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A LAMINAR FORM OF THE PERIODIC TABLE PART
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A. N. WRIGLEY and W. C. MAST' U. S. Bureau of Agricultural and Industrial Chemistry's Eastern Regional Research Laboratory2 T. P. MCCUTCHEON University of Pennsylvania, Philadelphia, Pennsylvania
Tm purpose of this paper is to describe the const ruction and use of a simple and compact form of the periodic table. This table js designed to exhibit the relations among the atomic number of each element, its electronic configuration, and its position in the periodic system. This end is achieved by inscribing the table on a sequence of seven laminated cards, so that a threedimensional effect is obtained, without sacrificing the advantages inherent in planar models. It is believed that such a table could be constructed readily by a chemical student a t any level, and that such an exercise would be a valuable introduction to the systematic study of the chemical elements. A serious shortcoming of most presently accepted tables is the failure to reflect in their design the electronic configuration of the elements. In recent years Figure 2. Pkn of construction of Laminar Form of the Po~iodis Table. Design 2 some versions of the orthodox tables have given configuration data in small print or in diagrams near each element's symbol. However, the large and growing use of electronic configuration in the study of the chemistry of the elements demands tables that make electronic they cover many columns horizontally or vertically, they suffer from large space requirements. confignration an integral part of their framework. More serious both chemically and pedagogically, the The present authors acknowledge a considerable debt last two tables sacrifice what is most basic to the to the table of Gardner (4) with its fourfold classificaperiodic system, the order of atomic numbers. In 1944 tion; to that of Ebel (S), whose classification of the 13abor ( I ) proposed a modification of Luder's chart elements as "Representative Elements," "Related vhich remedied this defect, but a t the expense of an Metals," and "Rare Earths," based on the shell of the additional extension, vertically, like Gardner's. differentiating electron seems of cardinal importance; Further search for a design that would embody the and to that of Luder (6), which embodies in addition n important advances of the Gardner, Ebel, and Luder classification according to the s, p, d, and f subshells. tables without making the same sacrifices, and that In Luder's table the section for the Related Metals apwould reflect both electronic configuration and atomic pears to the right of that for the Representative Elenumber, simply and compactly, led to the laminar table ments, and is so aligned as to show that the differproposed in this paper. entiating electron for scandium, for instance, enters the It is apparently difficult to give a proper idea of electhird shell rather than the fourth like calcium's last tronic configuration in two dimensions without spreadelectron. The section for the Rare Earths appears in ing out vertically or horizontally, and thereby sacrificing similar alignment further to the right. the order of atomic number, or compactness, or both. These modern tables, particularly the last, succeed In three dimensions it is entirely feasible, but the first in giving electronic configuration its proper prominence reaction is to discard three dimensions as too awkward. as a framework for the periodic system. Still, since The laminar chart here proposed seems to the authors to possess the advantages of both the two dimensional ' Present address, Research Laboratory, The Goodyear Tire and three dimensional charts and to have none of their and Rubber Co., Akron, Ohio. disadvantages. 8 Private publication. 2:16
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APRIL. 1949
the "Actinide Series" (2, 5 , 7 , 8) of Seahorg, shown on the bottom of the fifth card.
SUBSHELLS
ELECTRONIC STRUCTURE
d
Some of the tables now in use print the electronic I A UA &A mn nn =A =A rm7 1 s n 3 ms ms ns x m ~ms o structure of each element in whole or in part beside its symbol. This could of course he done with equal convenience in the laminar table. However, the laminar structure and the shell and subshell divisions themselves indicate the electronic configuration of all the elements which are "normal" in this respect. Let it he required, for inSERES 90 91 92 93 94 95 96 stance, to read off the elecN 4L5ggN1ECePr Afd Sm Eu Gd Tb Dy Ho Er T i YS Lu tronic structure of nitrogen. ,RI(RL EAR THSI 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Card 1 darries under the letter s the svmbols of two elements, thus indicating Figure 1. A L a m i n u Form o€ the P-iodic Tsbl. ,, Design I the occurrence of two i s electrons. On card 2 the two For classroom use an actual, large model of this chart symbols under s mean that two 9s electrons are present. is entirely practical, and smaller models for individual Since N is the third symbol on card 2 under p we assign use can easily be constructed. For reproduction on a nitrogen three d p electrons. Recapitulating, the elecplane surface, as in a book, an artist's drawing can tronic configuration of nitrogen is 1sZ,ds2,dp3. readily convey the idea of the laminated structure withLet the electronic configuration