Edited by GEORGEWlGER
textbook forum
California State University Camon. CA 90747
Confusion in the Periodic Table of the Elements W. C. Fernelius Kent State University, Kent, OH 44242 W. H. Powell Chemical Abstracts Service, Columbus, OH 43210
The periodic table of the elements is the most widely distributed and the most used single source of information in chemistry and related fields. Everyone involved with chemistry has had at least an occasional use for it, and everyonewho has studied chemistry has become more or less familiar with it, usually beginning with high school. Consequently, i t i s distressing for manv to discover that a recent chart of the periodic tihle differs from earlier charts i n the designation of nuhrroups (or families) of elements bv the letters A and H in a way which may not be immediatelybbvious. It is an unfortunate fact that over the course of history, these letters have been used in two entirely different and opposing ways to designate subgroups, and not surprisingly, this has led to much confusion in the minds of those who consult the charts. An increasing number of inquiries are being received asking for an explanation of the differences and requesting guidance for the future. This report will document events leading to the present confusion in the periodic tahle and point out some considerations to keep in mind in developing a satisfactory solution to the problem. A wide variety of periodic table formats has appeared in the literature, both three-dimensional and two-dimensional. For the,Committee on Nomenclature of the American Chemical Society. Dr. K. L. Loening. Chairman, Chemical Abstracts Sewice. 2540 Oientangy River Road, P.O. Box 3012, Columbus. Ohio 43210.
Often differencvs arc. slight, but rertainly earh designer was a t c e n ~ ~ t i ntoa illustrate R wrhin viewuoint ohout fhr r)eric,dic nature of ihe elements with a particilar format. his report is concerned only with the most general periodic tahle formats: (1)short, or condensed (Fig. 1);(2) long, or expanded (Fig. 2); and (3) pyramidal (Fig. 3). Details of the many variations within these broad classifications and of several other formats may he found in various reviews ( I ) . The short, or condensed, format of the periodic tahle has appeared in many versions; even Mendeleev used several variations in his publications. Often the general formula of the oxide andlor hydride characteristic of that group of elements was given a t the top of each column: EzO EO Ez03 EOz En05 EOs E ~ 0 7 EO* . .. EH EH2 EHx EHI EHB EH2 EH
Although by no means universal, a common practice was to separate the elements in each group into two subgroups beginning with the fourth period, placing some to the left side of their boxes and others to the right. Sometimes the elements in the first three periods were centered in their respective boxes; however, for the most part, the elements in periods 2 and 3 were moved to the right or left side of their boxes so that they would he directly above the elements in periods 4,5, and 6, which they more closely resembled. In later versions, these suhgrou~s . were designated hv the letters a and b (or A and B ) , respectively. ~ l t L o u ~ thkse h letters were often placed at the top of each column, occasionallv - thev - began - with the elementiin the fourth period. The long, or expanded, format of the periodic table has been around almost as long as the short format. Actually, Mendeleev used one variant of it ( 2 )and Werner another (3a). Expanded tnhles with the inert gas elementa i u n middle wlumn and the i8tht.r families of rlements to the right and l e t are as old as any expanded format but have not been a t all popular; in fact, so much were they forgotten that as recently as 1973, such a format was claimed to be "new" (4). . . 'l'he pyramidal furmat of the perivdir table is svnietinies attributed to Thwnsen (5)and s~metimosto i h h r ( 6 ) :actw ally, it appears to have been used first by Bayley (7).1 t was
Ediiw's Note: We wish to call all of our reader's attention tothis article and the request at its end, for teachers' input to the Comminee on Nomenclature. Attendees at the 7th Biennial Conference will have a particularly good opportunity to express h i r opinions,as Dr. Ferneliuswill present this paper and discuss the problem with those who are interested.
