# C2O42- Lewis structure

C2O42- (oxalate) has two carbon atoms and four oxygen atoms.

In C2O42- Lewis structure, there is a single bond between the two carbon atoms, and each carbon is attached with two oxygen atoms. There are two lone pairs on each oxygen atom with a double bond, and three lone pairs on each oxygen atom with a single bond.

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

Contents

## Steps

To properly draw the C2O42- Lewis structure, follow these steps:

#1 Draw a rough sketch of the structure
#2 Next, indicate lone pairs on the atoms
#3 Indicate formal charges on the atoms, if necessary
#4 Minimize formal charges by converting lone pairs of the atoms
#5 Repeat step 4 if necessary, until all charges are minimized

Let’s break down each step in more detail.

### #1 Draw a rough sketch of the structure

• First, determine the total number of valence electrons

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

Hence, carbon has four valence electrons and oxygen has six valence electrons.

Since C2O42- has two carbon atoms and four oxygen atoms, so…

Valence electrons of two carbon atoms = 4 × 2 = 8
Valence electrons of four oxygen atoms = 6 × 4 = 24

Now the C2O42- has a negative (-2) charge, so we have to add two more electrons.

So the total valence electrons = 8 + 24 + 2 = 34

• Second, find the total electron pairs

We have a total of 34 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 = 34 ÷ 2 = 17

• Third, determine the central atom

We have to 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 oxygens on either side.

• And finally, draw the rough sketch

### #2 Next, indicate lone pairs on the atoms

Here, we have a total of 17 electron pairs. And five bonds are already marked. So we have to only mark the remaining twelve 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.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are oxygens.

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

Mark the lone pairs on the sketch as follows:

### #3 Indicate formal charges on the atoms, if necessary

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

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

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

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.

### #4 Minimize formal charges by converting lone pairs of the atoms

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

### #5 Repeat step 4 (minimize charges again)

Since there are charges on carbon and oxygen atoms, again convert a lone pair of the right oxygen atom to make a new C — O bond with the right carbon atom as follows:

In the above structure, you can see that the central atom (right carbon) forms an octet. And the outside atoms (left carbon and oxygens) also form an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the two oxygen atoms.

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 C2O42-.

And since the C2O42- has a negative (-2) charge, mention that charge on the Lewis structure by drawing brackets as follows: