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AP Notes Chapter 9
Hybridization and the Localized Electron Model
Valence Bond Theory
Molecular Orbital Theory
Metals & Semiconductors
Hybridization and the Localized ElectronModel
Localized Electron Model developed fromValence Bond Theory
Why do we need it?Why do we need it?
Consider the water species.Consider the water species. H 1sH 1s11
H 1sH 1s11
O 1sO 1s22 2s 2s22 2p 2p44
Gives 2 H’s with no e- and O with full octet.Gives 2 H’s with no e- and O with full octet.
2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___
1s ___1s ___
1s ___1s ___
We GetWe Get
H 1sH 1s11
H 1sH 1s11
O 1sO 1s22 2s 2s22 2p 2p44
Gives 2 H’s with no e- and O with full octet.Gives 2 H’s with no e- and O with full octet.
2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___
1s ___1s ___
1s ___1s ___
HybridizationHybridization Process that changes properties of valence Process that changes properties of valence
electrons by mixing atomic orbitals to form electrons by mixing atomic orbitals to form special orbitals for bondingspecial orbitals for bonding
atomic molecularatomic molecularorbitals orbitalsorbitals orbitals AO MO AO MO
PrinciplesPrinciples1. Conservation of orbitals1. Conservation of orbitals
2. Hybrid correlates with2. Hybrid correlates with molecular geometry molecular geometry
3. Energy level of MO is 3. Energy level of MO is between that of AO’sbetween that of AO’s
4. All bonded atoms hybridize4. All bonded atoms hybridize
atomicorbital
hybridorbital
WHEN ATOMS BOND
All hybrid orbitals of an atom are said to be
DEGENERATE (of equal energy)
CHCH44
C: AOC: AO
2p __ __ __ 2p __ __ __
22s ____s ____
CH
H
HH
CHCH44
MOMO
__ __ __ ____ __ __ __
CH
H
HH
sp3 hybrid orbitals
sp3 hybridizationsp3 hybrid orbitals
tetrahedral speciessp3 shape tetragonal
4 Items Equally Distributed
TetragonalTetragonal
Lewis StructureLewis Structure
Electron Pair GeometryElectron Pair Geometry
Molecular ModelMolecular Model
H
H
HH CH
H
HH
C
InClInCl33
In: AOIn: AO
5p __ __ __ 5p __ __ __
5s _____5s _____
In
Cl
ClCl
InClInCl33
MOMO
__ __ ____ __ __
In
Cl
ClCl 5p __
sp2 hybrid orbitals
sp2 hybridizationsp2 hybrid
trigonal planar speciessp2 shape
3 Items Equally Distributed
BaClBaCl22
Cl - Ba - ClCl - Ba - ClBa: AOBa: AO
6p ___ ___ ___6p ___ ___ ___
6s _____6s _____
BaClBaCl22
Cl - Ba - ClCl - Ba - ClBa: Ba: MOMO 6p ___ ___6p ___ ___
___ ______ ___ sp hybrid orbitals
sp hybridizationsp hybrid
linear speciessp shape
2 Items Equally Distributed
PFPF5 5
PP: AO : AO 3d ___ ___ ___ ___ ___3d ___ ___ ___ ___ ___
3p ___ ___ ___3p ___ ___ ___
3s ____3s ____
PFPF5 5
PP: : MOMO3d ___ ___ ___ ___3d ___ ___ ___ ___
___ ___ ___ ___ ___ ___ ___ ___ ___ ___
spsp33d hybrid orbitalsd hybrid orbitals
sp3d hybridizationsp3d shape
trigonal bipyramid species
5 Items Equally Distributed
SFSF66
S: AO S: AO 3d ___ ___ ___ ___ ___3d ___ ___ ___ ___ ___
3p _____ ___ ___3p _____ ___ ___
3s _____3s _____
SFSF66
S: S: MOMO 3d ___ ___ ___3d ___ ___ ___
___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
sp3d2 hybrid orbitals
sp3d2 hybridizationsp3d2 shape
octahedral species
6 Items Equally Distributed
Multiple BondsMultiple Bonds
sigma bonds (sigma bonds ())
pi bonds (pi bonds ())
EXAMPLESEXAMPLESOO2 2
O O 1s1s22 2s 2s22 2p 2p4 4 2p2p4 4 2s2s2 2 1s1s22 OO
2 p-orbitals touching end to end sigma - 2 p-orbitals touching end to end sigma - σσ
2p-electrons reaching over and under pi - 2p-electrons reaching over and under pi - ππ
2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___ 2p ___ ___ ___ 2s ___ 2p ___ ___ ___ 2s ___
___ ___ ___ ___
Valence Bond Theory Valence Bond Theory Multiple Bond Multiple Bond
ExamplesExamplesCC22HH4 4 (ethylene) (ethylene) (sp(sp33 hybridization)hybridization)
(( bonding) bonding) bothboth
EXAMPLESEXAMPLESCC22HH2 2
EXAMPLESEXAMPLESCHCH33COOHCOOH
Valence Bond Theory concentrates on
individual bonds in a molecule and tends to ignore electrons not
used in bonding.
MOLECULAR ORBITAL MODELMOLECULAR ORBITAL MODEL
Molecular Orbital Theory assumes ALL
the orbitals of the atoms are able to take
part in bonding.
Every atom has a complete set of
orbitals, but not all of them contain
electrons
Remember that orbitals are really the solutions
of Schrodinger’s equation, and that they
are called wave-functions
r
1s wavefunction
2pz wavefunction
-
+
Negativehere
Positivehere
2pz orbital
- +
+
1s orbital
While wave functions can be
positive or negative, probabilities can only be positive.
