Question

(b) Write two consequences of lanthanide contraction.

Hint:

The lanthanide contraction accounts for many of the similarities in the properties of d-block and f-block elements, especially concerning ionic radii and chemical behavior.

Answer 1

Lanthanide contraction refers to the gradual reduction in the ionic radius of the lanthanide series as the atomic number increases, due to the ineffective shielding of the 4f-electrons. Two significant consequences of lanthanide contraction are: 1. Decreasing ionic radii: As the atomic number increases from $La^{3+}$ to $Lu^{3+}$, the size of the ions decreases. This results in a higher effective nuclear charge acting on the electrons, causing the ionic radii to shrink. 2. Similarity between 3d and 4d/5d elements: Lanthanide contraction creates similarities in the properties of the lanthanide elements and the d-block elements in the same period. For example, $Zr$ (a 4d element) and $Hf$ (a 5d element) exhibit very similar ionic radii due to this contraction. \bigskip Step 2: Thus, lanthanide contraction leads to smaller ionic radii and greater similarities in the properties of lanthanides and d-block elements. \bigskip