Question

Define lanthanoid contraction. How does it affect the atomic radii of the third transition series and the second transition series?

Hint:

Lanthanoid contraction is caused by the poor shielding effect of 4f-electrons, leading to a consistent decrease in atomic size as we move across the lanthanoid series.

Answer 1

Lanthanoid Contraction refers to the gradual decrease in atomic size across the lanthanoid series, due to the ineffective shielding of the 4f-electrons. This contraction affects the atomic radii of the third transition series, which are smaller than expected compared to the second transition series. The increased nuclear charge in the lanthanoids results in a stronger pull on the electrons, reducing their size.