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  Home > JCE Print > Journal of Chemical Education > Issues > 2000  > June  >
In the Classroom
Melting Point and Molecular Symmetry
R. J. C. Brown
Department of Chemistry, Queen's University, Kingston, ON K7L 3N6, Canada

R. F. C. Brown
School of Chemistry, University of Melbourne, Victoria 3052, Australia

Cover
June 2000
Vol. 77 No. 6
p. 724
Abstract
In 1882 Thomas Carnelley observed that high molecular symmetry is associated with high melting point. The application of the rule to a number of different molecular crystals is discussed. The rule applies to different categories of crystal for different reasons, which can be explained by thermodynamic analysis. If the crystal is ordered, high melting point is usually due to high enthalpy change of fusion. If the crystal is disordered, high melting point is due to low entropy change of fusion. These effects can be displayed clearly on an enthalpy-entropy diagram.

See Letter re: this article.

More Information
*  Citation
 Brown, R. J. C.; Brown, R. F. C. J. Chem. Educ. 2000 77 724.
*  Keywords
 History / Philosophy; Liquids; Molecular Properties / Structure; Phase Transitions / Diagrams; Solids; Thermodynamics
*  History
 Created:
Last Updated:		 April 25, 2000
April 15, 2005
Link to Letter added (April 2004).
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