| Why has it taken so long for textbook authors to select one standard form of periodic table for use in introductory and general chemistry textbooks? The restriction of such tables to the flyleaf requires avoidance of the long forms, but the resultant shortening process requires the vivisection and subscripting of the lanthanoids and actinoids. This subscripting would not have presented a problem had all authors chosen the same cuts. As we know, they did not.
The result is that periodic tables differ from text to text, on the Internet, and around the world, no doubt confusing students and frustrating teachers. Researchers who use the table for its predictive power and organization can, and should, use any form of the table that they find most helpful in their research, but for educational purposes must we impose upon the novice the rather trivial reasoning by which we do our slicing for the three major versions? The beauty of the periodic table does not lie in its exceptions, but in its symmetry.
Three forms of the flyleaf periodic table are common:
- The lanthanoids and the actinoids are set below the table similar to a footnote. There are two rows of fourteen boxes, the first beginning with La, the lower one beginning with Ac. Lu and Lr are in the main table under Sc and Y. We call this the 14LaAc form.
- The footnote of 14 lanthanoids and actinoids begins with Ce and Th. La and Ac lie under Sc and Y in the main table. We call this the 14CeTh form.
- The lanthanoids and actinoids begin with La and Ac but continue through Lu and Lr. This makes a 15 column footnote and leaves a vacancy in the two positions under Sc and Y. We call this the 15LaAc form.
Out of curiosity as to which form was most popular over our combined careers we pooled our general chemistry text collections so that we might survey the trends from 1948 to 2008. Using this random selection of 35 texts we found the information that is depicted in Figure 1.
Figure 1. Use of the three kinds of periodic tables in selected textbooks published between 1948 and 2008. Text with 15LaAc on the flyleaf, but 14CeTh in the text is labeled a. The newest textbooks (labeled b) have these future copyright dates for reasons unknown.
As no doubt others have done we wondered why the chemistry education community has not standardized by choosing one of the three extant forms. We recalled the 1982 article in this Journal in which Jensen’s definitive arguments settled this once and for all (1). Jensen chose 14LaAc as the answer. This seems apparent in the chart. However this did not standardize anything. It multiplied the choices. Then we found that in 2005 the IUPAC had decided this question. The chosen standard subscripted-form table is 15LaAc (2).
We prefer the 15LaAc table as the flyleaf table. Our question now is when can we expect authors to become aware of this forward step and change their next editions? We have begun to hope that teachers can expect 15LaAc to be in their text, on the Internet, and also on the classroom wall.
Literature Cited
- Jensen, William B. J. Chem. Educ. 1982, 59, 634.
- IUPAC Periodic Tables (accessed Feb 2008).
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