Hoa dai cuong_chuong 12

Philip Dutton
University of Windsor, Canada
N9B 3P4

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General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Chapter 12: Chemical Bonding II:
Additional Aspects
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General Chemistry: Chapter 12
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Contents
12-1 What a Bonding Theory Should Do
12-2 Introduction to the Valence-Bond Method
12-3 Hybridization of Atomic Orbitals
12-4 Multiple Covalent Bonds
12-5 Molecular Orbital Theory
12-6 Delocalized Electrons: Bonding in the Benzene Molecule
12-7 Bonding in Metals
Focus on Photoelectron Spectroscopy
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General Chemistry: Chapter 12
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12-1 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 verses distance.
-ve energies correspond to net attractive forces.
+ve energies correspond to net repulsive forces.
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Potential Energy Diagram
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General Chemistry: Chapter 12
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12-2 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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Bonding in H2S
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General Chemistry: Chapter 12
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Example 12-1
Using the Valence-Bond Method to Describe a Molecular Structure.
Describe the phosphine molecule, PH3, by the valence-bond method..
Identify valence electrons:
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Example 12-1
Sketch the orbitals:
Overlap the orbitals:
Describe the shape: Trigonal pyramidal
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12-3 Hybridization of Atomic Orbitals
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sp3 Hybridization
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sp3 Hybridization
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Bonding in Methane
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sp3 Hybridization in Nitrogen
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Bonding in Nitrogen
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sp2 Hybridization
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Orbitals in Boron
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sp Hybridization
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Orbitals in Beryllium
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sp3d and sp3d2 Hybridization
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Hybrid Orbitals and VSEPR
Write a plausible Lewis structure.
Use VSEPR to predict electron geometry.
Select the appropriate hybridization.
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12-4 Multiple Covalent Bonds
Ethylene has a double bond in its Lewis structure.
VSEPR says trigonal planar at carbon.
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Ethylene
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Acetylene
Acetylene, C2H2, has a triple bond.
VSEPR says linear at carbon.
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12-5 Molecular Orbital Theory
Atomic orbitals are isolated on atoms.
Molecular orbitals span two or more atoms.
LCAO
Linear combination of atomic orbitals.

Ψ1 = φ1 + φ2 Ψ2 = φ1 - φ2
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Combining Atomic Orbitals
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Molecular Orbitals of Hydrogen
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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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Bond Order
Stable species have more electrons in bonding orbitals than antibonding.
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Diatomic Molecules of the First-Period
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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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Molecular Orbitals of the Second Period
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Combining p orbitals
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Expected MO Diagram of C2
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Modified MO Diagram of C2
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MO Diagrams of 2nd Period Diatomics
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MO Diagrams of Heteronuclear Diatomics
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12-6 Delocalized Electrons
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Benzene
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Benzene
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Ozone
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12-7 Bonding in Metals
Electron sea model
Nuclei in a sea of e-.
Metallic lustre.
Malleability.

Force applied
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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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Band Theory
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Semiconductors
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Photovoltaic Cells
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Focus on Photoelectron Spectroscopy
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General Chemistry: Chapter 12
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Chapter 12 Questions
1, 3, 8, 10, 16, 29, 33, 39, 45, 59, 68, 72, 76