Chemical Bonding II Molecular Geometry and Hybridization of Atomic Orbitals Chapter 10 Copyright The McGraw Hill Companies Inc Permission required for reproduction or display 10 1 Chelation binding of Fe3 by 1 2 dihydroxybenzene 3 5disulfonic acid disodium salt Tiron VSEPR VALENCE SHELL ELECTRON PAIR REPULSION The two rules of VSEPR 1 Count the number of bonds to the central atom AND the number of lone electron pairs on the central atom 2 Multiple e g double and triple bonds are treated as though they were SINGLE bonds RESULT Obtain a molecule described by ABmEn RESULT Determine geometry from Chang Tables 10 1 10 2 or equivalent references A central atom B bonding atom E lone electron pair m number of bonding atoms n number of lone epairs Geometries for simple molecules with no lone pairs on central atom AB2 linear AB3 trigonal planar AB4 tetrahedral AB5 trigonal bipyramidal AB6 octahedral 10 1 lone pair vs lone pair repulsion lone pair vs bonding pair repulsion bonding pair vs bonding pair repulsion Geometries for simple molecules with no lone pairs on central atom Geometries for simple molecules with one or more lone pairs on central atom AB2 linear AB3 trigonal planar AB2E bent tetrahedral AB3E AB2E2 trigonal pyramidal bent trigonal bipyramidal AB4E AB3E2 AB2E3 see saw T shaped linear octahedral AB5E AB4E2 square pyramid square planar AB4 AB5 AB6 10 1 Predicting Molecular Geometry 1 Draw Lewis structure for molecule 2 Count number of lone pairs on the central atom and number of atoms bonded to the central atom 3 Use VSEPR to predict the geometry of the molecule What are the molecular geometries of SO2 and SF4 O S AB2E bent F O F S F AB4E F distorted tetrahedron 10 1 Dipole Moments and Polar Molecules electron poor region electron rich region H F Qxr Q is the charge r is the distance between charges 1 D 3 36 x 10 30 C m 10 2 10 2 10 2 Which of the following molecules have a dipole moment H2O CO2 SO2 and CH4 O H H dipole moment polar molecule S O O dipole moment polar molecule H O C O no dipole moment nonpolar molecule H C H H no dipole moment nonpolar molecule 10 2 Does BF3 have a dipole moment Does CH2Cl2 have a dipole moment 10 2 10 2 Chemistry In Action Microwave Ovens How does Lewis theory explain the bonds in H2 and F2 Sharing of two electrons between the two atoms Overlap Of Bond Dissociation Energy Bond Length H2 436 4 kJ mole 74 pm 2 1s F2 150 6 kJ mole 142 pm 2 2p Valence bond theory bonds are formed by sharing of e from overlapping atomic orbitals 10 3 Change in Potential Energy of Two Hydrogen Atoms as a Function of Their Distance of Separation Change in electron density as two hydrogen atoms approach each other 10 3 Valence Bond Theory and NH3 N 1s22s22p3 3 H 1s1 If the bonds form from overlap of 3 2p orbitals on nitrogen with the 1s orbital on each hydrogen atom what would the molecular geometry of NH3 be If use the 3 2p orbitals predict 900 Actual H N H bond angle is 107 30 10 4 Hybridization mixing of two or more atomic orbitals to form a new set of hybrid orbitals 1 Mix at least 2 nonequivalent atomic orbitals e g s and p Hybrid orbitals have very different shape from original atomic orbitals 2 Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process 3 Covalent bonds are formed by a Overlap of hybrid orbitals with atomic orbitals b Overlap of hybrid orbitals with other hybrid orbitals 10 4 sp3 Hybridization of a Carbon Atom Ground state 2s 2p 2s 2p Promotion of electron sp3 hybridized state sp3 orbitals Formation of sp3 Hybrid Orbitals 10 4 10 5 Formation of sp2 Hybrid Orbitals 10 4 10 5 Formation of sp Hybrid Orbitals 10 4 sp3d Hybridization of a Phosphorus Atom Ground state 3s 3p 3d 3p 3d Promotion of electron 3s sp3d hybridized state sp3d hybrid orbitals leftover 3d orbitals sp3d2 Hybridization of a Sulfur Atom Ground state 3s 3p 3d 3p 3d Promotion of electrons 3s sp3d2 hybridized state sp3d2 hybrid orbitals leftover 3d orbitals How do I predict the hybridization of the central atom 1 Draw the Lewis structure of the molecule 2 Count the number of lone pairs AND the number of atoms bonded to the central atom of Lone Pairs of Bonded Atoms Hybridization Examples 2 sp BeCl2 3 sp2 BF3 4 sp3 CH4 NH3 H2O 5 sp3d PCl5 6 sp3d2 SF6 10 4 10 4 Describe the bonding in CH2O H H C O C 3 bonded atoms 0 lone pairs C sp2 10 5 C2H4 Pi bond electron density above and below plane of nuclei Sigma bond electron density between the 2 atoms of the bonding atoms 10 5 Bonding in Acetylene C2H2 10 5 Sigma and Pi Bonds 1 sigma bond Single bond Double bond 1 sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds How many and bonds are in the acetic acid vinegar molecule CH3COOH H C O H C O H bonds 6 1 7 bonds 1 H 10 5 Experiments show O2 is paramagnetic O O No unpaired eShould be diamagnetic Molecular orbital theory bonds are formed from interaction of atomic orbitals to form molecular orbitals 10 6 10 6 Energy levels of bonding and antibonding molecular orbitals in hydrogen H2 A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed 10 6 10 6 Two Possible Interactions Between Two Equivalent p Orbitals 10 6 Molecular Orbital MO Configurations 1 The number of molecular orbitals MOs formed is always equal to the number of atomic orbitals combined 2 The more stable the bonding MO the less stable the corresponding antibonding MO 3 The filling of MOs proceeds from low to high energies 4 Each MO can accommodate up to two electrons 5 Use Hund s rule when adding electrons to MOs of the same energy 6 The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms 10 7 1 bond order 2 bond order Number of electrons in bonding MOs 1 Number of electrons in antibonding MOs 0 10 7 10 7 Delocalized molecular orbitals are not confined between two adjacent bonding atoms but actually extend over three or more atoms 10 8 Electron density above and below the plane of the benzene molecule 10 8 10 8 Chemistry In Action Buckyball Anyone