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9 Molecular Geometry Solutions to Exercises The fundamental feature that determines molecular geometry is the number of electron domains around the central atom, and the number of these that are bonding domains. Although and BF₄⁻ are both of the form the central atoms and thus the number of valence electrons in the two ions are different. This leads to different numbers of domains about the two central atoms. Even though both ions have four bonding electron domains, the six total domains around Br require octahedral domain geometry and square planar molecular geometry, while the four total domains about lead to tetrahedral domain and molecular geometry. (b) 8 4 pr X H H All molecules in the series have tetrahedral electron domain geometry and bent molecular structure. To a first approximation, the H-X-H angles will be 109°. Any variation will be due to differences in repulsion among the nonbonding and bonding electron domains. The less electronegative the central atom, the larger the nonbonding electron domain, the greater the effect of repulsive forces on adjacent bonding domains. The less electronegative the central atom, the larger the deviation from ideal tetrahedral angles. The angles will vary as > > H₂Se. 9.36 (a) domains around tetrahedral e- domain geometry, bent molecular geometry bond angle ≤109.5° 3 e- domains about N (both resonance structures), trigonal planar e- domain geometry bent molecular geometry bond angle ≤ 120° Both molecular geometries are described as "bent" because both molecules have two nonlinear bonding electron domains. The bond angles (the angle between the two bonding domains) in the two ions are different because the total number of electron domains, and thus the electron domain geometries are different. (b) domains around Xe, trigonal bipyramidal domain geometry, linear molecular geometry 240