Q.How many bond order of N2?
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Bond Order Strength: From Intuition to Precision
Imagine two people holding hands. If they just touch fingertips, a gentle breeze can separate them. If they clasp firmly, it takes more effort to pull them apart. If they lock arms, you need real force. That's the core idea behind bond order — it tells you how strongly two atoms are connected in a molecule.
The Intuition
In a chemical bond, atoms share electrons. The more electron pairs they share, the tighter the grip. A single bond (one shared pair) is like a handshake — it works, but it's easy to break. A double bond (two shared pairs) is like a firm clasp — stronger, shorter, harder to pull apart. A triple bond (three shared pairs) is like a wrestler's lock — very strong and very short.
This directly translates to real molecules:
- C–C single bond: bond energy ≈ 350 kJ/mol, bond length ≈ 154 pm
- C=C double bond: bond energy ≈ 610 kJ/mol, bond length ≈ 134 pm
- C≡C triple bond: bond energy ≈ 835 kJ/mol, bond length ≈ 120 pm
More shared electrons → stronger bond → shorter bond. That's the pattern.
The Precise Definition
Bond order is the number of chemical bonds between a pair of atoms. For simple molecules, it's just the number of shared electron pairs:
Bond Order=2Number of bonding electrons−Number of antibonding electrons
This formula matters most when you move beyond simple Lewis structures — for molecules with resonance or molecular orbital theory.
How Bond Order Determines Strength
Bond order and bond strength are directly proportional. Here's why:
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More electron density between nuclei: Higher bond order means more electrons are concentrated in the region between the two nuclei. These electrons simultaneously attract both nuclei, pulling them together.
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Greater electrostatic attraction: The shared electrons act like "glue." More glue means stronger adhesion.
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Shorter bond length: Stronger attraction pulls the nuclei closer. Shorter bonds are harder to stretch or break.
Don't confuse bond order with bond energy. Bond order tells you the number of bonds; bond energy tells you the energy required to break them. They're proportional, but not identical — a C=C bond isn't exactly twice as strong as a C–C bond (it's about 1.7 times stronger).
Real Examples
| Molecule | Bond | Bond Order | Bond Energy (kJ/mol) | Bond Length (pm) |
|---|---|---|---|---|
| H₂ | H–H | 1 | 436 | 74 |
| O₂ | O=O | 2 | 498 | 121 |
| N₂ | N≡N | 3 | 945 | 110 |
| F₂ | F–F | 1 | 159 | 142 |
Notice how N₂ with a triple bond is the strongest diatomic molecule — it takes 945 kJ/mol to break that bond. That's why nitrogen gas is so unreactive.
When Bond Order Gets Tricky
Some molecules don't have simple whole-number bond orders. Consider ozone (O₃): …
Nitrogen exists as N2 with a triple bond (N triple-bonded to N) between the two atoms, so its bond order …
N2 has a bond order of 3 (a triple bond).
Using Molecular Orbital Theory, the electronic configuration of N2 (14 electrons) is: sigma1s2 sigma1s2 sigma2s2 sigma2s2 pi2px2 pi2py2 sigma2pz2. Bond order = half of (Number of bonding electrons - Number of antibonding electrons) = half of (10 - 4) = half of 6 = 3. This matches the simple Lewis-structure picture of N2 as …
- CBSE 2026Set ANNUAL1 markQ.Write true or false: Energy is required to break bond.
›Reveal solutionSolution
True. Bond formation releases energy (exothermic), so bond breaking must absorb the same amount of energy (endothermic) — this is called bond dissociation energy.
When two atoms come together to form a stable covalent bond, the system moves to a lower, more stable energy state, releasing energy in the process. Consequently, to reverse this and separate the bonded atoms, an equal amount of energy must be supplied to overcome the attractive forces holding them together. This requi …
- CBSE 2024Set ANNUAL1 markMCQQ.Which one of the following represents the correct order of bond strength for O2, O2+, O2(2+), O2-, O2(2-) ?(a) O2(2+) < O2+ < O2 < O2- < O2(2-)(b) O2(2+) > O2+ > O2 > O2- > O2(2-)(c) O2+ < O2(2+) < O2 < O2- < O2(2-)(d) None of these
›Reveal solutionSolution
Using molecular orbital theory, removing electrons from O2's antibonding pi* orbitals raises bond order (and bond strength), while adding electrons there lowers it.
Neutral O2 has the MO configuration (up to valence electrons):
sigma2s2 sigma2s2 sigma2pz2 pi2px2 pi2py2 pi2px1 pi*2py1
Bonding electrons = 8, antibonding = 4 (ignoring the core 1s pairs, which cancel), giving bond order = (8-4)/2 = 2.
Starting from O2 and changing the antibonding pi* electron count:
- O2(2+): remove both pi* electrons -> antibonding = 2 -> bond order = (8-2)/2 = 3 (highest, strongest bond)
- O2+: remove one pi* electron -> antibonding = 3 -> bond order = (8-3)/2 = 2.5
- O2: bond order = 2 …
- CBSE 2024Set ANNUAL1 markQ.Bond order in oxygen molecule (O2) is ___________.
›Reveal solutionSolution
[!TLDR]
2
Method
From molecular orbital theory, O2 has bond order = (10 bonding - 6 ant …
- CBSE 2023Set ANNUAL1 markQ.How do you express the bond length in terms of bond order?
›Reveal solutionSolution
Bond length decreases as bond order increases: a higher bond order pulls the bonded atoms closer together.
Bond order is the number of chemical bonds (sigma + pi) between a pair of atoms; bond length is the equilibrium distance between their nuclei. A higher bond order means greater electron density between the two nuclei, which pulls them closer together and shortens the bond, while also making it stronger. This is why a C≡C triple bond (bond order 3, ~120 pm) is shorter than a C=C double bond (bond order 2, ~134 pm), which in turn is shorter than a C-C single bond (bond order 1, ~154 pm).
…
- CBSE 2022Set ANNUAL1 markQ.How many bond order of N2?
›Reveal solutionSolution
N2 has a bond order of 3 (a triple bond).
Using Molecular Orbital Theory, the electronic configuration of N2 (14 electrons) is: sigma1s2 sigma1s2 sigma2s2 sigma2s2 pi2px2 pi2py2 sigma2pz2. Bond order = half of (Number of bonding electrons - Number of antibonding electrons) = half of (10 - 4) = half of 6 = 3. This matches the simple Lewis-structure picture of N2 as …
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