Transcript AP Notes Chapter 10

AP Notes Chapter 9
Hybridization and the Localized
Electron Model
Valence Bond Theory
Molecular Orbital Theory
Metals & Semiconductors
Hybridization and the Localized Electron
Model
Localized Electron Model developed from
Valence Bond Theory
Why do we need it?
 Consider
H
the water species.
1s1
1s ___
1s1
1s ___
H
O 1s2 2s2 2p4
2s ___ 2p ___ ___ ___
Gives 2 H’s with no e- and O with full octet.
We Get
H
1s1
1s ___
1s1
1s ___
H
O 1s2 2s2 2p4
2s ___ 2p ___ ___ ___
Gives 2 H’s with no e- and O with full octet.
Hybridization

Process that changes properties of
valence electrons by mixing atomic
orbitals to form special orbitals for
bonding

atomic
orbitals
AO
molecular
orbitals
MO
Principles
1. Conservation of orbitals
2. Hybrid correlates with
molecular geometry
3. Energy level of MO is
between that of AO’s
4. All bonded atoms hybridize
WHEN ATOMS BOND
atomic
orbital
hybrid
orbital
All hybrid orbitals of
an atom are said to be
DEGENERATE
(of equal energy)
CH4
C: AO
H
H
C H
H
2p __ __ __
2s ____
CH4
H
H
C H
MO
H
__ __ __ __
sp3 hybrid orbitals
3
sp
hybridization
sp3 hybrid orbitals
tetrahedral species
sp3 shape tetragonal
4 Items Equally Distributed

Tetragonal
H
Lewis Structure
H
C H
H
Electron Pair Geometry
H
Molecular Model
H
C H
H
InCl3
Cl
In: AO
In
Cl
5p __ __ __
5s _____
Cl
InCl3
Cl
MO
In
Cl
Cl
5p __
__ __ __
sp2 hybrid orbitals
2
sp
hybridization
2
sp hybrid
trigonal planar species
2
sp shape
3 Items Equally Distributed
BaCl2
Cl - Ba - Cl
Ba: AO
6p ___ ___ ___
6s _____
BaCl2
Cl - Ba - Cl
Ba:
MO
6p ___ ___
___ ___
sp hybrid orbitals
sp hybridization
sp hybrid
linear species
sp shape
2 Items Equally Distributed
PF5
P:
AO
3d ___ ___ ___ ___ ___
3p ___ ___ ___
3s ____
PF5
P:
MO
3d ___ ___ ___ ___
___ ___ ___ ___ ___
sp3d hybrid orbitals
3
sp d
hybridization
sp3d shape
trigonal bipyramid
species
5 Items Equally Distributed
SF6
S:
AO
3d ___ ___ ___ ___ ___
3p _____ ___ ___
3s _____
SF6
S:
MO
3d ___ ___ ___
___ ___ ___ ___ ___ ___
sp3d2 hybrid orbitals
3
2
sp d
hybridization
sp3d2 shape
octahedral species
6 Items Equally Distributed
Multiple Bonds
sigma bonds ()
pi bonds ()
EXAMPLES
O2
O 1s2 2s2 2p4
2p4 2s2 1s2 O
2s ___ 2p ___ ___ ___
2p ___ ___ ___ 2s ___
___ ___
2 p-orbitals touching end to end sigma - σ
2p-electrons reaching over and under pi - π
Valence Bond Theory
Multiple Bond Examples
C2H4 (ethylene)
3
  (sp hybridization)

 (

both
bonding)
EXAMPLES
C2H2
EXAMPLES
CH3COOH
MOLECULAR ORBITAL MODEL
Valence Bond Theory
concentrates on
individual bonds in a
molecule and tends to
ignore electrons not
used in bonding.
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
1s wavefunction
r
+
Negative
here
Positive
here
-
2pz wavefunction
+
1s orbital
-
+
2pz 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
.B
*
,
A sigma star,
anti-bonding orbital
The work on molecular
orbitals can be
generalized to
p-orbitals.
2pz
2pz
2p
A 2p bonding orbital
2pz
2pz
2p*
*
2p
A
antibonding orbital
A
2p
y
plus
2p
B
A
B
2p
A 2p bonding
orbital
y
A minus B
2py
A
B
2p*
2py
*
2p
A
antibonding orbital
Many combinations of
orbitals can produce
bonding and antibonding molecular
orbitals, s with p,
d with p, etc.
Orbitals on the two
bonding atoms must
meet 2 conditions
 They
must be similar in
energy
 They must have the right
symmetry
plus
2pz
2pz
2py
2py
Orbitals pointing in different
directions cannot overlap to
form molecular orbitals.
Molecular Orbital
Theory
1. Molecular orbitals are
made from atomic
orbitals
2. Orbitals are conserved
3. Molecular orbitals form
in pairs: bonding &
antibonding
Bonding
Molecular Orbital
Geometry
overlap
favorable to
When a bonding orbital
is formed, the energy of
the orbital is lower than
those of its parent
atomic orbitals.
Anti-bonding
Molecular Orbital
Geometry
not
favorable to overlap
Similarly, when an antibonding orbital is
formed, the energy of
the orbital is higher
than those of its parent
atomic orbitals.
Molecular Orbital Diagrams
Bond Order
# bonding e -  # antibonding e 2
Examine some
homonuclear diatomic
molecules
 Hydrogen
 Helium
2s*
1sA
1sB
2s
Paramagnetic
1. Responds to
magnetic field
2. Has unpaired
electrons
Diamagnetic
1. Does not respond to
magnetic field
2. All electron paired
2p*
2px 2py2pz
2p
2p*
2px 2py 2pz
2p
2s*
2s
2p*
2s
2p
2s
1s*
1s
fluorine gas
1s
1s
2p*
2px 2py2pz
2p
2p*
2px 2py 2pz
2p
2s*
2s
2p*
2s
2p
2s
1s*
1s
oxygen gas
1s
1s
Using MO Theory, molecules
have an
electron configuration
 Oxygen
gas
 (1s)2(1s*)2
 (2s)2(2s*)2
 (2py)2 (2py*)2
 (2pz)2 (2px)2
2p*
2px 2py2pz
2p
2p*
2px 2py 2pz
2p
2s*
2s
2p*
2s
2p
2s
1s*
1s
nitrogen gas 1s
1s
Magnet Movie
Bond Strength
Bond Length
Strengths of
Localized Electron
Model
1. Simple
2. Easy to understand
3. Predicts geometry of
molecule
Limitations of
Localized Electron Model
1. Does not address
concept of resonance or
unpaired e
2. Cannot explain color in
transition metal
compounds
Strengths of
Molecular Orbital Model
1. Better represents
actual molecular system
2. Provides basis for
explaining properties of
molecular systems
Limitations of
Molecular Orbital Model
1. 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
C6 H 6
Lewis Structure
C2H4 + Br2  C2H4Br2
C6H6 + Br2  NR
 bonds in benzene
 bonds in benzene
benzene
Isomerism


Isomers – two or more compounds with
same molecular formula but different
arrangements of atoms
Cis – Trans Isomerism (NOT mirror images
of each other NOT super imposable.
Cis
Trans
Resonance and MO
X
X
The more resonance structures the more
stable the molecule
Metals & Semiconductors
Read pg657-669
 Study Figures 1-23
Know

Insulators
Conductors, Semiconductors – intrinsic, extrinsic
Dopants