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Chapter6

# Surface the geometry which applies to a particular

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Unformatted text preview: pter 13 56 VSEPR Theory: The Basic Idea VSEPR Electron pairs in the valence shell of an atom repel each other on a spherical surface formed by the underlying core of the atom. surface The geometry which applies to a particular arrangement is determined by the The steric number (SN) of the central atom. The favored geometry is the one that steric of minimizes electron − electron repulsions. electron “Steric” means “having to do with space.” The steric number of an atom in a .” molecule can be determined by drawing the Lewis structure of the molecule drawing and adding the number of atoms that are bonded to it and the number of lone pairs that it has. pairs SN=number of atoms bonded to the central atom + number of lone pairs on the central atom 12/04/09 Zumdahl Chapter 13 57 Geometry and Steric Number • • • • SN = 2 SN = 3 SN = 4 SN = 5 Linear, 180° 180 Trigonal planar, 120° 120 Tetrahedral, 109.5° 109.5 Trigonal bipyramidal 90° (equatorial − axial) 90 120° (equatorial – equatorial) 120 (equatorial Lone pairs occupy equatorial positions in preference to axial positions. • • • SN = 6 Octahedral, 90° 90 SN for Double and Triple bonds count the same as single bonded atoms atoms When lone pairs are present, the situation is more complicated (with When regard to bond angles) due to varying repulsive forces regard Lone pair vs. lone pair > Lone pair vs. bonding pair > Bonding pair vs. bonding pair Lone bonding 12/04/09 Zumdahl Chapter 13 58 Examples with no Lone Pairs on the Central Atom 12/04/09 Zumdahl Chapter 13 59 SN= 2 = 2 bonded atoms + no lone pairs Geometry is linear 12/04/09 Zumdahl Chapter 13 60 SN= 3 bonded atoms + no lone pairs Geometry is Trigonal planar 12/04/09 Zumdahl Chapter 13 61 SN= 4 bonded atoms + no lone pairs = 4 Geometry is tetrahedral Geometry 12/04/09 Zumdahl Chapter 13 62 SN= 5 bonded atoms + no lone pairs = 5 Geometry is Trigonal bipyramidal Geometry 12/04/09 Zumdahl Chapter 13 63 SN = 6 bonded atoms + no lone pairs = 6 Geometry is octahedral Geometry 12/04/09 Zumdahl Chapter 13 64 3 Example: NH NH SN = 3 bonded atoms + 1 lone pair = 4 Geometry is Distorted tetrahedral Geometry 12/04/09 Zumdahl Chapter 13 65 2 Example: H O SN = 2 bonded atoms + 2 lone pairs = 4 Geometry is Distorted tetrahedral Geometry 12/04/09 Zumdahl Chapter 13 66 12/04/09 Zumdahl Chapter 13 67 Chapter 6 Bonding; General Concepts 6.1 Types of Chemical Bonds 6.2 Electronegativity 6.2 6.3 Bond Polarity and Dipole Moments 6.3 6.4 Ions: Electron Configurations and Sizes 6.5 Formation of Binary Ionic Compounds 6.5 6.6 Partial Ionic Character of Covalent Bonds 6.7 The Covalent Chemical Bond: A Model 6.8 Covalent Bond Energies and Chemical Reactions 6.9 The Localized Electron Bonding Model 6.9 6.10 Lewis Structure 6.11 Resonance 6.11 6.12 Exceptions to the Octet Rule 6.13 Molecular Structure: The VSEPR Model 6.13 12/04/09 Zumdahl Chapter 13 68...
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