Given the following targeted pairs of transition elements: , , , , . What is the exact total integer — d and f Block Elements Chemistry Question
Question
Given the following targeted pairs of transition elements: $(Ti, Zr)$, $(Zr, Hf)$, $(Nb, Ta)$, $(Y, La)$, $(Mo, W)$. What is the exact total integer count of the pairs that exhibit chemically indistinguishable atomic radii strictly as a direct result of the Lanthanoid contraction?
💡 Solution & Explanation
The lanthanoid contraction severely affects the $5d$ elements immediately following the lanthanide series ($Lu$, $Z=71$). It forces the $5d$ transition metals to shrink to the size of their $4d$ counterparts positioned directly above them. Therefore, $(Zr, Hf)$, $(Nb, Ta)$, and $(Mo, W)$ are all valid pairs showing this identical size anomaly. $(Ti, Zr)$ is a regular $3d/4d$ pair and shows an expected increase. $(Y, La)$ are Group 3 elements positioned before the $4f$ block fills, so $La$ is notably larger than $Y$. Thus, only $3$ pairs fit the criteria.