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Molecular Geometry and Bonding Theory

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## Molecular Geometry and Bonding Theory

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**Molecular Geometry and Bonding Theory**Chapter 9 AP Chemistry**Molecular Geometry**• Molecular Geometry- general shape of a molecule as determined by the relative position of the nuclei. • The geometry and size of a molecule helps to determine it’s chemical behavior. • VSEPR- Valence-Shell-Electron-Pair-Repulsion model- predicts geometry based upon e’s around the central atom.**Electrons are kept as far away from one another as possible**– minimizing e pair repulsions Electron pairs are considered as being bonding or non-bonding (lone pairs) A multiple bond counts as a single bonding pair Electron pair geometry is described by the regions of e’s around the central atom Molecular geometry is a consequence of electron pair geometry. Principles of the VSEPR theory**Predicting Structures VSEPR**• Derive the Lewis Structure to the form AXmEn • A = central atom • X = atoms bonded to the central atom • E = lone pairs of e’s on the central atom • M = # of bonded atoms • N = # of lone pairs**Example**Electron and Molecular Geometry Linear Bond angles 180 Sp Hybrid Non-polar Electron Geometry Linear**Electron Geom. Trigonal Planar**• Molecular Geom. Trigonal Planar bond angles exactly 120 non-polar Bent bond angles aprox 120 polar molecule • Sp2 hybridized**Electron Geom.Trigonal Planar**• Molecular Geometry: AX3 (3BP or 2BP + 1LP) ex. 3bp NO3- <>**Examples Cont. 3bp**• BF3 <> <>**Examples Cont. 2bp + 1 lp**• Ex O3 (ozone)**Electron Geom. Tetrahedral**• Molecular Geom. Tetrahedral bond angles exactly 109.5 non-polar molecule, Trigonal pyramidal bond angles aprox. 109.5 polar molecule, Bent bond angles aprox. 109.5 polar molecule • Sp3 hybridized**Molecular Geometry: AX4 [4BP or (3BP + 1LP) or (2BP + 2LP)]**• Electron Geometry: AX4Tetrahedral**Example**• BrO3F, Perbromyl fluoride**Example**• NF3, Nitrogen trifluoride**Example**ClOF, Chlorosyl fluoride • H2O, Water,**Electron Geom. Trigonal Bypyramidal**• Mol. Geom. Trigonal Bypyramidal – bond angles ax. exactly 108 deg. eq. exactly 120 deg. Non-polar, See-Saw – bond angles ax. aprox. 108 deg. eq. aprox. 120 deg. Polar, T-shaped - bond angles ax. aprox. 108 deg. No –eq, Linear – bond angle exactly 180 non-polar. • All sp3d hybridized**Mol geo. Trigonal bipramidal**• AX5 [5BP or (4BP + 1 LP) or (3BP + 2LP) or (2BP + 3LP)] • 5bp**Example**• PCl5(gas phase), Phosphorous pentachloride**Molecular Geometry:AX4E1See-saw**• Example IF2O2-**Molecular Geometry:AX3E2T-structure**• Example ClF3**Molecular Geometry:AX2E3Linear**• Examole XeF2**Electron Geometry Octahedrial**• Mol geo. Octahedral – bond angle exactly 90 - non-polar, square pyramidal – bond angle aprox 90- polar, square planar- bond angle exactly 90 non-polar • Sp3d2 hybridized**Molecular Geometry: AX6Octahedral**• Example SF6**Molecular Geometry: AX4E1Pyramidal Planar**• Example XeOF4**Molecular Geometry: AX4E2Square Planar**• Example XeF4**Bond Angles**• Non-bonding pairs of e’s take up more space (att. by one nucli) than bonded e pairs • Double and triple bonds take up more space than single bonds (more e’s) • Volume occupied lone pairs > triple bonds > double bonds > single bonds**Forces**• Non-bonding pairs exert repulsive forces on adjacent e pairs and compress angles • Multiple bonds also exert repulsive forces and compress angles