OCCURENCE & HISTORY
Where/how do rare earths/actinides fit into the PERIODIC TABLE?
Swedish Mineralogist A.F. Cronstedt discovers a new heavy mineral
Klaproth shows pitchblende contains a new element, uranium
isolated as a metal in 1841 by Peligot
J. Gadolin isolates "yttria",
but thought it was the pure oxide of Y
ca. 100 claims of elements in the rare earth group, due to:-
problems of separation (very similar properties)
lack of conclusive tests as to whether a mixture was involved
Mendeleevian Periodic table could only accommodate 1 element for this group, La
at one stage W. Crookes thought that apparently different rare earths were "simply different modifications of the same element."
Alfred Werner produced a Periodic table in 1905 of essentially current form, (though he did put spaces for 15 elements between La & Hf - there was no viable atomic theory at that time!)
W. Moseley shows from characteristic X-ray patterns conclusively that there are only 14 elements between La & Hf
Bohr interprets this as expansion of 4th quantum group from 18 to 32 e-
Lanthanides are therefore identified as the first f-series
Lanthanides recognised in fission products of uranium
Techniques to obtain lanthanide separation greatly improved
of the actinides only U(1789), Th (1829), Ac(1889), Pa (1913) are known
The nuclear age ~ uranium and plutonium chemistry
Trans-uranium elements synthesized by "bombardment" expts.
Actinides developed as the 5f series equivalent of the lanthanides (Seaborg's Actinide Concept), & proven not to be a 4th transition series
Lanthanides obtained in increasing amounts ~ increasing technological importanceBibliography [textbook & online resources]
Source: Dr. S.J. Heyes; University of Oxford