Wave functions, like waves, can overlap with one another. They can reinforce each other, or
they can cancel each other out.
..
..
..
+
+
+
+
+
plus
1sA 1sB
B
A
A
B
A sigma, , bonding orbital
..
..
.
+
+
+
-
+
minus
1sA 1sB
B
A
A
A sigma star, , anti-bonding orbital
-B.
The work on molecular orbitals can be generalized to
p-orbitals.
2pz2pz 2p
A 2p bonding orbital
2pz 2pz 2p
A 2p
antibonding orbital
plusA A BB
2p
y
2p
y
2p
A 2p bonding orbital
minusA AB B
2py2py
2p
A 2p
antibonding orbital
Many combinations of orbitals can produce
bonding and anti-bonding molecular orbitals, s with p,
d with p, etc.
Orbitals on the two Orbitals on the two bonding atoms must bonding atoms must
meet 2 conditionsmeet 2 conditions They must be similar in They must be similar in
energyenergy They must have the right They must have the right
symmetrysymmetry
2pz
2py
plus
2py
2pz
Orbitals pointing in different directions cannot overlap to
form molecular orbitals.
Molecular Orbital Molecular Orbital TheoryTheory
1. Molecular orbitals are 1. Molecular orbitals are made from atomic made from atomic orbitalsorbitals
2. Orbitals are conserved2. Orbitals are conserved3. Molecular orbitals form 3. Molecular orbitals form
in pairs: in pairs: bondingbonding & & antibondingantibonding
BondingBonding Molecular Orbital Molecular Orbital
Geometry favorable to Geometry favorable to overlapoverlap
When a bonding orbital is formed, the energy of the orbital is lower than
those of its parent atomic orbitals.
Anti-bonding Anti-bonding Molecular OrbitalMolecular Orbital
Geometry not Geometry not favorable to overlapfavorable to overlap
Similarly, when an anti-bonding orbital is
formed, the energy of the orbital is higher
than those of its parent atomic orbitals.
Bond Bond OrderOrder
# bonding e antibonding e
2
- - #
Molecular Orbital Diagrams
Examine someExamine somehomonuclear homonuclear
diatomicdiatomicmoleculesmolecules
HydrogenHydrogenHeliumHelium
1sA 1sB
2s
2s
ParamagneticParamagnetic
1. Responds to 1. Responds to magnetic fieldmagnetic field
2. Has unpaired 2. Has unpaired electronselectrons
DiamagneticDiamagnetic1. Does not respond to 1. Does not respond to magnetic fieldmagnetic field
2. All electron paired2. All electron paired
1s 1s
2s 2s
2px2px2py
2py2pz2pz
1s
1s
2s
2s
2p2p 2p
2p2p
2p
fluorine gas
1s 1s
2s 2s
2px2px2py
2py2pz2pz
1s
1s
2s
2s
2p2p 2p
2p2p
2p
oxygen gas
Using MO Theory, Using MO Theory, moleculesmolecules have an have an
electron configurationelectron configuration Oxygen gasOxygen gas ((1s1s))22((1s1s
**))2 2
((2s2s))22((2s2s**))2 2
((2py2py))2 2 ((2py2py**))22
((2pz2pz))2 2 ((2px2px))2 2
1s 1s
2s 2s
2px2px2py
2py2pz2pz
1s
1s
2s
2s
2p2p 2p
2p2p
2p
nitrogen gas Magnet Movie
Bond Strength
Bond Length
Strengths of Strengths of Localized Electron Localized Electron
ModelModel1. Simple1. Simple
2. Easy to understand2. Easy to understand
3. Predicts geometry of 3. Predicts geometry of molecule molecule
Limitations of Limitations of Localized Electron ModelLocalized Electron Model
1. Does not address 1. Does not address concept of resonance or concept of resonance or unpaired eunpaired e--
2. Cannot explain color in2. Cannot explain color in transition metal transition metal compounds compounds
Strengths of Strengths of Molecular Orbital ModelMolecular Orbital Model
1. Better represents 1. Better represents actual molecular systemactual molecular system
2. Provides basis for 2. Provides basis for explaining properties of explaining properties of molecular systemsmolecular systems
Limitations of Limitations of Molecular Orbital Molecular Orbital
ModelModel1. MO diagrams are complex.
2. MO diagrams are difficult for molecules with more than two atoms.
3. No prediction of geometry
Combining the Localized Electron
and Molecular Orbital
Models
Draw the Lewis structure of benzene
C6H6
Lewis Structure
C2H4 + Br2 C2H4Br2
C6H6 + Br2 NR
bonds in benzene
bonds in benzene
benzene
Isomerism Isomerism
Isomers – two or more compounds Isomers – two or more compounds with same molecular formula but with same molecular formula but different arrangements of atoms different arrangements of atoms
Cis – Trans Isomerism (NOT mirror Cis – Trans Isomerism (NOT mirror images of each other NOT super images of each other NOT super imposable.imposable.
CisCis Trans Trans
Resonance and MOResonance and MO
X X
The more resonance structures the more stable the molecule
Metals & SemiconductorsMetals & Semiconductors Read pg657-669Read pg657-669 Study Figures 1-23Study Figures 1-23
Know Know InsulatorsInsulators
Conductors, Semiconductors – intrinsic, Conductors, Semiconductors – intrinsic, extrinsicextrinsic
DopantsDopants