Figure 1. A short (condensed) format far the periodic table of the elements. 504
Journal of Chemical Education
Figure 2.A long (expanded)format for the periodic table of the elements. expanded even further to give each rare earth element a column of its own ( 3 6 , 8 ) .Bohr, whose work fully explained the basis for a periodic table, adopted the pyramidal format which became so popular that i t is now often called the Bohr table. As the relationship between chemical behavior and atomic structure became integrated into chemical thinking and teachine. the ~vramidalformat, or the expanded form derived from i t a s described below, became more and more popular. Although this shift occurred slowly, today these forms have almost completely displaced the short, or condensed, form.
I t is interesting to note that as early as 1939 a plea for the adoption of theexpanded form was made in asymposium on modernizing textbooks sponsored by the ACS Division of Chemical ducat ion (9). In 1923, H. G. Deming published an elementary chemistry textbook (10)which became very popular. In i t he included the pyramidal form of the periodic table used by Bohr (Fig. 3) hut with two very significant alterations: 1) The elements of periods 2 and 3 were separated by moving the first t w o groups I,, the 1rf1and the rest to che right.' 2) The columns uf elemmts (omitting the inert gaa famil?, were ~dentifirdb\, labeing the firit twoand the last fnr cdumns ns A subgroups, and the & x n n s in between as B subgroups in such a way that their characteristicoxides corresponded t o those of the
A subgroups.
I
Fr
I
Of much less significance, Deming also placed the column of inert gas elements a t the left side of the table and did not identify in any way the iron, cobalt, and nickel columns. With the Dassaae of time, minor modifications converted this format to the expanded form shown in Figure 1 that wni so cwnmon in this country hefore recent mudificatiuns. Al. though the assignment of A and B subgroups may be considered quite arbitrary, Deming was following the three-dimensional table proposed by Soddy ( l l a )and by Harkins, et al. ( I l b ) ,in making a clear distinction between the characelements and the transition elements. teristic or major This distinction is an important teaching device.
1
Ra Ac"
'
.
In me first edition of Deming's textbwk, boron and aluminum were also on the left: subsequently,these two elements were moved to their proper position on the right.
d-L*.
..An,"&."-
Figure 3. A pyramidal format for the periodic table of the elements.
lllA 1
5
1,
WI
MI
19
20 C.
K
1119 IVB 22
21
Sc
VIB
VIIB
23
24
25 Mn
V
Ti
I
VB
I
Cr
I
1
r~~~~ IB IIB 26
27
Fo
I
Figure 4. Subgroups in an expanded form of the periodic table as used by
28
I
I
30
29
Ni
Co
I
31
Zn
Cu
A1 Ca
VA
IVA 1
8
14
1
7
1
8
1
9
I 1
He 1
0
1,
Si
p
32
33
6.
'
A
As
31
I
36 Kr
35
SI
Br
I
1
Deming. Volume 59
Number 6
June 1982
505
Table 1. Subgroup Designations In Periodic Tables in Textbooks
such as the Princeton Testing Lahoratories and the Department of the Navy. However, the situation is not as one-sided as it might appear from the above discussion. The Sarpent-Welch Scientific Company produces a wall chart showing a condensed fimn of the periodic table hased on a mdernizatim of the .Mendeleev condensed tahle hv Dr. Henrv Huhhard. a former Secretnrv of the National ~ i r e a of u standards, and first published h; the W. M. Welch Manufacturine Comnanv . in 1924. As shown i l l Figure 5, the Hubhard chart luld.; the transition eleme~~Ls of Croups Ill-\'I1 and their corresuondinr main " emuu. elements by A and B in a way opposite to t h 2 in the expanded Deming tahle (Fig. 4). A few well-known textbooks have included an expanded form of the periodic tahle as shown in Figure 6, just like the Deming tahle, hut using the A and B designation of subgroups for Groups 111-VII in the opposite manner. Further, the situation outside the United States seems to he quite different from that in this country. In Europe, for example. the condensed form of the ~ e r i o d i tahle c nersisted muchi1&ger than in this country, and ;hen the extenhecitable format finally did heome popular, A and B were applied to the Groups 111-VII elements as shown in Figure 6, i.e., in a way opposite to that in the Deming tahle (Fig. 4). In addition; occasionally the A and B designations were applied only to the fourth and later ~eriods.Onlv one use of A and B in the Ileming sense has lwen ol,wrved thr authors in the European literature (24J.The 1970 IUI'AC' lnorrnnic Nomenrla&re Rules reflect the usual European practiEe (25). Although these rules do not state so unequivocally, minutes of the meetings (26) and subsequent correspondence with Prof. K. A. Jensen, Chairman of the IUPAC Commission on Nomenclature of Inorganic Chemistry during the preparation of the 1970 Inorganic Rules, make it quite clear that the letters A and B were not to he used with elements of the first three periods (27). Further, Prof. Jensen strongly endorsed the view that the use of A and B was purely arbitrary and had no implication as to the character, transitional or characteristic, of an element. However, in spite of the IUPAC rules, our survey indicates that A and B are almost invariably given a t the top of each column.
