DIAGRAMS RELATING THE PERIODIC TABLE TO GEOCHEMISTRY V. P. SOKOLOFF The Johns Hopkins University, Baltimore, Maryland
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periodicity of atomic strurtures of the chemical elements is illustrated in Figure 1. The figure consists of three parts: The central part shows the periodicity of atomic volumes by the means of horizontal bars in a column, from hydrogen to uranium. Elements are indicated only by their atomic numbers (Z). The length of the hars is roughly proportional to the atomic radii represented. The values for the radii are taken from the monumental work of Fersman' and the more recent one of Rankama.z Where more than one reliable measurement is cited, the volume is represented by two hars in line, e. g., the volume of No. 50 (tin), No. 33 (arsenic), No. 15 (phosphorus), and No. 6 (carbon). Atomic volumes for which no reliable references were available were left unrepresented. The visual effect of the central part of the diagram is that of a rough periodicity in the atomic volumes, a periodicity that can be related a t a glance to the electronic shell structures on the right and to some features of the nuclear structures on the
' FERSMAN,A.
left. The periodicity of atomic volumes so depicted constitutes a visual supplement to the well-known atomic volume curve of GoldschmidtSand, indeed, may he superior to the latter from the teacher's point of view. The structure of the electronic shells, in the right part of the diagram, is a pictorial representation of the data summarized by Pauling.' The ordinate of this part of the diagram is Z, the atomic number from 1 to 92. The seven electronic shells are shown on the abscissa as horizontal bars with their lengths proportional to the number of electrons they contain. Dark lines perpendirular to the bars indicate the electronic levels within the shells. The shells are identified conventionally, from K to Q, and their electron capacity is shown by subscript numbers along the abscissa. The eleven atomic cores, from helium to radon, are noted. The left part of the diagram shows the atomic weight-Z relationship, with an exaggeration of the a GOLDSCHMIDT, V. M., "Uber die Raumerfiillung der Atome (Ionen) in Kristallen und iiher des Wesen der Lithosphiire," Neues Jdarb. Mineral. Geol. BeilageBd., 57, 1119 (1928). ' PAWLING,L., "The Kature of the Chemical Bond," Cornell University Press, Ithaca, N. P.,1948.
E., "Geochimiia," Onti-Himteoret, Moscow,
1937, Vol. 111.
l R ~ ~ a K., n ~AND , T. G. SAHAMA, "Geochemistry," The University of Chicago Press, Chicago, 1950.
ri(yu." 1.
Periodicity of th. El.m.nt.
IS
JOURNAL OF CHEMICAL EDUCATION
ABUNDANT; 100 TO 10.000 BRAYS PER T O N ' A I D H I B H L I
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Y O D F I I I E L Y ABUNDANT; 100 TO I GRAMS PER TON RELITWELT SCARCE; I TO 0.001 GRAYS PER TON 4ND LOWER SO PAR MOT DISCOVERED IN NATURE
P i s " . .
2.
Abundance of tha Element.
is shown approximately, as horizontal bars, with suitable annotations, along the left ordinate, and the atomic weight scale along the upper abscissa. The relative abundance of chemical elements in the earth's crust in relation to the periodicity of atomic numbers is shown in Figure 2. The atomic numbers are arranged in the form of a spiral, with the unavoidable and useful repetition of the helium and the neon periods, and with the repeated placement of No. 1 (hydrogen). Both the continuity and the periodicity of the atomic structures suggested in Figure 1 are given further emphasis in Figure 2. The irregularly closed beginning and the open end of the spiral are in keeping with the current opinions of the origin and structures of matter and with the possibilities of further expansion of the transuranium series. The spiral arrangement illustrates the importance of both Groups 0 and VIII in the genesis of species of matter somewhat more graphically than the conventional rectangular arrangements The shaded background of the atomic numbers indicates the relative abundance of each element. It is shown in three categories, high, medium, and low, ss explained in the key. A more detailed breakdown would complicate the diagram unnecessarily and the interested student can be referred for this information to the recent summary of Rankama already cited. Although the diagram is highly generalized, it clearly in-
well known irregularities, and the straight lime relating "he spiral arrangement in Figure 2 is crude, in comparison, Z to the number of protons in the nuclei. The distance for example, with the admirably comprehensive and intricate orbetween these two lines is indicative of the number of ganization of the periodic table in J. Grant's "Hackh'a Chemical neutrons in the nuclei, in relation to the proton number Dictionary" (The Blaldston Co., Philadelphia, 1944, p. 631). Its crudeness and simplicity, however, permit a rapid grasp of the or Z. Other components of the nuclei are not con- subject on the part of the student-a response generally not afsidered in the diagram. The number of known isotopes forded by more elaborate diqrams.
A
SIMPLE IONS
0 FREE MOLECULES t
Figu..
METALLIC STRUCTURES IONIC OR MOLECULAR COMPLEXES
3. Form. of occurronc. of El.menta
in the E o r t h ' ~cruet
JANUARY, 1954
dicates certain anomalous abundances, such as No. 18 (argon) and No. 82 (lead). Plausible reasons for these abundances are found in the well known genetic relationship of argon to K40, and the "magic number" structure of the lead nucleus. The purpose of Figure 3 is to present an ordered generalization of the most common forms in which the chemical elements occur in the relatively simple environment of the planet's surface. It contains many approximations. The chemical elements are arranged in their periodic sequence, using a modified rectangular form of the periodic table. This arrangement is complementary to those used in Figures 1and 2 and is well suited to illustrate and to explain zonations and trends in the geochemical behavior of the elements. Four principal forms of the chemical elements are recognized in the table:
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(1) Free molecules, the sole form in Group 0 but common also for the elements carbon, nitrogen. - . and oxygen. (2) Simple ions, such as H+, F-, etc., common for the majority of the elements. (3) Ionic and molecular complexes, radicals, etc., such as H2POI-, Si02, etc., which are equally common. (4) Metallic structures, found chiefly in Groups VIII and I. ACKNOWLEDGMENT
I wish to thank Dr. G. F. Carter, Chairman of the Isaiah Bowman School of Geography, for his interest in and encouragement of my Chemical Introduction to Geography of Soils, and Dr. Bentley Glass, Department of Biology, the Johns Hopkins University, for his helpful criticism of the paper.
