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THE FABLE OF THE ATOMIC THEATER MILTON KERKER Clarkson College of Technology, Potsdam, New York
CmAcmmm events were occurrhg in the atomic world as a result of man's scientific investigations. It had been only a few years earlier that the electronic structure of the atom had been mastered by man, who was now advancing into the domain of the nucleus. The tension ran high as the electrons gathered in their atomic theaters to view man's latest efforts to comprehend the nucleus. Would he succeed again, and if so, to what use would he put his new knowledge? It might be well to say a few words about the seating plan of the theater in which the electrons assemble. This plan is represented in the figure. The seats, which are numbered, are arranged in blocks which form a short first row or period and then six successive wedgeshaped periods (rows). The theater is partitioned into a grid work of shells and subshells which are designated by K, L, M, N , 0,. P, Q, or 1, 2, 3, 4, 5, 6, 7, and s, p, d, f, respectively. A block of seats can be located by specifying any two of the three quantities-shell, subshell, and period-and also whether i t is on the right or left side of the theater. Thus a given block could be designated 4d (N or fourth shell, dth subsbell). The seats on the right side of the theater are odd numbered while. those on the left are even. The sequence of numbering is straightforward with two exceptions. The numbers increase with increasing period and from the outside of a period toward the
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center except for the s subshell of each period. In every case seats in this centrally located subshell are the lowest in their respective periods. The second exception involves seats 57 and 89 in the 5d and 6d blocks. These seats do not follow the regular pattern of increase from outside to center that is found in the rest of the theater. The numbers determine the order in which the electrons fill the seats when they enter the theater to observe an atomic drama. The electrons of each el* ment line up in single 6le outside the theater, and as the name of an element is called over the loud speaker system, its electrons file in, filling the seats in the designated order. Thus, when hydrogen is paged, one electron marches to seat number 1. The theater is then cleared before electrons of the nextelement areadmitted. Despite careful planning there is sometimes a mixup. On occasion, an electron which might be expected in one of the rear seats of subshell s is found in thed subshell of the same period such as occurs for chromium, copper, and several other elements. The regularity with which the electrons take their places has enabled man to- work out his theories of electronic structure and the periodic table, for these reflect the seating pian of the atomic theater. Thus the periods of the theater correspond to the periods of the periodic table and the analogues of the shells and subshells are found in the theory of electronic structure. Elements whose last electron is seated in the s subshell comprise the alkali and alkaline earth families. The main group elements are those whose last electron occupies a p subshell. The last electron of a halogen occupies the column of odd-numbered seats in the p subshell just across the aisle from the alkali metals while that of an inert gas occupies the column across from the alkaline earth metals. The transition metals are those whose last electron occupies a seat in the d subshells. Elements whose last electron is in a seat in the f subshell are members _ of the rare earth and actinide families. There are now sufficient seats in the theater to accommodate elements with atomic numbers as high as 118, and should the need arise the theat.er could easily be expanded by adding additional periods. For example, two additional periods could be added, including g subshells, which would accommodate 50 electrons each.
JOURNAL OF CHEMICAL EDUCATION
