O22− Lewis Structure
Peroxide ion · The anion in hydrogen peroxide and in sodium peroxide.
The O2 2- Lewis structure has 14 valence electrons - the 2− charge adds two, drawn as one O–O bond, with six lone pairs in total, all inside square brackets. The central O is sp3 hybridized and the ion is linear. Each of the two O atoms carries a 1− formal charge, and together those are the ion's 2− charge. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean.
- 14 valence e−
- linear
- sp3
- 2− charge
Calculated properties
| Total valence electrons | 14 |
|---|---|
| Bonding electrons | 2 (1 shared pairs) |
| Nonbonding electrons | 12 (6 lone pairs) |
| Electron domains (steric number) | 4 |
| VSEPR notation | AX1E3 |
| Electron geometry | tetrahedral |
| Molecular geometry | linear |
| Bond angle | no angle (only two atoms) |
| Hybridization | sp3 |
| Charge | 2− |
| Charge distribution | localised |
| Formal charges | O: -1, O: -1 |
| Resonance structures | none |
| Molar mass | 31.998 g/mol |
O Oxygen 2 atoms, 6 valence e− each
How to draw the O22− Lewis structure
Step through it. The bar shows how much of the 14-electron budget is spent at each stage - it never grows, which is the whole constraint.
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Skeleton. Join every connected pair with one bond. 1 bond spends 2 electrons.
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Outer octets. Spend electrons as lone pairs on the outer atoms. That uses the entire budget, and the central atom has nothing left over.
The reasoning at each step
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Count the valence electrons
Add up the outer-shell electrons every atom brings, then account for the charge. A 2- ion has gained two electrons, so they are added to the budget. Skip this and every count that follows will be wrong.
2 x 6 (O) + 2 (2- charge) = 14 valence electrons -
Work out what is bonded to what
Two atoms, one connection. The only question is the bond order.
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Join everything with single bonds first
Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.
1 bond x 2 = 2 electrons used, 12 left -
Work out how far short you are
Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.
needs 12, has 12, exactly enough -
Fill in the lone pairs
Every electron not in a bond sits as a lone pair on an atom. Each atom takes exactly what it needs to finish its shell - there is no choice left at this point.
O1: 3, O2: 3 (12 electrons) -
Check the formal charges
Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. They are not real charges, and they are not the ion's charge either - but they must add up to it. Adding these up gives 2-, which is the check that the structure is complete.
O1: 6 - 6 - 1 = -1 ; O2: 6 - 6 - 1 = -1 -
Work out the shape
Count the electron domains on O: 1 bonded group plus 3 lone pairs. A double or triple bond still counts as one domain, because it points in one direction. That gives tetrahedral electron geometry; ignore the lone pairs and the atoms themselves sit in a linear arrangement. Two atoms can only lie in a straight line, so there is no bond angle to measure.
steric number 4 -> sp3 -> linear -
Decide whether it is polar
Both atoms are O, so the bonding electrons are shared evenly and there is no dipole at all.
dipoles cancel -> nonpolar
Where the 2− charge sits
Each of the two O atoms carries a 1− formal charge, and together those are the ion's 2− charge. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean.
People also ask whether O22− is polar. Strictly it is neither: polar and nonpolar sort neutral molecules by whether their bond dipoles cancel. A 2− ion is pulled towards any nearby charge whatever its shape, which is why its salts dissolve in water regardless of geometry. The table below is still worth reading - it shows how unevenly each bond holds its electrons, which is what decides whether the charge ends up spread or concentrated.
| Bond | Electronegativity difference | Character |
|---|---|---|
| O–O | 0.00 | nonpolar covalent |
Common questions
How many valence electrons does O2 2- have?
O2 2- has 14 valence electrons. The atoms bring 12 between them, and the 2− charge adds two. 2 of them are in bonds and 12 sit in lone pairs.
Why does O2 2- have a 2− charge?
Each of the two O atoms carries a 1− formal charge, and together those are the ion's 2− charge. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean. The brackets around the drawing are part of the answer: they say the charge belongs to the whole ion rather than to whichever atom happens to be nearest.
What is the molecular geometry of O2 2-?
O2 2- is a linear ion. The central O has 1 bonded group and three lone pairs, a steric number of 4, which gives tetrahedral electron geometry and a linear ion.
What is the hybridization of O2 2-?
The central O in O2 2- is sp3 hybridized. Steric number 4 means 4 orbitals have to be mixed, which is exactly what sp3 gives you.
Is O2 2- polar or nonpolar?
Neither, strictly. Polar and nonpolar describe neutral molecules, by asking whether their bond dipoles cancel out. O2 2- carries a net 2− charge, so it is pulled towards any nearby charge whatever its shape - which is why ionic compounds dissolve in water regardless of geometry. The question the shape does answer is whether the charge is spread evenly: it is, because the linear arrangement puts every identical bond at the same angle to the others.