Bond Order
Bond order is a measure of the number of chemical bonds between two atoms in a molecule. It indicates the stability of a bond and helps predict the molecule's properties. The higher the bond order, the stronger and shorter the bond between the atoms.

Calculating Bond Order
Bond order can be calculated using the formula:
Bond Order = (Number of bonding electrons - Number of antibonding electrons) / 2
Where, bonding electrons are the electrons in bonding molecular orbitals, and antibonding electrons are the electrons in antibonding molecular orbitals.

Example
Let's consider the molecule O2:
- Oxygen has 6 electrons in its valence shell.
- When two oxygen atoms combine to form O2, they share 4 electrons.
- The molecular orbital diagram for O2 shows 2 electrons in the sigma bonding orbital and 2 electrons in the sigma antibonding orbital.
- Using the formula, the bond order for O2 is: (2 - 2) / 2 = 0
- Therefore, O2 has a bond order of 0, indicating a very weak bond between the oxygen atoms.

Significance
- Bond order helps predict the strength and length of a bond.
- A higher bond order indicates a stronger and shorter bond, while a lower bond order suggests a weaker and longer bond.
- It also influences the reactivity and stability of molecules.
In conclusion, bond order is a crucial concept in chemistry that helps understand the nature of chemical bonds in molecules. It plays a significant role in determining the properties and behavior of compounds.