1. I. Lewis Diagrams (p. 202 – 213)
Lecture 2

2. The Octet Rule
Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an (8) octet of electrons in its valence shell.
8 is Great! H He

3. Lewis Dot
Shows how valence electrons are arranged among atoms in a molecule.
Reflects central idea that stability of a compound relates to noble gas electron configuration.
CH4
H2O
I started it for you
Try one yourself NH3

4. A. Octet Rule
Remember…
Most atoms form bonds in order to have 8 valence electrons.

5. F B F F H O H N O F F F S F Very unstable!! A. Octet Rule Exceptions:
Hydrogen  2 valence e-
Groups 1,2,3 get 2,4,6 valence e-
Expanded octet  more than 8 valence e- (e.g. S, P, Xe)
Radicals  odd # of valence e-

6. B. Drawing Lewis Diagrams
Find total # of valence e-.
Arrange atoms - singular atom is usually in the middle.
Form bonds between atoms (2 e-).
Distribute remaining e- to give each atom an octet (recall exceptions).
If there aren’t enough e- to go around, form double or triple bonds.

7. B. Drawing Lewis Diagrams
CF4
1 C × 4e- = 4e-
4 F × 7e- = 28e-
32e- F
F C F
- 8e-
24e-

8. B. Drawing Lewis Diagrams
BeCl2
1 Be × 2e- = 2e-
2 Cl × 7e- = 14e-
16e-
Cl Be Cl
- 4e-
12e-

9. B. Drawing Lewis Diagrams
CO2
1 C × 4e- = 4e-
2 O × 6e- = 12e-
16e-
O C O
- 4e-
12e-

10. C. Polyatomic Ions To find total # of valence e-:
Add 1e- for each negative charge.
Subtract 1e- for each positive charge.
Place brackets around the ion and label the charge.

11. O O Cl O C. Polyatomic Ions ClO4- 1 Cl × 7e- = 7e- 4 O × 6e- = 24e-

12. H H N H C. Polyatomic Ions NH4+ 1 N × 5e- = 5e- 4 H × 1e- = 4e- 9e-

13. D. Resonance Structures
Molecules that can’t be correctly represented by a single Lewis diagram.
Actual structure is an average of all the possibilities.
Show possible structures separated by a double-headed arrow.

14. D. Resonance Structures
O S O O
O S O O
O S O

15. D. Resonance-Occurs when more than one valid Lewis structure can be written for a particular molecule.

16. Structural Formula
Shows shared pair of electrons by a dashed line.

17. Single bond- 1 pair of electrons
Double bond- 2 pair of electrons
Triple bond- 3 pair of electrons
Try a couple: O2 N2