Question

Why is the magnetic behaviour of the tripositive lanthanoid ions not a linear function of the number of unpaired electrons present in them?

Answer 1

1. Magnetic behavior is influenced by both electron spin and orbital motion.
2. For lanthanoids, the electrons causing magnetism are 4f electrons, which are deeply buried inside the ion.
3. The 4f orbitals are efficiently shielded by outer 5s² and 5p⁶ electrons, minimizing environmental effects.
4. Hence, magnetic moments depend on both electron spin and orbital angular momentum, not just the number of unpaired electrons.
5. This contrasts with d-block elements, where orbital contribution is minimal, and magnetism depends mainly on unpaired electron count.
6. Therefore, lanthanoid ions show magnetic moments that do not increase linearly with the number of unpaired electrons.