A New Spiral Form of the Periodic Table EDGAR I . EMERSON Trinity College, Hartford, Connecticut
T
HE PERIODIC chart should reflect the periodic law as accurately as possible. The many attempts to overcome the defects recognized in Mendeleeff's table have resulted in various modifications of essentially two types of periodic arrangements of the elements-the discontinuous and the continuous. The continuous arrangements take the forms of plane spirals or spirals wound around cones or cylinders (5.7). These continuous representations of the elements appear to offer the most logical arrangement when considered from the point of view of the periodicity of the properties of the elements as well as from the point of view of the general features of atomic structure. While the continuous three-dimensional types of the periodic system of elements are the most nearly perfect they suffer by plane representation as on a printed page. The plane spiral seems to offer the most promising form for portraying the periodic law in a twodimensional diagram.
opposed2on the spiral, and (6) to emphasize the great difference in the properties of the groups immediately to the right and left of the noble gases.3 The break between the periphery of the loops of the spiral along the spaces allotted to magnesium and the transition metals of the fourth period serves to indicate that beryllium and magnesium are not to be considered as a kind of prototype of these groups. In the same way the break between the spirals of periods 1 and 2 shows that hydrogen is not to he considered as a kind of prototype of any of the groups other than IA and VIIA.
c PAMILIES In order not to depart too far from the convention of lettering the subgroups or families the letters A and B have been retained. All of the subgroups designated by A contain elements formed when the newly added or "differentiating" electron4 entered the outer shell. The outer shell of anv series or oeriod miabt be called the A shell. The B families contain the elements THE CONSTRUCTION OP THE SPIRAL formed when the differentiating electron entered the The spiral is constructed as if the spaces assigned to next to outer shell which is designated as the B shell. the elements were elastic segments of a band which is Following the terminology used here the shdl twice spiraled to produce the form of the chart shown in removed from the outermost is called the C shell. Figure 1. Each of the segments occupies 18' except The rare earths are formed when the differentiating those for hydrogen, beryllium, magnesium, and the electron enters the C shell and, to comply with this noble gases. The reasons for these exceptions are dis- terminology, the rare earth group might be called the cussed later. Two separations occur along the pe- C group. The basis for the nomenclature used here, riphery of the loops of the spiral, each separation em- which gives meaning to the subgroup letters, rests phasizing series or periods of different lengths. The entirely on the manner in which anatom is formed from first period contains two elements starting with element the preceding one. number 0 and ending with number 1, thespaceallotted to The elements in the A groups are called the rephydrogen being spiraled around the apex of the wedge resentative elements because, as Eble (2) states, they formed by the noble gases.' The second and third "include metals, nonmetals, inert elements, liquids, periods contain eight elements each, while of the re- and gases." The term, transition, is retained for the maining four periods two contain eighteen, period six metals of the B groups because in that part of a series contains the rare earths, and period seven 1s incom- in which these elements are found there is a transition plete. ¶ I n some of the author's charts a SDace of 22.5' is allowed The spiral was wound counterclockwise so as to pregroup. With such an arrangement the A and B groups are sent the more familiar subgroups in the same order as each diam&icalIy opposed on the spiral but in periods 4.5, and 6, in the conventional tables. With these the group Group VIIIB contains 3 elements all in the space of 22.5'. In other arraneements hv the author a SDace of 20' is allowed as in numbers increase from left to right. Caswell's s&al (1). he arrangement in Figure 1 is probably The space of 54" was allowed the noble gases (a) to more similar to Caswell's than to any other. Color on some of emphasize the fact that these elements are the pro- the author's charts has been used to indicate similarities of the totypes of any given series, (b) to permit equal assign- groups. 8 The halogen group to the left is the most electronegative and ments of space, 18", for the other elements and a t the the most nonmetallic, whereas the alkali metals group to the right same time have the A and B mouos diametricallv is the most electropositive or most metallic. It is a singular fact
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Element 0, possibly neutron, is considered as a noble gas. Because of its probable chemical inertness and extreme density it might not be detected in a sizable amount until some future scientist succeeds in sampling the center of the earth. 1
THE A, B. AND
that some of the properties of these two such different groups are bridged by a single element, hydrogen. 'The t a m dzffercntiating electron was used by Ehle (2) because this newly added electron differentiates an atom from the one possessing the next lower atomic number.
