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8/6/2019 Notes Lecture 01 Ch 14
http://slidepdf.com/reader/full/notes-lecture-01-ch-14 1/17
Chemistry 162
Text: Chemical Principles, 6th Ed.- By Steven Zumdahl
Chapter #14 : Covalent Bonding: Orbitals
Chapter #15 : Chemical Kinetics
Chapter #16 : Liquids and Solids
Chapter #17 : Properties of Solutions
Chapters #18: Representative Elements
Chapter #19: Transition Metals and Coordination Chemistry
Chapter #14 - Covalent Bonding: Orbitals
14.1) Hybridization and the Localized Electron Model
14.2) The Molecular Orbital Model
14.3) Bonding in Homonuclear Diatomic Molecules
14.4) Bonding in Heteronuclear Diatomic Molecules
14.5) Combining the Localized Electron and Molecular Orbital
Models
14.6) Orbitals: Human Inventions
14.7) Molecular Spectroscopy
8/6/2019 Notes Lecture 01 Ch 14
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Hybridization and the Localized Electron Model
Chapter 12:Atomic orbitals, Properties of electrons, Wave functions,
Electronic configurations, Aufbau principle, etc.
Chapter 13:
General Concepts of Bonding in Molecules- Types of bonds: ionic, covalent, etc.
- Bond energies, lengths, polarities, etc.
Localized Electron Model
- Lewis dot structures- Resonance structures
- The octet rule
- VSEPR model
Chapter 14:
Central Themes of Valence Bond Theory
(Localized Electron Model)
1) Maximum overlap. The bond strength depends on the coulombic
attraction between the shared electrons and the two nuclei. The
greater the orbital overlap, the stronger the bond.
Basic Principle of Valence Bond Theory: A covalent bond formswhen the orbitals from two atoms overlap and a pair of electronsoccupies the region between the two nuclei.
8/6/2019 Notes Lecture 01 Ch 14
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Central Themes of Valence Bond Theory
(Localized Electron Model)
1) Maximum overlap. The bond strength depends on the coulombic
attraction between the shared electrons and the two nuclei. The
greater the orbital overlap, the stronger the bond.
2) Spins pair. The two electrons in the overlap region occupy thesame space and therefore must have opposite spins. (Pauli exclusion
principle)
Basic Principle of Valence Bond Theory: A covalent bond formswhen the orbitals from two atoms overlap and a pair of electronsoccupies the region between the two nuclei.
3) Hybridization. To explain experimental observations, Pauling proposed that the valence atomic orbitals in a molecule are
different from those in the isolated atoms. We call thisHybridization!
8/6/2019 Notes Lecture 01 Ch 14
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Example: Methane
• 4 equivalent C-H covalent bonds• VSEPR predicts a tetrahedral geometry
Lewis dot structure VSEPR 3D shape
Recall, the method of generating
Lewis dot structures
total # valence
electrons = 8
0 e – left
H CH HH
H C
H
H
H
CH4
1. determine the total # of valence electrons
2. use pairs of e – to connect terminal atoms tocentral atom, and then distribute the rest as
lone pairs
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Recall, the method of determining
3–D structure (VSEPR)
9
• Valence Shell Electron Pair Repulsion (VSEPR):
the!3-D geometric structure is determined by
minimizing repulsion of electron pairs (both bond
pairs and lone pairs).
H C
H
H
H
Lewis Structure VSEPR Structure
(VSEPR)
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(VSEPR)
Carbon: 2s22p2
So, how do we explain the formation of
4 equivalent C-H bonds?
The Valence Orbitals of a Carbon Atom
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Hybridization: Mixing of Atomic Orbitals to
form New Orbitals for Bonding
4 atomic orbitals 4 new hybrid orbitals
Grouped together, the four have
a tetrahedral shape
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!1
= 1/2[(2s) + (2px) + (2p
y) + (2p
z)]
!2
= 1/2[(2s) + (2px) - (2p
y) - (2p
z)]
!3
= 1/2[(2s) - (2px) + (2p
y) - (2p
z)]
!4
= 1/2[(2s) - (2px) - (2p
y) + (2p
z)]
Other Representations of Hybridization:
Hybridization is related to the number of
electron pairs determined from VSEPR:Methane
VSEPR:
tetrahedral
sp3 hybridized
Ammonia
VSEPR:
tetrahedralsp3 hybridized
Water
VSEPR :
tetrahedral
sp3 hybridized
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8/6/2019 Notes Lecture 01 Ch 14
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used for bonding
remaining p orbital used for bonding
Problem: Describe the hybridization and bonding of the
carbon orbitals in ethylene (C2H4)
VSEPR:
trigonal planarC C
H
H
H
H
The Formation of Involves the
Combination of an s–orbital with a px – and py –orbital
three atomic orbitals
three hybrid
orbitals
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One of the p–orbitals, the pz –orbital remains
unhybridized
The unhybridized pz –orbital will be used
to form a ! –bond
z
The ! (sigma) bonds in C2H4
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A carbon-carbon double bond consists
of a ! bond and a " bond
C C
H
H
H
H
bonding vs bondingRead pages 665 of Zumdahl
• Two modes of bonding are important for 1st and 2nd row elements: # bonding and " bonding
• These two differ in their relationship to the internuclear • axis:
# bonds have electron density ON the internuclear axis
" bonds have electron density ABOVE AND BELOW the internuclear axis
" bond
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Bonding in ethylene (C2H4)
Problem: Describe the hybridization and bonding of the
carbon orbitals in Carbon Dioxide (CO2)
VSEPR:
linear
sp hybridized orbitals for # bonding
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The ! (sigma) bonds in CO2
Two of the p–orbitals of CO2 remain
unhybridized
The unhybridized orbitals will be used
to form two ! –bonds
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Bonding in Carbon Dioxide (CO2)
5- and 6-Coordinate Molecules: e.g. PCl5
VSEPR: AB5
trigonal bipyrimidal
Expanded Octet for P
(10 valence electrons)
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1. Molecular Formula
2. Lewis Structure
3. VSEPR- shape and arrangement
4. Hybrid orbitals
Strategies used in forming
Hybrid Orbitals
Summary:hybrid
combination
sp
sp2
sp3
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Summary:
hybrid
combination
dsp3
d2sp3
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