Question

In the transition series, with an increase in atomic number, the atomic radius does not change very much. Why is it so?

Answer 1

1. With increasing atomic number, nuclear charge increases, which tends to decrease atomic size.
2. However, the added electrons enter the (n − 1)d subshell, which is inner to the outermost shell.
3. These (n − 1)d electrons shield the outer electrons from the increased nuclear charge.
4. The shielding effect increases as more d-electrons are added, reducing the net attraction on outer electrons.
5. This balance between increasing nuclear charge and increasing shielding keeps the atomic radius almost constant as the atomic number increases.
6. Near the end of the series, electron-electron repulsions in the d-subshell slightly increase atomic size.

Thus, the atomic radius varies very little across the transition series because the effect of increased nuclear charge is counterbalanced by the increased d-electron shielding.