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General Chemistry Principles, Patterns, and Applications, 2011

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9.1 "Common Structures for Molecules <strong>and</strong> Polyatomic Ions That Consist of a Central Atom Bonded to Two or Three<br />

Other Atoms".<br />

AX 3 : CO 3<br />

2−<br />

1. The central atom, carbon, has four valence electrons, <strong>and</strong> each oxygen atom has six valence electrons. As you<br />

learned in Chapter 8 "Ionic versus Covalent Bonding", the Lewis electron structure of one of three resonance forms is<br />

represented as<br />

2. The structure of CO3 2− is a resonance hybrid. It has three identical bonds, each with a bond order of<br />

1<br />

1<br />

3<br />

. We minimize repulsions by placing the three groups 120° apart (Figure 9.2 "Geometries for Species with Two to Six<br />

Electron Groups").<br />

3. All electron groups are bonding pairs (BP). With three bonding groups around the central atom, the structure is<br />

designated as AX3.<br />

4. We see from Figure 9.3 "Common Molecular Geometries for Species with Two to Six Electron Groups*" that the<br />

molecular geometry of CO3 2− is trigonal planar.<br />

In our next example we encounter the effects of lone pairs <strong>and</strong> multiple bonds on molecular geometry for the first<br />

time.<br />

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

Saylor.org<br />

773

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