C2O42- Lewis structure

C₂O₄^2- (oxalate) has two carbon atoms and four oxygen atoms.

In C₂O₄^2- 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.

Alternative method: Lewis structure of C₂O₄^2-

Rough sketch

• 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 C₂O₄^2- 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 C₂O₄^2- has a negative (-2) charge, so we have to add two more electrons.

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

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

• 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

Lone pair

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:

Formal charge

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.

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

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:

Final structure

The final structure of C₂O₄^2- comprises two central carbon atoms linked by a single covalent bond, with each carbon atom also connected to two oxygen atoms. In this configuration, each carbon atom forms one double bond with one oxygen and one single bond with the other, allowing both carbons to satisfy the octet rule. Within this layout, the two double-bonded oxygen atoms carry a formal charge of zero and maintain two lone pairs, while the two single-bonded oxygen atoms each hold a -1 formal charge and retain three lone pairs. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of the oxalate ion.

To properly represent this as a polyatomic ion, the entire Lewis structure is enclosed within square brackets. The overall charge of 2- is then written as a superscript outside the brackets at the top right, indicating that the structure possesses two additional electrons beyond the valence count of the neutral atoms.

Next: BrCl₅ Lewis structure

External video

• How to Draw the Lewis Structure for C2O4 2- (The Oxalate Ion) – YouTube • Wayne Breslyn

External links

• https://www.chemistryscl.com/general/lewis-structure-of-C2O42-/index.php
• https://homework.study.com/explanation/draw-all-reasonable-lewis-structures-for-the-oxalate-ion-c2o42-how-many-resonance-structures-exist-for-this-ion-assign-formal-charges-to-all-atoms-in-the-ion.html
• https://oneclass.com/homework-help/chemistry/6918588-oxalate-dianion-lewis-structure.en.html
• https://www.bartleby.com/questions-and-answers/1.-for-the-oxalate-ion-c2o42-a.-draw-the-lewis-structure.-hint-the-two-carbon-atoms-are-bonded-to-ea/94581830-b390-44bb-aa15-f0f8da7855a8
• https://www.chegg.com/homework-help/questions-and-answers/3-write-lewis-structure-including-resonance-structures-appropriate–oxalate-ion-c2o42-c-c–q3653132