Positions of Thorium and Uranium in the Periodic Table

Abstract

ELEMENT 90 of the Periodic Table, thorium, ordinarily appears as the first element of the actinide series, appended below cerium at the bottom of Table 1. This construction gives the impression that thorium is the second member of a series starting with actinium in the scandium group, just as cerium is the second member of a series starting with lanthanum in the scandium group. From the point of view of alloying behaviour it is inconsistent to consider thorium as related to the scandium group. During the course of a continuing investigation into the alloying behaviour of scandium and titanium group elements with the platinum metals, it was noted that thorium behaves as if it were a member of the titanium group. Evidence is given in Table 1 in which the crystal structure of an intermetallic compound of composition AB ₃ is identified in the usual manner by the prototype of the compound family. Crystal structure data pertaining to certain of these compounds have been published¹, and for the remainder will be published shortly.