Chapter 5, Problem 52AP

a)

Interpretation Introduction

Interpretation: The general trend in radii of rare earth metals should be reported and the reason behind the trend should be explained.

Concept introduction: Lanthanoid contraction is the steady decrease in the size of the atoms and ions of the rare earth elements with increasing atomic number from lanthanum( $Z$ equal to57) through lutetium( $Z$ equal to71). For each atom across period the nuclear charge increases with unit positive charge, accompanied by increase in count of electrons present in $4f$orbitals. $4f$ electrons poorly shield each other from increased charge of nucleus so that $Z_{\text{eff}}$ that attracts each electron steadily increases through rare earth elements, which results in successive decrease of atomic and ionic radii.

b)

Interpretation Introduction

Interpretation: The two elements that are exception to the general trend of radii of rare earth metals should be reported.

Concept introduction: Lanthanoid contraction is the steady decrease in the size of the atoms and ions of the rare earth elements with increasing atomic number from lanthanum( $Z$ equal to57) through lutetium( $Z$ equal to71). For each atom across period the nuclear charge increases with unit positive charge, accompanied by increase in count of electrons present in $4f$orbitals. $4f$ electrons poorly shield each other from increased charge of nucleus so that $Z_{\text{eff}}$ that attracts each electron steadily increases through rare earth elements, which results in successive decrease of atomic and ionic radii.