of vanadium be required. Inspection of card 1 shows that two i s elecout sacrificing the convenience of a plane. The proposed table applies the principle of lamination trons are present. Card 2 indicates two 2s and six 2p to a long form of the periodic table. In the model it- electrons. Card 3 shows two Ss, six Qp, and three 3d self the use of both different colors and different kinds electrons. Card 4 shows two 4s electrons. of lettering gives additional emphasis to the threefold Similarly we can read off the structure of lutecium, classification of the elements. Figure 1 is an artist's card by card, as i s 2 ; k2,$p6; Qs2,Qp6,Qdl0; 4sZ,4p6, drawing reproducing, except for color, the actual lami- 4d1°, 4f14; 5s2,5p6,5d1; 6sZ. The case of abnormal elements is only slightly difnar model, the plan of which is the following: Each main shell is represented by a separate card, so ferent: the addition of a single number to the right of that card 1 corresponds to the principal quantum num- the symbol for the element calls attention to the irber 1, and so on to card 7 for quantum number 7. regularity, and supplies the additional information The cards are held apart by spacers of cardboard or necessary to write its configuration. Thus we read to the right of the symbol Cr the number 5, which tells us wood. The elements with differentiating electron in the out- to assign chromium five instead of the expected four 3d ermost shell ( s and p subshells) are shown in black bold electrons. We compensate for this by giving it only lettering on the same card as their principal quantum one 4s electron. Similarly the figure 9 beside I r tells number. These are the Representative Elements of us to assign iridium nine 5d electrons instead of the seven suggested by its position as the seventh member Ebel. The elements with differentiating electron in the of the 5d subgroup; we compensate by assigning it no second-from-outermost shell (d subshell) are shown in electrons in the 6 s shell. red less boldly on the card corresponding to the next A consequence of the arrangement employed is that lower principal quantum number. These are the Re- the abnormal configurations can be recognized a t a lated Metals. glance, together with the fact that the irregularities inThe elements with differentiating electrons in the volve electrons of the d subshells. This serves to emthird-form-outermost shell (f subshell) are shown in phasize the small difference in energy between 3d and green script lettering on the card for principal quantum 4s, between 4d and 6s, and between 5d and 6 s electrons, number two units lower. These are the "Lanthanide respectively, and calls attention to the ease with which Series," shown on the bottom of the fourth card, and the Related Metals can shift an electron from one sub-
K
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H1 H2e
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shell to another. The tendency to form half-filled and still find active use as classifying labels. Other or filled d subshellsi. e., five or ten electrons-is also objects in making the artificial break were to minimize more graphically portrayed by this method of high- the resemblance between hydrogen and the alkali lighting irregularities and assigning normal configura- metals and to emphasize helium's character as an inert tions by the systematic and orderly completion of shells. gas (completed i s subshell), rather than, as might In order to facilitate the preparation of a laminar otherwise be supposed, a member of the alkaline earth chart as a student project the individual laminae are family. shown in Figure 2, together with suggested proportions. An outstanding virtue of the laminar chart is its The symbol and atomic number of each element might simplicity. Consequently, though more data than occupy, for instance, an area one inch square. Pieces have been given here can be added if desired, the less of wood and of white display card may be cut to the incidental data used, the easier it is to see and remember right dimensions, the symbols and numbers may he the main burden of the chart: the shells and subshells, printed on each card, and the cards glued to the boards the groups, and the electronic configurations. which are then all fastened together with glue, screws, or nails. Alternatively, spacers of cormgated card- LITERATURE CITED board, cut somewhat smaller than the corresvonding J. A., J. CHEW.EDUC.,21,25 (1944). white'cards, may be used to keep the "shells;' apart. ( I ) BABOR. )' BOnRr N., Nature, 43 (lgZ3). Four-tenths of the width of the space assigned to each ((3) EBEL,R.I,., J. &EM. EDTIC.,15,575 (1938) chemical symbol seems a satisfactory distance between \., 14, C,6nnNm ~ ,---,-.125_ . Iq6 ~ (1030,_ ~ ~ ~ ~ ~ , the layers. ( 5 ) K~ess.C. C., C. J. H U M P ~ E YAND S , D. D. LATIN, J. Research Nnt. RUT.Standavds, 37,57 (1946). A minor feature of the table, introduced for reasons of exvediency, is the artificial break between the first ( ~ ~ ) . + E R V W. F., J. CHEM.EDUC.,2% 21 (1943); 169 393 Use is made of this space (7)(1Y'BYJ. and main SEABORO, G . T.,Chem. Eng. Hews,23, 2190(1945); 24,1197 to print the traditional group headings, I A, 111A, I V (1946); Record of Chem. Progress, 8,73 (1947). B, etc., which are firmly entrenched in the literature, (8) VILL*~,G . E., A m . acad. brasil. science, 12,51(1940). ~
