The Noble Gas Compounds: The Views of William Ramsay and Giuseppe Oddo in 1902 Leonello Paolonl Gruppo di Chirnica Teorica, University of Palerrno, 90123 Palermo, Italy The discovery of the rare gases in the atmosphere ( 1 8 9 6 1898) posed a number of problems for chemists with regard to their placement in the periodic table, and a few G a r s elapsed before they were recognized as a new aroup of zerova6nt elements. Since all attempts to combine them had failed, i t was difficult to establish, by experiment, that they were monatomic eases and then to acceotthe inversion of the argon-potassium atomic weight sequence. One of Ramsay's great contributions, along with discovery of the rare gases themselves, was in overcoming these two difficulties'. Many chemists of that time considered the zerovalency of the elements not necessarily equivalent to chemical inertness. They looked a t the periodic table with a rather pragmatic attitude, and read it more as a code through which chemical orooerties of the elements could be discovered rather than a system of laws which atoms were hound to obey2. Giuseppe Oddo3 was one of the few who stated that the noble gases should combine with other elements long before this was actuallv observed4. It is also overlooked, or foreotten, that ~ a m i a shared y the same view and expressed it in correspondence exchanged with Oddo. The main point of the argument, stated in a letter by Odd& on July 24,1902, reads as follows: v
". . .the valence of the elements in the Mendelejeff classification is modified not only when one moves horizontally, but alsovaries somewhat when one moves vertically.. . .'I
When the so-called zero valent elements are placed between the halogens and the alkali metals, the ability of iodine to form ICIs and IF5 and that of potassium and cesium to form KIs and Csls show that the elements below the line have a modified valency.
seems that these eases. esoeciallv helium. can combine at verv high temperatures. but the compounds (11formed) derompaae when the temperature 13Ihwered I t ir a phenomenonent~relyunknown with inorganic compounds.' T h e further correspondence involved a discussion of the structure of the alkali metal iodides, in which Ramsay was essentially closer to the correct view. In his letter of September 25.1902. while criticizine Oddo's model for CsL. Ramsav aeain wr& that such a disagreement ". . .did not d e ~ i a cin t aily'kay from the streneth of IOddo'sl remark- concernine"the ~mszihle . existence of xenon compounds more stable than those of neon and areon. . . ."The real orohlem was to obtain the ~. eas.. since ". . . xenon is contained in the atmosphere at the ratio 11 3.500.000. lmarine the difficultv of eettinc 5 cc of it!" . . In conclusion, it seems fair to;oinkamsiy and Oddo, with A. von Antro~off.E. H. Boomer. L. Pauline. D. M. Yost.A. L. Kaye, and G: C. ~ i m e n t e lon , the short list of scientists who expected the noble gases to form compounds during the 65 years which elapsed before these were actually prepared'.
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(a) Hiebert E. N.. "Histwical Remarks on the Discovery of Argon." in "Noble-gas Compounds." Hyman H. H. (Editor).The University of Chicago Press, Chicago. 1963, p. 3. (b) van Spronsen. J. W.. "The Periodic System of Chemical Elements: A History of the First Hundred Years." Elsevier Publishing Co.. Amsterdam. 1969, Ch. 8 and 9. The latter view developed during the following years when the electronic t h e w of atomic sbucture cofrelated the chemical inertness of the elements with the noble gas Selecbon configuration, and based on it a theow of valence and of the chemical bond. ~ i u s e o oOddo i (Palerrno. Sicilv. .~~ .- ..doctorates ,. 1865-1954), earned in chemlstv an0 In medlc ne at the age of 26, at the Universty of Palermo. Appomted 10 tne char of chemistry at the University of Caghari (Sardinia) n 1898 ne moved to me Un versify of Pawa in 1905am I mlly to Paiermo in 1919. where he remained until his retirement in 1935. He was the authot of two texmooks and of about 200 papers and wofked until a late age in a home-built laboratory. (a1Goodman G. L.. Editwial note in the volume ouoted in reference ~
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"I have had far a lone time the idea that k r, ~ .t o ~ and n xenon mav ~, entpr int,, comhinnt~onsmuch more ~nrllythan the other gnue5; but how to bring nt about? I have available only :$or 4 ccof krvpton, and hope to make some attempts in the next semester. It ~
758
Journal of Chemical Education
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potof chem~stryin the Univers ty of Cagliar The whole correspondence is published here and the letters by Ramsay (who read Italian and answered in French) are also fully reproduced in facsimile. Their publication was stimulated by a paper of A. von Antropoff. K. Weil and H. Frauenhof [Natunviss.. 20, 688 (1932)lreporting success in obtaining a krvoton chlwide. But attemots to reoeat .~ their exoerimms failed. ~.~ and ,. aboLt a year ate, von ~ntroboffadmlned hts ta i i e INarwwrss . 21, 315 1193311 *hie announc ng that he was con1 nulng to wor* toestaolrsh enether or not krypton entereo tnto chem ca comomat on Evidence for the combination of He with W. Hg. I. P, and S, even if not conclusive, was obtained in Rutherford'slaboratory some twenty years later by E. H. Bwmer. [Proc. Roy. Soc.. A-109, 198 (1925)l. G..
This suggests that similar combinations should he found for krypton and xenon. In his letter of August 4,1902 Ramsay accepted the argument for the halogens and the noble gases but rejected the part concerning the alkali metals and added%
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