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Copyright©2000 by Houghton Mifflin Company. All rights reserved.
1
Covalent Bonding: Hybrid Atomic Orbitals
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2
Bonding
– Write Lewis Structures.
– Determine the Arrangement of e- pairs using VSEPR Theory.
– Determine the hybrid atomic orbitals used to form bonds.
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3
Hybridization
• The mixing of atomic orbitals to form special orbitals for bonding.
• The atoms are responding as needed to give the minimum energy for the molecule.
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4
Hybrid Orbitals
• Orbitals used to describe bonding that are obtained by taking combinations of atomic orbitals of the isolated atoms.
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5
Figure 9.1(a) Lewis Structure (b) Tetrahedral Molecular Geometry of the Methane Molecule
By experiment, CH4 know to be tetrahedral with bond angles of 109.5.
Experiments show 4 equivalent bonds.
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6
• Valence electrons of carbon:
2s2 2p2
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7
Figure 9.2
The Valence Orbitals on a Free Carbon Atom: 2s, 2px, 2py, and 2pz
• Bonding assumed to involve only the valence electrons.
• Overlap with these orbitals would not give 109.5 bond angles.
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8
Hybridization
• ☻☻☻
• A new set of atomic orbitals might better serve the C atom in forming molecules.
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9
Hybridization
• ☻☻☻
• Hybridization = Modification of model to account for the observation.
• Atoms seem to use special orbitals when forming molecules.
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10
Figure 9.3
The Formation of sp3 Hybrid Orbitals
“sp3 hybridization.”
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11
Figure 9.5
An Energy-Level Diagram Showing the Formation of Four sp3 Orbitals
Four equivalent carbon orbitals.
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12
Figure 9.6
Tetrahedral Set of Four sp3 Orbitals
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13
Figure 9.7
The Nitrogen Atom in Ammonia is sp3 Hybridized
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14
Ethylene
• H2C==CH2
• Each carbon atom is surrounded by three effective pairs.
• Requires a set of 3 orbitals with a trigonal planar geometry and 120 bond angles.
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15
Figure 9.8
The Hybridization of the s, px, and py Atomic Orbitals
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16
Figure 9.9
An Orbital Energy-Level Diagram for sp2 Hybridization
One 2p orbital of carbon is not used..
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17
Figure 9.10
An sp2 Hybridized C Atom
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18
(sigma) bonds
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19
Figure 9.11
The Bonds in Ethylene
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20
Double Bond
• Double bond results from an additional bond----- a (pi) bond.
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21
Figure 9.12
Sigma and Pi Bonding
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22
Figure 9.13
The Orbitals for C2H4
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23
Whenever an atom is surrounded by3 effective e- pairs,
a set of sp2 hybrid orbitals is required.
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24
• A sigma () bond centers along the internuclear axis.
• A pi () bond occupies the space above and below the internuclear axis.
CCH H
HH
Double Bonds
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25
CO2
• O==C==O
• 2 effective pairs around central atom at an angle of 180
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26
Figure 9.14
When One s Orbital and One p Orbital are Hybridized, a Set of Two sp Orbitals
Oriented at 180 Degrees Results
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27
Figure 9.16
The Orbital Energy-Level Diagram for the Formation of sp Hybrid Orbitals on Carbon
A set of two sp orbitals.
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28
Figure 9.17
The Orbitals of an sp Hybridized Carbon Atom
Two sp hybridizedorbitals.
Two p unhybrizedOrbitals.
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29
Sigma Bonds
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30
Figure 9.19
The Orbitals for CO2
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31
PCl5
• 5 e- pairs requires a geometry of
trigonal bipyramidal.
• Requires dsp3 hybridization.
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32
Figure 9.21
A Set of dsp3 Hybrid Orbitals on a Phosphorus Atom
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33
Each Cl is surrounded by 4 e- pairs.
They require sp3 hybridization.
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34
Figure 9.22
(a) The Structure of the PCl5 Molecule (b) The Orbitals Used to Form the Bonds in PCl5
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35
SF6
• 6 e- pairs requires a geometry of
octahedral.
• Requires d2sp3 hybridization.
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36
Figure 9.23An Octahedral Set of d2sp3 Orbitals on a Sulfur Atom
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37
The Localized Electron Model
Draw the Lewis structure(s)
Determine the arrangement of electron pairs (VSEPR model).
Specify the necessary hybrid orbitals.
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