Question

Which of the following orders of atomic radii is correct?

• A. Zr > Hf
• B. W > Mo
• C. W ≈ Mo
• D. Mo > W

Answer 1

The correct option is C W ≈ Mo

The lanthanide contraction counterbalances almost exactly the normal size increase on descending a group of the transition elements. This extends across the 4d and the 5d series elements. (Example - covalent and ionic radii of Nb (5th period) and Ta (6th period) are almost the same due to poor shielding by f-orbital electrons). Thus, the size of Mo is similar to that of W.