Question

The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.

Answer 1

Chemistry of actinoids

Lanthanoids project three oxidation states $(+2,+3,+4).$ From these, $+3$ state is the most common. Lanthanoids display a limited number of oxidation states because the energy difference between $\text{4f, 5d}$ and $\text{6s}$ orbitals is quite large.

While the energy difference between $\text{5f, 6d}$ and $\text{7s}$ orbitals is very less in actinoids and hence they display a large number of oxidation states. For example, neptunium displays $+3,+4,+5,$ and $+7$ while uranium and plutonium display $+3,+4,+5,$ and $+6$ oxidation states. The most common oxidation state in case of actinoids is also $+3$ but due to its wide range of other oxidation states, their chemistry is not smooth like lanthanoids.