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Unformatted text preview: 173 Chapter 12 Molecular Structure Review Skills 12.1 A New Look at Molecules and the Formation of Covalent Bonds The Strengths and Weaknesses of Models The Valence-Bond Model 12.2 Drawing Lewis Structures General Procedure More Than One Possible Structure 12.3 Resonance Internet: Resonance 12.4 Molecular Geometry from Lewis Structures Chapter Glossary Internet: Glossary Quiz Chapter Objectives Review Questions Key Ideas Chapter Problems Section Goals and Introductions Section 12.1 A New Look at Molecules and the Formation of Covalent Bonds Goals To describe the strengths and weaknesses of scientific models. To introduce a model, called the valence-bond model, which is very useful for describing the formation of covalent bonds. To explain the most common covalent bonding patterns for the nonmetallic atoms in terms of the valence-bond model. This section shows how the information learned in Chapter 11 can be combined with a model for covalent bonding called the valence-bond model to explain the common bonding patterns of the nonmetallic atoms. The most common of these bonding patterns were listed in Chapter 3, but now you have the background necessary for understanding why atoms have the bonding patterns that they do. Its important to recognize that although the valence bond model is only 174 Study Guide for An Introduction to Chemistry a model (and therefore a simplification of reality), it is extremely useful. You will find the information in Table 12.1: Covalent Bonding Patterns very helpful when drawing Lewis structures (the task described in Section 12.2). Section 12.2 Drawing Lewis Structures Goal: To show how Lewis structures can be drawn from chemical formulas. In Chapter 3, you learned to draw simple Lewis structures by arranging the atoms to yield the most common bonding pattern for each atom. This technique works very well for many molecules, but it is limited. For example, it does not work for polyatomic ions. This section describes a procedure for drawing Lewis structures from chemical formulas that works for a broader range of molecules and polyatomic ions. Section 12.3 Resonance Goal: To introduce a concept called resonance and show how it can be used to explain the characteristics of certain molecules and polyatomic ions. The Lewis structures derived for some molecules and polyatomic ions by the technique described in Section 12.2 do not explain their characteristics adequately. One way that the valence-bond model has been expanded to better explain some of these molecules and polyatomic ions is by introducing the concept of resonance described in this section. See the related section on our Web site: Internet: Resonance Section 12.4 Molecular Geometry from Lewis Structures Goals To show how you can predict the arrangement of atoms in molecules and polyatomic ions (called molecular geometry)....
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