Because of lanthanoid contraction, which of the following pairs of elements have nearly same atomic radii? (Numbers in the parenthesis are atomic numbers)
- Zr(40) and Hf(72)
- Zr(40) and Ta(73)
- Ti(22) and Zr(40)
- Zr(40) and Nb(41)
Answer
(1) Zr(40) and Hf(72)
Solution
As per NCERT, the filling of 4f orbitals before 5d orbitals results in a regular decrease in atomic radii (lanthanoid contraction), which compensates the expected increase in size with increasing atomic number.
⇒ The radii of the 5d series elements are virtually the same as those of the corresponding 4d series members.
e.g. Zr (160 pm) and Hf (159 pm), both in group 4.
Answer: (1)