LBL-9074 :!"4 Preprint Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA 1l Published in Chemical and Engineering News, Vol. 57, pp. 46-52. April 16, 1979 THE PERIODIC TABLE TORTUOUS PATH TO MAN-MADE ELEMENTS Glenn T. Seaborg rhE Y L.OATQ!Y AUG 2E 1979 April 1979 L1BR/RY 1.ND DOCUMENTS SEc.iN TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. DIvision, Ext. 6782 (1 Ill IT T 1 Vjs%0 Prepared for the U. S. Department of Energy under Contract W-7405-ENG-48 DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. 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The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. nemui Engineering THE PERIODIC TABLE Tortuous path to man-made elements Glenn T. Seaborg Reprinted from CHEMICAL & ENGINEERING NEWS, Vol. 57, April 16, 1979, pp. 46-52 Copyright 9 1979 by the American Chemical Society and reprinted by permission of the copyright owner Priestley Medal Address THE PERIODIC TABLE Tortuous path to man-made elements Glenn T. Seaborg, University of California, Berkeley This article is based on the Priestley Medal Ad- or simply to the fact that certain elements had not yet dress presented by Glenn T. Seaborg of the Uni- been discovered. Indeed, Mendeleev's claim to priority in the discovery of the periodic system was not completely versity of California, Berkeley, on April 2 during accepted until his predictions of missing elements were the ACS/CSJ Chemical Congress in Honolulu. proved by experimental evidence in later years. Sea borg, winner of the Nobel Prize for Chemistry The periodic table Mendeleev published in 1871, which (with E. M. McMillan) in 1951 and president of incorporates improvements made in the original version ACS in 1976, received the medal, ACS's highest of 1869, predicts the existence and properties of the ele- ments with atomic weights of 44, 68, and 72. These cor- award, in recognition of his distinguished services respond to scandium, gallium, and germanium, as we to chemistry. know them. These three elements were actually found in nature during the period from 1875 to 1886. Many other experimental proofs of Mendeleev's "law" were made in the years that followed. The periodic table of the chemical elements has been As time progressed, adjustments had to be made to the the key to the discovery of many elements since its for- periodic table to accommodate the rapidly expanding mulation as a guiding principle almost exactly 110 years knowledge of the properties of the elements and their ago. Occasionally, when improperly used, it has misled atomic and nuclear structures. Also, additional elements investigators into temporary excursions along erroneous were discovered during the late 19th century and the first routes to new elements. However, even these tortuous part of the 20th century which required some recon- paths eventually have led to the correct destination. I struction of the Mendeleev periodic system. The most shall describe the part that the periodic table has played significant changes were the addition of another vertical in the discovery of the man-made elements, especially the row, or group, of elements now known as the noble gases, transuranium elements, and its possible future role. and the substitution of a series of elements—the rare The story begins, of course, on March 6, 1869, when earths, or lanthanides—in the place of a single element Dmitri Ivanovich Mendeleev and his associate, Nikolai (placed between barium and hafnium). Menshutkin, presented a paper to the Russian Chemical By the end of the first decade of the 20th century the Society in St. Petersburg (now Leningrad) which postu- total number of elements had increased to 85, and soon lated that the elements showed a periodicity in their thereafter the concept of atomic number, as the funda- chemical properties when they were arranged in the order mental basis for the ordering of the elements in the pe- of their atomic weights. This in itself was not novel. riodic table, was established. During the next 25 years, Several chemists in other countries had observed some three more elements were discovered, leaving below kind of orderliness in the elements then known, the most uranium (element 92, the