computer ~erie~. 72 Features Associated with Chemical Elements IF-sl Russell D. Larsen Texas Teeh University Lubbock. TX 79409
edited by Eastern Michigan university.JOHN Ypsilanti. w.MiMOORE 48197
Table 1. Face Parameters for Elements Eyebrow density Eyebrow curvature Vertical position of eyebrow and eye on len side Upper hair line on belt Lower hair line on right Eye size and pupil size Nose Position 01 pupil Face line Size of mouth on leR and curvature d m u t h on right Eye slant
Atomic weight Energy, rydbergs Ionization potential Boiling polnt Melting point Atomic radius
Effectivenuclear charge Chemical education is in need of new and better visual Electron affinity representations for correlating and condensing the vast Absolute entropy amount of experimental data that has been accumulated for physical and chemical phenomena. We are confronted with Heat of vapwization characterizing elements and compounds by literally dozens Specific heat of different chemical and physical properties. Most of these nronerties are interrelated hut revresent distinct phvsical measurements nonetheless. The ~ o ~Society a l of chemistry although they give interesting character and visual appeal to neriodic table1 is a splendid examvle that shows the prohthe o v & U face appearance (gestalt). iem. In this periodiE table color photographs are used to We have constructed facial representations for the chemidisplay the bulk appearance of the chemical elements. I t is cal elements in order to ascertain whether or not such revrestriking that most of the metals (over 60) look alike-they sentations are useful for identifying trends and homologous are silver-colored and shiny. Few professional chemists can series. Feature assienments are arhitrarv hut fairly impordifferentiate one metal from another hased on their hulk tant for clearly identifying trends. I t seems advantageous, appearance, altbnugh the metals are quite different in their for example, to assign the eyebrow density to the atomic chemical and obvsical orooerties. The oroblem of differentiweight and the face line (fat or thin face) to the absolute ating shiny keials fromone anothe; is analogous to the entropy. Heavy eyebrows thus represent heavier elements formidable task of differentiating between hundreds of white crystalline substances hased on their appearance alone. "The Periodic Table of the Elements"; The Royal Society of This task can be considered t o be a multivariate statistical Chemistry. Distribution Centre: Blackhorse Road, Letchworth. Herts oroblem of associatine m nhvsical or chemical properties SG6 IHN. k of kith n species (elemen& orcokpounds). ~ u m e r o ways Chernoff.H. J. Amer. Stat. Assn. 1973, 68, 361. representing multivariate properties have been developed in Bruckner, L. A. In "Graphical Representation of Multivariate Dathe field of statistics. Chernoffz proposed a graphical t a : Wang, P. C. C., Ed.: Academic: New York, 1978. representation of multivariate data by associating face feaHuff, D. L.: Black. W. In "Graphical Representation of Multivariate tures with variables, a procedure which is now a standard Datzi': Wang, P. C. C., Ed.; Academic: New York, 1978. FIury, 6.; Riedwyi, H. J. Amer. Stat. Assn. 1981, 76, 757. tool of multivariate analysis. Several improvements upon the unrealistic appearance of the initial Chemoff faces have heen devel0ped.3.~Central among these are the special faces constructed by Flury and Riedwyls of the University of Berne. We have employed the Berne construction to display the mnltivariate physical properties of the chemical elements and certain chemical compounds. One attractive feature of the Berne construction is the use of asymmetric faces by Figure 1. FACES for the first two rows of the periadic table; see Table 1 for which an equal number of paassignmems ol features to physical properties. rameters (up t o 18) can be assigned to the left and right sides of the face, so that atotal of 36 variables can be differentiated. Rarely are more than 13or 14 variables needed to express the most important p h p ical properties of an element or compound. Moreover, asymFigure 2. FACES far the first-row transnlon metals. metric faces are not necessary, ~~~~~~
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Volume 63 Number 6 June 1986
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and fat faces indicate gases. We have found that a child that is shown these facial representations can be quickly taught to differentiate between a solid and a gas or a light or heavy element on this basis alone. Other face feature assignments are given in Tahle 1. The first two rows of the periodic table are shown in Figure 1.Trends are apparent given the feature assignment code. The transition metals are shown in Figure 2. The trends are obvious. In this latter series the hairshading density corresponds t o the magnetic susceptibility and identifies the ferromagnetic elements, Fe, Co, and Ni. Series of similar chemical compounds can be represented in this way also. We show the hydrogen halides and the alkali fluorides. In the case of the hydrogen halide series, the eyehrow density represents the molecular weight, the hair density is the density of the compound, the horizontal position of the eye is the gas-phase dipole moment, whereas the size of the nose is a constant. The 14 variables for the hydrogen halides are given in Table 2; they appear in Figure 3. The alkali fluorides are shown in Figure 4; the face feature assignments are given in Tahle 3. The Faces subroutine is written in Fortran and uses standard Calcomp plotting software. Hair-shading requires access t o the Caleomp applications package. At present these routines are not able to he run on microcomputers.
