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General Chemistry Principles, Patterns, and Applications, 2011

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Chapter 9<br />

Molecular Geometry <strong>and</strong> Covalent Bonding Models<br />

In Chapter 8 "Ionic versus Covalent Bonding", we described the interactions that hold atoms together in chemical<br />

substances, focusing on the lattice energy of ionic compounds <strong>and</strong> the bond energy of covalent compounds. In the<br />

process, we introduced Lewis electron structures, which provide a simple method for predicting the number of bonds<br />

in common substances. As you learned in Chapter 8 "Ionic versus Covalent Bonding", the dots in Lewis structures<br />

represent the valence electrons of the constituent atoms <strong>and</strong> are paired according to the octet rule. As you will soon<br />

discover, however, the bonding in more complex molecules, such as those with multiple bonds or an odd number of<br />

electrons, cannot be explained with this simple approach. The purpose of this chapter is to introduce you to<br />

conceptual models used by chemists to describe the bonding in more complex compounds.<br />

An experimental image of a covalent bond. This image shows that the bonding electrons on the copper<br />

atom in Cu2O occupy dz2 orbitals that point toward the oxygen atoms located at the center <strong>and</strong> corners of a cube.<br />

In this chapter, we begin with a general method for predicting the structures of simple covalent molecules <strong>and</strong><br />

polyatomic ions; then we discuss the actual distribution of electrons in covalent bonds. We apply two distinct<br />

approaches for describing covalent bonds: (1) a localized model to describe bonding in molecules with two or more<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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