ABSTRACT
The actinides are the 14 elements that follow actinium (Z = 89) in the periodic table, just as the lanthanides are the 14 elements that follow lanthanum (Z = 59). The electronic structures of the gaseous atoms in the ground state of the lanthanides and actinides. The multiplicity of the valency states of some actinides leads to very complicated redox behavior. The case of plutonium, for which four oxidation states can coexist at equilibrium in solution, is unique in the periodic table. With the exception of thorium and protactinium all actinides display the +3 oxidation state, which becomes progressively more stable with increasing Z. At the levels of americium, trivalency becomes predominant, and there is a close analogy between heavy actinides and the corresponding lanthanides. A trend toward divalency arises with the heavier actinides from californium to nobelium. The last actinide lawrencium, is strictly trivalent, as this state also represents the filled 5f shell.
