Question

Why do the atomic radii of transition elements decrease with increase in atomic number across a particular series?

Answer 1

1. Across a transition series, atomic number increases, so nuclear charge increases.
2. Electrons are added to the inner (n − 1)d-subshell, which partly shields outer electrons from the nucleus.
3. Initially, the increased nuclear charge pulls electrons closer, decreasing atomic radii.
4. Shielding by (n − 1)d electrons increases with added electrons, opposing the pull of the nuclear charge.
5. Thus, after midway in the series, the atomic radii decrease slowly or remain almost constant.
6. Near the series end, electron repulsion in paired d-orbitals causes a slight increase in atomic size.