1. Valence Shell Electron Pair
VSEPR
Valence Shell Electron Pair
Repulsion Theory
e–’s spread out in different shapes
to minimize repulsions.

2. How does a molecule get its shape?
assume e– pairs are spread out,
then predict the shape.

3. Electron Domains
All (single, double, or triple) bonds, are only 1 e– domain.
How many e– domains around the central atom A? 2 3
3 e– domains around A:
AB3 1
AB3
3 atoms

4. B AB3E AB3 Electron Domains
All (single, double, or triple) bonds, are only 1 e– domain.
Each lone e– pair is 1 e– domain.
How many e– domains around the central atom A? 2
4 e– domains around A: B 1
AB3E 3 4
AB3
3 atoms
1 e– pair

5. Molecular Geometry (shapes)
general form
example
AB2
linear
CO2
bond angle = ___o
around central atom
180
180o
AB3
trigonal planar
120o
BF3
bond angle = ___o
around central atom
120

6. Molecular Geometry (shapes)
general form
example
AB4
tetrahedral
90o ?
CH4
bond angle = ____o
around central atom
109.5
NH3
AB3E
trigonal pyramidal
H2O
AB2E2
bent

7. Molecular Geometry (shapes)
AB2
linear
(180o)
AB3
trigonal planar
(120o)
AB4
tetrahedral
(109.5o)
AB3E
trigonal pyramidal
AB2E2
bent

8. How to Predict Molecular Geometry
(shape)
(in 3 easy steps)
Draw the Lewis structure
Count e– domains (and types)
Name the shape.
Example: NH3 (ammonia)
tetrahedral?
4 domains =
AB4 ?
AB3E
trigonal pyramidal

9. Quick Quiz! What is the molecular geometry of the PH3 molecule? linear
trigonal planar
tetrahedral
trigonal pyramidal
AB3E

10. Quick Quiz. AB3 Which molecule has a trigonal planar geometry? NH3
H2O
CH3F
BH3
trigonal pyramidal
AB3E
AB2E2
bent
AB4
tetrahedral