Dipole-Dipole Attractions (OpenStax Chemistry 2e)
Polar molecules have a partial positive charge on one side and a partial negative charge on the other side of the molecule—a separation of charge called a dipole. Consider a polar molecule such as hydrogen chloride, HCl. In the HCl molecule, the more electronegative Cl atom bears the partial negative charge, whereas the less electronegative H atom bears the partial positive charge. An attractive force between HCl molecules results from the attraction between the positive end of one HCl molecule and the negative end of another. This attractive force is called a dipole-dipole attraction—the electrostatic force between the partially positive end of one polar molecule and the partially negative end of another, as illustrated in Figure 1.
The effect of a dipole-dipole attraction is apparent when we compare the properties of HCl molecules to nonpolar F2 molecules. Both HCl and F2 consist of the same number of atoms and have approximately the same molecular mass. At a temperature of 150 K, molecules of both substances would have the same average KE. However, the dipole-dipole attractions between HCl molecules are sufficient to cause them to “stick together” to form a liquid, whereas the relatively weaker dispersion forces between nonpolar F2 molecules are not, and so this substance is gaseous at this temperature. The higher normal boiling point of HCl (188 K) compared to F2 (85 K) is a reflection of the greater strength of dipole-dipole attractions between HCl molecules, compared to the attractions between nonpolar F2 molecules. We will often use values such as boiling or freezing points, or enthalpies of vaporization or fusion, as indicators of the relative strengths of IMFs of attraction present within different substances.
Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019, February 14). Chemistry 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/books/chemistry-2e
Research Article: Dipole Source Localization of Mouse Electroencephalogram Using the Fieldtrip Toolbox
Date Published: November 14, 2013 Publisher: Public Library of Science Author(s): Chungki Lee, Robert Oostenveld, Soo Hyun Lee, Lae Hyun Kim, Hokun Sung, Jee Hyun Choi, Alexander Annala. http://doi.org/10.1371/journal.pone.0079442 Abstract: The mouse model is an important research tool in neurosciences to examine brain function and diseases with genetic perturbation in different brain regions. However, the … Continue reading
Date Published: April 11, 2013 Publisher: Public Library of Science Author(s): Mayya Tokman, Jane HyoJin Lee, Zachary A. Levine, Ming-Chak Ho, Michael E. Colvin, P. Thomas Vernier, Jose M. Sanchez-Ruiz. http://doi.org/10.1371/journal.pone.0061111 Abstract: Electroporation is the formation of permeabilizing structures in the cell membrane under the influence of an externally imposed electric field. The resulting increased permeability … Continue reading
Date Published: September 21, 2012 Publisher: Public Library of Science Author(s): Olga S. Ostroumova, Svetlana S. Efimova, Evgeny G. Chulkov, Ludmila V. Schagina, Peter Butko. http://doi.org/10.1371/journal.pone.0045135 Abstract: Recently, we showed that the effect of dipole modifiers (flavonoids and styrylpyridinium dyes) on the conductance of single amphotericin B (AmB) channels in sterol-containing lipid bilayers primarily resulted from … Continue reading