Bond Order Calculator
Calculate bond order for chemical bonds using Lewis structures, molecular orbital theory, or resonance hybrid averaging. Determine bond strength, bond length, and magnetic properties of diatomic and polyatomic molecules.
For Lewis structure method
For resonance hybrids like benzene (1.5)
Electrons in bonding MOs (MO theory)
Electrons in antibonding MOs (MO theory)
Bond order in first resonance structure
Bond order in second resonance structure
Optional third resonance structure
What is bond order?
Bond order indicates the number of chemical bonds between a pair of atoms. It is a measure of bond strength: higher bond order means stronger, shorter bonds. A single bond has bond order 1, double bond = 2, triple bond = 3. Fractional bond orders (like 1.5 in benzene) indicate resonance hybrids where electrons are delocalized.
How do you calculate bond order using Lewis structures?
For simple molecules, bond order equals the number of bonds: single = 1, double = 2, triple = 3. For resonance structures, calculate the average: add bond orders from all resonance forms and divide by the number of forms. Benzene (C₆H₆) has resonance between single and double bonds, giving an average bond order of 1.5 for each C-C bond.
What is the molecular orbital theory formula for bond order?
Bond Order = (Number of electrons in bonding MOs - Number of electrons in antibonding MOs) ÷ 2. For example, O₂ has 10 bonding and 6 antibonding electrons: (10-6)/2 = 2, confirming a double bond. This method also predicts magnetic properties—O₂ has 2 unpaired electrons in antibonding orbitals, making it paramagnetic.
What does fractional bond order mean?
Fractional bond orders (like 1.33, 1.5, 1.67) occur in resonance hybrids where electrons are delocalized across multiple atoms. Examples: benzene (1.5), carbonate ion CO₃²⁻ (1.33), nitrate ion NO₃⁻ (1.33). The fractional value represents the weighted average across all resonance contributors, indicating stronger/shorter bonds than pure single bonds.
How does bond order relate to bond length and strength?
Bond order has inverse relationship with bond length (higher BO = shorter bond) and direct relationship with bond strength (higher BO = stronger bond). Approximate ratios: triple bonds are ~15% shorter and ~3× stronger than single bonds; double bonds are ~10% shorter and ~2× stronger. Bond dissociation energy increases with bond order.
How do you determine bond order for diatomic molecules?
Use molecular orbital diagrams: fill electrons from lowest to highest energy (σ1s, σ*1s, σ2s, σ*2s, π2p, σ2p, π*2p, σ*2p). Then: BO = (bonding - antibonding)/2. Examples: H₂ = (2-0)/2 = 1; N₂ = (10-4)/2 = 3 (triple bond); O₂ = (10-6)/2 = 2 (double bond, paramagnetic); F₂ = (10-8)/2 = 1 (single bond).