Molecular Orbital Theory Bond Order Calculator: ...

Molecular Orbital Theory

Molecular Orbital (MO) theory treats electrons as delocalized over the entire molecule rather than localized between atoms. Electrons fill molecular orbitals in energy order (analogous to atomic orbitals). Bond order from MO theory determines bond strength, length, and whether the molecule is paramagnetic (unpaired electrons) or diamagnetic.

🧬 MO Bond Order Calculator

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📐 Formula

Bond Order = (Bonding e⁻ − Antibonding e⁻) / 2

Bonding MOs are lower in energy; antibonding (σ*, π*) are higher. Filling order: σ1s, σ*1s, σ2s, σ*2s, π2p, σ2p, π*2p, σ*2p.

📝 Worked Example

O₂ molecule (16 electrons total):
MO filling: ...σ2p², π2p⁴, π*2p² (two unpaired in π*)
Bond Order = (8−4)/2 = 2 (double bond)
Paramagnetic: 2 unpaired electrons ✓ (explains why O₂ is attracted to magnets)

📝 How to Use

Enter MoleculeSelect homonuclear diatomic (H₂ through Ne₂) or enter total electrons.

Fill OrbitalsView the MO energy diagram with electrons filled by Aufbau/Hund rules.

Calculate Bond OrderView bond order and determine bond stability (BO>0 = stable).

Magnetic PropertySee if paramagnetic (unpaired e⁻) or diamagnetic (all paired).

❓ FAQ

What does bond order 0 mean?

Bond order = 0 means no net bonding — the molecule is unstable and does not exist (e.g., He₂ has BO=0).

How does MO theory explain O₂ paramagnetism?

Lewis structures predict all electrons paired (diamagnetic), but MO theory correctly predicts two unpaired electrons in degenerate π*2p orbitals — making O₂ paramagnetic, confirmed by experiment.