Lewis Structure for C2O42- | Oxalate ion

Lewis structure of oxalate ion is drawn in this tutorial step by step. Total valence electrons concept is used to draw the lewis structure of C2O42-. After finishing the lewis structure of C2O42-, there should be a -2 charge and a stability. You will learn about these things in this tutorial.

Oxalate ion | C2O42-

Carbonate ion has a -2 charge. There are two carbon atoms in the oxalate ion.

C2O42- Lewis structure

C2O42- lewis structure

Two carbon atoms are joint to one carbon atom. As like that, other two oxygen atoms has joint to other carbon. In the lewis structure of C2O42- ion, ion is symmetrical around the C-C bond.

Steps of drawing lewis structure of C2O42-

Following steps are required to draw the C2O42- lewis structure and they are explained in detail in this tutorial.

  1. Find total number of electrons of the valance shells of carbon and oxygen atoms. This is used to determine the number of bonds, lone pairs around atoms.
  2. Total electrons pairs around atoms
  3. Center atom selection according to the maximum valence
  4. Put lone pairs on atoms
  5. Check the stability and minimize charges on atoms to build the most stable structure by converting lone pairs to bonds.

Like these steps, following facts are important to draw the lewis structure.

Oxygen should hold negative charges in the lewis structure because oxygen likes to keep electrons than carbon atom.

Electronegativity of oxygen is higher than carbon.

Drawing correct lewis structure is important to draw resonance structures of CO32- correctly.

Total number of electrons of the valance shells of C2O42-

Carbon is located in group 4 in the periodic table. So, carbon has four electrons in its valence shell. Oxygen is located at 6th group. It has six electrons in valence shell.

  • Total valence electrons given by carbon atom = 4 * 2 = 8

There are four oxygen atoms in C2O42- ion, Therefore

  • Total valence electrons given by oxygen atoms = 6 *4 = 24

There are -2 charge on C2O42- ion. Therefore there are two more electrons which contribute to the valence electrons.

  • Total valence electrons = 8 + 24 + 2 = 34

Total valence electrons pairs

Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells

Total electron pairs are determined by dividing the number total valence electrons by two. For, C2O42- ion, Total pairs of electrons are 17.

Center atom of C2O42- ion

To be the center atom, ability of having higher valance is important. Carbon has the more chance to be the center atom (See the figure) because carbon can show valance of 4. Oxygen's highest valence is 2. So, now we can build a sketch of C2O42- ion.

sketch of C2O42-

Lone pairs on atoms

  • There are four C-O bonds and one C-C bond in the above sketch making five bonds. Therefore only twelve (17-5 = 12) valence electrons pairs are remaining.
  • First, mark those twelve valence electrons pairs as lone pairs in outside atoms (on oxygen atoms). One oxygen atom will take three lone pairs following the octal rule (oxygen atom cannot keep more than eight electrons in its valence shell).
  • For four oxygen atoms, twelve electrons pairs are spent. Now, there is no more lone pairs to mark on carbon atoms after marking lone pairs on oxygen atoms (outside atoms).
mark lone pairs on C2O42- lewis structure sketch

Charges on atoms

After, marking electron pairs on atoms (in this case, only on oxygen atoms), we should mark charges of each atom if there is a charge. Marking of charges are significant because it is used to determine the best lewis structure of the ion. After marking charges, you will see, every oxygen atom will get a -1 charge and both carbon atoms will get a +1 charge.

mark charges on atoms when drawing C2O42- lewis structure

This structure is very unstable because there are charges everywhere in the ion.

Check the stability and minimize charges on atoms by converting lone pairs to bonds

  • Oxygen atoms should hold negative charges because electronegativity of oxygen atom is higher than carbon atom. Otherwise, we can say, ability of holding negative charges is greater in oxygen atoms than carbon atoms.
  • The drawn structure is not a stable one because all atoms have a charge (Lewis structure should be a stable one with less charges).
  • Now, we should try to minimize charges by converting lone pair or pairs to bonds. So convert one lone pair of one oxygen atom to make a C-O bond.
  • Now there is a double bond between one carbon atom and one oxygen atom (one C=O bond). Now, there are three single bonds between carbon atom and other three oxygen atoms (two C-O bonds).
reduce charges of atoms in oxalate lewis structure

In new structure, charges of atoms are reduced than previous structure. Now there are no charge on on one oxygen atom and one carbon atom. But, there are still charges on three oxygen atoms (have -1 negative charges) and other carbon atom. Now you understand this structure of C2O42- is more stable than previous structure. But, we try to reduce charges as much as if it is possible.

Reduce charges furthermore

You can convert lone pair of another oxygen atom to a C-O bond as below.

reduce charges on CO32- lewis structure

Lewis structure of C2O42- (carbonate) ion

oxalate lewis structur


Lewis Structures of Molecules