heaviest element) those having prominent being the German Johan W. Dobereiner and atomic number 43, 61, 85, and 87 as the missing elements. his triads (1829), the Frenchman A. E. Béguyer de Even these properly empty places in the periodic table Chancourtois and his "telluric screw" (1862), and the were filled under names such as masurium for element Englishman John A. R. Newlands and his "law of oc- 43, illinium for element 61, alabamine for element 85, and taves" (1864). virginium for element 87. These "discoveries," however, It is not generally known that some American chemists were erroneous. The state of the understanding of the of the 19th century also proposed various forms of peri- atomic nucleus was such in the 1930's that it could be odic classifications, including Oliver W. Gibbs in 1845 and shown that the missing elements were all radioactive, Josiah P. Cooke Jr. in 1854. The only real challenge to the with such short half-lives that their existence in appre- generally accepted validity of Mendeleev's originality, ciable concentration on earth was not possible. however, has come from the work of Lothar Meyer in The periodic table, as it looked before World War II Germany, who in 1870 produced independently a gen- when scientists first tried to produce elements beyond eralization almost identical to that of Mendeleev. uranium, includes elements 43, technetium (Tc); 61, The reason for the general acceptance of Mendeleev's promethium (Pm); 85, astatine (At); and 87, francium pre-eminence is straightforward: Not only did he show (Fr), although they were actually given their names later, that periodicity existed in the properties of the elements and some were first synthesized or discovered at a later then known, but he had the courage and the vision to date. state that his method of classification constituted a Thoughts on the position in the periodic table of the fundamental law of nature, and that where there ap- heaviest elements varied considerably before the final peared to be deficiencies in his periodic table, they were recognition that another series of elements, resulting from due to gross errors in the measurement of atomic weights the addition of electrons to an inner shell (5!), should 46 C&EN April 16, 1979 I'pynna 1 1'pynna II I'pynria III Fpynn.i IV [pynila V Fpyiiva VI rpynna Vii TRnM'IoeKue 0=Ifi F=l9 aJleMeHTL.i L17 Be9,4 B=ll C=12 N=l4 PA.Z 1 Na=23 \Ig==24 Al=27,3 Si=2. )'=31 S=32 CI=35,5 Fe=56, to=59, - 241 K=39 Ca==40 —=11 Ti=.14.' V=)l Cr=2 'NI I I = 55 Ni=59, Cu=6 - 3 (Cu63) Zn=r65 —=6- —=72 .s=75 Se=7S I.Ir=80 - 4-u Rb=85 Sr=7 (?), t='') Z1=90 NIi=91 y10=96 —=l() Hiu= 104, Rh=104 Pd= 104, Ag= UP - 5-il (Ag=I0) Cd==112 In==113 Sri = 118 Sb=122 Tc=128? J 1 27 - 6-9 Cs 13.,1 Ba=137 ---137 Ce=136? - - - - - - - - - U - 8-fi Ta= I2 V = I$4 - Os=199', Jr= 19 Pt=197?,Au=Ri7 - 94 (Au = 197) Hg=200 TI=204 Pb=207 Bi=20S - - — 104 Th=232 - Ur= 240 - R20b LIMeruaR coiu 1120 11 202 110 H?W 11205 B206 RO HOl uan OlCUch itiu HO ii.-in 1102 11.1H H03 Bu.jenuee 8o210- (Rli') RH 4 RH 3 RH 2 RH - pojwue coe)u- Heue Mendeleev's periodic fable of 1871 predicted three (hen-unknown elements occur somewhere in the heavy-element region. This new The synthesis and identification (i.e., discovery) of an family of elements would be similar to the 14-member element with atomic number higher than 92, neptunium, rare-earth or lanthanide (chemically similar to lantha- at the University of California, Berkeley, came in 1940 num) series of elements which results from the addition as a result of the work of Edwin M. McMillan and Philip of inner 4f electrons. H. Abelson. This was followed shortly by the discovery Even until World War II, however, the three heaviest of plutonium by McMillan, Joseph W. Kennedy, Arthur known elements—thorium, protactinium, and ura- C. Wahi, and me in late 1940, also at the University of nium—were believed to be related to hafnium, tantalum, California, Berkeley. The tracer chemical experiments and tungsten, respectively. The next element—number with neptunium (atomic number 93) and plutonium 93—was thus expected to have chemical properties re- (atomic number 94) showed that their chemical proper- sembling those of rhenium.