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Molecular 9 Geometry and Bonding Theories Visualizing Concepts 9.1 Removing an atom from the equatorial plane of trigonal bipyramid in Figure 9.3 creates a seesaw shape. It might appear that you could also obtain a seesaw by removing two atoms from the square plane of the octahedron. However, one of the B-A-B angles in the seesaw is 120°, so it must be derived from a trigonal bipyramid. 9.2 (a) 120° (b) If the blue balloon expands, the angle between red and green balloons decreases. (c) Nonbonding (lone) electron pairs exert greater repulsive forces than bonding pairs, resulting in compression of adjacent bond angles. 9.3 Analyze/Plan. Visualize the molecular geometry and the electron domain geometries that could produce it. Confirm your choices with Tables 9.2 and 9.3. On Table 9.3, note that octahedral electron domain geometry results in only 3 possible molecular geometries: octahedral, square pyramidal and square planar (not T-shaped, bent or linear). Solve. (a) 2. Molecular geometry: linear. Possible electron domain geometries: linear, trigonal bipyramidal (b) 1. Molecular geometry, T-shaped. Possible electron domain geometries: trigonal bipyramidal (c) 1. Molecular geometry, octahedral. Possible electron domain geometries: octahedral (d) 1. Molecular geometry, square-pyramidal. Possible electron domain geometries: octahedral (e) 1. Molecular geometry, square planar. Possible electron domain geometries: octahedral (f) 1. Molecular geometry, triangular pyramid. Possible electron domain geometries: trigonal bipyramidal. This is an unusual molecular geometry which is not listed in Table 9.3. It could occur if the equatorial substituents on the trigonal bipyramid were extremely bulky, causing the nonbonding electron pair to occupy an axial position. 9.4 (a) 4e- domains (b) The molecule has a non-zero dipole moment, because the C-H and C-F bond dipoles do not cancel each other. (c) The dipole moment vector bisects the F-C-F and H-C-H angles, with the negative end of the vector toward the F atoms. 230