CH3COO- Lewis Structure

CH3COO- Lewis Structure

CH3COO (acetate) has two carbon atoms, three hydrogen atoms, and two oxygen atoms. In the lewis structure of CH3COO, 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.

Steps

Here’s how you can draw the CH3COO lewis structure step by step.

Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)

Let’s break down each step in detail.

#1 Draw 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

  • 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
CH3COO- Lewis Structure (Step 1)

#2 Mark Lone Pairs

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:

CH3COO- Lewis Structure (Step 2)

#3 Mark Charges

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:

CH3COO- Lewis Structure (Step 3)

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.

#4 Minimize Charges

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

CH3COO- Lewis Structure (Step 4)

In the above structure, you can see that the central atom (right carbon) forms an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the top oxygen atom.

This is okay, because the structure with a negative charge on the most electronegative atom is the best lewis structure. And in this case, the most electronegative element is oxygen.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the most stable lewis structure of CH3COO.

And since the CH3COO has a negative (-1) charge, mention that charge on the lewis structure by drawing brackets as follows:

CH3COO- Lewis Structure (Final)

Next: HClO2 Lewis Structure

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