lecture 5 - best represented as a single resonance form....

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318M– Krische, Lecture 5: M - 09/08/08, Ch. 1, Covalent Bonding and Shapes of Molecules Today, we concluded our discussion on resonance structures. Resonance structures may be viewed as alternative representations of the electronic configuration of a fixed set of nuclei. An actual molecule is a resonance hybrid, i.e. the weighted average of its composite resonance structures. In principle, one can draw a multitude of resonance structures for any given molecule. However, as the term “weighted average” implies, some structures contribute more to the “real-life structure” than others. The rules for drawing resonance structures and assessing their relative importance are given below. Rules for Drawing Resonance Structures : Depending on the importance of the alternative structures, some molecules are best represented as combinations of resonance forms, while other molecules are
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Unformatted text preview: best represented as a single resonance form. The following generalizations regarding resonance structures can be made. • Resonance structures do not involve a change in the positions of the nuclei. • Resonance structures in which atoms have filled octets are more important than resonance structures with unfilled octets. However, the contribution of the non-octet structure increases as the difference in electronegativity between the atoms increases. • The more important structures are those involving a minimum of charge separation. • All contributing structures must have the same number of paired and unpaired electrons. • We concluded this lecture by reexamining the shapes of atomic orbitals....
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This note was uploaded on 02/09/2009 for the course CH 318M taught by Professor Bocknack during the Fall '08 term at University of Texas.

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