1. Molecular Orbital Diagram of Oxygen
* Atomic Orbitals: Start with the atomic orbitals of oxygen. Each oxygen atom has the electronic configuration 1s²2s²2p⁴. We are primarily interested in the 2p orbitals, which have three orbitals (2px, 2py, 2pz).
* Overlapping: When two oxygen atoms come together to form O₂, the 2p orbitals overlap to form molecular orbitals.
* Sigma and Pi Bonds:
* The 2pz orbitals overlap head-on to form a sigma (σ) bonding orbital (σ2p) and a sigma antibonding orbital (σ*2p).
* The 2px and 2py orbitals overlap side-by-side to form two sets of pi (π) bonding and antibonding orbitals (π2p and π*2p, respectively).
* Filling Molecular Orbitals: The 12 valence electrons (6 from each oxygen atom) are filled into the molecular orbitals following Hund's rule and the Aufbau principle:
* σ2p, σ*2p, π2p, π*2p
* This results in two unpaired electrons in the π*2p antibonding orbitals.
2. Paramagnetism
* Unpaired Electrons: The presence of two unpaired electrons in the π*2p antibonding orbitals is what makes oxygen paramagnetic.
* Magnetic Field: Paramagnetic substances are weakly attracted to a magnetic field. This is because the unpaired electrons have their own magnetic moments, which align themselves in the direction of an external magnetic field.
In Summary:
Oxygen's paramagnetism arises because its molecular orbital configuration leaves two unpaired electrons in the π*2p antibonding orbitals. This gives oxygen a net magnetic moment, causing it to be weakly attracted to a magnetic field.
