The bond order of nitrogen dioxide (NO2) is 1.5.
To explain this, we first need to consider the molecular structure of NO2. Nitrogen dioxide has an incomplete octet on the nitrogen atom and is a resonance hybrid of two major Lewis structures. These structures show that there is one double bond and one single bond between nitrogen and oxygen. However, due to resonance, the bonding electrons are delocalized across the nitrogen-oxygen bonds.
The bond order can be calculated using the formula:
Bond Order = (Number of bonding electrons – Number of antibonding electrons) / 2
In NO2, we can estimate that there are a total of 3 bonding pairs (two from the double bond and one from the single bond) contributing to the bond order. Since the molecule is resonant, these bonding pairs are effectively shared, leading to an average bond order of 1.5 for each N-O bond.