According to the observed trends in the atomic radii of the transition series, the atomic radii steadily decrease from to , but the atomic sizes of , , and are experimentally found to be almost identi

Question

According to the observed trends in the atomic radii of the $3d$ transition series, the atomic radii steadily decrease from $Sc$ to $Cr$, but the atomic sizes of $Fe$, $Co$, and $Ni$ are experimentally found to be almost identical. What is the fundamental physical reason for this constancy in size for $Fe$, $Co$, and $Ni$?

Prashant Kotian · Accepted Answer

Correct answer: B. In a transition series, moving left to right increases the nuclear charge, which tends to pull electrons inward (decreasing size). However, electrons are simultaneously added to the inner subshell, increasing the shielding effect and inter-electronic repulsion. For , , and , these two opposing factors essentially cancel each other out, keeping their atomic radii nearly constant.

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