Lanthanide Contraction and Its Consequences

(a) Define the lanthanide contraction and explain its cause. (b) How does the lanthanide contraction affect the atomic radii and chemistry of the 5d transition metals compared to 4d? (c) Explain why hafnium (Hf) has nearly the same atomic radius as zirconium (Zr) despite being one period below. (d) Discuss two chemical consequences of the lanthanide contraction for group 4 and 5 elements.