Melting Point and Molecular Symmetry

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 thermodynam...

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Bibliographic Details
Published in:Journal of chemical education 2000-06, Vol.77 (6), p.724
Main Authors: Brown, R. J. C, Brown, R. F. C
Format: Article
Language:English
Subjects:
Alkanes
Chemistry
Climate
Evidence
Experiments
Melting
Melting point
Melting points
Methane
Molecular Structure
Organic Chemistry
Physics
Scientific Concepts
Temperature
Textbooks
Thermodynamics
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Summary: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.
ISSN:0021-9584
1938-1328
DOI:10.1021/ed077p724