Question

Write any two consequences of Lanthanoid Contraction.

What are the consequences of lanthanoid contraction?

Describe briefly·the consequences of lanthanoid contraction.

Discuss the important consequences of lanthanoid contraction.

Answer 1

1. Due to the close similarity in electronic configuration and ionic radii, the lanthanides have identical chemical properties, which makes their separation difficult.
2. Due to lanthanide contraction, the size of Ln³⁺ ions decreases regularly with an increase in atomic number. According to Fajan’s rule, a decrease in the size of Ln³⁺ ions increases the covalent character and decreases the basic character between Ln³⁺ and OH^– ion in Ln(OH)₃. Since the order of size of Ln³⁺ ions is La³⁺ > Ce³⁺ ... > Lu³⁺.

Answer 2

1. Atomic and ionic radii: From Sc to La, the atomic radii increase steadily. Lanthanoid contraction causes this tendency to vanish in each of the subsequent groupings. The atomic radii of the Zr-Hf, Nb-Ta, Mo-W ...., Pd-Pt, and Ag-Au elements are nearly identical. The atomic radii of Hf, Ta, W, ....., etc., would have been significantly larger than those of Zr, Nb, Mo, ...., etc., respectively, if the fourteen lanthanoids between La₅₇ and Hf₇₂ had not been present. The anticipated rise in the atomic radii values from Hf to Hg is negated by the occurrence of lanthanoid contraction. Zr-Hf, Nb-Ta, and other element pairings have almost identical atomic radii, making them extremely difficult to distinguish due to the close solubilities of their salts.
2. Basicity of oxides and hydroxides: As the atomic number of lanthanoids increases, the basic strength of their oxides and hydroxides falls because of lanthanoid contraction. The least basic is Lu(OH)₃, and the most basic is La(OH)₃. The size of lanthanoid cations is continuously reduced by the lanthanoid contraction. Consequently, the polarizing strength of lanthanoid cations rises as the atomic number does; because of this, oxides and hydroxides gradually lose their ionic nature and become less basic.
3. Density: The density of all elements positioned after lanthanoids abnormally increases as atoms shrink as a result of lanthanoid contraction. Group 4 and later groups have third row element densities that are about twice as high as those of matching second row elements, but group 3 has a highly consistent density increase from Sc (3.0) to La (6.2). Only lanthanoid contraction is responsible for the anomalous rise in the densities of the third transition series' constituent elements.
4. Ionisation potential: The ionization potential values of the elements in the third transition series, starting with tungsten, are similarly impacted by the phenomena of lanthanoid contraction. These values should have been significantly lower and should have declined steadily as the group dipped if there had been no lanthanoid contraction.
5. Occurrence of yttrium with heavy lanthanoids: Yttrium is classified as group 3 and belongs to the d-block of the periodic table. This element, somewhat unexpectedly, coexists alongside the heavier lanthanoids (Ho, Er, etc.) in nature. Lanthanoids belong to the f-block and should arise independently. This rare occurrence is due to lanthanoid contraction. The y³⁺ ion has a lower size (88pm) compared to the next member of the same group, La³⁺ ions. La is followed by fourteen lanthanoids, whose size decreases owing to contraction. Higher lanthanoid ions, such as Ho³⁺ −89pm, Er³⁺ −88pm, and Tm³⁺ −87pm, have similar sizes to y³⁺ ions. Y³⁺ ions are similar in size, charge, and electronic configuration to Ho³⁺, Er³⁺, Tm³⁺, and other ions. This is why yttrium is found alongside lanthanoids in nature. Separating yttrium from lanthanoids is challenging due to comparable crystal shapes, chemical characteristics, and solubility of their compounds.