Bond Order
Definition and meaning of Bond Order in chemistry.
Bond order is a specific number that describes the total amount of chemical bonding between two atoms. It provides a highly useful measure of how tightly those two individual atoms are held together.
In more detail
In basic chemistry classes, students find the bond order by simply looking at a drawn Lewis structure. You just count the number of shared electron pairs between the two target atoms. One shared pair creates a single bond with a bond order of one.
Two shared pairs create a double bond with a bond order of two. More advanced molecular orbital theory calculates this number in a slightly more complex way. It takes the total number of helpful bonding electrons and subtracts the harmful antibonding electrons.
The formula then divides that remaining difference in half. A higher bond order generally means the two atoms are pulled much closer together. It also means the resulting bond is significantly stronger and requires more energy to break.
The bond order does not always have to be a perfect whole number. Molecules with shared or moving electrons can easily feature fractional bond orders. Electrons can spread evenly across an entire molecular ring. This equal sharing creates intermediate bond strengths between a single and double bond.
Key facts
| Field | Physical Chemistry |
|---|---|
| Simple calculation | Count shared electron pairs |
| Advanced formula | (bonding e⁻ − antibonding e⁻) / 2 |
| General trend | Higher bond order means a shorter and stronger bond |
| Zero bond order meaning | The bond cannot exist and atoms will drift apart |
The nitrogen gas in our air contains two nitrogen atoms tightly linked together. Molecular orbital theory reveals eight total electrons sitting in helpful bonding spaces. It also reveals two electrons sitting in unhelpful antibonding spaces. We subtract two from eight to get a remainder of six. We divide six by two to find a final bond order of exactly three. This high number accurately confirms that nitrogen has a powerful triple bond. This incredibly strong triple bond explains why nitrogen gas remains highly stable and mostly unreactive.
Frequently asked questions
Can a bond order be a fraction instead of a whole number?
Yes. Molecules that share electrons across multiple atoms will have fractional numbers. The carbon bonds in a benzene ring all share a bond order of exactly 1.5.
What does a bond order of zero actually mean in chemistry?
A bond order of zero means the atoms have no net attraction to each other. The atoms will not stay together to form a stable molecule.
How does a higher bond order change the physical bond length?
A higher bond order pulls the two atoms much closer together. A triple bond is physically much shorter than a single bond between the same two atoms.