Lanthanoids and actinoids are f-block transition elements, but their general properties differ significantly from those of d-block transition metals. These elements are placed in separate positions in the periodic table showing that the periodicity of their electronic structures differs from the main stream. Although lanthanoids are called rare-earth elements, their abundance in the crust is by 110 means rare and chemistry utilizing their unique properties is likely to develop significantly in the near future. Actinoids are closely related to nuclear chemistry and nuclear energy. Since the amount of superheavy elements "synthesized" in accelerators is very minute, they are very significant from the viewpoint of applied chemistry.
Thumbnail: A billet of highly enriched uranium that was recovered from scrap processed at the Y-12 National Security Complex Plant. (Public Domain).