The bond order of O2 is 2.
To understand why, we first need to look at how bond order is calculated. Bond order can be defined as the difference between the number of bonding and antibonding electrons divided by two:
Bond Order = (Number of Bonding Electrons – Number of Antibonding Electrons) / 2
In the case of molecular oxygen (O2), it consists of two oxygen atoms, each contributing six valence electrons, giving us a total of 12 valence electrons. In molecular orbital theory, these electrons fill the molecular orbitals in the following order:
- σ1s (2 electrons)
- σ*1s (2 electrons)
- σ2s (2 electrons)
- σ*2s (2 electrons)
- σ2pz (2 electrons)
- π2px, π2py (4 electrons)
- π*2px, π*2py (0 electrons)
This leads to 10 bonding electrons (in σ1s, σ2s, σ2pz, and π2px + π2py) and 2 antibonding electrons (in σ*1s and σ*2s). Plugging these into our formula gives us:
Bond Order = (10 – 2) / 2 = 4 / 2 = 2.
Thus, the bond order of O2 is 2, indicating a strong double bond between the two oxygen atoms, which is consistent with its well-known properties as a diatomic molecule.