9/29/2008
Chem 4A F2008 Lecture 13: Molecular
Structure VSEPR
Molecular Structure and
Geometry
H
H
: :
H C
0
C O H
H
H
O
0
0
O S O
-1
O -1
Steric Number = #LP + # bonded atoms
© 2008 A. Pines M. Kubinec
L13-1
VSEPR Shapes
Valence Shell Electron Pair Repulsion
2
Linear
180º
180º
Trigonal
Bipyramidal
5
90º
90º,120º
,120º
Trigonal
3
120º
120º
Octahedral
6
Tetrahedral
4
4
90º
90º
109.5º
109.5º
© 2008 A. Pines M. Kubinec
L13-2
VSEPR Examples
O C O Cl B Cl
H
H
+
C H
H
+
N H
H
H
H
H
C
H
C
: :
O
H
+
Cl
Cl
H
H
F
F
Cl
P Cl
Cl
F
:
F
F
: I
F
..
F F
F
S
Xe
F F
F
..
F
© 2008 A. Pines M. Kubinec
L13-3
© 2008 A. Pines M. Kubinec
1
9/29/2008
Chem 4A F2008 Lecture 13: Molecular
Structure VSEPR
ChemQuiz© 13.1
In the following acidacid-base
reaction, which species has
the largest bond angle?
angle?
NH4+ + H2O
H3O+ + NH3
A) H3O +
+
C) NH4
B) NH3
© 2008 A. Pines M. Kubinec
L13-4
ChemQuiz© 13.2
A) CH2Cl2
-
+
Which of the following
has an electric dipole
moment?
moment?
C) BrF
BrF3
B) SO2
© 2008 A. Pines M. Kubinec
L13-5
ChemQuiz© 13.3
How does the bond angle C2C2-C1C1-O
change in the oxidation reaction
OH
CH3CH2
2
O2
2
1
A) increase
O
CH3CH
B) same
1
C) decrease
© 2008 A. Pines M. Kubinec
L13-6
© 2008 A. Pines M. Kubinec
2
9/29/2008
Chem 4A F2008 Lecture 13: Molecular
Structure VSEPR
Isomers
Molecules of the same formula with different
arrangements of the atoms
Stereo
Structural
- - -
HH
H-C-C-O-H
HH
- -
- -
H H
H-C-O-C-H
H H
Cl
Cl
Cl
C= C
H
H
H
Cl
H
C= C
C= C
H
Cl
Cl
H
© 2008 A. Pines M. Kubinec
L13-7
ChemQuiz© 13.4a
C5H12
How many structural
isomers are there of
CH2 CH2
the hydrocarbon
“pentane”
pentane”?
H3C
CH2
CH3
A) 3
B) 5
C) 7
© 2008 A. Pines M. Kubinec
L13-8
Isomers: Stereo (Chiral)
Enantiomers
L
D
© 2008 A. Pines M. Kubinec
L13-9
© 2008 A. Pines M. Kubinec
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9/29/2008
Chem 4A F2008 Lecture 13: Molecular
Structure VSEPR
Non Superimposable
Mirror Images
© 2008 A. Pines M. Kubinec
L13-10
Non Superimposable
Mirror Images
© 2008 A. Pines M. Kubinec
L13-11
Chiral Molecules
Alanine
N
C
C
O
O
C
C
O
LeftLeft-handed
DNA Helix
L
N
C
C
O
D
RightRight-handed
DNA Helix
© 2008 A. Pines M. Kubinec
L13-12
© 2008 A. Pines M. Kubinec
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9/29/2008
Chem 4A F2008 Lecture 13: Molecular
Structure VSEPR
ChemQuiz© 13.4b
Which of the following structural
isomers of octane is chiral?
chiral?
C
C
C) C-C-C-C
C
© 2008 A. Pines M. Kubinec
-
C-C
B) C-C-C-C-C
C H2
C
- -
C
C H3
C H3
-
C
-
- -
C
A) C-C-C-C-C
C H2
C H2
-
C H3
C H2
-
C H2
C
L13-13
© 2008 A. Pines M. Kubinec
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