VSEPR Theory Valence Bond Theory Molecular Orbital Theory Molecular Geometry.
Lecture 11 - VSEPR Theory, Molecular Shape
27
Theory, Molecular Shape 5 Base e - pair geometries will predict 13 Molecular geometries STEPS FOR SUCCESS: 1. draw Lewis 2. bonding pairs 3. lone pairs 4. multiple bonds count as one bonded pair
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Lecture 11 - VSEPR Theory, Molecular Shape. 5 Base e - pair geometries will predict 13 Molecular geometries STEPS FOR SUCCESS: draw Lewis bonding pairs lone pairs multiple bonds count as one bonded pair. Resonance Structures. e.g. O 3 (ozone). :. :. OOO OOO. OOO - PowerPoint PPT Presentation
Transcript of Lecture 11 - VSEPR Theory, Molecular Shape
Lecture 11 - VSEPR Theory, Molecular Shape
5 Base e- pair geometries will predict
13 Molecular geometries
STEPS FOR SUCCESS:1. draw Lewis
2. bonding pairs
3. lone pairs
4. multiple bonds count as one bonded pair
Resonance Structures
e.g. O3 (ozone)
O O O O O O..
.... ..
..:.... ..
..:
..
e.g. SO3
O O O
S O S O S O
O O O
e.g. carbonate ion, CO3-2
O O O
C O C O C O
O O O
-2 -2-2
Molecules that don’t obey rules
Case 2. Incomplete octets
F
B F
F
H - Cl
Molecules that don’t obey rules
Case 3. Expanded Octets
e.g. Phosphorus [Ne] 3s2 3p3
e.g. Sulfur [Ne] 3s2 3p4
e.g Xenon [Ne] 3s2 3p6
3d sublevel is close in energy to 3p!
Molecules that don’t obey rules
Case 3. Expanded Octets
Cl FCl F F
Cl P SCl F F
Cl F
10 electrons! 12 electrons!
Molecules that don’t obey rules
Case 3. Expanded Octets
Xe
F
F
F
F
: :
12 electrons!
Predicting Molecular Shapes
VSEPR Theory
(Valence Shell Electron Pair Repulsion)
- Electron clouds repel one another
- Terminal atoms move as far apart as possible
- Distinctive geometry results
VSEPR
Step 1.
- count the number of total electron pairs around the central atom
- count # Bonding Pairs - count # Nonbonding or Lone Pairs
Step 2. Predict the shape!
VSEPR
Electron Bonds Lone Notation Shape
Pairs Pairs
2 2 0 AX2 linear
3 3 0 AX3 trigonal
planar
3 2 1 AX2E bent
AX2 e.g. CO2
(Linear)
O = C = O
bond angle = 180o
AX3 e.g. BF3
(trigonal planar)
bond angle = 120o
BF
FF
AX2E e.g. SO2
(bent)
bond angle = 105o
SO
O
:
VSEPR
Electron Bonds Lone Notation Shape
Pairs Pairs
4 4 0 AX4 tetrahedral
4 3 1 AX3E trigonal pyramidal
4 2 2 AX2E2 bent
AX4 e.g. methane
C
All angles 109.5o(tetrahedral)
AX3E e.g. ammonia
..
107o
(trigonal pyramidal)
AX2E2 e.g. water
..
..105o
(bent)
VSEPR
Electron Bonds Lone Notation Shape
Pairs Pairs
5 5 0 AX5 trigonal bipyramidal
5 4 1 AX4E see-saw
5 3 2 AX3E2 T-shaped
5 2 3 AX2E3 Linear
AX5
ClCl
Cl PCl
Cl
ideal angles: 90o, 120o
(trigonal bipyramidal)
AX4E
FF
SF
F
:
ideal angles: 90o, 120o
(seesaw)
AX3E2
Cl
Cl I
Cl
:
:
ideal angles: 90o
(t-shaped)
AX2E3
F
Xe :
F
:
:
angle: 180o
(linear)
VSEPR
Electron Bonds Lone Notation Shape
Pairss Pairs
6 6 0 AX6 octahedral
6 5 1 AX5E square pyramidal
6 4 2 AX4E2 square planar
AX6
F
F FS
F F
Fall angles 90o
(octahedral)
AX5E
F
F FI
F F:
all angles 90o
(square pyramidal)
AX4E2
:
F FXe
F F :all angles 90o
(square planar)
