A
SYMPOSIUM
The New Elemenws Introductory Remarks T m s symposium1 is on the new elements, or more properly speaking, the man-made or synthetic elements. The periodic table has provided a sort of blueprint which indicated, as the elements were being discovered, how many elements were possible up t o the heaviest natural element, uranium, No. 92. By about the middle of the third decade of this century all 92 elements had been discovered with the exception of those with the atomic numbers 43, 61, 85, and 87. Even these found their way into the periodic table under uames such as masurium for element 43, illinium for element 61, alabamine for element 85, and virginium for elemelit 87. These "discoveries" were erroneous, however, and the state of the understanding of the atomic nucleus was such in the 1930's that it could he shown that these elements are all radioactive with such short half lives that their existence in appreciable concentrations on the earth is not possible. Actually all four elements do exist in nature. Elements 85 and 87 occur as a result of rare branching decay in natural radioactive series and are present in quantities so small that there is possibly less than an ounce of each in the total crust of the earth. Elements 43 and 61 are present as radioactive fission products but a t conceiltrations so small that they have not yet been detected. These four elements have heen synthesized by man and the synthetic are by far their most important sources. The first papers give an account of their present status. All the other synthetic elements must have atomic uumhers higher than that of uranium, No. 92, that is
must be "transuranium elements." All of the presently known transuranium elements are memhers of n secoud rare earth group of elements and are kilowll as the actinide elements. This transition series will end with the undiscovered element 103. TTO of t,hetransuranium elements, neptunium, No. 93, and plutouium, No. 94, exist in nature a t very small concentrations as a result of their continuous production by the action of neutrons on uranium, while the heavier transuranium elements exist in concentrations too small to make their detection feasible t o date. The synthetic is the only important source for the transuranium elements. Much of the present known information about these elements will be reviewed. It should be possible t o synthesize elements beyond element KO. 103, that is, t o prepare transactinide elements. The early investigations of all these man-made elements were made by the tracer technique. Following this, the next investigations were usually made with macroscopic quantities using very small quantities and the very ingenious techniques of microrhemistry and ultramicrorhemistry. Most of the presently known synthetic elements, with the possible exceptions of astatine, No. 85, francium, No. 87, and elements with atomic numbers greater than 99, have isotopes with sufficiently long half lives so that they can be isolated in weighable or macroscopic form. By the use of new techniques permitting special observations, such as spectroscopic measurements, it may be possible t,o work with macroscopic quantities of astatine, francium, and some of the elements beyond element 99.
' A ~ympo~ium presented before the Division of Chemical Education st the 133rd Meeting of the American Chemical Society, San Francisco, April, 1958.
Glenn 1. Seaborg, chairman of symposium
Lanthenid. serism
Actinid. Series
2
/
51
La 138.92
59
58 Ce
Pr
140.13
140.92
60
Nd 144.27
89
90
91
92
Ae
Th
Pa
U
227.04 232.05 231.05 238.04
Journal of Chemical Education
University
of California, Berkeley
