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Philip Dutton University of Windsor, Canada N9B 3P4 Prentice-Hall © 2002 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition Chapter 11: Chemical Bonding II: Additional Aspects
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 2 of 47 Contents 11-1What a Bonding Theory Should Do 11-2Introduction to the Valence-Bond Method 11-3Hybridization of Atomic Orbitals 11-4Multiple Covalent Bonds 11-5Molecular Orbital Theory 11-6Delocalized Electrons: Bonding in the Benzene Molecule 11-7Bonding in Metals Focus on Photoelectron Spectroscopy
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 3 of 47 11-1 What a Bonding Theory Should Do Bring atoms together from a distance. –e - are attracted to both nuclei. –e - are repelled by each other. –Nuclei are repelled by each other. Plot the total potential energy versus distance. –-ve energies correspond to net attractive forces. –+ve energies correspond to net repulsive forces.
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 4 of 47 Potential Energy Diagram
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 5 of 47 11-2 Introduction to the Valence-Bond Method Atomic orbital overlap describes covalent bonding. Area of overlap of orbitals is in phase. A localized model of bonding.
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 6 of 47 Bonding in H 2 S
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 7 of 47 Example 11-1 Using the Valence-Bond Method to Describe a Molecular Structure. Describe the phosphine molecule, PH 3, by the valence-bond method.. Identify valence electrons:
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 8 of 47 Example 11-1 Sketch the orbitals: Overlap the orbitals: Describe the shape: Trigonal pyramidal
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 9 of 47 11-3 Hybridization of Atomic Orbitals
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 10 of 47 sp 3 Hybridization
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 11 of 47 sp 3 Hybridization
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Methane sp 3 hybrid orbitals General ChemistrySlide 12 /69 Tetrahedron in a cube Coordinates: sxyz 1111 11 1 1 1 1 Gábor I. Csonka © 2013
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 13 of 47 Bonding in Methane
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 14 of 47 sp 3 Hybridization in Nitrogen
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 15 of 47 Bonding in Nitrogen
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 16 of 47 sp 2 Hybridization
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 17 of 47 Orbitals in Boron
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 18 of 47 sp Hybridization
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 19 of 47 Orbitals in Beryllium
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 20 of 47 sp 3 d and sp 3 d 2 Hybridization
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 21 of 47 Hybrid Orbitals and VSEPR Write a plausible Lewis structure. Use VSEPR to predict electron geometry. Select the appropriate hybridization.
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 22 of 47 11-4 Multiple Covalent Bonds Ethylene has a double bond in its Lewis structure. VSEPR says trigonal planar at carbon.
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 23 of 47 Ethylene + - + + - -
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Double bond = 1 C-C + 1 C-C bonds. + - Notice that the C-C MO is antisymmetric to the molecular plane, it is positive above and negative below the plane.
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General Chemistry: Chapter 12Slide 25 of 47 Acetylene Acetylene, C 2 H 2, has a triple bond. VSEPR gives linear at carbon. C: sp hybrid ++ ++ - - - - There are two bonds in acetylene (ethyne)
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 26 of 47 11-5 Molecular Orbital Theory Atomic orbitals are isolated on atoms. Molecular orbitals span two or more atoms. LCAO –Linear combination of atomic orbitals. Ψ 1 = φ 1 + φ 2 Ψ 2 = φ 1 - φ 2
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 27 of 47 Combining Atomic Orbitals
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 28 of 47 Molecular Orbitals of Hydrogen
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 29 of 47 Basic Ideas Concerning MOs Number of MOs = Number of AOs. Bonding and antibonding MOs formed from AOs. e - fill the lowest energy MO first. Pauli exclusion principle is followed. Hund’s rule is followed
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 30 of 47 Bond Order Stable species have more electrons in bonding orbitals than antibonding. Bond Order = No. e - in bonding MOs - No. e- in antibonding MOs 2
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 31 of 47 Diatomic Molecules of the First-Period BO = (1-0)/2 = ½ H2+H2+ BO = (2-0)/2 = 1 H2H2 BO = (2-1)/2 = ½ He 2 + BO = (2-2)/2 = 0 He 2 BO = (e - bond - e - antibond )/2
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 32 of 47 Molecular Orbitals of the Second Period First period use only 1s orbitals. Second period have 2s and 2p orbitals available. p orbital overlap: –End-on overlap is best – sigma bond (σ). –Side-on overlap is good – pi bond (π).
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 33 of 47 Molecular Orbitals of the Second Period
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 34 of 47 Combining p orbitals
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The energy level diagram for MOs General Chemistry: Chapter 12Slide 35 of 47 The AOs are on the left and right (yellow and blue), the MOs are in the center (orage and green). MO labels are and for bonding * and * for antbonding.
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Inversion of the MO energies between N 2 and O 2 General Chemistry: Chapter 12Slide 36 of 47 For diatomic molecules with 7 Z the 2p orbital energy is above 2p molecular orbital energy. The latter is filled first.
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General Chemistry: Chapter 12Slide 37 of 47 MO Diagrams of 2 nd Period Diatomics C 2 electron configuration:
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 38 of 47 MO Diagrams of Heteronuclear Diatomics
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General Chemistry: Chapter 12Slide 39 of 47 11-6 Delocalized Electrons
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General Chemistry: Chapter 12Slide 40 of 47 Benzene: delocalized bonding Delocalized bonding is not localized between two atoms: instead, each link has a 'fractional double bond order’. There is a corresponding 'delocalization energy', identifiable with the stabilization of the system compared with a hypothetical alternative in which formal (localized) single and double bonds are present. Bond order = 1.5 Delocalization energy = –263.7 kJ mol -1
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 41 of 47 Benzene, 6 MO energies
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Benzene 6 MO shapes Slide 42 /69 Bonding orbitals 6 e - Non bonding orbitals
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The charge distribution in benzene Általános Kémia, Kötés szerkezetSlide 43 /69 The electrostatic potential surface. Red: negative charge Blue: positive charge
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The charge distribution in borazine Általános Kémia, Kötés szerkezetSlide 44 /69 Uneven charge distribution Less stable 6 electrons delocalized system
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Pyridine Slide 45 /69 _ _ _ 6 delocalised electrons
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Butadiene Slide 46 /69 4 delocalised electrons
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CO 3 2- Slide 47 /69 6 delocalised electrons 6 e 2 e from the 2 negative charge + 4 e from the 2p atomic orbitals of the 3 O and 1 C atoms..
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 48 of 47 Ozone
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 49 of 47 11-7 Bonding in Metals Electron sea model –Nuclei in a sea of e -. –Metallic lustre. –Malleability. Force applied
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 50 of 47 Bonding in Metals Band theory. Extension of MO theory. N atoms give N orbitals that are closely spaced in energy. N/2 are filled. The valence band. N/2 are empty. The conduction band.
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 51 of 47 Band Theory
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 52 of 47 Semiconductors
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General Chemistry: Chapter 12Slide 53 of 47 Photovoltaic Cells
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Solar cell details General Chemistry: Chapter 12Slide 54 of 47
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 55 of 47 Focus on Photoelectron Spectroscopy
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Prentice-Hall © 2002General Chemistry: Chapter 12Slide 56 of 47 Chapter 12 Questions 1, 3, 8, 10, 16, 29, 33, 39, 45, 59, 68, 72, 76
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