Actinium and Actinides

The actinide or actinoid (IUPAC nomenclature) series includes the 15 metallic chemical elements along with atomic numbers from 89 to 103, actinium via lawrencium.

The actinide series obtains its name from the group 3 element actinium. Every but one of the actinides are f-block elements, subsequent to the filling of the 5f electron shell; lawrencium, a d-block element, is also usually referred an actinide. In comparison with the lanthanides, also mainly f-block elements, the actinides depict very much variable valence.