Advanced Theories of
Chemical Bonding
1
Chapter 10
Atomic Orbitals
• MOLECULAR
ORBITAL THEORY —
Robert Mullikan (18961986)
• valence electrons are
delocalized
• valence electrons are
in orbitals (called
molecular orbitals)
orbitals)
spread over entire
molecule.
Molecules
Sigma Bond Formation by
Orbital Overlap
Two Theories of Bonding
2
4
• VALENCE BOND THEORY —
Linus Pauling
• valence electrons are localized
between atoms (or are lone pairs).
• half-filled atomic orbitals overlap
to form bonds.
• See Screen 10.3 and Figures 10.1
and 10.2.
Sigma Bond Formation
Two s
orbitals
overlap
Two s orbitals
overlap
Two Theories of Bonding
3
Two p
orbitals
overlap
5
6
Using VB Theory
Bonding in BF3
•• ••
F ••
Boron configuration
B
••
••••
F
F•
2p
2s
••
•• • 1s
planar triangle
angle = 120o
Page 1
7
Bonding in BF3
8
Bonding in BF3
• How to account for 3 bonds 120o apart using
a spherical s orbital and p orbitals that are 90o
apart?
• Pauling said to modify VB approach with
hydridize orbs.
Bonding in BF33
•
The three hybrid orbitals are made
from 1 s orbital and 2 p orbitals
3 sp2
hybrids.
2p
2s
9
rearrange electrons
ORBITAL HYBRIDIZATION
• — mix available orbitals to form a new
set of orbitals — HYBRID ORBITALS
— that will give the maximum overlap
in the correct geometry. (See Screen 10.6)
three sp 2
hybrid orbitals
unused p
orbital
10
Bonding in BF33
11
Bonding in CH4
How do we account for 4
C—H sigma bonds
109o apart?
An orbital from each F overlaps one of the
sp2 hybrids to form a B-F bond.
FF
FF
•
Now we have 3, half-filled HYBRID orbitals
that can be used to form B-F sigma bonds.
See Figure 10.9 and Screen 10.6
BB
FF
Need to use 4 atomic
orbitals — s, px, py,
and pz — to form 4 new
hybrid orbitals
pointing in the correct
direction.
Page 2
o
109
109o
Bonding in a Tetrahedron —
Formation of Hybrid Atomic Orbitals
4 C atom orbitals
hybridize to form
four equivalent sp 33
hybrid atomic
orbitals.
orbitals.
12
Bonding in a Tetrahedron —
Formation of Hybrid Atomic Orbitals
13
14
15
Orbital Hybridization
Bonding in CH 4
Figure
Figure 10.5
10.5
44 C
C atom
atom orbitals
hybridize
hybridize to
to form
form
four
four equivalent
equivalent sp
sp33
hybrid
atomic
hybrid atomic
orbitals.
orbitals
orbitals..
BONDS
SHAPE
HYBRID REMAIN
2
linear
sp
2 p’s
3
trigonal
planar
sp2
1p
4
tetrahedral sp 3
none
Figure 10.6
16
17
18
Bonding in
Glycine
sp
3
H
••
H N
sp
3
Bonding in
Glycine
C
H H
C ••
O H
••
sp
Page 3
sp
sp 2
O
3
3
H
••
H N
sp
3
C
H H
O
sp 2
C ••
O H
••
sp 3
19
20
Bonding in
Glycine
sp
H
••
H N
sp
3
C
H H
sp
••
H N
sp
C
H H
C
sp
2
sp
2
3
H
O
C
H H
C
••
H N
••
O H
••
sp
3
sp 3
H
C
sp
C
H
H
H
2
2
••
O H
••
24
Bonding in C 2H4
The unused p orbital on
each C atom contains an
electron and this p orbital
overlaps the p orbital on
the neighboring atom to
form the bond. (See Fig.
10.9)
2s
Page 4
sp
sp 3
23
H
C
sp
3
120˚
H
H
O
Sigma Bonds in C2H4
Consider ethylene, C 2H4
H
H
3
Bonding in
Glycine
3
22
Multiple Bonds
C
sp
2
C ••
O H
••
sp
120˚
Bonding in
Glycine
3
O
21
2p
3 sp 2
hybrid
orbitals
p
orb.
for
bond
25
26
Bonding in C 2H4
and
Multiple Bonding
in C2H4
The unused p orbital on each C atom contains
an electron and this p orbital overlaps the p
orbital on the neighboring atom to form the
bond. (See Fig. 10.9)
27
Bonding in C2H4
Figure 10.11
28
and
Bonding in CH2O
29
and
Bonding in C2H2
Consequences of Multiple
Bonding
There is restricted rotation around C=C bond.
Figure 10.13
Figure 10.12
Figure 10.14
Page 5
30
Consequences of Multiple
Bonding
31
32
Double Bonds and Vision
Restricted rotation around C=C bond.
See Butene
Butene.Map
.Map in ENER_MAP in CAChe models.
See Screen 10.13, Molecular Orbitals and Vision
See also Chapter Focus 10, page 380
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