Secon 9.1 Hybridiza)on and the Localized Electron Model Chapter 9 Molecular Geometry and Bonding Theories Secon 9.1 Hybridiza)on and the Localized Electron Model VSEPR Model § VSEPR: Valence Shell Electron-Pair Repulsion. § The structure around a given atom is determined principally by minimizing electron pair repulsions. Copyright © Cengage Learning. All rights reserved 2 Secon 9.1 Hybridiza)on and the Localized Electron Model Steps to Apply the VSEPR Model 1. Draw the Lewis structure for the molecule. 2. Count the electron pairs and arrange them in the way that minimizes repulsion (put the pairs as far apart as possible. 3. Determine the posi$ons of the atoms from the way electron pairs are shared (how electrons are shared between the central atom and surrounding atoms). 4. Determine the name of the molecular structure from posi$ons of the atoms. Copyright © Cengage Learning. All rights reserved 3 Secon 9.1 Hybridiza)on and the Localized Electron Model Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB2 2 0 linear linear Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB3 3 0 planar planar Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB4 4 0 tetrahedral tetrahedral Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 5 0 trigonal trigonal 5 bipyramidal bipyramidal Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB6 6 0 octahedral octahedral Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model Arrangements of Electron Pairs Around an Atom Yielding Minimum Repulsion Copyright © Cengage Learning. All rights reserved 9 Secon 9.1 Hybridiza)on and the Localized Electron Model lone-pair vs. lone pair lone-pair vs. bonding bonding-pair vs. bonding repulsion > pair repulsion > pair repulsion Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 3 0 3 planar planar trigonal AB E 2 1 bent or 2 planar .. V-shaped Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB4 4 0 tetrahedral tetrahedral trigonal AB E 3 1 tetrahedral 3 pyramidal Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB4 4 0 tetrahedral tetrahedral trigonal AB E 3 1 tetrahedral 3 pyramidal AB2E2 2 2 tetrahedral bent or V-shaped Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model Structures of Molecules That Have Four Electron Pairs Around the Central Atom Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 5 0 5 bipyramidal bipyramidal trigonal distorted AB E 4 1 4 bipyramidal tetrahedron Copyright © Cengage Learning. All rights reserved Secon 9.1 Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 5 0 5 bipyramidal bipyramidal trigonal distorted AB E 4 1 4 bipyramidal tetrahedron trigonal AB E 3 2 T-shaped 3 2 bipyramidal Copyright © Cengage Learning. All rights reserved Secon 9.1 VSEPR Hybridiza)on and the Localized Electron Model # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 5 0 5 bipyramidal bipyramidal trigonal AB E 4 1 See-saw 4 bipyramidal trigonal AB E 3 2 T-shaped 3 2 bipyramidal AB E 2 3 trigonal linear 2 3 bipyramidal Secon 9.1 Hybridiza)on and the Localized Electron Model Structures of Molecules with Five Electron Pairs Around the Central Atom Copyright © Cengage Learning. All rights reserved 18 Secon 9.1 Hybridiza)on and the Localized Electron Model Hybridizaon and the “Localized Electron” Model Bonding in Methane § Assume that the carbon atom has four equivalent atomic orbitals, arranged tetrahedrally. Hybridizaon § Mixing of the nave atomic orbitals to form special orbitals for bonding. Copyright © Cengage Learning. All rights reserved 19 Secon 9.1 Hybridiza)on and the Localized Electron Model sp3 Hybridizaon § Combinaon of one s and three p orbitals. § Whenever a set of equivalent tetrahedral atomic orbitals is required by an atom, the localized electron model assumes that the atom adopts a set of sp3 orbitals; the atom becomes sp3 hybridized. § The four orbitals are iden$cal in shape. Copyright © Cengage Learning. All rights reserved 20 Secon 9.1 Hybridiza)on and the Localized Electron Model Orbital Energy-Level Diagram for sp3 Hybridizaon Copyright © Cengage Learning. All