Molecular Orbital Diagrams, Bond Order, and Number of Unpaired Electrons

Draw the molecular orbital diagram for the oxygen molecule, O2. From this diagram, calculate the bond order for O2. How does this diagram account for the paramagnetism of O2?

We draw a molecular orbital energy diagram similar to that shown in [link]. Each oxygen atom contributes six electrons, so the diagram appears as shown in [link].

The molecular orbital energy diagram for O2 predicts two unpaired electrons.

We calculate the bond order as


Oxygen’s paramagnetism is explained by the presence of two unpaired electrons in the ($π_{2p_y}$, $π_2p_z$)* molecular orbitals.

Check Your Learning
The main component of air is N2. From the molecular orbital diagram of N2, predict its bond order and whether it is diamagnetic or paramagnetic.

N2 has a bond order of 3 and is diamagnetic.