Comparing the successive contractions observed across the Lanthanoid and Actinoid series, which of t — d and f Block Elements Chemistry Question

💡 Solution & Explanation

While both series experience a contraction due to the progressive filling of inner $f$ -orbitals, the $5f$ orbitals in Actinoids are more deeply buried and diffuse than the $4f$ orbitals. Consequently, $5f$ electrons provide an even poorer shielding effect than $4f$ electrons against the increasing nuclear charge, making the Actinide contraction noticeably greater from element to element.