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Superoxide ion (O₂⁻) Lewis structure

13 valence electrons, linear, a charge of −1

O O − −
O₂⁻ as the Lewis Structure Generator draws it: lone pairs as dots, the odd electron ringed, nonzero formal charges circled.

Build O₂⁻ step by step in the Lewis Structure Generator

What is the Lewis structure of O₂⁻?

Superoxide ion, O₂⁻, has 13 valence electrons. Its two atoms are joined by one O−O single bond. It carries two lone pairs on the O with the odd electron and three on the other O. Its only formal charge is −1, on the other O. It has two equivalent resonance forms. As two atoms it is linear.

Valence electrons in O₂⁻

Element Group Valence electrons Atoms Electrons
Oxygen 16 6 2 12
Charge of 1− +1
Total 13

In one line: 2 × 6 + 1 = 13. Each atom brings the valence electrons its group gives it, and the negative charge adds one electron for each unit.

How to draw the O₂⁻ Lewis structure

  1. Count the valence electrons. Valence electrons: each O 6, and the 1− charge adds 1. 2 × 6 + 1 = 13.
  2. Join the two atoms. With only two atoms there is no choice to make: they bond to each other.
  3. Join the atoms with single bonds. One single bond uses 2 electrons, leaving 13 − 2 = 11.
  4. Place the lone pairs. Neither atom is an outer one, so the 11 left go on the two atoms as two lone pairs on one O and three on the other, with the odd electron on the first. Now one O has 7 electrons round it and the other 8.
  5. Make multiple bonds where needed. One O has 8 electrons and the other 7, the odd electron among them. A double bond would take a lone pair from the first and give the second 9, more than a period-two atom holds, so the bond stays single.

Lone pairs and formal charges in O₂⁻

Atom Number Bonds Lone pairs Electrons round it Formal charge, V − N − B/2
O 1 one single bond 2 and 1 unpaired electron 7 6 − 5 − 1 = 0
O 1 one single bond 3 8 6 − 6 − 1 = −1

V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to −1, the charge on the ion.

Resonance structures of O₂⁻

The two forms differ only in where the electrons sit, so the real ion is one structure, their average, the resonance hybrid. Two O atoms share a formal charge of −1 between them, −1/2 each.

O O − −
Form 1
O O − −
Form 2
O O −1/2 −1/2 −
Resonance hybrid, partial bonds dashed

Shape and polarity of O₂⁻

Central atom none, two atoms
Electron geometry linear
Molecular geometry linear
Ideal bond angle none, two atoms
Polarity, an estimate not applicable

An ion carries a net charge, so whether its bond dipoles cancel is not the question polarity asks.

Notes on the O₂⁻ Lewis structure

O₂⁻ Lewis structure compared with its molecular orbital diagram

Lewis structure Molecular orbital diagram
Bond order 1 1.5
Unpaired electrons 1 1

In the molecular orbital diagram O₂⁻’s 13 valence electrons put 8 in bonding orbitals and 5 in antibonding ones, so its bond order is (8 − 5)/2 = 1.5. The Lewis structure gives a bond order of 1 against the diagram’s 1.5. The Molecular Orbital Diagram Visualizer draws the diagram level by level.

Work with O₂⁻