Question

Why are the ionisation potentials of the elements of third transition series higher than the expected ones?

Why are the ionisation energies of the elements of third transition series higher than those of the elements of first and second series?

Answer 1

1. Their atoms have filled 4f orbitals beneath the valence shell.
2. The 4f electrons provide poor shielding due to their peculiar shapes.
3. This poor shielding causes valence electrons to experience a stronger nuclear attraction.
4. As a result, more energy is required to remove an electron, raising the ionisation potential.
5. This phenomenon is linked to lanthanoid contraction, which affects atomic size and shielding.

Hence, the third transition series elements show higher ionisation energies compared to the first and second series.