29 No. 2
The Periodic Table: Its Story and Significance
Eric Scerri, Oxford Univ. Press, 2006
xxii + 346 pp. ISBN 0195305736
reviewed by Herbert D. Kaesz
The form of the periodic table arouses strong partisan feelings. This was evidenced when the Commission on Nomenclature of Inorganic Chemistry of IUPAC decided to resolve the dichotomy of A/B usage in the Roman numeral column heads of periodic tables. The U.S. sequence differed from the European version, leading to an ambiguity in indexing. IUPAC incurred the wrath of individuals in both camps by proposing to replace the group headings I though VIII, A/B with the Arabic numbering 1 through 18. The flames of conflict have by now died down and for instructional purposes, most textbooks now show all three conventions in the column labels of their periodic tables. The column labels of 1 through 18, however, have taken hold in the scientific literature.
This story is one of the interesting accounts that can be found in a comprehensive treatise on the periodic system compiled by Eric Scerri, a philosopher of chemistry. The work begins with 14 introductory pages in which, among other topics, Scerri presents the concept of the elements in the abstract (termed “basic substances”). In the abstract view, the symbol of element represents nothing more than its atomic number. By contrast, and to some chemists, the symbols of the elements represent their actual form in nature as gases, liquids, or solids; in their actual form the elements are termed “simple substances.” One learns that Lavoisier renounced the metaphysical (abstract) concept, preferring to think of the elements in their tangible forms. In a modern sense, to emphasize the electronic structure of the elements in this manner, one may think of the symbol as representing an isolated atom of the element in a vacuum.
The first chapter is a useful overview, which is followed by a historical survey spread over chapters 2 to 5. The latter concludes with the acceptance of Mendeleev’s periodic system based on the predictions and accommodations that derive therefrom.
Chapters 6, 7, 8, and 9 deal, respectively, with the nucleus and the periodic table, the electron and chemical periodicity, electronic explanations of the periodic table developed by chemists, and quantum mechanics and the periodic table. The last chapter (10) is intriguingly titled, “Astrophysics, Nucleosynthesis, and More Chemistry” in which the author presents a survey of various forms of the periodic table that have been proposed over the years. Two of these are noted here by way of example.
Many years ago, Linus Pauling placed the symbols for hydrogen and helium at the head and center of the table with arrows indicating the chemical relationship of hydrogen to two families of elements, the alkali metals on the left and the halogens toward the right. The symbol for helium was connected by an arrow to the noble gas family as displayed in the now classic textbook College Chemistry (W.H. Freeman & Co., 1954). One popular current text adopts a version of the Pauling table by placing hydrogen in a central position over the other elements.
A greater departure from the classical Mendeleevian form of the periodic table is the left-step or Janet table based on the periodicity of values of (n+ l) (i.e., based on similarities of electronic structure of the isolated atoms). The first row of the left-step table consists of the symbols of the two elements whose (n+ l) value is 1, namely H and He. The second row consists of the symbols of the elements Li and Be whose (n+ l) value is 2; they are placed in positions immediately below H and He, respectively. The third row consists of elements whose (n+ l) value equals 3 and is composed of the element symbols B, C, N, O, F, Ne, Na, and Mg, right justified so that Na and Mg appear below Li and Be, respectively. The fourth row of elements with (n+ l) value equal to 4 is composed of the element symbols Al, Si, P, S, Cl, Ar, K, and Ca, also right justified, and so forth.
The column at the extreme right of the left-step table thus consists of the element symbols He, Be, Mg, Ca, Sr and Ba, departing from the standard form both in the position of this column at the far right of the table and because helium is at the head of the traditional group 2 metals. The left-step or Janet Table has not made it out of the circle of periodic table specialists. In my opinion, this is where it should stay because I believe it is more important to emphasize similarities in chemical properties than similarities in ground state electronic arrangements.
I recommend this interesting and well-written book to anyone interested in science and especially to individuals who are charged with the teaching of chemistry.
Herbert D. Kaesz <[email protected]>, a professor of chemistry emeritus at the University of California in Los Angeles, is an IUPAC Fellow. When active in IUPAC, Kaesz was a member of the Inorganic Chemistry Division, the Chemical Nomenclature and Structure Representation Division, and the Standing Committee on Chemistry and Education.
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