111
112 from a stable electronic configuration of 8 to one of 18, that the peripheral similarity reaches a maximum in the rare earth group where the A and B shells contain or, in the case of the rare earths, from 18 to 32. The properties of the elements in the A group are the same number of electrons. On the chart presented here the A and B groups are similar radially, while in the B and C groups the properties are similar peripherally. Since the number of separated by the double lines on the spiral and the C electrons in the outer shells is the most important single p u p is shown as a separate segment. If one were not determinant of chemical properties it is not surprising concerned by plane representation the rare earths
could be represented as a loop or bulge above the surface of the plane. One might imagine that this group of metals is a sort of hernia of nature that has been excised so as to maintain a flat surface. The A and B groups are diametrically opposed on the spiral and it is interesting to note that in those groups close to the line dividing the transition metals from the representative elements the A and B families are similar while the groups further removed from the dividing line are dissimilar. Compare the properties of the A and B families of Groups 11, 111, and IV, and then the properties of the A and B families of Groups VI, VII, and VIII. A properly colored chart helps to emphasize this point.
electrons has dropped back to the B level. These elements could be indicated on the chart by asterisks in the manner of Gardner (3). In palladium apparently both of the A shell electrons dropped back to the B level. However, as Gardner points out, since most of the transition elements "give divalent ions, the point is of minor interest chemically." THE NORMAL ELEMENTS AND COLORED IONS
The basis for the division of the elements into the A, B, and C groups in this chart is the manner in which the elements were formed. Another scheme might have been based on the level of the electrons involved in chemical reactions. Wherever chemical activitv is displayed by the elements of the A groups only the THE ELECTRONIC STRUCTURE OF THE ELEMENTS outer shell electrons are involved, never the B and C This continuous arrangement of the elements is shell electrons so far as is known. These elements capable of portraying the electronic structure of an might be called normal in contradistinction to abnormal atom in so far as the number of electrons in the various for elements where electrons in the next to outermost shells is concerned. The number of electrons in the shell may be involved. The transition elements A and B shells is read directly from the chart. For the including the rare earths are abnormal except for silver, elements of the A families the B shells have a com- zinc, cadmium, and mercury. These excepted eleplete complement of electrons, 8 for groups I and 11, ments form a compact group in the table and might except for period 1 which has no B shell and period be called the "normal transition elements." This 2 in which the helium configuration of 2 is found. In name gives a clue to the manner of formation of these the other A groups the B shell is complete with 18 elements as well as to the behavior of the electrons in electrons except for period 2 in which there are 2 chemical reactions electrons in the B shell and period 3 in which there are It should be noted that the groups containing the 8 electrons in this sheU. abnormal elements rest on the separation of the spiral To find the electronic configuration of an element, along the periphery of the space allotted to magnesium. read from the segments of the circles enveloping the This separation which underscores the abnormal groups spiral the number of electrons in the A and B shells. also marks those in which the elements may form colThen, starting a t the element in auestion, move uxru ---a :--IUIL~. clockwise in th; series to the noble gas which starts the THE POSITION OF HYDROGEN period. At the right-hand side of the segment contaming the noble gas, the letter(s) of the s h e W will Hydrogen finds a definite and logical space in the be found. Thus manganese set down and 13. table and its relation to lithium and fluorine is clearly Then a t the right of the argon segment it is found that shown. With elements in the short ~eriodsloss or disthe A is and the is M. Thus, the placement of electrons from an atom tends to result in a shell contains 2 electrons while the M shell contains 13. structure having the of The number of electrons in the other shells of manganese noble gas which starts the period, while attractionof is found by setting down the number of electrons in the electrons by an atom tends to produce the electronic L and K shells. These are found in the left-hand side configuration of the noble gas ending the series (or Of thewedgecOntainingthenoble gases,68andK-2. starting the next one). These facts are clearlv shown of the elements, inclucmg ~h~ Another example will illustrate the method further. for Mercury is found from the chart to contain 2 electrons electronic structure of hydrogen either as H+ or Hin the A and IS i~ the finds a counterpart in the structure of element 0 or 2. in the series to xenon we oass the star indicatin~the rare earths. Thus we know that the C shell has 32 THE POSITION OF BERYLLIUM AND MAGNESIUM electrons. The A, B, and C shells are found to be the It is a controversial question as to whether beryllium P, 0, and N shells, respectively, as indicated a t the and magnesium belong in the zinc or in the alkaline right-hand side of the xenon segment. The number earth group. From the point of view of atomic of electrons in the other shells of mercury are found structure and properties these elements could belong from the left-hand side of the noble gas segments to be to either Group IIA or IIB. From the chemical prop18 in the M, 8 in the L, and 2 in the K shell. The com- erties it is difficult to determine whether magnesium plete configuration for mercury is should be placed with zinc or calcium. In analytical K L M N O P reactions magnesium is closer to calcium than i t is to 2 8 18 32 18 % zinc, while on the other hand magnesium, beryllium, Several of the transition metals contain only one and the zinc group form no well-defined hydrides electron in the A shell because one of the two outer whereas the elements of the calcium group do. Thus it
hydrogen,
seemed advisable to stretch the space allotted to the I t is perhaps significant that magnesium and berylelements beryllium and magnesium, thus placing them lium bridge the subgroups of Group I1 which is the on the chart as sort of prototypes of the elements of only p u p in which all of the elements in both of the Groups IIA and IIB. This arrangement implies no families are normal, a fact which undoubtedly accounts break between the second and third group and a t the for the diiculty experienced in placing these elements same time stresses the similarity of magnesium to both in a chart. If the mode of formation of these elements calcium and zinc. is the consideration, they should be placed in the A The separation along the periphery of the space group since the differentiating electron entered the occupied by magnesium begins a t Group IIIB and, outer shell. However, from the point of view of the continuing counterclockwise, ends on Group IIB. electrons involved in chemical reactions, those in the It is to be noted that this separation embraces all of A shell, these elements could belong to either the A the abnormal groups. One might wonder whether this or B group. And finally, since the reactions of the is a purely fortuitous fact or whether i t has a theoretical organometallic compounds of beryllium and magnesium foundation. are similar to the organometallic compounds of the
BERYLLIUM. AND MAGNESIUM AND FIGWRB 2.-ANALOGY BETWEEN HYDROGEN,
THE
TRANSITION METALS(Note that the
assigned to these elements are all in the same general area of the chart.)