Comments and Conclusions
Several comments are necessary. Students are intrigued by facial representations and seem t o grasp quickly the implications of a face-feature change corresponding to a change in a physical property. However, in their enthusiasm, they may he misled unless several points are made clear. First, no element or compound, of course, actually "looks like" any of the facial representations. In fact, a given species may he made to "look" very different depending on the selection of face features used to represent a property. Second, it should he clear that for any set of species that are plotted the assignments are relative for only that set and have no correspondence to assignments computed for another set independently. For example, the 10 transition metals may he accorded internally consistent assignments. A member of the transition metal set cannot be compared t o an alkali metal set computed independently. Such a comparison could be made only if both species were included in a lareer set-for example. theentire set of 106+ elements. The latter task is a formGable plotting operation. Third, all com~arisonsimplv l tahulat. . ~-h-v s i c aproperties ed under the s&e conditions of temperature, pressure, etc. Moreover, for the elements i t is necessary to specify whether atomic or molecular properties are being compared (e.g., N or Nz versus Be). Fourth, the use of facial multivariate representations shows how a set of physical properties taken as a whole can give rise to a gross macroscopic change (in appearance). However, an apparent change in appearance between, say, iron and zinc, may he emphasized or deemphasized dependingnot only on the choice of face features hut the selection of which ~hysicalproperties will he disdaved. . . Again, changes are oniy r e p ~ ~ n t a t i changes. ve With the above clear stipulations, little danger of an anthropomorphic association should result. The faces technique is, after all, merely a device to display multivariate properties in a compact manner. I t is no more. Table 2.
Face Parameters tor Hydrogen Halldes
Eye size Pupll size Eyebrow density Hair density Lower hair line Upper hair line Hair shading slam Vertical position eyebrow Horizontal positin eyebrow Sized m o w Horizontal position eye Eye slant Face line on right side Faca line an len side
Nose
Table 3.
Figure 3. (lefl) FACES for hydrogen halides; see Table 2 for assignments of features to properties. Figure 4. (right) FACES fw alkalimetal flwrides: sac Table 3 in a s s i g n m h of features to properties.
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Journal of Chemical Education
lonizatlon potential, eV Interatomic distance Molecular weight Density Melting point Boiling point Electrnnegatlvity difference Dissociation energy Heat 01 formlon Heat of dilution Dipole moment, gas phase Boiling point Absolute entropy Atomic volume of anion Constant
Face parameters lor Alkall Fluorides
Eyebrow density Hair density Lower hair line Curvature of mouth Eye sire H~rizontalpositlon eyebrow Vertical position eyebrow Eye slant Hair shading slant Upper hair line Horizontal position eye Nose Face llne on right side Face line on ien side
Molecular weight Density Melting point Solubility, g I i 0 0 mL Interionic Radius Lanice Energy. Jlmol Magnetic Surceptibillty, IO-'cgs Bond Sbength, kJImol Heat 01 Formation, condensed phase Heat of Fusion, glmol Dipole Moment Heat of Solution Atomic Volume of Cation, cm3 mol-' Atomic Volume Anlon
