1. Timberlake LecturePLUS
4.8 Shapes of Molecules
Determined by number of valence electrons of the central atom
3-D shape a result of bonded pairs and lone pairs of electrons
Use VSEPR theory (valence-shell-electron-pair repulsion
Timberlake LecturePLUS

2. Timberlake LecturePLUS
Using the VSEPR Model
1. Draw the electron-dot structure
Identify the central atom
Count the total number of electron pairs around central atom
Predict the electron shape
Predict the shape of the molecule using the bonding atoms
Timberlake LecturePLUS

3. Timberlake LecturePLUS
Shapes of Molecules
Number of electron pairs 2
(= negative charge clouds)
Number of bonded atoms
Angle °
Name of shape linear
Timberlake LecturePLUS

4. Timberlake LecturePLUS
BeCl2
Be 2 valence electrons
: Cl : Be : Cl :
: Cl Be Cl : linear, 180°
Timberlake LecturePLUS

5. Timberlake LecturePLUS
More Electron Pairs
Electron Angle Bonded Name of
Pairs Atoms Shape
3 120° trigonal planar
3 120° angular
Timberlake LecturePLUS

6. Electron Shape with 3 Pairs
Timberlake LecturePLUS

7. Timberlake LecturePLUS
BF3
B has 3 valence electrons °
F trigonal
planar B
F F
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8. Timberlake LecturePLUS
SO2
S has 2 bonded atoms , 1 lone pair (electron cloud)
120°, angular
:O:: S:O: S ..
O O
Timberlake LecturePLUS

9. Timberlake LecturePLUS
More Electron Pairs
Electron Angle Bonded Name of
Pairs Atoms Shape
4 109° tetrahedral
4 109° pyramidal
4 109° bent, angular
Timberlake LecturePLUS

10. Timberlake LecturePLUS
Tetrahedral CH4
4 electron Pairs, 4 bonded atoms, 109°
H H
C H C H H
H H H
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11. Timberlake LecturePLUS
NH3 Pyramidal
N has 4 electron pairs, 3 bonded H atoms
Shape is called pyramidal ..
H : N : H N
H H
H H ..
Timberlake LecturePLUS

12. Timberlake LecturePLUS
H2O Bent or Angular
O has 4 electron pairs, 2 bonded H atoms
Shape is called bent or angular, 109° ..
: O : H O H
H H .. ..
Timberlake LecturePLUS

13. Timberlake LecturePLUS
Learning Check
Determine the molecular geometry of each of the following:
A. CCl4
1) tetrahedral 2) pyramidal 3) angular
B. SO3
1) trigonal planar 2) pyramidal 3) angular
C. PCl3
1) trigonal planar 2) pyramidal 3) angular
Timberlake LecturePLUS

14. Timberlake LecturePLUS
Solution
Determine the molecular geometry of each of the following:
A. CCl4
1) tetrahedral
B. SO3
1) trigonal planar
C. PCl3
2) pyramidal
Timberlake LecturePLUS