the 3 atoms and it also contains no lone pair of electrons.
Steric number of carbon(C2) = 3 + 0
∴ ∴ for the steric number of 3, we get Sp2 hybridization according to the VSEPR theory.
∴ The C-C bond in the CH3COOH structure is formed by Sp3 – Sp2 overlap.
Acetic acid polarity: is CH3COOH polar or nonpolar?
Acetic acid(CH3COOH) is a polar molecule because it contains double-bonded oxygen which is more electronegative than a carbon atom, so, the difference of electronegativity in carbon and oxygen atom, generates a dipole moment in the C-O bond because of inducing a positive and negative charge on them.
Also, by looking at the lewis diagram of acetic acid, its structure doesn’t seem to appear symmetrical, which means, it has unequal or unsymmetrical sharing of valence electrons.
This unequal distribution of charge generates a net dipole moment which makes the CH3COOH molecule polar in nature.
Acetic acid has a net dipole moment of 1.74 D which is close to water, hence, it forms hydrogen bonds easily in water which shows its true polar nature.
What is the electron dot structure of ethanoic acid?
“Electron dot diagrams are diagrams in which the valence electrons of an atom are shown as dots distributed around the element’s symbol.”
Electron dot structure is the same as the lewis structure, it just represents the valence electron as dots or you can say in Venn diagram form.
Image credit – Weebly
So, this is the electron dot structure of ethanoic acid which represent all their valence electron as dots and with small circles.
How many lone pair and bonded pair electrons are present in the CH3COOH lewis structure?
As per the electron dot structure of CH3COOH, there are a total of 8 lone pair electrons present that are situated around both oxygen atoms.
And the total bonded pair of electrons are in the acetic acid lewis structure is 16 (8 single bonds).
Bonded pair electrons are shareable electrons that take part in chemical bonding whereas lone pair electrons are unshared electrons.
- The total valence electron available for drawing the Acetic acid lewis structure is 24.
- The hybridization of the carbon(C1) is Sp3 and carbon(C2) is Sp2.
- CH3COOH is the polar molecule in nature because of unequal distribution of charge on the atom that leads to some net dipole moment.
- Total 8 lone pairs electrons and 16 bonded pairs electrons present in CH3COOH Lewis structure.