Asia-Pacific Forum on Science Learning and Teaching, Volume 5, Issue 1, Article 3 (Apr., 2004) Daniel Kim Chwee TAN and Kim Seng CHAN An analysis of two textbooks on the topic of intermolecular forces Previous Contents Next

Results and Discussion

Polarity of a bond/molecule and permanent dipole-permanent dipole interactions

There seemed to be a lack of integration between the concepts presented in the topic of intermolecular forces and those in topic such as atomic structure and valence bond theory. For example, both Ramsden and Hill and Holman did not attempt to discuss the polarity of a molecule from a net dipole moment perspective using the valence shell electron pair repulsion (VSEPR) theory. Students needed to use the VSEPR theory to deduce the shape, and from there, consider the vector sum of each of the individual dipole moments (qualitatively only, no calculation required) to determine whether the molecule was polar. If the dipole moments in a molecule did not cancel each other out, there would be a separation of both the positive and negative centers, and the molecule would be considered to be polar. If a molecule had a net dipole moment, there would be permanent dipole-permanent dipole interactions in addition to the instantaneous dipole-induced dipole interactions. If the molecule was non-polar, then there would only be instantaneous dipole-induced dipole interactions present. This would enable students to appreciate one rationale of learning the VSEPR theory. It would also be meaningful if the concept of dipole moment with the concept of electronegativity (which could also be related to the concepts of nuclear charge, shielding by inner shell electrons and distance from the nucleus). This would integrate the concepts from both the topics of atomic structure and intermolecular forces.

 

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