Question

What is the molecular orbital diagram and electronic structure of the diatomic molecule O2?

Answer 1

The molecular orbital  MO  diagram and electronic structure of the diatomic molecule O2 can be determined by considering the atomic orbitals of the two oxygen atoms and how they combine to form molecular orbitals. Oxygen has the electron configuration 1s² 2s² 2p⁴. In a diatomic O2 molecule, we only need to consider the valence electrons, which are the 2s and 2p electrons. There are a total of 12 valence electrons in O2  6 from each oxygen atom . The molecular orbitals formed from the combination of 2s orbitals are σ2s  bonding  and σ2s*  antibonding . The molecular orbitals formed from the combination of 2p orbitals are σ2p  bonding , π2p  two degenerate bonding orbitals , σ2p*  antibonding , and π2p*  two degenerate antibonding orbitals . The MO diagram for O2 can be constructed by placing these molecular orbitals in increasing order of energy: 1. σ2s  lowest energy 2. σ2s* 3. σ2p 4. π2p  two degenerate orbitals 5. π2p*  two degenerate orbitals 6. σ2p*  highest energy Now, we can fill the molecular orbitals with the 12 valence electrons, starting from the lowest energy orbital and following Hund's rule: 1. σ2s: 2 electrons 2. σ2s*: 2 electrons 3. σ2p: 2 electrons 4. π2p: 4 electrons  two in each degenerate orbital 5. π2p*: 2 electrons  one in each degenerate orbital 6. σ2p*: 0 electrons The electronic structure of O2 can be represented as:  σ2s ² σ2s* ² σ2p ² π2p ⁴ π2p* ² σ2p* ⁰ The bond order, which indicates the stability of the molecule, can be calculated as: Bond order =  number of electrons in bonding orbitals - number of electrons in antibonding orbitals  / 2 Bond order =  8 - 4  / 2 = 2 Thus, O2 has a double bond and is a stable molecule. The presence of two unpaired electrons in the π2p* orbitals makes O2 a paramagnetic molecule.