Carbon monoxide (CO) Lewis structure
10 valence electrons, linear
Build CO step by step in the Lewis Structure Generator
What is the Lewis structure of CO?
Carbon monoxide, CO, has 10 valence electrons. Its two atoms are joined by one C≡O triple bond. It carries one lone pair on the C and one on the O. Its formal charges are −1 on the C and +1 on the O. As two atoms it is linear, and the molecule is polar.
Valence electrons in CO
In one line: 4 + 6 = 10. Each atom brings the valence electrons its group gives it.
How to draw the CO Lewis structure
- Count the valence electrons. Valence electrons: C 4 and O 6. 4 + 6 = 10.
- Join the two atoms. With only two atoms there is no choice to make: they bond to each other.
- Join the atoms with single bonds. One single bond uses 2 electrons, leaving 10 − 2 = 8.
- Complete the outer atoms. The outer O takes 6 electrons as lone pairs to reach eight, leaving 8 − 6 = 2.
- Put the rest on C. The 2 left go as one lone pair on C, and C now has 4 electrons round it.
- Make multiple bonds where needed. C has only 4 electrons, so two lone pairs move into the bond, making a C≡O bond, and C now has 8.
Lone pairs and formal charges in CO
| Atom | Number | Bonds | Lone pairs | Electrons round it | Formal charge, V − N − B/2 |
|---|---|---|---|---|---|
| C | 1 | one triple bond | 1 | 8 | 4 − 2 − 3 = −1 |
| O | 1 | one triple bond | 1 | 8 | 6 − 2 − 3 = +1 |
V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to 0, the molecule’s overall charge.
Shape and polarity of CO
| Central atom | none, two atoms |
|---|---|
| Electron geometry | linear |
| Molecular geometry | linear |
| Ideal bond angle | none, two atoms |
| Polarity, an estimate | polar |
The electronegativities differ by 0.89, so the shared electrons sit nearer O.
Notes on the CO Lewis structure
- The triple bond gives both atoms an octet. One of its three pairs came from oxygen alone, a dative bond, which is why the formal charges look backwards: −1 on carbon, +1 on oxygen.
CO Lewis structure compared with its molecular orbital diagram
| Lewis structure | Molecular orbital diagram | |
|---|---|---|
| Bond order | 3 | 3 |
| Unpaired electrons | 0 | 0 |
In the molecular orbital diagram CO’s 10 valence electrons put 8 in bonding orbitals and 2 in antibonding ones, so its bond order is (8 − 2)/2 = 3. The Lewis structure gives the same bond order and the same number of unpaired electrons. The measured bond length is 113 pm (Huber and Herzberg, Constants of Diatomic Molecules, 1979). The Molecular Orbital Diagram Visualizer draws the diagram level by level.
Work with CO
- Lewis Structure Generator: CO built step by step, with every formal charge worked out
- VSEPR Molecular Geometry: every VSEPR shape in 3D, with its bond angles
- Molecular Orbital Diagram Visualizer: the bond order and unpaired electrons of CO
- All 78 Lewis structures: valence electrons, resonance, shape and polarity in one table