Write the differences between lanthanoids and actinoids.

Q.5 Write the differences between lanthanoids and actinoids.

Doubtly Asked 28 Oct 2026 Board exam · March 2025 hsc 12th Save WhatsApp Report

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Answer: Lanthanoids fill 4f orbitals; actinoids fill 5f orbitals and differ as below.

Lanthanoids	Actinoids
The differentiating electron enters 4f orbitals.	The differentiating electron enters 5f orbitals.
Common oxidation state is +3; a few show +2 and +4.	Show +3 and many higher oxidation states (+4, +5, +6, +7), because 5f, 6d and 7s energies are close.
Except promethium, they are non-radioactive.	All are radioactive.
Less tendency to form complexes; do not form oxo-cations.	Greater tendency to form complexes; form oxo-cations such as UO₂²⁺, PuO₂²⁺.
Lanthanoid contraction is smaller.	Actinoid contraction is larger (poor shielding by 5f electrons).

(Any four points.)

Doubtly AI · 28 Oct 2026 AI-verified · Oct 2026 Report

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