Both yttrium and lanthanum were discovered by the Swedish chemist, Carl Gustav Mosander. He isolated lanthanum from cerium nitrate in 1839, and yttrium from a mixture of rare earths in 1843.
Scandium is found in small quantities in the minerals from which yttrium and lanthanum were extracted. Its existence was predicted by the Russian chemist, Dmitri Mendeleyev, and its oxide was first isolated by Lars Fredrik Nilson in 1879.
Actinium, a radioactive element, was discovered by Andre Louis Debierne, a French scientist, in 1899.
