Bond Order Calculator

Subtract the antibonding electrons from the bonding electrons and divide by two. O₂ has 10 bonding and 6 antibonding electrons, giving a bond order of 2.

The molecule does not form. He₂ has two bonding and two antibonding electrons, which cancel exactly — which is why helium exists as single atoms even though a Lewis structure for He₂ can be drawn.

Its two highest electrons occupy separate π* antibonding orbitals with parallel spins, following Hund's rule. Those unpaired electrons make liquid oxygen stick to a magnet — something the Lewis structure, which pairs every electron, cannot explain.

Yes. Odd electron counts give half-integer bond orders: NO has a bond order of 2.5, and the O₂⁻ superoxide ion has 1.5. Resonance produces fractional bond orders too, as in benzene at 1.5.

Higher bond order means shorter and stronger. Across N₂, O₂ and F₂ the bond order falls from 3 to 2 to 1 and the bond length rises from 110 to 121 to 142 pm.

Paramagnetic species have at least one unpaired electron and are drawn into a magnetic field. Diamagnetic species have all electrons paired and are weakly repelled by one.

Lowest energy first, two electrons per orbital with opposite spins, and degenerate orbitals get one electron each before any pairs up. That last rule — Hund's — is what produces oxygen's two unpaired electrons and its paramagnetism.

Because of s–p mixing, which pushes σ2p above π2p for B₂, C₂ and N₂. From O₂ onwards the 2s and 2p energies are far enough apart that mixing is negligible and the normal order returns. It is why B₂ is paramagnetic and C₂ is not.

It predicts the trend reliably within a series. Across N₂, O₂ and F₂ the bond order falls 3, 2, 1 and the length rises 110, 121, 142 pm. Comparing across different elements is less reliable, since atomic radius changes too.

The average across the contributing structures. Benzene's carbon–carbon bonds are all 1.5, and the measured length of 140 pm sits between ethane's 154 and ethene's 134 — exactly where an average predicts.

By weighing a sample in and out of a magnetic field — a Gouy balance — or by the NMR shift a paramagnetic sample produces in a reference, which is the Evans method. Both give the number of unpaired electrons back.

Yes, and it is the foundation of computational chemistry. Hand-drawn diagrams stop being practical past diatomics and small symmetric molecules, so the same theory is applied numerically instead — which is what a DFT calculation is doing.