A LAMINAR FORM OF THE PERIODIC TABLE Part 11: Theoretical and Modijcations
Development,
A. N. WRIGLEY and W. C. MAST1 U. S. Bureauof Agricultural and Industrial Chemistry's Eastern Regional Research Laboratorys T. P. McCUTCHEON University of Pennsylvania, Philadelphia, Penna.
INTEE preceding paper (9) the p.inciple of lamination was established, from a practical point of view, as a clear and logical manner of portraying the electronic configurationa and the relationship of chemical properties to the position of an element in the periodic table. In order to encourage its acceptance the first arrangement departed as little as possible from a familiar form of the periodic table and consequently did not take full advantage of the laminar principle. In the present paper the development of the laminar table will be presented from a theoretical point of view together with modifications of the original design. To base the table finnly upon quantum-mechanical rules the arrangement was made according to (1) electronic contigumtion, (2) energy level requirements, and (3) increasing atomic number. Thus the first four quantum series when complete are conventionally described (1) in the following manner. TABLE 1 Kahell L-shell Mabell N-shell
I.
.
Isx 2 9 , 2pe 3s2,3pe,3d'o
4s'..4p" . . 4d'o. . 4f1' .
While the above notation shows which electronic groups are possible it does not show the order in which they will be filled. It is necessary to turn to energy level diagrams and atomic numbers to gain this information. Pauling (6) gives an energy level diagram in which atomic orbitals are represented by circles grouped to show their corresponding relative energies (Figure 1). Luder (3) has expressed the desirability of referring to an energy level diagram in the study of atomic structure charts. I t will be seen that the electrons enter the subshells in the order given by the following notation: ls2, 2s2, 2ps, 3.9, 3pe, 4s2, 3d1', 4p6, 5s2, 4d1', 5p6, 6 9 , 5d1,4p" 5d2th'ulo, 6pq 7s2,6d1, 5 7 .
0
Appmdmat. Stability Sequenoe for a t o m i c Orbitah Each circle represents sn atomia orbital which may contain one or t w o deotrona. Modified from Pauling (6) br the addition of oireles representing energy values for 7r.~.8d. and 6f orbitals. Pi-
1.
Representing more conveniently the information shown in Table 1 and in Figure 1, we have the f o m shown in Figure 2, wliere the numbers beside the parentheses indicate the relative order in which the subshells are filled. Note that after one electron is present a t the 5d level the entire 4jsubshell(14 electrons) is completed before additional electrons are present a t the 5d level. Applying the principle of lamination to this extended tabulation and adding the corresponding symbols we can compress it into a more familiar design, that of a long form of the periodic.table. The principle of l m i nation thus preserves the order of increasing energy and maintains the strict sequence of atomic numbers in an arrangement which reflects electronic configuration. Preaent address, Research Laboratory, The Goodyear 'l'h All that has been required is to laminate the seven layera and Rubber Co., Akron. Ohio. corresponding to the seven principal quantum num' Private Publication. w o r m a l state electronic configurations of elements in the bers, aligning them so that the atomic numbers are in order from top to bottom and from left to right. The gsseous state. 248
MAY, 1949
249 SUBSHELLS
SHELLS Pr. X-Ray
Qu. rota- r
f
d
P
NO, tion A
1
K
0'
-
A
Recent developments, however, require a reconsideration of the question. The elements of the Lanthanide and Actinide Series are now more readily available because of improved methods of separation (use of ionexchange resins) and from work on radioactive materials. The electronic configurations of the elements can be properly presented and they can be easily differentiated from neighboring elements in a laminar chart without horizontal expansion of the table, and the growing importance of members of the Actinide Series (t, 6, 7) highlights the need for representing them correctly. These facts led the authors to believe that it is now desirable to assign these series their rightful places in the main part of the table. The recognition of the f series and their differentiation from the d series is attained by the use of Werent colors (when possible), diierent types of lettering, closer spacing, and brackets superinscribed with the legends "Lanthanide Series" and "Actinide Series." The complete table utilizing this arrangement is shown in Figure 3, and a plan for tile construction of such a table appears in Figure 4.
