A Numerical Periodic Table and the f-Series Chemical
H e r n k von Marltens Oswio Santiago College and Facultad de Ciencias Fisicas y MatemAtlcas, Universidad de Chile. Casilla 2777. Santiago, Chile The periodic table of the elements has been one of the major contributions to the teaching of chemistry since the proposal of D. Mendeleev and L. Meyer, in 1869, for the orderine of the chemical elements. I t had the DurDose of system&ing the study of chemistry, because it &owed the nhvsical and narticularlv the chemical .ropert . ties of the eleme& to be rationalized. By understanding the periodic table students are able not only to understand redox reactions and the reasons for bondine between the elements, to name iust a few aspects, but al& to deduce, from their locations in the table, the nossible behaviors of other elements that they have not studied yet in detail. The periodic tables in current use have been overloaded with physical and chemical data that, though of high practical value, in attempting to provide the maximum usefulness heve unwittinelv masked the didactic character that the table inheren&"possesses. Moreover, these periodic tables have deformed the loeical arraneement that was visualized by their originators. Thus, for example, for reasons of space, those elements that beein filling their f orbitals are placed outside the proper sequential context. They are relegated to a second plane, therebv breaking the harmonic sequence and, whatis woise, hindering the study of the periodiE table as a unit and that of the f-period elements in particular. Technological advancesi are requiring the use of these elements either in their pure form, as compounds, or in alloys, compelling us to study them and give them the same kind of treatment granted to the other elements (see appendix). In order to have a periodic table in which all the elements can be easily visualized without losing track of the correlation with their atomic number, a numerical periodic system is proposed as a more didactic version of the electronic periodic table2. The numerical periodic system retains the periods of the periodic tables (Fig. 1) and specifies the sublevels, arranging them according to their relative e n e r g i e ~ ,that ~ is, just as they exist in the atoms (Fig. 2). The periods and sublevels are placed in an isosceles trapezoid (Fig. 3), which has on its left side, in square brackets, the symbol of the inert gas that starts the period, followed by the number that corresponds ~
~~
THEORETICAL
~
Flgure 1. Fllllng order for me dlffemntatomlcsubleve s ofmoat atoma. It stsns with sublsvs 1s and comlnues M sbwn by me arrow$.
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' Bound J. (Chemldldactlek)vrlje, Universltelt de Boeleloan 1083. ML-1081 HY. Amsterdam, The Netherlands. von Marltens, ti.; Goldschmldt,A. J. Chem. Educ., 1989.86.758761. ..
Thls order may be obtalned by adding the prlnclpal quantum number (n)and me azimuthal quantum numoer ( I ) that corresponds to each sublevel, i.e.. s (1 = 0). p (I = I), d ( 1 = 2). and f ( l = 3).
+
The sublevels fill In the order of n 1. For example, the 3d and 4s sublevels have (n 1) equal to 5 and 4, respectively; therefore 4s fillsbefore 3d. If two sublevels have the same (n I), the one of lower n fllls first. For example, 2p and 3s both have (n 1) = 3, but 2p fills before 3s.
+
+
+
See Ebbing. D. D. General Chemistry: Houghton Mifflin: Boston, 1984: p 170.
Figure 2. Real electronic fllllng order from which the relatlve energles of the ~~blevels were obtained. The atomic sublevels ere arranged In the order of Increasing energy content to that period; in the center are the sublevels, carrying a t the bottom right a number that corresponds to the relative energy value; and on the right there is the symbol of the inert element that ends the period, followed by its traditional electronic configuration. e the numerical periodic system is conBased on ~ i g k 3, structed by placingwithin each period, arranged in the order Volume 67 Number 7 July 1990
583
of increasing atomic number, the symbols of the elements. Under the symbols are the corresponding atomic numbers, and above the numbers of electrons in the last sublevels, which are identified by means of arrows starting from small rectangles that enclose the sublevek themselves and are located a t the center of the low isosceles trapezoids that
Figure 3. Location of lhe sublevel~in the corresponding periods of lhe isosceles hsparoid according to their relative energy. The periods correspond to me principal quantum numbers.
correspond t o each period (Fig. 4). Those elements called "elements with irregular electronic configuration", whose electronic sublevels are incomplete in terms of their relative energy content, are easily visualized because they carry an asterisk above the symbol. How TOUse the Numerical Periodlc System To illustrate the use of the numerical periodic system, let us determine the electronic configuration of the element whose atomic number is 35. This element is bromine (Br), which is located in period 4 (Fie. 5). and above its svmbol one finds the numbers 5, 10, tki 2 on the same linesas sublevels 4p, 3d, and 49, respectively. Therefore, the electronic configuration of its highest energy level (n= 4) is 4s23d'04pS, and its complete electronic 4s23d104p5.Since sublevels 4s and configuration is x,Br: [h] 3d are full, the valence electrons are those that belong to sublevel 4p. h o t h e r application becomes evident when one answers the question, what kind of element is platinum (Pt) from the standpoint of its electronic configuration? From its atomic number (2 = 78) (Fig. 6), and in accordance with the explanations given ahove for bromine, the electronic configuration platinum is [Xe] 6s'4f"5d%pp0. From the relative enerev content of each sublevel (6s = 6.4f = 7,5d = 7 and 6p =?), Pt should have completed its 6s sublevel with two electrons, and its electronic configuration should have been [Xe] 6s24f145d96p0.Because P t does not follow the rule of electronic filling from low t o high energy content, it is classified as an element with irregular electronic configuration. The numerical periodic system makes it possible to place all the chemical elements in a chart of sequential atomic numbers.
I Figure 4. The numerical periodic system. with all the elements arranged In the order of increasingatomic number.
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Journal of Chemical Education
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ing irregular electronic configurations to b e perceived a n d understood. I0
h.1 3
Kr
[MI
Appendlx Some applications off series elements in the form of compounds:
3da 4%' 49'
5
Field
Element
Use
Ceramic
Pr (praseodymium) Nd (neodymium) Sm (samarium)
Elecbonics
Pm (prometMml)
Ceramlc coloring Ceramic condensers Permanent magnets Nuclear batterles Computer memory Mercury lamps Color TV screens Nuclear batteries Nuclear batteries Nuclear fuel Neutron source Neutron source
Od (gadolinium)
Figure 5. Location of bromine h period 4 of
Me numerical periodic table.
Elemicily
Eu (europium)
Radioactlvlly
Pu (plutonium)
Pm (pmmthium) Th (thorium) Cf (californium)
Am (americium) Rn
CX.1 41*
6 ' 50'
Some applications off series elements in the form of alloys: Gd (gadolinium): Chromium steel, permanent magnets. Dy (dysprosium): Airplane alloys Er (erbium): Vanadium steel. Ce (cerium): Fluorescent tubes. Catalytic converters. As the element:
Flgure 6. Location of platinum in period 6 ol the numerical perlodic table.
It enables t h e determination of t h e electronic c o n f i p r a tion of t h e elements t o b e m a d e readily. It allows t h e reason for classifying some elements a s hav-
U (uranium) as nuclear fuel.
Blbllography - . . Eichinger, J. W. J. Chem.Edur. 1957.34,70-71. Ferneliua, W. C.;Powel, W. H. J. ChemEdvr. 1982.59,50&508. ~ o r v a t hA. , L. J. cham. ~duc. 1973.50.335-336. Mason, J. J Cham. Educ. 1988,65.11-20. Temg,W. K.J. Chem. Edue. 1972,49,59. TO. spmnsen, J. J. Chem.~duc. 1~~9.36.565-567.
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Volume 67
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