Mendeleev's "Family": The Actinides

Abstract

When Dmitri Mendeleev laid out his ordered grid of the then-known elements in 1869, he could not have predicted the overwhelming and all-encompassing effect that his idea would have on scientific theory for the next 150 years. Nevertheless, he knew, presciently and from the start that he had conceived and laid claim to a powerful predictive tool that would bring some kind of order to a seemingly random set of fundamental substances. It is not within the scope of this paper to detail how the thought currents of his day were converging, little by little, on the realization that the universe was an intrinsically ordered one, nor is it our purpose to award to Mendeleev the title of sole “discoverer” of the periodic system. We wish merely to point out that he now occupies a well-deserved place within the system under the title of “mendelevium,” element 101, and that, by this attribution, he belongs to a special “family,” the actinides. How this family was uncovered, grew, and developed is the topic of this essay.