Comparison of the solution chemistry of the actinides and lanthanides

The chemical behavior of the lanthanide and actinide elements in aqueous media is compared for similarities and differences. The stability of oxidation states and the thermodynamic parameters of complexation are evaluated to reflect how the decreased shielding of the 5f orbitals relative to that of the 4f orbitals causes the actinides to have somewhat different properties from those of the lanthanides. Although the interaction of the cations of both series with complexing ligands can be described satisfactorily by an ionic model, the freeenergy and enthalpy values of complexation of the trivalent actinides indicate a slightly greater covalency in bonding than that of the comparable lanthanide complexes. This is seen particularly in the metal-nitrogen-bonded systems.