1. Electron Dot Structures

2. Lewis Structures
- Diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule.
- Introduced by Gilbert Lewis in 1916.

3. Drawing Lewis Structures for Covalent Compounds
Let’s try SiH4 (silane)
1) First count all the valence electrons
2) Decide which atom will be your central atom
-Carbon is always in the center
-Hydrogen is never in the center
-If no carbon, least electronegative element is placed in center
3) Decide which atom will be your central atom and then
connect the atoms by electron-pair bonds
4) Make sure all H’s have two electrons and all other
nonmetals satisfy the “Octet Rule”
5) Make sure your final structure has same number of
electrons as you had in step 1

4. Electron-dot formula for Methane (CH4)
Here is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

5. Electron-dot formula for Methane (CH4)
Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet. H C H
Each H atom “feels” like a stable “He” atom with 2e-s H

6. Electron-dot formula for Ammonia (NH3)
Here is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each) H

7. Electron-dot formula for Ammonia (NH3)
“N” now feels like it has a stable octet
Each “H” feels like it has 2 e- like Helium. H N H H

8. Write the electron-dot formula for CF4
Because “F” is a halogen, it has 7 valence e-s, so you must show all 7 red dots around each “F” atom! C F

9. Write the Electron-Dot Formula for SeF2
Because “F” is in Group 17, they have 7 valence e-s, so they must have 7 red dots around them. Se F

10. Formaldehyde CH2O
Some elements, especially C, N, and O can share more than one
pair of electrons!!
Two pairs of electrons shared = double bond
Three pairs of electrons shared = triple bond

11. Resonance Structures Ozone, O3
Resonance - Bonding in molecules cannot be correctly represented
by a single Lewis structure
Actual structure of ozone is an average of these two structures

12. Benzene: Classic Case of Resonance
kekule's dream

13. Yes, we can see molecules!

14. Bond Energy vs Bond Length
Bond length (ppm)
Bond Energy (kJ/mol)
H-H 74
436
C-C
154
346
F-F
141
159
C-N
147
305
Cl-Cl
199
243
C-O
143
358
Br-Br
228
193
C-H
109
418
I-I
267
151
C-Cl
177
327
H-F 92
569
C-Br
194
285
H-Cl
127
432
N-N
145
163
H-Br
366
N-H
101
386
H-I
161
299
O-H 96
459

15. Bond Energy vs Bond Length
Bond length (ppm)
Bond Energy (kJ/mol)
H-H 74
436
C-C
154
346
F-F
141
159
C-N
147
305
Cl-Cl
199
243
C-O
143
358
Br-Br
228
193
C-H
109
418
I-I
267
151
C-Cl
177
327
H-F 92
569
C-Br
194
285
H-Cl
127
432
N-N
145
163
H-Br
366
N-H
101
386
H-I
161
299
O-H 96
459

16. Bond Energy vs Bond Length
Bond length (ppm)
Bond Energy (kJ/mol)
H-H 74
436
C-C
154
346
F-F
141
159
C-N
147
305
Cl-Cl
199
243
C-O
143
358
Br-Br
228
193
C-H
109
418
I-I
267
151
C-Cl
177
327
H-F 92
569
C-Br
194
285
H-Cl
127
432
N-N
145
163
H-Br
366
N-H
101
386
H-I
161
299
O-H 96
459

17. Ionic Structure
Calcium Sulfide