1. [ [ Topics for Today O O O O O O Lewis Dot Structures II
Nonbonding electrons
Resonance
Electronegativity [ O O [ O O O O

2. Readings for Today (Review)
Atomic Structure and Periodicity Section 2.2
What’s in a bond? Seeing Electrons Section 2.3 [ O O [ O O O O

3. “We’ve got Styrofoam boxes for the ozone layer”
Topics for Wednesday
CFCs and the Ozone Hole
The Cl. Radical
Properties and Uses of CFCs!
“We’ve got Styrofoam boxes for the ozone layer”

4. Readings for Wednesday
Review 2.9 CFCs: Properties, uses and interactions with ozone
2.11 Responses to a global concern
2.12 Looking to the future

5. [ [ Topics for Today O O O O O O Lewis Dot Structures II
Nonbonding electrons
Resonance
Electronegativity [ O O [ O O O O

6. Non-Bonding Electrons
Handout B!

7. What are non-bonding electrons?

8. Valence electrons that do not partake in bonding.
What are non-bonding electrons?
Valence electrons that do not partake in bonding.
Easy enough….

9. Valence Electrons .. .. .. .. . . . . . . . . . . C N :O :Cl 4 5 6 7 43 2 1
# of bonds
Review

10. 2) KNOW the octet (or duet) rule!!
Drawing Lewis Dot Structures!!
2) KNOW the octet (or duet) rule!!
1) MEMORIZE the # valence electrons for C, H, O, N, Cl and related elements!

11. How many nonbonding electrons are in methane, ammonia, water, and HCl?

12. How many bonds will form?
REVIEW .
How many bonds will form? . . C .

13. REVIEW H H C H H
Methane, CH4
4 bonds around C (8 electrons)

14. How many bonds are likely to form?

15. Note the nonbonding pair.
Ammonia, NH3
Note the nonbonding pair. N H H H
3 bonds around N

16. O
How many bonds?

17. How many nonbonding pairs?
Water
How many nonbonding pairs?
O — H H
2 bonds around O

18. How many bonds is Cl likely to form?

19. How many nonbonding pairs?
Hydrogen chloride
How many nonbonding pairs?
H — Cl
1 bond from Cl

20. What happens to CFCs when they get into the atmosphere?

21. . . Cl Cl C F Cl C F + Cl F F What does UV light usually do to bonds?
Don’t forget about the nonbonding electrons!
What does UV light usually do to bonds?
UV-C Cl . . Cl C F Cl C F + Cl F F
FREON-12 (dichlorodifluoromethane)

22. λ < 220 nm
CCl2F2
.CClF2 +
Cl.
UV-C light

23. Where in the atmosphere does this take place?

24. Cl. Cl- .. .. . - :Cl :Cl: .. .. Draw the Lewis structure for each!
What is the difference between Cl. And Cl-?
Which one is more reactive?
Why????
What do we do with the charge?
Cl.
Cl- .. .. . -
:Cl
:Cl: .. ..
Chlorine radical
Chloride ion

25. ON YOUR OWN Be able to write the same thing for OH. and OH-1
Which is more reactive? Why?

26. Which is more reactive? Why? Don’t forget the nonbonding electrons!
ON YOUR OWN
Write the complete reaction for the ionization of H2O in Lewis structure form!!
Which is more reactive? Why?
Don’t forget the nonbonding electrons!
H2O vs H2O.+

27. 1. Count the valence electrons
ON YOUR OWN
Why do CO and N2 look the same?
2. Follow the octet rule!
1. Count the valence electrons

28. Be able to complete this worksheet from all directions!

29. Handout C!
(resonance forms!)

30. Handout C
Be careful of resonance forms!

31. Resonance
Sometimes just one Lewis structure cannot completely describe the actual chemical structure…

32. Resonance structures will always involve a double bond!
Sometimes one Lewis structure cannot completely describe the structure…
Resonance structures will always involve a double bond!

33. Look at Handout C!

34. Resonance - EXAMPLE
AHEAD

35. .. O .. .. O O .. .. .. Ozone, O3 How many valence electrons?
Is this the only way we could write this structure? .. O .. .. O O .. .. ..

36. .. .. O .. O .. .. OR .. O O .. .. O O .. .. .. ..
They are both equal!
Neither ONE is correct!

37. Resonance structures for O3[ .. .. O O [ .. .. .. .. O O .. .. O O .. .. .. ..
No one resonance form actually represents the true structure of ozone.

38. An average of the two resonance structures Actual structure for ozone…

39. Compare with O2
Which bond is stronger? O
O=O
oxygen ozone O O

40. UV- C
O O + O
λ< 242 nm
O O2 + O
λ< 320 nm
UV- B

41. Try the rest of the worksheet on your own!
HINT: Don’t forget the charge on nitrate!
Try the rest of the worksheet on your own!
HINT: SO2 will look a lot like ozone… WHY?

42. How many valence electrons?
Benzene
C6H6
A hydrocarbon
How many valence electrons?

43. Fig.10.04a
Figure 10.4
p. 438

44. Fig.10.04b
Figure 10.4
p. 438

45. Is there any other way to draw this structure?
Fig.10.04b
Is there any other way to draw this structure?
Figure 10.4
p. 438

47. So, how do we usually draw benzene?
How many bonds are between each carbon?
So, how do we usually draw benzene?

48. Fig.10.04d
Figure 10.4
p. 438

49. Fig.10.04c
Figure 10.4
p. 438

50. What is ANOTHER way that atoms can differ??
Their “greediness” for electrons.

51. Every element has its own electronegativity!
Electronegativity – the measure of an atom’s attraction for electrons in a chemical bond (CiC)!
(RANGES FROM 0 to 4)
Every element has its own electronegativity!

52. 2.1
2.5
3.0
3.5
4.0
1.0
2.5
3.0
0.9
1.2
2.8
0.8
1.0
2.5

53. Increases to the right and up the periodic table!
Electronegativity:
Increases to the right and up the periodic table!
(RANGES FROM 0 to 4)
WHY?

55. Why do we worry about electronegativity?

56. Not all covalent bonds are created equal!!!
A bond where two atoms share electrons .. ..
Not all covalent bonds are created equal!!!
O::
C:: O
O=C=O .. ..
carbon dioxide, CO2 H H
. . : : H C H H C H
. . H H
methane, CH4

57. COVALENT BONDS
NONPOLAR
POLAR

58. TYPES OF BONDS Electronegativity Difference COVALENT NONPOLAR POLAR
IONIC
Low
High
Electronegativity Difference

59. Polar Bonds: Unequal sharing of electrons in a chemical bond
Polar Bonds: Unequal sharing of electrons in a chemical bond. Still a covalent bond!

60. Cl pulls the electrons towards it!
High difference in EN! δ+ δ-
Cl pulls the electrons towards it! EN H Cl H
2.1 Cl
3.0
Read as “delta minus”
Means “slightly negative”

61. H — Cl or H :Cl
Unequal sharing of 2 electrons by 2 atoms. The bond in HCl is a polar bond.

62. The C-H bond is nonpolar!
High difference in EN! δ+ δ- EN
HCl is a polar bond! H Cl H
2.1 Cl
3.0 C
2.5 H
What about methane?
The C-H bond is nonpolar! H C H H

63. The electrons are shared (relatively) equally by the two atoms
. . : : H C H
. . H