solution to the problem of representing the 4 j and 5 j subshells conveniently then also suggests itself. They are merely slipped in below the 4d and 5d positions respectively, which has the double advantage of conserving space and portraying the close chemical resem- USE OF THE MODIFIED LAMINAR TABLE blance. of. these goups to lanthanum and actinium reI t is not necessarv to urint the electronic structure of spectively. each element beside it; symbol, because the laminar It has always been a problem to assign the Rare structure and the shell and subshell divisions indicate Earths their proper position in planar tables. The the expected electronic configuration of all the elements. treatment of the Lanthanide and Actinide Series may The method of determining electronic configuration is follow one of three basic plans: the members of these essentially the same as that described previously (9); f series may be shown in full in such a way as to extend a few additional examples are given below. the table horizontally by fourteen spaces; they may "Normal" Configurations: be releeated to a footnote section or a little table of Oxygen. Card 1 carries rmder the letter s the symtheir own; they may be shown in full immediately bols of two elements, indicating the possession of after their introductory elements, La and Ac, but phctwo 1s electrons. On card 2, the two symbols ing the remainder of the d series on the next line in such a way as to avoid a horizontal extension of the table. The first method, although very old (8),has been commonly regarded as too space-consuming. The second one, which is most commonly used, was adopted for the original laminar chart (9). This treatment avoids any possibility of confusing the Rare Earth Series with adjacent elements and was excused for a long time by the fact that the elements were rarely used, and were indeed TI Pb Bi PO At Rn "rare earths." 81 82 83 84 85 86 The third attack has already been proposed (4) hut there is some difficultv in u planar diagram in --..disfillguidhin the Runs Earths from adjacent el+
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and actinium. On the other hand, it is felt that however continuous the trend of chemical properties, there are real breaks in electronic configurations between beryllium and boron, and magnesium and aluminum. Blank spaces are left corresponding to the l p , Id, and 2d subshells, forbidden by the quantum number rules. In addition to portraying electronic configuration the laminar table reflects changes in energy level. Whereas laminar changes in depth indicate entrance into subshells of higher or lower principal quantum number, laminar breaks crossed from left to right and from top to bottom show changes (always increases) in the energy level of the subshell entered. The table is in this sense a relative energy-level diagram. CONTOUR LAMINAR TABLE
By another modification, constmctiig the Periodic Chart in the form of contour laminae, i t is possible to Figu,.a 4. Plan for construction of a L a m i n u Form of the Periodia represent actual energy levels without the necessity of Tpble. Design I1 referring to auxiliary tables. This is done by proportioning the rises between each subshell to correspond to under s mean that two 2s electrons are present. the Pauling energy diagram. Thus, although the subSmce 0 is the fourth symbol on card 2 under p, we shells having the same principal quantum number will assign oxygen four 2p electrons. Recapitulating, be on the same contour lamina, they will not he on the the electronic configuration of oxygen is i s 2 ; 2s2, spme planar level. The recognition of these contour zp4. laminae is facilitated by the use of a different color for Europium. The structure is read off, card by card, each one. A table of this type will then be more physias l s 2 ; 2s2, 2p6; 3s2, 3p6, 3d1°; 4s2, 4p6, 4d1°, 4fB; cally correct than the previous laminar models, and it is 5s2, 5p6, 5d1; 6s2. a question as to which form has the most practical utilAmericium. The electronic stmcture is seen to be: ity. Is2; 2s2, 2p6; 3s2, 3p6, 3d1°; 4s2, 4ps, 4d1°, 4 p 4 ; We believe that the laminar periodic tables, in either 5s2, 5p6, 5d10,5f6; 6s2, 6p6, 6d1; 7s2. the original or a modified form, will greatly facilitate "Ahnormal" Configurations. Elements with "ab- systematic teachmg of the properties of the chemical normal" configurations are marked by a single super- elements. Students indoctrinated with the new sysscript placed a t the right, which serves the double pur- tem cannot fail to obtain a clearer and more lasting conpose of distinguishing them from L'normal" elements ception of the fundamental principles of inorganic and of giving the information required to write their chemistry. actual configurations. For example, the superscript LITERATURE CITED 10 associated with the symbol Ag tells us to assign silver S., "Textbook of Physical Chemistry." 2nd ed., ten instead of the expected nine 4d electrons. This is (1) GLASSTONE, D. Van Nostrand, New York City, 1946, p. 84. done a t the expense of one of the 5s electrons. (2) KIESS.C. C., C. J. HWMPBREYS. AND D. D. LAWN, J. ReObjections to long tables which ignore breaks in elecsearch Nal. Bur. Standards,37,57 (1946). tronic configuration a t calcium, strontium, barium, (3) Lunsn, W.F.,J. CHEX.Eouc., 20,21 (1943). T. P.,H. SELTZ,AND J. WARNER,"General lanthanum, and radium and which introduce "non- (4) MCCUTCEEON. Van Nostrand, New YorkCity, 1939, p. 129. existent" breaks after beryllium and magnesium have (5) P aChemistry,"D. n m q L. "The Nature of the Chemical Bond," 2nd been raised by Luder (5) who recommended a departure ed., Cornell University Press, Ithaca, 1940, p. 26. from the order of increasing atomic number and used (6) SEABORG, Chem. Eng. News, 23, 2190 (1945); 24, 1197 (1946); Ree. Chem. Prog., 8,73 (1947). electronic configuration as the sole basis for the conG.E., Ann. a d . brapil. seiace, 12,51 (1940). VILLAE, struction of an "Atomic Stmcture Chart of the Ele- (7) (8) WERNER. Ber., 38, 914 (1905); reproduced by G.N. QCAM, ments." AND M. B. QUAM, J. CKEM.EDUC.,11,217 (1934). The laminar charts do recognize the breaks that occur (9) WRIGLEY, A. N., W. C. MAST,AND T. P. MCCUTCHEON. J. CHEM. EDUC.26, 216(1049). after calcium, strontium, barium, lanthanum, radium,