-
The expanded format introduced hy Deming was not immediately adopted for use in textbooks or handbooks. However. over the vears more and more authors used it. and hv the 1976s the tahie shown in Figure 4 was by far the most co&& one used in this country. This is shown clearly by the results of our survey of 195 textbooks given in Table 1.Sanderson reported similar results in a study of textbooks published during the period 1961-1971 (12). Thus, American chemists, for the most part, were introduced to this form of the periodic tahle through Deming's textbook or through authbrs who adopted i t for their own texts. The "Deming tahle" first appeared in the "CRC Handbook of Chemistry and Physics" in 1934 (13) and in Lange's "Handbook of Chemistry" in 1944 (14); it appears in the current Merriam Webster's (15) and American Heritage (16) dictionaries, and in McGraw-Hill's "Encyclopedia of Science and Technology" (17) and "Dictionary of Scientific and Technical Terms" (IS), the "International Encyclopedia of Chemical Science" (19), and the "Condensed Chemical Dictionary" (20). Perhaps the most significant event to promote the use of the Deming tahle was its distribution by Merck & Co. in a convenient notebook size (8'12" X 11") as part of a company promotional campaign in the spring of 1928 (21). Today, they receive and fill approximately 200,000 requests for copies of the tahle each year (22). The tahle first appeared in the "Merck Index" in 1952 (23) (no tahle of any sort previously bad been included). Several scientific supply companies have provided both wall charts of the expanded periodic tahle and notebook- or pocket-size charts with the A and B desienation as used in the ~ e m i n tahle. g Notebook-size editions wgh the same subgroup designation also are available from a variety of other sources,
,
19
K
20
CI
lllA
IVA
VA
VIA
VllA
21 Sc
22 Ti
23 V
24
25 Mn
I
I
CI
I
I
,--VlllA 26 F
I
Figure 5. Subgroup designation in the Hubbard C h m
7
27 Co
I
28 Ni
I
1%
118
A
29
30 Zn
31
Cu
I
6s
Si 32
Gr
P 33 As
S
34 Y
Cl 35 Br
Ar 36
Kt
I
Figure 6. Subgroups in an expanded farm of the periodic table assigned according to Me 1970 IUPAC inorganic nomenclature rules (25)bui placed at ihe head of each column.
506
Journal of Chemical Education
Table 2.
