Chapter 10 Chemical Bonding II Molecular Shapes Valence Bond Theory and Molecular Orbital Theory Georgia Gwinnett College Chem 1212K Fall 2013 Chapter 10 1 Valence Shell Electron Pair Repulsion Theory VSEPR A way of predicting molecular structures from the localized electron model The structure around a given atom is determined principally by minimizing electron pair repulsions The lone and bonding pairs should be located as far from one another as possible The geometry is determined by the electron groups of the central atom The number of electron groups is equal to the sum of the bonded atoms and lone pairs about a central atom A double triple bond only counts as 1 bonded atom Chapter 10 2 Electron groups 5 Basic Arrangements of Electron Groups about a Central Atom Chapter 10 3 Electron groups 2 Linear Examples CS2 HCN BeF2 Chapter 10 4 Electronic geometry vs Molecular Geometry Electronic geometry does not differentiate between electrons in bonds and lone pairs However differentiating between lone pairs and bonding electrons is quite important to the shape of the molecule This is also called the molecular geometry Chapter 10 5 Electron groups 3 Electron Geometry Trigonal Planar Examples SO3 BF3 NO3 CO32 Electron Group Arrangement Examples SO2 O3 PbCl2 SnBr2 Molecular Geometry or Shape Chapter 10 6 Electron groups 4 Electron Geometry Tetrahedral Examples CH4 SiCl4 SO42 ClO4 NH3 H2O PF3 OF2 ClO3 SCl2 H3O Chapter 10 7 Lone Pairs Have Greater electron electron Repulsion than bonding groups Chapter 10 8 Lone Pair Effect on Geometry Chapter 10 9 Electron groups 5 Electron Geometry Trigonal bipyramidal PF5 SF4 AsF5 XeO2F2 SOF4 IF4 IO2F2 ClF3 XeF2 BrF3 I3 IF2 Chapter 10 10 Chapter 10 11 Electron groups 6 Octahedral SF6 IOF5 BrF5 XeF4 TeF5XeOF4 Chapter 10 ICl4 12 13 14 More Than One Central Atom ethane ethanol CH3CH3 CH3CH2OH Chapter 10 15 More Than One Central Atom Determine the shape around each of the central atoms in acetone CH3 2C O H H C O C H C H H H Chapter 10 16 Polarity of Molecules In order for a molecule to be polar it must have 1 polar bonds electronegativity difference theory bond dipole moments measured 2 an unsymmetrical shape vector addition Polarity affects the intermolecular forces of attraction therefore boiling points and solubilities like dissolves like nonbonding pairs affect molecular polarity they pull the electron density strongly 17 Chapter 10 Molecule Polarity The H Cl bond is polar The bonding electrons are pulled toward the Cl end of the molecule The net result is a polar molecule 18 Chapter 10 Chapter 10 19 Molecule Polarity The O C bond is polar The bonding electrons are pulled equally toward both O ends of the molecule The net result is a nonpolar molecule 20 Chapter 10 Molecule Polarity The H O bond is polar Both sets of bonding electrons are pulled toward the O end of the molecule The net result is a polar molecule 21 Chapter 10 Molecule Polarity The H N bond is polar All the sets of bonding electrons are pulled toward the N end of the molecule The net result is a polar molecule 22 Chapter 10 More Advanced Theories of Covalent Bonding Apply Quantum Mechanics to Molecules Valence Bond Theory We will be introduced to this theory Molecular Orbital Theory Unfortunately we don t have time MO Theory is AWESOME TAKE P CHEM 23 Chapter 10 Orbital Interaction As two atoms approach the partially filled or empty valence atomic orbitals on the atoms interact to form molecular orbitals Covalent bonds are the result of the OVERLAP of atomic orbitals The shapes of the atomic orbitals are important s orbitals px py and pz orbitals 24 Chapter 10 Sigma bonds 25 Pi Bonds Chapter 10 26 Carbons s and p Atomic Orbitals Predict the Wrong Bonding and Geometry 27 Chapter 10 Hybridization Some atoms hybridize their orbitals to maximize bonding Hybridizing is mixing different types of orbitals to make a new set of degenerate orbitals sp sp2 sp3 sp3d sp3d2 Same type of atom can have different hybridizations depending on the compound C sp sp2 sp3 28 Chapter 10 29 Chapter 10 Orbital Diagram of the sp3 Hybridization of C 30 Chapter 10 Methane Formation with sp3 C 31 Chapter 10 Orbital Hybridization The number of electron groups can be used to determine the orbital hybridization 2 electron groups sp 3 electron groups sp2 4 electron groups sp3 32 Chapter 10 Ammonia Formation with sp3 N 33 Chapter 10 34 Chapter 10 sp2 hybridization 36 Chapter 10 37 Chapter 10 sp Hybridization 39 Chapter 10 Example Predict the hybridization and bonding scheme for CH3CHO Determine the hybridization of the interior atoms C1 tetrahedral C1 sp3 C2 trigonal planar C2 sp2 Sketch the molecule and orbitals 40