Question

Compare the chemistry of actinoids with that of the lanthanoids with special reference to chemical reactivity.

Answer 1

Generally, the initial members of the series are very reactive like calcium in their chemical behaviour, but with increasing atomic number they behave like aluminium.

The value of E^Θ for the half-reaction \[\ce{Ln^{3+}_{ (aq)} + 3e- -> Ln_{(s)}}\] is in the range of −2.2 V to −2.4 V. For Eu, the value of E^Θ is −2.0 V. Of course, there is a slight variation in the value. These metals combine with hydrogen on being gently heated in an atmosphere of hydrogen gas. On heating these metals with carbon, the carbides Ln₃C, Ln₂C₃ and LnC₂ are formed. These metals liberate hydrogen gas from dilute acids and on burning in an atmosphere of halogens, form halides. These form oxide M₂O₃ and hydroxide M(OH)₃. Hydroxides are definite compounds and not just hydrated oxides. They are basic, like the oxides and hydroxides of alkaline earth metals. Their general reactions are shown in the figure.

Actinoids are very reactive metals, especially when they are finely divided. The action of boiling water on them gives a mixture of oxide and hydride and combines with most non-metals at normal temperatures. Hydrochloric acid affects all metals, but most metals are little affected by nitric acid. The reason for this is that a protective surface of oxide is formed on these metals. Alkalis have no effect on these metals.

Answer 2

Actinoids are far more reactive than lanthanoids. They interact with nonmetals at moderate temperatures. In contrast, lanthanoids react at high temperatures. The majority of actinoids are attacked by HNO₃ has a small effect on HCl, although the creation of a protective layer of oxide. Alkalies cause no reaction. Lanthanoids extract hydrogen from dilute. Acids and halogens burn together to generate halides.