Molecular Interpretation of Surface Tension

Throughout this chapter we have dealt with surface tension from a phenomenological point of view almost exclusively. From fundamental perspective, however, descriptions from a molecular perspective are often more illuminating than descriptions of phenomena alone. In condensed phases, in which interactions involve many molecules, rigorous derivations based on the cumulative behavior of individual molecules are extremely difficult. We shall not attempt to review any of the efforts directed along these lines for surface tension. Instead, we consider the various types of intermolecular forces that exist and interpret 7 for any interface as the summation of contributions arising from the various types of interactions that operate in the materials forming the interface. 

10a Some Molecular Interactions Important in Interpreting Interfacial Phenomena 

To develop the above idea, several broad categories of molecular interactions should be considered. 

Metallic bonding A sea of mobile electrons shared by the atoms of a metal contributes to the attraction between metal atoms in bulk samples. 

Permanent dipole interactions Polar molecules have relatively positive and negative regions. Regions of opposite charge on different molecules result in an attraction between these molecules. Molecules must possess a permanent dipole moment to display this effect. 

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