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The d-And-f-Block Elements

Short Answer Type

191.

Why Am and Cm have exceptional configuration in actinoids?

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Long Answer Type

192. Write the main differences in lanthanides and actinides.

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Short Answer Type

193. Why the actinoids show more variable oxidation states than lanthanoids?

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194. What is actinoid contraction? How is it different from lanthanoid contraction?

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195. Why are Ni²⁺ compounds thermodynamically more stable than Pt²⁺ compounds while Pt⁴⁺ compounds are relatively more stable than Ni⁴⁺ compounds?

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196. Compare the magnetic behaviour of actinoids with lanthanoids.

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197.
Compare the chemical reactivity of actinoids with lanthanoids.

Actinoids are far more reactive than lanthanoids especially in the powdered form. They react with non-metals at moderate temperatures whereas lanthanoids needs high temperature.
They are not affected by nitric acid as protective oxide layer prevents their further reaction. They do not react with alkalies. With water they form both oxides and hydrides whereas lanthanoids form hydroxide and H₂ gas.

$Ln + H_{2} O \overset{∆}{\to} Ln (OH)_{3} + H_{2} Ac + H_{2} O \to {Ac}_{2} O_{3} + {AcH}_{3}$