Question

Why do Zr and Hf exhibit similar properties ?

Hint:

Zr and Hf are often called "chemical twins" because separating them is extremely difficult due to this similarity.

Answer 1

1. Zirconium (Zr) belongs to the 4d series and Hafnium (Hf) belongs to the 5d series of transition elements.
2. Usually, atomic size increases down a group. However, the filling of 4f orbitals before Hf results in "Lanthanoid Contraction" (poor shielding by f-electrons).
3. This contraction causes the atomic radius of Hf (159 pm) to be virtually identical to that of Zr (160 pm).
4. Because they have similar atomic radii and the same valence shell configuration, they possess very similar physical and chemical properties.