PERIODIC CHART JOHN D. CLARK Stanford University, California
Twenty-two preYious periodic arrangements of the elements have been briefly discussed. A new arranfement, based on a jfattened s & d , hns been $ro$osed.- Some definite adwantages of this arrangement have been $&nted out.
1. That of MeudeMeff1 which has the defects already mentioned. 2. The type proposed by Werner2 whose periods are of unequal length, leaving many blank spaces not corresponding to missing elements, and which, although it provides extensively for the rare earths T IS universally recognized that there are several and separates the main groups from the subgroups defects in Mende16eff's periodic arrangement of neither shows the relationship between the latter the elements. Among these are the similar arrangetwo nor provides satisfactorily for hydrogen. It ment of the main and the subgroup elements of each is also somewhat awkward and unsymmetrical in group, the extremely doubtful position of hydrogen, appearance. the inadequate representation of the rare earths, and, finally, the psychological fault of a lack of emphasis on 3. Deming's3 arrangement is a compromise between Mendeleeff's and Werner's, being eighteen spaces the continuity of the series of elements, breaking them across, instead of eight or nine in the former or arbitrarily, as it does, into periods of eight, eighteen, thirty-two in the latter. It compresses the rare and thirty-two elements. earths into the space normally occupied by one These defects have long been recognized, and a great element, provides, though awkwardly, for hymany different representations of the table of the drogen, and shows the relationship between the elements have been suggested. It will perhaps be main and the subgroups. I t is probably one of convenient in criticizing some of these representations the best of the discontinuous two-dimensional arto list first some of the qualities of an ideal periodic rangements, but is a trifle complicated. Antrochart, over and above those possessed by Mendel&eff's. poff4 has published an improved chart that is 1. It should be as simple as possible. closely related to Deming's. 2. It should separate the main and the subgroups, but The continuous types of arrangement are more should, a t the same time, show the relationship varied. They usually take a spiral form of one sort or between them. another, of which there are four general types. 3. It should have a natural and inevitable location for hydrogen, showing its relationship both to the 1. The elements are arranged spirally around hydroalkali metals and to the halogens, but a t the same gen, making one complete turn for a short period time emphasizing its unique position in the series. and two for a long. Partington's5 chart is of this 4. It should emphasize the idea of continuity as well type, although hydrogen is not exactly a t the as that of periodicity. center and the arrangement suffers to that extent. 5. It should treat the rare earths adequately, but The rare earths are arranged radially. However, should not confuse them with the other groups. the subgroups are too closely tied to the main 6. It should be convenient in shape and in representagroups, as in the Mendel6eJT table. Wells'sa artion. rangement is also of this type. Tansley' has used
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The attempts that have been made to produce a more nearly perfect representation may be classified first as two-dimensional or three-dimensional. The two-dimensional representations may be divided again into two g r o u p s t h e discontinuous and the continuous arrangements. Among the former there are three general types.
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D. MENDEL~EPP, J. Russ. Phys.-Cham. Soc.. 1,60 (1869); 2, 14 (1870); 4,25.348 (1871). A. WenNEn. Ber.. 38.914 (Feb. 27. 1905). 8 B. S. HOPX~NS. ' ~ h e m i s & yof the rar& elements," D. C . Heath & Co., New York City, 1923, p. 14. A. v. ANTROPOPP, Z. angew. C h a . , 39,722 (June 10,1926). Chem. News, 127,304(Dec.24.1926). J.R. PARTINGTON, qP. V. WELLS,J. Wash. Acad. Sci., 8 , 2 3 2 (1918). 7 L. B. TANSLEY, Chem. N m s , 122,121 ( M a r . 18,1921).
the opposite arrangement, with uranium in the center and hydrogen on the rim, over fluorine, which is not completely satisfactory. Likewise, the rare earths are arranged spirally with the other elements, which arrangement does not, in general, agree with their chemical nature. 2. The elements are arranged spirally around hydrogen, making one complete turn for a long period, and one for two short periods. This arrangement has the disadvantage that it separates lithium from sodium, and shows the former as being more closely related to copper, and similarly for the other elements of the first period. Loew and Erdmann8 use this arrangement, although they omit hydrogen. They arrange the rare earths spirally, confusing them with the other groups, while Ryberg9 arranges them radially. Johnson Stoney'~'~ arrangement is similar to that of Loew and Erdmann. This arrangement, of course, fails to show the relationship between the main and the subgroups, and separates the first two periods. 3. Caswell" uses a spiral which makes one turn for either a long or a short period. In the case of the latter, there is a gap of approximately 220' between the second and third groups. In the outer turns this gap is of course filled by the transition elements. The rare earths are given the space of one element. This arrangement has the serious disadvantage that it implies a break between the second and third groups in the continuity of the first two periods. 4. A double, or figure eight, spiral may be used, one loop being centered on hydrogen for the main groups, and the other for the transition groups. Nodder12 uses an arrangement of this type. It is unduly complicated, and the relationship between the main and the subgroups is not distinctly indicated, and unfortunately the rare earths are misplaced, but it is more satisfactory than most of the other arrangements. Three-dimensional arrangements show even more variation than do the two-dimensional schemes. The commonest arrangement is the heliu, simple or com-1-" psc...
1. The best known helical arrangement, the single-
centered type, is that of Harkins,l3 which makes two loops of unequal radii for each long period. This model is quite satisfactory in most respects. It has a logical position for hydrogen, although i t does not show its relationships with the I and V I I groups, it separates the main and the subgroups but shows the relationship between them, and it disposes of the rare earths in a most satis-
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L. BIGELOW. "Theoretical and ohvsical chernistrv." The Centuri Co.. N& Y
