Lewis structure of CH3COO-

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Lewis structure of CH3COO-
Lewis structure of CH3COO

The Lewis structure of CH3COO contains five single bonds and one double bond, with two carbons in the center, and three hydrogens and two oxygens on either side. The top oxygen atom has two lone pairs, the right oxygen atom has three lone pairs, and carbon atom and hydrogen atom do not have any lone pair.

Plus, there is a negative (-1) charge on the right oxygen atom.

Steps

By using the following steps, you can easily draw the Lewis structure of CH3COO.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

  • Let’s calculate the total number of valence electrons

We know that… carbon is a group 14 element, hydrogen is a group 1 element, and oxygen is a group 16 element. Hence, carbon has four valence electrons, hydrogen has one valence electron, and oxygen has six valence electrons.

Now CH3COO has two carbon atoms, three hydrogen atoms, and two oxygen atoms.

So the total number of valence electrons = (valence electrons of carbon atom × 2) + (valence electrons of hydrogen atom × 3) + (valence electrons of oxygen atom × 2)

And CH3COO has a negative (-1) charge, so we have to add one more electron.

Therefore, the total number of valence electrons = 8 + 3 + 12 + 1 = 24

  • Now decide the central atom

We can not assume hydrogen as 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.

Therefore, choose the central atom from carbon and oxygen.

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for carbon and oxygen as follows:

Electronegativity value of carbon = 2.55
Electronegativity value of oxygen = 3.44

Obviously, carbon is less electronegative than oxygen. Hence, assume that right carbon is the central atom (as there are two carbons).

So now, put two carbons in the center and hydrogens and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of CH3COO something like this:

Skeleton structure for Lewis structure of CH3COO

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since carbon is surrounded by hydrogens and oxygens, use twelve electrons to show six chemical bonds as follows:

Six chemical bonds shown between atoms

#3 Mark lone pairs

As calculated earlier, we have a total of 24 valence electrons. And in the above structure, we have already used twelve valence electrons. Hence, twelve valence electrons are remaining.

Two valence electrons represent one lone pair. So twelve valence electrons = six lone pairs.

Note 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.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are hydrogens, oxygens, and left carbon. But hydrogen can not keep more than 2 electrons in its last shell. Hence, don’t mark the lone pairs on hydrogen.

So each oxygen will get three lone pairs. And left carbon and central atom (right carbon) will not get any lone pair, because all six lone pairs are used.

Now draw the Lewis structure of CH3COO something like this:

Lone pairs marked on Lewis structure of CH3COO

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (right carbon) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

#4 Complete octet on central atom

Remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now right carbon already has six valence electrons. Hence, right carbon needs two more valence electrons to complete its octet.

So convert one lone pair from one oxygen atom to make a new bond with the right carbon atom. And then, the Lewis structure of CH3COO looks something like this:

Lone pair of top oxygen is converted, and octet is completed on atoms

In the above structure, you can see that the octet is completed on the central atom (right carbon), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

#5 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

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

Collect the data from the above structure and then, write it down below as follows:

  • For each carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

  • For each hydrogen atom

Valence electrons = 1
Nonbonding electrons = 0
Bonding electrons = 2

Formal charge = 1 – 0 – ½ (2) = 0

  • For top oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

  • For right oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of CH3COO looks something like this:

Formal charges are calculated, and got the most stable Lewis structure of CH3COO

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of CH3COO.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now CH3COO is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of CH3COO looks something like this:

Lewis structure of CH3COO showing a negative (-1) charge

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Deep

Rootmemory.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.

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