Llterature Usage of A and B to Denote Element Subqrouos of the Periodic Table
The result of this difference in the use of A and B in the periodic tahle is utter confusiou. When reference is made simply to the Group VIA elements, for example, i t can be totally unclear, without additional information, which set of elements: Cr, Mo, W; or 0 , S, Se, Te, Po; or even just Se, Te, P o is under discussion. The severity of the problem was determined by retrieving all articles that had been abstracted for "Chemical Ahstracts" from 1972 throueh most of 1981 using terms like Group VA or Group VIB f o ; ~ r o u ~111-VII s in their titles and determining the subgroup of elements meant in each article. The results of this study are given in Table 2. I t is quite clear that there is indeed a great deal of confusion in the use of A and B in designating groups of elements in the periodic tahle. I t is noteworthy that in more than 10%of the Aicles studied, we could not determine the specific subgroup of elements discussed in the article without further information. In the late 1970's, a t least two of the companies supplying wall charts and notebook-size versions of the periodic table became aware that the IUPAC recommendation for the use of A and B was different from what they were using on their charts of the expanded form of the periodic table and decided to change to the IUPAC recommended usage. However. in doing sothey placed the letters a t the top of the respective columns. therebv i m ~ l v i n that z thev applied to the elements of the fir& threeberibds. ?he resu~iwdLanexpanded form of the periodic table shown in Figure 6, looking iust like the modern Deming tahle, but with the A and M subgroups in (houps 111-V11 exactly reversed. This change can be iustified histo;ically and (except for the implication that A andB apply to the first three periods) authoritatively according to current IUPAC recommendations (25). However, the change will not remove the existing confusion and will, in fact, very probably add to it. Unfortunately, even if one use of A and B were to be selected bv national or international ameement. there still would remain confusion in the designation of subgroups nf the periodic table, and it still could tnkc a lone time before it would be certain 'that almost everyone was-using the approved subgroup designation. There have been expressions of concern about this confusion in the use of A and H (28,29,30)and alwrnati\.e systems have heen propusd. Three of these alternatives are mentioned here briefly. Sanderson (30a)proposed the use of the letter M with the group numher for main-group (or characteristic) elements and T with the group number for transition elements in order to differentiate clearly between them. The elements Zn, Cd, and Hg were designated as M2' since they have complete inner shells of electrons and thus are not considered transition elements. One consequence of the arbitrary assignment of A and B in the Deming table is that, as IIB elements, Zn, Cd, and Hg have been classified erroneously as transition elements. The Sanderson designation has appeared in general reference works (29, 31), and another reference work uses the general headings "Main Groups" and "Transition Groups" (32).
The Swedish National Complittee for Chemistry has apnroved (33) . . a .nronosal bv A. Olander (34) to designate the vertical columns df the eipanded table by consecu~venumbers 0-17, beginning with the inert gas family. This notation has been used in at least one textbook (35).Of course, these numbers could be 1-18, ending with the inert gas family. There is a clear advantage to this proposal; the A subgroups according to the usage shown in Figure 6 wonld have the numbers 1-10 and the B subgroups 11-17. Thus, the elements N, 0 , and F (now belonging either to the VA, VIA, VIIA, or VB, VIB, VIIB subgroups) would belong to groups 15,16,17. The simple addition of a tens digit to the present group number would make this system very easy to learn. This proposal was submitted to the IUPAC Commission on Nomenclature of Inorganic Chemistrv" (27.36) . . . but was reiected in favor of the A and B usage recommended in the 19?0 Inorganic Rules (26). A proposal to designate subgroups by the letters s,p, d, and f , referring directly to electronic structure, was recently