Why do zirconium and Hafnium exhibit similar properties?

Explanation

(i) The element of second and third transition series resemble each other closely than the elements of first and second transition due to lanthanoid contraction.
(ii) e.g., Zr - 4d series - Atomic radius radius 145 pm
Hf - 5d series - Atomic radius 144 pm
(iii) zr and Hf have are very similar even though the number of electronics. increase.
(iv) zx and Hf have very similar chemical behaviour, having closely similar radii and electronic configuration.
(v) Radius dependent properties such as lattice energy , salvation energy are similar.
(vi) Thus lanthanides contraction leads to formation of pari of elements and those known as chemical twins . e.g. Zr - Hf