The Transuranium Elements

Abstract

The place of the very heaviest elements in the periodic system is of great scientific interest and is of crucial importance in understanding the physical and chemical properties of these elements. Ideas on this question have varied considerably over the years. Periodic charts have commonly placed thorium, protactinium, and uranium in positions immediately below the elements hafnium, tantalum, and tungsten. The latter group of elements are members of a transition series in which the 5d electron shell is being filled. Hence this earlier placement of the three heavy elements corresponded to the assumption that they are members of a 6d transition series. Indeed thorium, protactinium, and, to a much smaller extent, uranium do show considerable resemblance in chemical properties to the 4d and 5d transition series elements. The electronic configuration beyond the radon core on this basis would be written thus: thorium (6d 27s 2), protactinium (6d 37s 2), and uranium (6d 47s 2).