On the basis of Lanthanoid contraction, explain the following :
(i) Nature of bonding in La2O3 and Lu2O3.
(ii) Trends in the stability of oxo salts of lanthanoids from La to Lu.
(iii) Stability of the complexes of lanthanoids.
(iv) Radii of 4d and 5d block elements.
(v) Trends in acidic character of lanthanoid oxides.
(i) Due to lanthanide contraction, size reduces. With reduction in size, covalent character increases. Therefore, Lu2O3 is more covalent than La2O3
(ii) Oxosalts contain oxygen as anion. As the size of cation reduces from La to Lu, according to Fajan’s rules, the polarizing power of the cation will increase and it will distort the cloud of oxygen(anion) greatly, thus the bond weakens and the stability also reduces.
(iii)As the size of central atom reduces, stability of complex increases. A small metal ion with greater charge attracts the ligands better.
(iv) In 5d block elements, due to poor shielding of f orbitals, the effective nuclear charge increases, thereby reducing the size. This is called lanthanide contraction. So, the radii of 4d and 5d block elements end up being very similar.
(v) From La to Lu, the acidic character increases. As the size reduces from La to Lu, the ability to lose electrons(Lewis base character) reduces, so acidity will increase.