Oxidation states and colour of lanthanide ions
f-Block Elements · Chemistry
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Ce⁴⁺ is a strong oxidiser but La³⁺ shows only +3. Explain. Step 1: Ce is [Xe]4f¹5d¹6s²; losing 4 e⁻ gives Ce⁴⁺ = [Xe]4f⁰ (noble-gas-like, stable). Step 2: But Ce⁴⁺ + e⁻ → Ce³⁺ regains f¹ easily — so Ce⁴⁺ oxidises others to get there. Step 3: La is [Xe]5d¹6s²; La³⁺ = [Xe] (already noble gas). Step 4: La⁴⁺ would break the xenon core — impossible. f⁰ stability drives Ce chemistry!