Bond order is a number that indicates the number of bonds, or shared pairs of electrons, between atoms in a molecule. Bond order is 1 for a single bond, 2 for a double bond, and 3 for a triple bond. When two or more resonance structures can be drawn, electron pairs are delocalized over more than one bond. This gives rise to fractional bond orders. See the discussion of Resonance for more information.

A graphic showing bond order shows the bond colored halfway by each atom color because it is no longer a single bond or a double bond.

Compare Bonds

One way to visualize the bond order is to increase the relative thickness of the bond rod as shown in this comparison of single, double, and triple bonds.

Nitrite Bond Order

A PM3 MOPAC energy calculation was done on each molecule in this database. From this, a bond order is given both numerically and visually by the thickness of the bond. This is most useful in understanding resonance structures. In this case, the two resonance structures differ in the location of the single and double bonds. According to experiment, the two bonds are identical. The calculated bond order is 1.47.