1. Chapter 13 Molecular Shapes VSEPR Theory

2. Molecular Shape
Molecular shape or molecular geometry is the three-dimensional arrangement of the atoms in a molecule.

3. Molecular Shape
Molecular shape determines several properties of a substance including:
reactivity
polarity
phase of matter
color
magnetism
biological activity

4. Olfaction – sense of smell
Lock-and-Key Theory: humans can smell various odors because each three-dimensional odor molecule fits into only one type of receptor.

6. Gustation – the sense of taste
Taste receptors are located on the tongue and are sensitive to four major tastes: salty, sweet, sour and bitter.
Taste receptors respond differentially to the varying shapes of the food molecules that we eat.

7. H2
2(1) = 2e- H H
Any 2 atoms
linear

8. What about molecules consisting of more than two atoms
For this we must use the VSEPR Theory

9. VSEPR Theory Valence Shell Electron Pair Repulsion Theory
Predicts the molecular shape of a bonded molecule containing a central atom(s).
Electrons around the central atom arrange themselves as far apart from each other as possible
So only electrons (lone pairs or bonds) connected to the central atom are important.

10. See the table in your notes
Five Molecular Shapes
See the table in your notes

12. Steps in Determining Molecular Shape
Draw the Lewis Structure for the Molecule.
Count the number of atoms attached to the central atom.
Count the number of lone pairs attached to the central atom.
Use your counts on steps 2 and 3 to determine the shape of the molecule.

14. H2S
2(1)+6 = 8e-
Dihydrogen monosulfide is commonly known as sewer gas. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs. ••
2/2
angular H S H ••

15. H2S
Dihydrogen monosulfide is commonly known as sewer gas. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs. •• •• S H H

16. Methane (CH4)
4 + 4(1) = 8e-

17. Methane (CH4) Tetrahedral shape 4 + 4(1) = 8e-
4 atoms attached to the central atom.
0 lone pairs on the central atom.
4/0
Tetrahedral shape

18. Methane (CH4) Tetrahedral shape 4 + 4(1) = 8e-
4 atoms attached to the central atom.
0 lone pairs on the central atom.
4/0
Tetrahedral shape

19. HCN
1+4+5 = 10e- •• •• H C N • •• ••

20. HCN
1+4+5 = 10e- •• •• H C N • •• ••

21. HCN
1+4+5 = 10e- •• •• H C N • •• ••

22. HCN
1+4+5 = 10e- •• •• H C N ••

23. HCN
1+4+5 = 10e- •• •• H C N ••

24. HCN
1+4+5 = 10e- •• H C N
2/0
linear

25. H2S •• •• S H H
2/2
angular

26. SO2
6+2(6) = 18e- •• •• •• O S O • • •• •• ••

27. SO2
6+2(6) = 18e- •• •• •• O S O • • •• •• ••

28. SO2
6+2(6) = 18e- •• •• •• O S O • • •• •• ••
2/1
angular

29. CH4
4/0
tetrahedral

30. NO3-
5+3(6)+1 = 24e- •• •• •• O N O • • •• •• O • • ••

31. NO3-
5+3(6)+1 = 24e- •• •• •• O N O • • •• •• O • • ••

32. NO3-
5+3(6)+1 = 24e- •• •• •• O N O • • •• •• O • • ••

33. [ ]- O N O O NO3- 3/0 trigonal planer 5+3(6)+1 = 24e- •• •• • • •• ••
[ ]- •• •• O N O • • •• •• O
3/0
trigonal planer • •

34. SOCl2

35. SOCl2

36. Draw the Lewis structure for an acetate ion?
You learned acetate as C2H3O2-. However writing it as CH3CO2- will give you a better understanding of its Lewis structure.

37. Draw the Lewis structure for an acetate ion?

38. What’s the shape of acetate?
3/0
trigonal planer
4/0
tetrahedral

39. Homework Worksheet Chapter 13 (due tomorrow).
Study Guide Chapters 12 – 14 (due next week?).