Question

Which of the following properties of Zr and Hf can be explained due to lanthanide contraction?

• A. Radius of Zr and Hf is same
• B. Their EN is same
• C. Their position in periodic table
• D. All

Answer 1

The correct option is A Radius of Zr and Hf is same

The elements following the lanthanides in the periodic table are influenced by the lanthanide contraction. For example, the atomic radius of the metal zirconium, Zr, (a period-5 transition element) is 159 pm and that of hafnium, Hf, (the corresponding period-6 element) is 156 pm. The radii are very similar even though the number of electrons increases from 40 to 72 and the atomic mass increases from 91.22 to 178.49 g/mol. The increase in mass and the unchanged radii lead to a steep increase in density from 6.51 to 13.35 g/cm3.Zirconium and hafnium therefore have very similar chemical behaviour, having closely similar radii and electron configurations. Radius-dependent properties such as lattice energies, solvation energies, and stability constants of complexes are also similar.