Question

Explain the phenomenon of magnetism in oxygen molecules

Answer 1

We can easily understand this phenomenon from MO (Molecular Orbital) theory. The energy diagram of the oxygen molecule O₂ is shown below. Liquid oxygen is paramagnetic., the atoms or molecules of the substance have net orbital or spin magnetic moments that are capable of being aligned in the direction of the applied field. Paramagnetism occurs in all atoms and molecules with unpaired electrons; e.g. free atoms, free radicals, and compounds of transition metals containing ions with unfilled electron shells. It also occurs in metals as a result of the magnetic moments associated with the spins of the conducting electrons.

Two oxygen atoms (at the two sides) form a oxygen molecule (in the middle). As the oxygen molecule has two unpaired electrons in two anti-bonding MO"s, π*2p_y and π*2p_z. So all atoms with incompletely filled atomic orbitals are paramagnetic. Due to their spin, unpaired electrons have a magnetic dipole moment and act like tiny magnets. An external magnetic field causes the electrons' spins to align parallel to the field, causing a net attraction.This means that the oxygen molecule will be paramagnetic.

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