General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Chapter 12: Chemical Bonding II:
Additional Aspects
Philip Dutton
University of Windsor, Canada
N9B 3P4
Prentice-Hall © 2002
(modified 2003 by Dr. Paul Root and 2005 by Dr. David Tramontozzi)
Contents
12-1
12-2
12-3
12-4
12-5
12-6
12-7
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What a Bonding Theory Should Do
Introduction to the Valence-Bond Method
Hybridization of Atomic Orbitals
Multiple Covalent Bonds
Molecular Orbital Theory
Delocalized Electrons: Bonding in the
Benzene Molecule
Bonding in Metals
Focus on Photoelectron Spectroscopy
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.
• A bonding theory should help us understand why.
– Lewis theory: ease of application.
– VSEPR theory: propose molecular shapes.
– Quantitative limitations (bond energies, bond lengths)
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General Chemistry: Chapter 12
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Potential Energy Diagram
Repulsive
forces exceed
attractive
forces
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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.
– Core electrons and lone-pair electrons retain orbital
location.
– Charge density of the bonding electrons is concentrated
in the region of orbital overlap.
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General Chemistry: Chapter 12
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Bonding in H2S
Valence bond method predicts 90° bond angles
VSEPR method predicts tetrahedral
arrangement (109.5°)
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General Chemistry: Chapter 12
Actual bond
angles in H2S
are 92° !!!
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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 of separate atoms:
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General Chemistry: Chapter 12
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Example 12-1
Sketch the orbitals:
Overlap the orbitals:
Describe the shape:
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Trigonal pyramidal
General Chemistry: Chapter 12
Experimentally
determined bond
angles are 93-94°
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12-3 Hybridization of Atomic Orbitals
Hybridization occurs only when the bonds are being formed.
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General Chemistry: Chapter 12
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sp3 Hybridization
Combine to generate four equivalent sp3 orbitals
Which are represented as the set
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These four sp3 hybrid
orbitals point to the
corners of a
tetrahedron…accounting
for the shape of CH4
General Chemistry: Chapter 12
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sp3 Hybridization
In a hybridization scheme, the number of hybrid
orbitals equals the total number of atomic orbitals that
are combined.
Note how the energy is conserved during hybridization.
The three p energies move down by ¼ each and the
single s orbital increases by 75%
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General Chemistry: Chapter 12
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Bonding in Methane
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General Chemistry: Chapter 12
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sp3 Hybridization in Nitrogen
Because one of the sp3
hybrid orbitals is occupied
by a lone pair, only three
are available for bonding
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General Chemistry: Chapter 12
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sp2 Hybridization
The hybridization scheme above describes the
hybridization in most boron compounds.
The 2s and 2 of the 2p orbitals combine to make 3
equivalent sp2 hybrid orbitals.
This type of hybridization is important in carbon atoms
involved in double bonds.
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General Chemistry: Chapter 12
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Orbitals in Boron
Combine to generate 3 sp2 orbitals
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sp Hybridization
The hybridization scheme above best describes some
gaseous beryllium compounds.
The 2s and 1 of the 2p orbitals combine to make 2
equivalent sp hybrid orbitals.
This type of hybridization is important in carbon atoms
involved in triple bonds.
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General Chemistry: Chapter 12
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Orbitals in Beryllium
Combine to generate 2 sp orbitals
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sp3d and sp3d2 Hybridization
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General Chemistry: Chapter 12
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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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General Chemistry: Chapter 12
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Summary
Number
of bonds
Number of
Lone pair e-
VSEPR
Notation
Molecular Shape
Hybrid
Orbital
2
0
AX2
Linear
sp
2
1
AX2E
Angular
sp2
(Trigonal Planar)
2
2
AX2E2
sp3
Angular
(Tetrahedral)
2
3
AX2E3
sp3d
Linear
(Trigonal bi-pyramidal)
(brackets) indicate the electron group geometry
Hybrid orbitals are assigned based on electron group geometry
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General Chemistry: Chapter 12
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Summary
Number
of bonds
Number of
Lone pair e-
VSEPR
Notation
3
0
AX3
3
1
AX3E
Molecular Shape
Hybrid
Orbital
Trigonal Planar
sp2
Trigonal Pyramidal
sp3
(tetrahedral)
3
2
AX3E2
T-Shaped
sp3d
(trigonal bi-pyramidal)
(brackets) indicate the electron group geometry
Hybrid orbitals are assigned based on electron group
geometry
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General Chemistry: Chapter 12
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Summary
Number Number of
of bonds Lone pair e-
VSEPR
Notation
4
0
AX4
4
1
AX4E
Molecular Shape
Hybrid
Orbital
Tetrahedral
sp3
Seesaw
sp3d
(Trigonal bi-Pyrimidal)
4
2
AX4E2
sp3d2
square planar
(octahedral)
(brackets) indicate the electron group geometry
Hybrid orbitals are assigned based on electron group
geometry
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General Chemistry: Chapter 12
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Summary
Number Number of
of bonds Lone pair e-
VSEPR
Notation
5
0
AX5
5
1
AX5E
Molecular Shape
Hybrid
Orbital
Trigonal bi-Pyrimidal
sp3d
Square Pyramidal
sp3d2
(octahedral)
6
0
AX6
sp3d2
Octahedral
(brackets) indicate the electron group geometry
Hybrid orbitals are assigned based on electron group
geometry
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General Chemistry: Chapter 12
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