1. Unit 12, Part II: VSEPR Theory
Molecular Geometry
Unit 12, Part II: VSEPR Theory
Unit 12: Molecular Structure
LPChem: Wz

2. Molecular Geometry Geometry = shapes VSEPR Theory Valence Shell
Electron
Pair
Repulsion
AKA: electrons hate each other
LPChem: Wz
Unit 12: Molecular Structure

3. VSEPR Theory mutual repulsion.
The electrons interacting in molecules (valence shell electron pairs)
Are REPULSED by each other.
The electron pairs around the central atom orient themselves as far apart as possible– in order to minimize their
mutual repulsion.
LPChem: Wz
Unit 12: Molecular Structure

4. VSEPR Shapes
“Atoms bonded to the same central atom, orient themselves as far apart as possible.”
The central atom in a Lewis Dot Structure could be bonded to:
Only 1 other atom or…
As many as ____ other atoms
LPChem: Wz 6
Unit 12: Molecular Structure

5. VSEPR Shapes
If there are 2 atoms bonded to the same central atom, what is the farthest apart they can be?
LPChem: Wz
Because they are repulsed by each other.
The 2 atoms bonded to the center atom are trying to stay far away from each other.
Unit 12: Molecular Structure

6. VSEPR Shapes
Try it!
What happens when 3 atoms are bonded to the same central atom?
4 atoms? 5? 6?
(Hint: with 4, 5, or 6 secondary atoms, the molecule will NOT be flat!)
LPChem: Wz
Unit 12: Molecular Structure

7. Center atom (A) = large marshmallow
Toothpicks = bonds (Use single bonds only.)
Secondary atoms (B) = small marshmallow
(5 large, 20 small, 20 toothpicks)
Build 5 molecules:
AB2
AB3
AB4
AB5
AB6
LPChem: Wz
These three should
NOT be flat!
Unit 12: Molecular Structure

8. VSEPR Shapes We built: Their electron domain shapes: Linear
AB2
AB3
AB4
AB5
AB6
Their electron domain shapes:
Linear
Trigonal Planar
Tetrahedral
Trigonal Bipyramidal
Octahedral
LPChem: Wz
Unit 12: Molecular Structure

9. About your VSEPR notes:
ABxEy form
A = central atom
B = bonding domains
E = unshared electron pairs
Bond angle: the angle between the bonds to two secondary atoms.
LPChem: Wz
Unit 12: Molecular Structure

10. VSEPR Shapes AB2: Linear 2 domains 180º Linear CS2
LPChem: Wz
180º
Linear
CS2
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

11. About your VSEPR notes:
AB2: Linear
2 domains
LPChem: Wz
180º
Linear
CS2
Electron Domain Shape and Molecular Shape are the same when there are no unbonded pairs (E).
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

12. About your VSEPR notes:
AB2: Linear
2 domains
LPChem: Wz
If one end of the molecule is more electronegative than the other, it is a POLAR molecule.
Molecules that are symmetrical (in 3D) are NONPOLAR.
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

13. About your VSEPR notes:
AB2: Linear
2 domains
LPChem: Wz
180º
Linear
CS2
Bonds only count as ONE bonding domain (B) even if they are double or triple bonds!
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

14. VSEPR Shapes AB1Ex : Linear 2 domains 180º
LPChem: Wz
180º
Linear (two points make a line) CO
Polar (unless both atoms are identical)
Unit 12: Molecular Structure

15. VSEPR Shapes AB3: Trigonal planar 3 domains 120º Trigonal planar NO3-
LPChem: Wz
120º
Trigonal planar
NO3-
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

16. VSEPR Shapes AB2E: Trigonal planar 3 domains (2B +1E) <120º
LPChem: Wz
<120º
Bent 120
SO2
Always Polar
(because of the unshared pair)
Unit 12: Molecular Structure

17. VSEPR Shapes AB4: Tetrahedral 4 domains ~109º Tetrahedral CH4
LPChem: Wz
~109º
Tetrahedral
CH4
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

18. VSEPR Shapes AB3E: Tetrahedral 4 domains (3B + 1E) <109º
LPChem: Wz
<109º
Trigonal Pyramidal
NH3
Always Polar
(because of the unshared pair)
Unit 12: Molecular Structure

19. VSEPR Shapes AB2E2: Tetrahedral 4 domains (2B + 2E) <<109º
LPChem: Wz
<<109º
Bent 109
H2O
Always Polar
(because of the unshared pairs)
Unit 12: Molecular Structure

20. AB5: Trigonal Bipyramidal
VSEPR Shapes
AB5: Trigonal Bipyramidal
5 domains
LPChem: Wz
120º & 90º
Trigonal Bipyramidal
PF5
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

21. AB4E: Trigonal Bipyramidal
VSEPR Shapes
AB4E: Trigonal Bipyramidal
5 domains (4B + 1E)
LPChem: Wz
<120º & <90º
See-saw
SF4
Always Polar
(because of the unshared pair)
Unit 12: Molecular Structure

22. AB3E2: Trigonal Bipyramidal
VSEPR Shapes
AB3E2: Trigonal Bipyramidal
5 domains (3B + 2E)
LPChem: Wz
<90º
T-Shaped
ClF3
Always Polar
(because of the unshared pairs)
Unit 12: Molecular Structure

23. AB2E3: Trigonal Bipyramidal
VSEPR Shapes
AB2E3: Trigonal Bipyramidal
5 domains (2B + 3E)
LPChem: Wz
180º
Linear
XeF2
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

24. VSEPR Shapes AB6: Octahedral 6 domains 90º Octahedral SF6
LPChem: Wz
90º
Octahedral
SF6
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

25. VSEPR Shapes AB5E: Octahedral 6 domains (5B + 1E) <90º
LPChem: Wz
<90º
Square Pyramidal
ClF5
Always Polar
(because of the unshared pair)
Unit 12: Molecular Structure

26. VSEPR Shapes AB4E2: Octahedral 6 domains (4B + 2E) 90º Square Planar
LPChem: Wz
90º
Square Planar
KrF4
Nonpolar (if the secondary atoms match)
Unit 12: Molecular Structure

27. Remember: VSEPR Theory H N
Shape is defined by the CENTRAL atom.
LPChem: Wz
The total number of electron domains touching the CENTRAL ATOM is what determines the shape of the molecule.
Electron domain:
Bonded electron pair(s) OR
Unshaired pair
Unit 12: Molecular Structure

28. VSEPR Theory O S Electron domains: Bonded electron pair(s)
A single bond = 1 electron domain.
LPChem: Wz S O
A double bond = 1 electron domain (surprise!)
A triple bond? Still just 1 domain.
Unshaired pair = 1 electron domain
Unit 12: Molecular Structure