With an atomic structure wholly different from that of the rare earth inner transition series, does lanthanum even belong with the rare earth elements?
By: Ringo Bones
Element 57, lanthanum, symbol La, can be considered a maverick among the rare earth elements. In the strictest sense, it is not actually a member of the rare earth inner transition series since it does not have a 4f-electron. Lanthanum’s differentiating electron – from barium – is found in the 5d-orbital. And yet lanthanum’s chemical properties so resemble those of rare earth metals that analytical chemists for much of the 20th Century had placed lanthanum among the rare earth elements.
Given that the Periodic Table of the Elements is based on the periodic law – which according to the wisdom and insight of Dimitri Ivanovich Mendeleyev – revolves around the law in chemistry where he ordered the elements in the sequence of their increasing atomic numbers that show a periodic – as in chemical property variation – in most of their properties. Because of this, groupings of elements are decided more on their chemical properties rather than their atomic structure.
And lanthanum’s chemical properties does resemble very much like that of its rare earth sister metals as opposed to the first transition metals where it resembles in atomic structure. At present, the International Union of Pure and Applied Chemistry (IUPAC) still places lanthanum snugly within the confines of the rare earth metals group even though its atomic structure is a bit suspect for a true blue rare earth element.