CHEMICAL ELEMENTS and THEIR ATOMIC NUMBERS as POINTS on a SPIRAL NICHOLAS OPOLONICK*
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2 West 120th Street, New York City
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ENDELfiEFF published his famous work on the periodic table of elements in 1869 (I). At that time many elements were not discovered and vacant places were left for them: Most of these were filled by elements discovered subsequently, and today the periodic table is almost complete. The inert or noble gases of the atmosphere, discovered later, were added to the periodic table as a zero group. At that time the existence of atomic numbers and isotopes was not known. Before Mende16eff's publication, the arrangement of the elements in the form of a spiral was suggested by a number of workers in this field. De Chancourtois in 1862 used the atomic weights of the elements as the basis of arrangement (2). The unit of measure was oxygen, with intervals of sixteen, therefore, between the various elements. Since Mendeleeff, the spiral has again been employed, in the form of a helix, for the arrangement of the elements, notably by Harkins in 1916 (3). Harkins placed hydrogen as the first element at the upper end of the helix, and uranium as the last, with intervals of one centimeter for one gram of
* Associate member of the American Institute of Chemists.
atomic weight; thus constructing a cylinder 240 centimeters in height. In 1913 Moseley discovered atomic numbers (4) and it has been shown that the atomic numbers are much more fundamental and significant than the atomic weights. Consequently the relative positions in the table of argon and potassium, tellurium and iodine, cobalt and nickel, which seemed inexact according to the arrangement by atomic weights, were found, on the basis of atomic numbers, to becorrect. The discovery of atomic numbers and isotopes, however, did not clear up the difficultyof the periodic table in regard to the position of hydrogen and the rare-earth elements. Chemists and physicists have been trying to improve the periodic table by writing the elements in a graphic or tabular form slightly diierent from that of Mendelbeff. Examples of these are the Thomson-Bohr table (5) and its modifications (6). These new arrangements of the elements, of course, have their merits and defects. A recent excellent survey of types of graphic classification of the elements was made by G. N. Quam and M. B. Quam (7). Hydrogen occupies a unique position in the periodic table on account of its valency and its chemical be-
havior. The positive univalence of hydrogen consigns the halogens in many chemical compounds. This it to the same group with the alkali metals. But hydro- shows it to possess a negative univalence, and from this gen, so far as, we know, is not a metal. It combines chemical behavior it may be classified with the halogen with metals to form hydrides, and it may he replaced by group.
CHART-TABLE
In the chart-table that the author now desires to describe, the acuities in arrangement heretofore encountered seem to be eliminated. The position for hydrogen in this table is easily found and explained; the rare earths are in the right place; the periods and series of elements are conspicuously shown; and the idea of atomic structure from the simplest, starting with hydrogen, to the more complex, like uranium, is introduced graphically. For our purpose, to make a spiral not longer than 370 degrees and to have enough space to write the chemical symbols all along the spiral, the equation P = 48 in polar coordinates is most convenient. Upon this spiral, the plotting of the positions of the elements is very simple. For instance the atomic number of argon is 18, then 0 = 18, 46 = 72 degrees, and one degree is equal to 0.0174 radian; therefore P = 1.253 radians, which indicates the position on the spiral of the element argon. In this chart-table the atomic numbers of the elements are arranged as points on the spiral P = 48, and six lineal concentric circles are drawn through He, Ne, A, Kr, Xe, and Ru, dividing the elements into seven periods, and three dotted concentric circles are drawn through Ni, Pd, and Pt, dividing the 4th, 5th, and 6th periods each into A and B series. In denoting the series on the spiral, it is convenient to arrange one series on one side of the spiral and the next series on the opposite side. This arrangement emphasizes the existence of the periodic series and brings out graphically and more clearly than otherwise the periodic relationship among the elements. On the chart-table we have the center as a point of reference. The iirst element after every lineal circle, a t which a new period begins, namely Li, Na, K, Rb, and Cs, is electropositive, and the chemical activity increases from Li to Cs. The fist element before every lineal circle (not on the circle), which is the end of the period, namely F, C1, Br, and I, is el~trouegative, and the chemical activity decreases from F to I. In our chart-table hydrogen occupies a unique posi-
F~cuna2 NOTE: On account of the reduction in size of the charts, many elements are omitted between H and Xe. The omitted elements are represented in Figure 1. The black-point circles indicate transitional elements.
tion. It is the first element of the period. Consequently, it has positive univalence, and its electropositive activity, in accordance with the periodicity of the elements, is weaker than that of lithium. Hydrogen is also the f i s t element in front of the lineal circle. Consequently, i t also has negative univalence according to the periodicity of the elements. Since hydrogen is the fist element of the perio$ and also the last element of the period, on the basis of the periodicity of the elements, it should have a chemical behavior more tempered than that of the alkali metals or the halogens, Furthermore, the chemical behavior of hydrogen as a metal and as a halogen gives us v e , strong evidence of the non-existence of elements before hydrogen in the periodic table. This is a crucial conclusion strongly suggested by the chart-table that we propose above.
LITERATIJRE CITED 2, 14, (5) TIMM, J. A. AND
MENDEL~EFP, J. RUSS.Chem. Soc., 1 , 60 (1869);
(1870); 4,25,348 (1871). DE CEIANCOURTOIS, Compt. rend., 54,757,840,967 (1862). HARKINS, D. AND HALL, R. E.. "The periodic system and the properties of the elements" (fifth paper on atomic structure), J. Am. Chem. Soc., 38, 169 (1916). MOSELEY, H. B., Phil.Mag., 26,1029 (1913).
JOHNSTON, J., "An introduction to chemistry,:; McGraw-Hill Book Company, New York, 1932. (6) S ~ r r n , Inorganic chemistry," revised and rewritten by Tames Kendall. The Centwv Comnanv. New York. 1931. (7) Q ~ A G M. ,N. ANDQUAM. M. BY, ' ' ~ ~ p gfe sgraphic cl&sifica11, 27, 217, 288 tion of the elements." J. CHEM.EDUC., (1934).
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