Prentice-Hall © 2007 General Chemistry: Chapter 11 Slide 1 of 53
Contents
11-1 What a Bonding Theory Should Do
11-2 Introduction to the Valence-Bond Method
11-3 Hybridization of Atomic Orbitals
11-4 Multiple Covalent Bonds
11-5 Molecular Orbital Theory
11-6 Delocalized Electrons: Bonding in the Benzene
Molecule
11-7 Bonding in Metals
11-8 Some Unresolved Issues:
Can Electron Charge-Density Plots Help?
Focus On Photoelectron Spectroscopy
Prentice-Hall © 2007 General Chemistry: Chapter 11 Slide 2 of 53
11-1 What a Bonding Theory Should Do
Bring atoms of H together from a distance.
Each e- is attracted to the other nucleus.
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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Potential Energy Diagram
Objectives
Introduction to the Valence-Bond Method
Use the Valence-Bond Method to describe
a molecular structure.
Hybridization of Atomic Orbitals
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Introduction to the
Valence-Bond Method
Recall the region of high electron
probability in a H atom, 1s orbital.
A covalent bond is produced between two
atoms because of the overlap of two Atomic
orbitals.
The increased electron density, with its
negative charge, attracts the two positively
charged nuclei.
Interference of two waves
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Bonding in H2S
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Using the Valence-Bond Method to Describe a Molecular
Structure.
Describe the phosphine molecule, PH3, by the valence-bond
method..
Identify valence electrons:
EXAMPLE 11-1
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Sketch the orbitals:
Overlap the orbitals:
Describe the shape:
EXAMPLE 11-1
H
H
H
H
Trigonal pyramidal
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11-3 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
The hybridization adopted for the central atom must produce
the same number of hybrid orbitals as there are Valence Shell Electron
groups.
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Hybrid Orbitals and VSEPR
Write a plausible Lewis
structure.
Use VSEPR to predict
electron geometry.
Select the appropriate
hybridization.
Refer to Table 11.1, P 459
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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.
Refer to Table 11.1, P 459
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11-4 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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11-5 Molecular Orbital Theory
MOT assigns the electrons in a molecule to a
series of orbitals that belong to the molecule
itself, these are called Molecular Orbitals; the
probability of finding electrons in certain
regions of a molecule.
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
when two H atoms merge to form a chemical bond
As the atoms approach, the two 1s orbitals, wave
functions, combine.
Constructive interference (2 waves are in phase)
corresponds to adding the two mathematical
functions;
Destructive interference corresponds to
subtracting the two wave functions, two wave are
out of phase.
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Combining Atomic Orbitals
Addition leads to a greater probability of finding electron between
two nuclei; this causes the two nuclei to draw closer together and
form a chemical bond.
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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
(maximum number of e- in a MO is two).
Hund’s rule is followed; e- enter Mos of
identical energies singly before they pair up.
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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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Diatomic Molecules of the First-Period
BO = (1-0)/2 = ½ H2
+
BO = (2-0)/2 = 1 H2
BO = (2-1)/2 = ½ He2
+
BO = (2-2)/2 = 0 He2
BO = (e-bond - e
-antibond )/2
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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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11-6 Delocalized Electrons
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Benzene
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Benzene
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Benzene
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Ozone
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End of Chapter Questions
Set up a strategy for your problem.
This is your road map.
In a time of stress (i.e. an exam) your strategy
will keep you on the path of the problem.
