O₂^2- (peroxide ion) Lewis Structure

O₂^2- (peroxide ion) anion contains only two oxygen atoms. Peroxide anion has -2 charge. In O₂^2- lewis structure, each oxygen atom has -1 charge and three lone pairs. Both oxygen atoms are joint through a single bond. In this tutorial, we are going to draw the lewis structure of O₂^2- ion step by step.

Peroxide ion contains only one O-O bond. Both oxygen atom has -1 charges and three lone pairs. Therefore, overall charge of O^22- is -2. Usually, we see peroxides as sodium peroxide, potassium peroxide and more.

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Steps of drawing the lewis structure of O₂^2-

There are several steps to draw a lewis structure of a molecule or ion. Those steps are used in detail in this tutorial in the drawing of O₂^2- lewis structure.

1. Find total number of electrons of the valance shells of oxygen atoms.
2. Determine total electrons pairs as lone pairs and bonds
3. Selection of center atom and the basic sketch
4. Mark lone pairs on atoms
5. Mark charges on atoms if there are charges.
6. Check the stability and minimize charges on atoms by converting lone pairs to bonds to obtain best lewis structure.

Total number of electrons of the valance shells of O₂^2-

Because there are only one element in O₂^2-, it is easy to find to Total number of electrons of the valance shells of O₂^2-. Oxygen is a group IA element and has six electrons in its last shell (valence shell). Also, when we calculate ho many electrons of the valance shells exist, we should consider the charge of the ion. Because, it is -2 in this case, we should add two more electrons to the total number of electrons of the valance shells.

• valence electrons given by oxygen atoms = 6 * 2 = 12
• valence electrons given due to -2 charge = 2

• Total valence electrons = 12 + 2 = 14

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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, O₂^2-, total pairs of electrons are 7 (=14/2) in their valence shells.

Selection of center atom and sketch of O₂^2- ion

To be the center atom, ability of having greater valance and being a electropositive element are important facts. But, because there are only two atoms and both atoms are similar ones, we do not have a problem to select the skech of O₂^2-.

Mark lone pairs on oxygen atoms

After deciding the basic sketch of O₂^2- ion , we can start to mark lone pairs on atoms. Remember that, there are total of seven electron pairs to mark on atoms.

• There is already one sigma bond in the above drawn sketch. Now only 6 (6-1) electron pairs are remaining to mark on atoms.
• Usually as a theory, those remaining electron pairs should be first marked on outside atoms. In O₂^2-, we do not have a specified center atom. Therefore, mark those electrons pairs on oxygen atoms.
• Each oxygen atom will take 3 lone pairs and all 6 lone pairs are marked on oxygen atoms.

Mark charges on atoms

In above sketch, each oxygen atom will take -1 charge. So overall charge of ion is -2.

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

Usually we convert lone pairs to bonds to reduce charges. But, O₂^2- it is not required because if we convert a lone pair to a bond, all charges are lost and we will get the lewis structure of oxygen.

Therefore, above structure should be the lewis structure of O₂^2- ion.

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Questions

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