Chapter 10: Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals
Chapter 10 Problem Set
Pages 473-478
1, 16, 18, 19, 20, 21, 25, 29, 36, 37
10.1
ORBITALS AND BONDING THEORIES
Orbitals are regions in space in which there is a high probability of finding the electron
The valence bond (VB) theory was developed by Linus Pauling.
It provides a qualitative, visual picture of molecular structure and bonding.
Works well in describing electrons in the ground state.
The molecular orbital (MO) theory was developed by Robert Milliken.
It helps to describe molecules in “excited states.”
It provides a description of the bonding in such compounds as NO and O2.
It is more quantitative.
10.2
VALENCE BOND THEORY
The Orbital Overlap Model of Bonding
Valence bond theory involves the overlap of orbitals.
For Ex: H2 and F2
Sigma () bonds – any 2 atomic orbitals from different atoms that overlap on the same axis.
Hybridization of s and p Atomic Orbitals
In order to account for the bonding in CH4, for equivalent bonds and tetrahedral anlges of
109.50, it is necessary to develop the theory of orbital hybridization.
Hybrid orbitals – atomic orbitals mix to form the same number of hybrid orbitals.
one s-orbital & one p-orbital form two sp hybrids AX2
one s-orbital & two p-orbitals form three sp2 hybrids AX3
one s-orbital & three p-orbitals form four sp3 hybrids AX4
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EXERCISE 10.1 Page 447 Valence Bond Description of Bonding in H3O+
What is the hybridization for the central atom in a molecule that has a trigonal planar
electron pair geometry?
What is the hybridization of the central atom which has a linear electron-pair geometry?
Hybridization Involving s, p, and d Atomic Orbitals
A basic assumption of Pauling’s valence bond theory is that the number of hybrid orbitals
equals the number of valence orbitals.
Ex:
one s-orbital, three p-orbitals, and one d-orbital form five sp3d hybrids AX5
one s-orbital, three p-orbitals, and two d-orbitals form six sp3d2 hybrids AX6
See Page 450 for diagrams
EXAMPLE 10.4 Page 451 Recognizing Hybridization
Identify the hybridization of the central atom in the following compounds and ions.
(a) CF4
(d) SF3+
(b) SF4
(e) I3(c) PO2F2(f) SO4-2
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Multiple Bonds
Double Bonds have 1 sigma bond () and 1 pi ( bond
EXERCISE 10.4 Page 455 Bonding in Acetone
Triple Bonds have 1 sigma bond () and 2 pi (bonds
EXERCISE 10.5 Page 456 Triple Bonds Between Atoms
Carbon-Carbon Double Bonds: Cis and Trans Isomers
Isomers are cmpds that have the same formula but different structures.
Benzene: Structure and Bonding (resonance structures)
10.3
MOLECULAR ORBITAL THEORY
Molecular Orbitals – pure s and p atomic orbitals of the atoms in the molecule combine to
produce orbitals that are spread out over several atoms or even an entire molecule
“delocalization of electrons”
Principles of Molecular Orbital Theory
The first principle of molecular orbital theory is that the number of molecular orbitals
produced is always equal to the total number of atomic orbitals contributed by the atoms that
have combined.
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Bonding and Antibonding Molecular Orbitals in H2
A bonding molecular orbital is the addition of atomic orbitals and is the same as that
described by valence bond theory. It is labeled 1s
An antibonding molecular orbital is constructed by subtracting one atomic orbital from the
other. It is labeled 1s. Antibonding orbitals have no counterpart in valence bond theory. The
group of atoms has lower energy than the separate atoms. The system is “stabilized” and
chemical bonds can be formed.
A second principle of molecular orbital theory is that the bonding molecular orbital is
lower in energy than the parent orbitals and the antibonding orbital is higher in energy
A third principle of molecular orbital theory is that the electrons of the molecule are
assigned to orbitals of successively higher energy according to the Pauli exclusion principle
and Hund’s rule
Bond Order for MO Theory
Bond Order = ½ (number of e- in bonding MOs – number of e- in antibonding MOs
Fractional bond orders are possible.
EXAMPLE 10.7 Page 462 Molecular Orbitals and Bond Order
Write the electron configuration of the H2- ion in molecular orbital terms. What is the bond
order of the ion?
EXERCISE 10.7 Page 462 Molecular Orbitals and Bond Order
What is the electron configuration of the H2+ ion? Compare the bond order of this ion with
He2+ and H2-. Do you expect H2 to exist?
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Molecular Orbitals of Li2 and Be2
A fourth principle of molecular orbital theory is that atomic orbitals combine to form
molecular orbitals most effectively when the atomic orbitals are of similar energy.
Molecular Orbitals for Homonuclear, Diatomic Molecules
EXAMPLE 10.8 Page 463 Molecular Orbitals in Diatomic Molecules
Be2 does not exist. But what about Be2+ ion? Describe its electron configuration in molecular
orbital terms and give the net bond order. Do you expect the ion to exist?
EXERCISE 10.8 Page 463 Molecular Orbitals in Diatomic Molecules
Could the anion Li2- exist? What is the ion’s bond order?
Molecular Orbitals from Atomic p Orbitals
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Electron Configurations for Some Homonuclear Molecules
Fig 10.27
EXAMPLE 10.9 Page 466 Electron Configuration for a Homonuclear Diatomic Molecule
Write the electron configuration for O2-. Predict its bond order and magnetic behavior.
O2-, superoxide MO theory works much better
*Read blurb on pg 467
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Electron Configurations for Heteronuclear Diatomic Molecules
EXERCISE 10.9 Page 467 Molecular Electron Configurations
Write the electron configuration for O2+. Predict its bond order and magnetic behavior.
Resonance and  Bonds
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10.4
METALS AND SEMICONDUCTORS Read section and take notes that help you

Appreciate band theory and how it applies to solids, especially metals

Understand the difference between a conductor of electricity, a semiconductor, and an
insulator.

Recognize how dopants such as Group 3A and Group 5A elements affect semiconductor
properties.
Conductors, Insulators, and Band Theory
Semiconductors
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