Lewis Structure for CO32- | Carbonate ion

Lewis structure of carbonate ion is drawn in this tutorial step by step. Total valence electrons concept is used to draw the lewis structure of CO32-. After finishing the lewis structure of CO32-, there should be a -2 charge and it should be stabile structure. You will learn about these facts in this tutorial.

Carbonate ion | CO32-

Carbonate ion has a -2 charge. Metal carbonate compounds are common in the world. As an CaCO3 can be given.

CO32- Lewis structure

CO32- lewis structure

There are three σ bonds and π bond around carbon atom in the Lewis structure of CO32- ion.

Steps of drawing lewis structure of CO32-

Following steps are required to draw the CO32- 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
  2. Total electrons pairs
  3. Center atom selection
  4. Put lone pairs on atoms
  5. Check the stability and minimize charges on atoms by converting lone pairs to bonds.

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

Total number of electrons of the valance shells of CO32-

Carbon is located at 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

There are three oxygen atoms in CO32- ion, Therefore

  • Total valence electrons given by oxygen atoms = 6 *3 = 18

There are -2 charge on CO32- ion. Therefore there are two more electrons which contribute to the valence electrons.

  • Total valence electrons = 4 + 18 + 2 = 24

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, CO32- ion, Total pairs of electrons are 12.

Center atom of CO32- 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 CO32- ion.

carbonate ion (CO32-) sketch structuree.jpg

Lone pairs on atoms

  • There are already three C-O bonds in the above sketch. Therefore only nine (12-3 = 9) valence electrons pairs are remaining.
  • First, mark those nine 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 three oxygen atoms, nine electrons pairs are spent. Now there is no more lone pairs to mark on carbon atoms after marking on oxygen atoms (outside atoms).
mark valence electrons CO32- lewis structure

Charges on atoms

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

mark charges on carbonate lewis structure

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 carbon atom and one oxygen atom (one C=O bond). Now, there are two single bonds between carbon atom and other two oxygen atoms (two C-O bonds).
reduce charges on CO32- lewis structure

In new structure, charges of atoms are reduced than previous structure. Now there are no charge on on one oxygen atom and the carbon atom. Also, only two oxygen atoms have -1 negative charges. Now you understand this structure of CO32- is more stable than previous structure. So, this structure has more chance to be the lewis structure of CO32- ion.

Lewis structure of CO32- (carbonate) ion

lewis structure of CO32


carbonate lewis structure and bicarbonate lewis structure

In carbonate ion, there is two oxygen atoms which has -1 charge on each of them. One of these oxygen atom take a proton (H+ ion) and form a -OH group.