Question

In a given transition series, there is no significant change in the atomic radii of elements with increase in atomic number. Explain why.

Answer 1

1. Added electrons in a transition series go into the (n−1)d subshell; the rising nuclear charge tends to pull the electron cloud in, reducing radius.
2. Simultaneously, the growing number of d‑electrons increases shielding of the outer electrons, counteracting the increased nuclear attraction.
3. Electron pairing partway through the series raises electron–electron repulsion, which also offsets contraction; the net result is little change in size.
4. Thus, nuclear charge, d‑shielding, and repulsion balance each other, so atomic radii stay nearly constant.