He also isolated the first sample of uranium metal by heating uranium tetrachloride with metallic potassium.
He then reduced the obtained yellow powder with charcoal, and extracted a black substance that he mistook for metal.
Only 60 years later, the French scientist Eugène-Melchior Péligot identified it as uranium oxide.
Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, but both elements are often included in any general discussion of the chemistry of the actinide elements.
Actinium is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "actinide" means "like actinium", it has been argued that actinium cannot logically be an actinide, even though IUPAC acknowledges its inclusion based on common usage.
All but one of the actinides are f-block elements, with the exception being either actinium or lawrencium.
The series mostly corresponds to the filling of the 5f electron shell, although actinium and thorium lack any f-electrons, and curium and lawrencium have the same number as the preceding element.
By reduction of thorium tetrachloride with potassium, he isolated the metal and named it thorium after the Norse god of thunder and lightning Thor.
Actinium was discovered in 1899 by André-Louis Debierne, an assistant of Marie Curie, in the pitchblende waste left after removal of radium and polonium.
The most abundant or easily synthesized actinides are uranium and thorium, followed by plutonium, americium, actinium, protactinium, neptunium, and curium.