Actinoids

The fourteen elements in the bottom row of the inner-transition elements of the periodic table that follow the element Actinium (Ac #89). Some reference sources include actinium in this series others do not. For these elements the 5f orbital is the filling orbital. This series is a sub-series of the transition metals. All actinoids are radioactive.

Only thorium and uranium occur naturally in the earth's crust in anything more than trace quantities. Neptunium and plutonium have been known to show up naturally in trace amounts in uranium ores as a result of decay or bombardment. The remaining actinoids were discovered in nuclear fallout, or were synthesized in particle colliders. The latter half of the series possess exceedingly short half-lives.

See Also

Transactinides and Rare Earth Elements.