published (37). The author claims that the proposal "has met with student favor for didactic advantages and easy scientific correlations," when used in chemistry courses at the University of Milan. This proposal provides for designating the inner transition elements; neither Sanderson nor Olander do so. Our clear finding is that there is complete confusion in the use of A and B to designate subgroups of elements in the periodic table. It appears more and more certain that an entirely new. different designation is needed because a choice between the two methods now in cnmmon use cannot be made binding or unambiru~nmThe Nomenclature Committee of thr A C i Division ofinorganic Chemistry is studying the situation (38). The ACS Committee on Nomenclature, a t its meeting in November 1981, suggested some very important considerations to keep in mind in investigating alternatives to the A and B system. First, the system should be as clear and as simple as possible. The most vulnerable users of the periodic table are students, who see it, along with textbooks, as the sum total of the material universe. Hence, the needs of this audience must be given very high priority. Second, it is important t o decide whether the labeling should make a distinction between the characteristic and the transition elements, or whether a purely arbitrary labeling wonld suffice. (Of course, two systems could complement each other.) Third, the requirements of secondary publications and of the patent literature must be considered, particularly from the standpoint of data retrieval and legal consequences. Comments and suaeestions from groups and individuals, ... especially iron1 those artive in education, are earnestly solicited, and ma!. hr sent t t ~either of the author$ of this report: toDr. T. D. doyle, Chairman of the Nomenclature Committee, ACS Division of Inorganic Chemistry, Materials Chemistry Division, National Bureau of Standards, Washington, D.C. 20234; or to Dr. K. L. Loening, Chairman of the ACS Committee on Nomenclature, Chemical Abstracts Service, 2540 Olentangy River Road, P.O. Box 3012, Columbus, Ohio 43210. Literature=Ited (11 (a)venab~e, F. P.. he Deudopment af the ~eriodie~aw:chemical Publishing Co., Emton, PA, 189%(bl Qusm, G. N. and Quam, M. B., J. CHN. EDUC.11,2732: 217-%%$and 288-297 (1934): (el van Spronsen, J. W.."The PeriodieSyshof the ~ l ~ m e n t s ~lsevier, ," 1969: (dl ~ a z u r sE. , G., "Graphic Representations chemical of the periodic system,"he university of ~ h b s m apress. university, Alabama. Revised (2nd) Fd., 1974; (el Dostsl K. P..Isofopanproria,345-51: 377-83 (19801. (21 M~ndeleeu,D.,Z.Chsm.. 12.405 (1869). (31 wernqr,A,, RPI. DIE^ chsm G ~ S (s13~.914-921(19051; . (b) 38,2022-2027 (19051. (41 Perrin, P., C. R. Hebd. Seancrs Acod Sci., SO,.C, 809312 (19731. ,J,,Z Chpm,,P, 190(1s951, (6) B O ~ ~ . N . , Z phys.,9. . 1(19221. (7) B ~ ~ ~ ~ , T . ,M=&. P ~ 5~ [131,2637 I o ~ . (1882):~ A~W chrm . ~oc..20.9n434:935-98 (1898): Chrm. Newa, 77.157-180 (1898). (81 ~ ~ H ~..ch. ~m ~N ~t U t65 , w, . 19 (18921. (9) poster. L.s.,J. CHEM.EDUC.. 16.410 (193% (101 Demiw,H. G.."General Chemistry,"John Wilwand Sons.Inc.. N-York, lW3,and
(51
s~~uent~ditim. soddy,P., "chemistry of the ~ a d i E o I ~ ~ W Ipart ~ ~ 11. , "~h~ ~ a d i o ~ ~ e m m t s a n d
(111 (a,
Volume 59
Number 6 June 1982
507
istry and Phyrics, C. D. Hodgman. (Editor), 14th Ed.. Chemical blihing Co., 1934. Handbook 01 Chemistry, N. A. Lango, (Editor). 5th Ed., Handbook Publishern, Inc., Sandusky,Ohia, 1944. of the ~ w l i a k ~anguoge,P. B. Gove. Webrlar's Third Nrw ~ n t a r n o r i o~~ilr t i o n o r y (Editor), G. and C. MariamCo., 1976. The American Haritoge 1>ietiamry o/ the English Lawuoge, W. Morris, (Edzfor). Houghto" Miinin Co., 13orton. 1969. McCrom-Hill Engvlopedi o o/Scisnce end Technology, 4th Ed., MeGrsw-Hill, Now
Chemistry: 2nd Ed., Rutteteterths, London, 1971,~.11:111xAppl. Chem ,2.11 11971). 1261 IUPAC Commlaainn on Nomenclsture of Inorganic Chemlatry. Minute6216 and 6317 of the 1962 and 1963 Commission meetings, respectively. (27) Jensen, K. A.. Letter to the IUPAC InteidivisionalCommitteeon Nomenclature and Symbois and to the IUPAC Commission en Nomendatumof LnorganieChemistry. June 1973. (281 ~ e m l i u s W. , C., Laening, K. L., and Adams, R. M.. J. WeM. Enuc.. 48 191, 594
