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ERIC Number: EJ1028694
Record Type: Journal
Publication Date: 2013-Aug
Pages: 6
Abstractor: As Provided
ISSN: ISSN-0021-9584
The Periodic Pyramid
Hennigan, Jennifer N.; Grubbs, W. Tandy
Journal of Chemical Education, v90 n8 p1003-1008 Aug 2013
The chemical elements present in the modern periodic table are arranged in terms of atomic numbers and chemical periodicity. Periodicity arises from quantum mechanical limitations on how many electrons can occupy various shells and subshells of an atom. The shell model of the atom predicts that a maximum of 2, 8, 18, and 32 electrons can occupy the shells identified by the principle quantum numbers n = 1, 2, 3, and 4, respectively. The numbers 2, 8, 18, and 32 are shown in this work to be related to the triangular numbers from mathematical number theory. The relationship to the triangular numbers, in turn, suggests an alternate method for arranging elements in terms of periodicity. The resulting three-dimensional "periodic pyramid" is highly symmetric in shape. Just as is true in the modern periodic table, each layer of the periodic pyramid can be separated into shell and subshell contributions. Examining the pyramid's structure is arguably a pedagogically useful activity for college-level introductory or physical chemistry students, as it provides an opportunity to further ponder the shell model of the atom and the origins of periodicity. The connections to number theory are used to show that the outermost subshell of a given shell contains (2n - 1) orbitals.
Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society. 1155 Sixteenth Street NW, Washington, DC 20036. Tel: 800-227-5558; Tel: 202-872-4600; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Research
Education Level: Higher Education; Postsecondary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A
Grant or Contract Numbers: N/A