CH3COO- Lewis structure

CH₃COO^– (acetate) has two carbon atoms, three hydrogen atoms, and two oxygen atoms.

In the CH₃COO^– Lewis structure, there is a single bond between the two carbon atoms. The left carbon is attached with three hydrogen atoms, and the right carbon is attached with two oxygen atoms. The oxygen atom with a single bond has three lone pairs, and the oxygen atom with a double bond has two lone pairs.

Also, there is a negative (-1) charge on the oxygen atom with a single bond.

Alternative method: Lewis structure of CH₃COO^–

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, hydrogen lies in group 1, and oxygen lies in group 16.

Hence, carbon has four valence electrons, hydrogen has one valence electron, and oxygen has six valence electrons.

Since CH₃COO^– has two carbon atoms, three hydrogen atoms, and two oxygen atoms, so…

Valence electrons of two carbon atoms = 4 × 2 = 8
Valence electrons of three hydrogen atoms = 1 × 3 = 3
Valence electrons of two oxygen atoms = 6 × 2 = 12

Now the CH₃COO^– has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 8 + 3 + 12 +1 = 24

Learn how to find: Carbon valence electrons, Hydrogen valence electrons, and Oxygen valence electrons

• Second, find the total electron pairs

We have a total of 24 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 24 ÷ 2 = 12

• Third, determine the central atom

Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.

Now we have to choose the central atom from carbon and oxygen. Place the least electronegative atom at the center.

Since carbon is less electronegative than oxygen, assume that the central atom is carbon.

Here, there are two carbon atoms, so we can assume any one as the central atom.

Let’s assume that the central atom is right carbon.

Therefore, place carbons in the center and hydrogen and oxygen on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 12 electron pairs. And six bonds are already marked. So we have to only mark the remaining six electron pairs as lone pairs on the sketch.

Also remember that both (carbon and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell. And hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens and oxygens. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for each oxygen, there are three lone pairs, and for carbon, there is zero lone pair because all six electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For left carbon atom, formal charge = 4 – 0 – ½ (8) = 0

For right carbon atom, formal charge = 4 – 0 – ½ (6) = +1

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

For each oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

Here, both carbon and oxygen atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both carbon and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the right oxygen atom to make a new C — O bond with the carbon atom as follows:

Final structure

The final structure of CH₃COO^– features two carbon atoms connected by a single covalent bond. The first carbon atom is bonded to three hydrogen atoms, while the second carbon atom is bonded to two oxygen atoms. Within this arrangement, the second carbon atom forms a double bond with one oxygen atom and a single bond with the other. The double-bonded oxygen atom satisfies its octet with two lone pairs, while the single-bonded oxygen atom holds three lone pairs, resulting in a formal charge of -1 on that specific oxygen. All other atoms, including the carbon atoms and the double-bonded oxygen, maintain a formal charge of zero. This layout is the most stable because it allows for resonance between the two oxygen atoms, distributing the negative charge evenly. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the acetate ion.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 1- is then written as a superscript outside the brackets at the top right, reflecting the presence of an additional electron beyond the total valence count of the neutral atoms.

Next: HClO₂ Lewis structure

External video

• CH3COO- Lewis Structure: How to Draw the Lewis Structure for CH3COO- – YouTube • Wayne Breslyn

External links

• https://www.thegeoexchange.org/chemistry/bonding/Lewis-Structures/CH3COO–lewis-structure.html
• https://www.chemistryscl.com/general/CH3COO–acetate-ion-lewis-structure/