Question

which pair of elements among the following have atomic radii very close to each other a) Li & Na b) Ti & Zr c) Zr & Hf 4) La & Hf

Answer 1

the elements are lithium and sodium

Answer 2

Zr and Hf have similar atomic radii due to lanthanide contraction

• The similarity in the atomic radii of Zirconium(40) and Hafnium(72) can be explained based on the shielding effect

• The electrons present in the inner shells of an atom shields the outermost electrons from nuclear attraction, making them experience a low effective nuclear charge

• The shielding effect decreases if we move away from the nucleus. So the shielding effect exerted by the electrons in subshells decreases in the order s > p > d > f

• In Hafnium 4f sub-shell is filled and it is not effective at shielding the outermost electrons in an atom

• Therefore Halfnium will have an atomic radius of 208 pm which is very similar to Zirconium having atomic radius 206 pm