1. Valence Shell Electron Pair Repulsion Theory
VSEPR Theory
Valence Shell Electron Pair Repulsion Theory
“Atomium Building”, Andre Waterkeyn (architect), 1958

3. VSEPR Theory
A method for predicting the shape of a molecule from the knowledge of the groups of electrons around a central atom.
The shape of a molecule is very important for its physical and chemical properties.

4. Demo: Water and a Balloon

5. Electron pairs (bonding and nonbonding electrons) repel one another
Electron pairs (bonding and nonbonding electrons) repel one another. As a result, the electron pairs remain as far apart as possible from another as possible to minimize the repulsion.

6. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2

7. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
linear

8. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3

9. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer

10. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4

11. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4
Tetrahedral

12. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4
Tetrahedral 5

13. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4
Tetrahedral 5
Trigonal bipyramidal

14. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4
Tetrahedral 5
Trigonal bipyramidal 6

15. Electron Pairs Around a Central Atom (bonding or nonbonding
Arrangement
Diagram 2
Linear 3
Trigonal planer 4
Tetrahedral 5
Trigonal bipyramidal 6
Octahedral

16. Lone Pairs
The shapes on the previous slides are the general arrangements for electron domains. Whether the domain is a lone pair or a bonding pair affects the geometry of the molecule.
Repulsion Strength
lone pair-lone pair  lone pair-bond pair  bond pair-bond pair

17. Geometries 2 Linear 180 # of Electron Domains # of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 2
Linear
180

18. Geometries 3 120 Trigonal Planer # of Electron Domains # of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 3
Trigonal Planer
120

19. Geometries 3 120 2 1 Bent <120 Trigonal Planer
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 3
Trigonal Planer
120 2 1
Bent
<120

20. Geometries 4 109.5 Tetra-hedral # of Electron Domains # of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 4
Tetra-hedral
109.5

21. Geometries 4 109.5 3 1 Tetra-hedral Trigonal Pyrami-dal <109.5
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 4
Tetra-hedral
109.5 3 1
Trigonal Pyrami-dal
<109.5

22. Geometries 4 109.5 3 1 2 Bent Tetra-hedral Trigonal Pyrami-dal
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 4
Tetra-hedral
109.5 3 1
Trigonal Pyrami-dal
<109.5 2
Bent

23. Geometries 5 90 & 120 Trigonal Bipyramidal # of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 5
Trigonal Bipyramidal
90 &
120

24. Geometries 5 4 1 90 & 120 <90 & See-saw <120
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 5
Trigonal Bipyramidal
90 &
120 4 1
See-saw
<90 &
<120

25. Geometries 5 4 1 3 2 90 90 & 120 <90 & See-saw <120 T-shape
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 5
Trigonal Bipyramidal
90 &
120 4 1
See-saw
<90 &
<120 3 2
T-shape 90

26. Geometries 5 4 1 3 2 90 90 & 120 See-saw <90 & <120 T-shape
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 5
Trigonal Bipyramidal
90 &
120 4 1
See-saw
<90 &
<120 3 2
T-shape 90
Linear
180

27. Geometries 6 90 Octahedral # of Electron Domains # of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 6
Octahedral 90

28. Geometries 6 5 1 90 Square Pyramidal <90 Octahedral
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 6
Octahedral 90 5 1
Square Pyramidal
<90

29. Geometries 6 5 1 4 2 90 Square Pyramidal <90 Square Planer
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 6
Octahedral 90 5 1
Square Pyramidal
<90 4 2
Square Planer

30. Geometries 6 5 1 4 2 3 90 Square Pyramidal <90 Square Planer
# of Electron Domains
# of Bonds
# of Lone Pairs
Molecular Geometry
Name
Model
Approx. Bond Angle 6
Octahedral 90 5 1
Square Pyramidal
<90 4 2
Square Planer 3
T-Shape

31. Seesaw

32. Molecular Polarity Molecules can be polar or nonpolar.
Molecular polarity depends on the symmetry of the molecule.
(Remember, polar means “having two sides”)

33. Nonpolar Molecules
Nonpolar molecules are symmetrical and have dipoles that cancel out.

34. Polar Molecules
Polar molecules are asymmetrical and have dipoles that do not cancel out.

35. Practice
Determine whether each of the following molecules is polar or nonpolar.
Polar

36. Practice
Determine whether each of the following molecules is polar or nonpolar.
Nonpolar

37. Practice
Determine whether each of the following molecules is polar or nonpolar.
Nonpolar

38. Practice
Determine whether each of the following molecules is polar or nonpolar.
Polar