1. Launch: 11/4
 Grab your binder and immediately take a seat!
 Place homework (practice questions) on desk
1. Draw the correct Lewis structures for the following
atoms. Be sure to use the 3-steps!
i. Br2
ii. H2S
iii. CCl4

2. Schedule
 We have an exam in 6 days!
 We don’t have time to waste!
 Follow our 7 class rules
 You may not use inappropriate language
 If you have a question, ask!

3. What are Lewis
structures? – Part II
Mr. Heffner
11/4/09

4. What are Lewis structures?
 Lewis structures are…
 pictures of covalent molecules
 nonmetal and nonmetal share to get 8
• • • •
Covalent Bond
F- F
(dash = 2 electrons)
• •
• •
Lewis
Structure
• • = • •
8

5. What are Lewis structures?
 Cocaine
Double Bond
 C17H21NO4 2 dashes = 4 electrons

6. What are Lewis structures?
 Large biological molecules are made of
 carbon (C) – 4 bonds
 nitrogen (N) – 3 bonds
 oxygen (O) – 2 bonds
 hydrogen (H) – 1 bond
 To fill octet C, N, & O sometimes form double/triple
bonds
 H, I, Br, Cl and everything else = only single bonds

7. What is a Lewis structure?
 There is a 3-step process for creating Lewis
structures:
1. Draw Lewis symbols & count dots
2. Arrange atoms so they have a full octet
 If necessary form a double/triple bond
3. Count dots & make bonds

8. Example
Draw the Lewis structure for O2
 Step 1: Draw Lewis symbols & count dots
• •
• • O
O
• •
•
• •
•
•
• 12 dots

9. Example
Draw the Lewis structure for O2
 Step 2: Arrange atoms so they have a full octet
• •
• • O
O
• •
•
• •
• •
7=
• 7=

10. Example
Draw the Lewis structure for O2
 Step 2: Arrange atoms so they have a full octet
• •
• •
•
O
O•
• •
•
• •
• •
• 8 =
8=

11. Example
Draw the Lewis structure for O2
 Step 3: Count dots & make bonds
• •
• •
•
O
O•
• •
•
• •
•
12 dots Double Bond
2 dashes = 4 electrons

12. Example
Draw the Lewis structure for N2

13. Whiteboards
 Work in pairs
 Trade-off marker every question
 You have 60 seconds to draw the answer
 Show all three steps!
 Lift board only when prompted

14. CCl4

15. CO2

16. CH2Cl2

17. N2

18. Molecular Models
 Work with partner
1. draw all the Lewis symbols
2. draw the correct Lewis structure
3. !"#$%&''(&"$ a model using toothpicks and)*+$%,-.,"/$
build $
candy
4. 01&2345"-$ a picture of your model (label the 6678$
draw $
atoms)
*",9539&$:;&453<(4=$$!<>&9;>,"$!</&>4$
5. identify the types of bonds present in molecule
$
+3(A>&B$
01&239,>$
)&.34$+-2@<>4$
Step 1 )&.34$+5";95;"&$
Step 2 !</&>$*395;"&$
Step 3 C<;@>&B$
?<"2;>,$
D"3E>&F$
$
%0>$ $ $ $
$

19. Exit Slip
1. The bonds in water (H2O) are
a. single bonds
b. ionic bonds
c. triple bonds
d. double bonds

20. Exit Slip
2. The correct Lewis structure for CO2 is

21. Exit Slip
3. Which of the following molecules contains a
covalent triple bond?
a. C2H2
b. I2
c. NH3
d. N2

22. Exit Slip
4. Bubble in A
Then, draw the Lewis structure for SiF4

23. Exit Slip
5. Bubble in A
Then, draw the Lewis symbol for O2

24. Homework
 Finish Lewis symbol and ions worksheet