rights reserved 21 Secon 9.1 Hybridiza)on and the Localized Electron Model Formaon of sp3 Hybrid Orbitals Copyright © Cengage Learning. All rights reserved 22 Secon 9.1 Hybridiza)on and the Localized Electron Model Tetrahedral Set of four sp3 Orbitals Copyright © Cengage Learning. All rights reserved 23 Secon 9.1 Hybridiza)on and the Localized Electron Model sp2 Hybridizaon § Combinaon of one s and two p orbitals. § Gives a trigonal planar arrangement of atomic orbitals. § One p orbital is not used. § Oriented perpendicular to the plane of the sp2 orbitals. Copyright © Cengage Learning. All rights reserved 24 Secon 9.1 Hybridiza)on and the Localized Electron Model Sigma (σ) Bond § Electron pair is shared in an area centered on a line running between the atoms. Pi (π) Bond § Forms double and triple bonds by sharing electron pair(s) in the space above and below the σ bond. § Uses the unhybridized p orbitals. Copyright © Cengage Learning. All rights reserved 25 Secon 9.1 Hybridiza)on and the Localized Electron Model Orbital Energy-Level Diagram for sp2 Hybridizaon Copyright © Cengage Learning. All rights reserved 26 Secon 9.1 Hybridiza)on and the Localized Electron Model Hybridizaon of the s, px and py Atomic Orbitals Copyright © Cengage Learning. All rights reserved 27 Secon 9.1 Hybridiza)on and the Localized Electron Model Formaon of C=C Double Bond in Ethylene Copyright © Cengage Learning. All rights reserved 28 Secon 9.1 Hybridiza)on and the Localized Electron Model sp Hybridizaon § Combinaon of one s and one p orbital. § Gives a linear arrangement of atomic orbitals. § Two p orbitals are not used. § Needed to form the π bonds. Copyright © Cengage Learning. All rights reserved 29 Secon 9.1 Hybridiza)on and the Localized Electron Model Orbital Energy-Level Diagram for sp Hybridizaon Copyright © Cengage Learning. All rights reserved 30 Secon 9.1 Hybridiza)on and the Localized Electron Model When one s orbital and one p orbital are hybridized, a set of two sp orbitals oriented at 180 degrees results. Copyright © Cengage Learning. All rights reserved 31 Secon 9.1 Hybridiza)on and the Localized Electron Model The Orbitals for CO2 Copyright © Cengage Learning. All rights reserved 32 Secon 9.1 Hybridiza)on and the Localized Electron Model dsp3 Hybridizaon § Combinaon of one d, one s, and three p orbitals. § Gives a trigonal bipyramidal arrangement of five equivalent hybrid orbitals. Copyright © Cengage Learning. All rights reserved 33 Secon 9.1 Hybridiza)on and the Localized Electron Model The Orbitals Used to Form the Bonds in PCl5 Copyright © Cengage Learning. All rights reserved 34 Secon 9.1 Hybridiza)on and the Localized Electron Model d2sp3 Hybridizaon § Combinaon of two d, one s, and three p orbitals. § Gives an octahedral arrangement of six equivalent hybrid orbitals. Copyright © Cengage Learning. All rights reserved 35 Secon 9.1 Hybridiza)on and the Localized Electron Model How is the Xenon atom in XeF4 hybridized? Copyright © Cengage Learning. All rights reserved 36 Secon 9.1 Hybridiza)on and the Localized Electron Model Using the Localized Electron Model § Draw the Lewis structure(s). § Determine the arrangement of electron pairs using the VSEPR model. § Specify the hybrid orbitals needed to accommodate the electron pairs. Copyright © Cengage Learning. All rights reserved 37 Secon 9.2 The Molecular Orbital Model The Molecular Orbital Model § Regards a molecule as a collec$on of nuclei and electrons, where the electrons are assumed to occupy orbitals much as they do in atoms, but having the orbitals extend over the en$re molecule. § The electrons are assumed to be delocalized rather than always located between a given pair of atoms. Copyright © Cengage Learning. All rights reserved 38 Secon 9.2 The Molecular Orbital Model The Molecular Orbital Model § The electron probability of both molecular orbitals is centered along the line passing through the two nuclei. § Sigma (σ) molecular orbitals (MOs) § In the molecule only the molecular orbitals are available for occupaon by electrons.