Epaccs
zinc group and not to the alkaline earth group, these elements should be associated with Group IIB. If one retains the loops of the spiral (Figure 2) but removes the segment lines along with the symbols and atomic numbers of the elements in the area of the transition elements, a pattern is produced which makes one wonder why three of the elements difficult to place properly on a periodic table, hydrogen, beryllium, and magnesium, should occupy positions on the loops of the spiral in the same general area as the transition elements. Are these three elements in periods 1, 2, and 3 in some way analogs of the transition elements of periods 4, 5, 6, and 7? VALENCE
Oxides and Double Periodicity. The valence with respect to oxygen starts a t 1 with Group IA and increases counterclockwise to a maximum of 8 with Group VIIIB. Then continuing in the same direction the valence starts with 1 in Group IB and reaches a maximum of 7 in Group VIIA. The same general formulas for the oxides are found diametrically opposed on the spiral. Ifydrides. The elements fonning well-defined hydrides are located immediately to the right or left of the noble gases. In general the hydrides to the right, in Groups IA and IIA, are saltlike solids, while those to the left are nonpolar liquids or gases when dry. The singular role of hydrogen should again be noted. Considered as its own hydride, hydrogen bridges the polar and nonpolar hydrides. It can be observed that with a spiral arrangement of this type elements forming hydrides are all found in a confined area on the chart.' THE METALS AND NONMETALS
The nonmetals and metalloids are separated from the metals by the dotted lines. As in the case of the hydrides it will be seen that the nonmetals are confined to a limited area of the chart.
on a spiral chart than on the conventional tables or on the more recent ones where the elements are not arranged according to atomic numbers (2, 4, 6 ) . CONCLUSION
The term periodic table, or chart, means to most chemists a compact arrangement of the elements so ordered that they portray the periodic law. a law based on atomic numbers. That the properties of the elements are intimately bound with the number of outer electrons of the atom cannot be doubted. Nature built the atoms of the elements in an orderly way by increasing, from one element to the next, the number of electrons by one. Were the natural laws such that these newly added electrons all entered and remained in one shell the properties of the elements would be functions of the total number of electrons, hence direct functions of the atomic number. But the properties are periodic functions of the atomic numbers, and the reason for this fact is found in the periodic occurrence of similar outer orbital structures. If an arrangement of the elements is made according to the natural sequence of atomic numbers and the periodic occurrence of similar outer orbital configurations as well as the periodic occurrence of properties, it should faithfully reflect the periodic law. The spiral arrangement, as has been shown here, is capable of this reflection, and greater attention to truly continuous charts of the elements is urged as a means of discovering new relationships of the elements as well as a means of interpreting the periodic law. ACKNOWLEDGMENT
The author expresses his sincere thanks to Mr. John C. E. Taylor, Department of Art, Trinity College, for his interest and help in drawing the chart. LITERATURE CITED
(1)
CASWELL, "A new graphical arrangement of the periodic table," Phyr. Rm.. [2], 34, 543 (1929).
(2) EBLE."Atomic structure and the periodic table,"
RADIOACTIVITY
All of the naturally occurring radioactive elements are found along the outer loop of the spiral. To determine the end product of a radioactive series move clockwise two atomic numbers for each alpha particle lost (one number for each positive charge) and move counterclockwise one atomic number for, each beta particle lost. These changes are more easily followed
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The alloy type of hydride has not been considered here.
J. CHEM.
EDUC., 15, 575 (1938). (3) Gan~mn,"A table of electronic configurations of the ele-
,,
ments," Nature, 125, 146 (1930). periodic table," CHEm, 393 (1939); "Electronic configuration as the basis of the periodic table," ibid., 20, 21 (1943). (5) QUAM AND QUM, "Tmes of Paphic classifications of the elements," ibid., 11, 288 (1934). (6) VANRYSSELBERGHE, ,'A new periodic table." ibid., 12, 474 (1935). (7) Zm~czmsm,"Periodic system of the elements in a new form,'' Oid., 14, 232 (1937). (4) Lwen,
CORRECTION I N DR. HAUSER'S article in our January number, "Synthetic rubber and plastics," 700,000 long tons were
incorrectly translated into pounds. This conversion, in the 7th line, should have been "1,500,000,000 pounds."
