Question

Why do lanthanoid ions having the same number of unpaired electrons have different values of magnetic moments?

Answer 1

1. Lanthanoid ions have magnetic moments due to both the spin and orbital motion of electrons.
2. The electrons responsible for magnetism are 4f electrons, which are deeply buried inside the atom.
3. The 4f orbitals are well shielded by the outer 5s and 5p orbitals, so their states are less affected by the surrounding environment.
4. Hence, magnetic moments depend not only on the number of unpaired electrons (spin) but also on their orbital contribution.
5. This is different from d-block elements, where only spin contributes significantly, so the magnetic moment depends mostly on unpaired electrons.
6. Because of combined spin and orbital effects, lanthanoid ions with the same number of unpaired electrons show different magnetic moments.
7. The total magnetic moment μ_J can be calculated considering both spin quantum number S and orbital quantum number L, using proper formulae.