Chapter 12, Problem 109E

Interpretation Introduction

Interpretation:Reason behind significantly small radius even though it lies beneath in the group should be suggested.

Concept introduction: As one moves from top to bottom the shells expands and size increases, while it decreases as one move along the period because of gradual increases in effective nuclear charge. This in turn increases influence of nucleus on valence electron and shrinks the radius along the horizontal row.

Lanthanide contraction is phenomenon that leads to significant reduction in sizes along the period in lanthanides. This is attributed to gradual fill up of $4f$ orbitals that are highly diffused in shape. Poor overlap increases influence of nucleus for outermost electron manifolds for lanthanides and hence size reduces considerably.