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  Home > JCE Print > Journal of Chemical Education > Issues > 2005  > November  >
In the Classroom
Predicting the Atomic Weights of the Trans-Lawrencium Elements: A Novel Application of Dobereiner's Triads
Sami A. Ibrahim
Division of Math and Science, San Jose City College, San Jose, CA 95128
Cover
November 2005
Vol. 82 No. 11
p. 1658
Abstract
In 1829, J. W. Dobereiner reported that some elements may be grouped into triads, groups of three elements that showed a smooth gradation in properties and in which the atomic weight and properties of the middle element lie midway between those of the other two elements. Dobereiner's assertion was doomed to failure because of two reasons; namely, many elements were yet undiscovered and because of the difficulty of fitting many of the known elements into recognizable triads. Unlike Mendeleev, Dobereiner did not use his triads predictively. However, Dobereiner's concept of triads provided Mendeleev with a method of estimating the properties of eka-boron, eka-aluminum, and eka-silicon. Moreover, Dobereiner's groupings remain useful for predicting the properties of the super-heavy elements (113–118) and for providing reasonable estimates of the atomic weights of all 16 trans-lawrencium elements. Indeed a total of 26 triads can now be recognized, thus attesting to the ubiquitousness of Dobereiner's assertion.
More Information
*  Citation
 Ibrahim, Sami A. J. Chem. Educ. 2005 82 1658.
*  Keywords
 Atomic Properties / Structure; First-Year Undergraduate / General; High School / Introductory Chemistry; History / Philosophy; Inorganic Chemistry; Main-Group Elements; Periodicity / Periodic Table; Textbooks / Reference Books; Transition Elements
*  History
 Created:
Last Updated:		 9/22/2005
9/29/2005
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