Chemistry - f-block Question with Solution | TestHub

In the lanthanide series with increasing atomic number, in general, there is a progressive decrease in the size from Lanthanum to Lutetium and regular decreases in ionic size from La^3⊕ to Lu^3⊕ . This decrease in size is known as lanthanide contraction. The general electronic configuration of these elements is 4f^1-14 5d^0-1 6s² . In these elements the added electron enters the deep-seated f-orbitals. Due to very poor shielding effect of (n-2)f electrons, they exert very little screening effect on the outermost 6s² electrons and therefore experiences considerable pull by the nucleus. Hence, with increasing atomic number, the enhanced nuclear charge leads to contraction in the size of atoms and ions. The atomic volumes of Europium and Ytterbium are unexpectedly large. The large atomic size of Eu and Yb suggest weaker bonding in the solid elements. Both these elements have only two electrons extra than the stable configurations (half filled, f⁷ , and completely filled, f¹⁴ ), hence they utilise two electrons in metallic bonding as in the case with Barium.