1. Do Now What is a chemical bond?
Homework
Check
Do Now
What is a chemical bond?
What is the difference between an ionic bond and a covalent bond?
What is the difference between resonance structures and isomers?
What are the five types of molecular geometry and bond angles we learned?

2. Do Now What is a chemical bond? A force that holds atoms together
What is the difference between an ionic bond and a covalent bond?
Ionic bonds involve the transfer of electrons while covalent bonds involve sharing of electrons

3. Do Now
What is the difference between resonance structures and isomers?
Resonance structures are two or more correct Lewis dot structures where the atoms are connected the same way but the electrons are distributed differently
Isomers are two or more molecules with the same chemical formula but different structures

4. Do Now
What are the five types of molecular geometry and bond angles we learned?
Linear, 180°
Trigonal Planar, 120°
Tetrahedral, 109.5°
Trigonal Pyramidal, 107.5°
Bent, 104.5°

5. Answers to Homework

7. Test 7 - Covalent Bonding
Honors Test: 25 questions, 9 pages
Chemistry Test: 17 questions, 6 pages
This is a hard test
Period
Cold Call Date
Test Date 3
Wed, Apr 27
Fri, Apr 29 4
Thu, Apr 28 6
Mon, May 2 7

8. Department Night No Department Nights on Wednesday
Faculty Meeting
Department Night moved to Thursday

9. Easy Lewis Dot Structures
Write this in your notes
Easy Lewis Dot Structures
Students will be able to draw Lewis dot structures using an easier method

10. Background There is lots to know about Lewis dot structures
single bonds, double bonds, triple bonds, coordinate covalent bonds
octets, suboctets, expanded octets, odd electron structures
charges, formal charges, resonance structures
Now that we know all of this, we can learn an easier method for finding the correct Lewis dot structure of a molecule

11. Comments on Easy Method
The easy method has advantages:
Easier
Faster
Usually gives correct answer
The easy method also has disadvantages:
Series of rules must be memorized & followed precisely to ensure correct answer
Users who don't truly understand bonding theory can get lost on challenging molecules

12. Write this in your notes
6 Steps of Easy Method
Add up all electrons
Arrange all non-H atoms
Connect all non-H atoms using e pairs
Complete octets using e pairs and bonds to H
Create multiple bonds to finish all octets
Calculate formal charges to get best structure
Lots of details on handout

13. Detailed Steps of Easy Method Steps 1-5
Add up all electrons
add up all valence electrons, then add or subtract for charge
divide the total by 2 to get pairs & assign pairs to each H
Arrange all non-H atoms
start with least electronegative alone in the center
Connect all non-H atoms using e pairs
can create expanded octets for atoms of Period 3 or higher
Complete octets using e pairs and bonds to H
start with more electronegative atoms on outside
use both e pairs and bonds to H
if isomers possible, draw structures for each
Create multiple bonds to finish all octets

14. Detailed Steps of Easy Method Step 6
Calculate formal charges to get best structure
For Period 2 elements, the best structure is defined as:
Never exceeds octet rule (suboctets okay, but no expanded octets)
Lowest formal charges on the most appropriate atoms
For Period 3 and higher elements, the best structure is defined as:
Expanded octets okay
Lowest formal charges
0 for all atoms is the best
+1 and ‒1 are tolerable, but the number of atoms with charges should be minimized
+2 and ‒2 are very unstable & exceptionally rare
Most appropriate atoms
Negative formal charge on more electronegative atom
Positive formal charge on less electronegative atom

15. Br2 Br Br 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
14 / 2 = 7 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H
5) Create multiple bonds to finish all octets Br Br
6) Calculate formal charges to get best structure

16. Check for Understanding 1
OF2
PCl3

17. O2 O O 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
12 / 2 = 6 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H
5) Create multiple bonds to finish all octets O O

18. O2 O O 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
12 / 2 = 6 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H
5) Create multiple bonds to finish all octets O O
6) Calculate formal charges to get best structure

19. Check for Understanding 2
CO2

20. Elements from Period 3 and higher can form expanded octets
PCl5
1) Add up all electrons
2) Arrange all non-H atoms
5 + 5(7) = 40 e
3) Connect all non-H atoms using e pairs
40 / 2 = 20 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H P Cl
5) Create multiple bonds to finish all octets
6) Calculate formal charges to get best structure
Elements from Period 3 and higher can form expanded octets

21. Check for Understanding 3
SF6

22. CH4O C O 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
14 / 2 = 7 e pairs
4 bonded to H
4) Complete octets using e pairs and bonds to H C O

23. H C O H O C H H
When completing octets, first start by making bonds to hydrogen.
Place these so that each element gets its normal number of bonds
Carbon normally has 4 bonds. It has one to oxygen, so add three bonds to hydrogen to get a total of 4 bonds
Oxygen normally has 2 bonds. It has one to carbon, so add one bond to hydrogen to get a total of 2 bonds
Now used the non-bonding electrons to complete octets

24. H H O C H O C +1 ‒1 +2 ‒2 O C
If you can give all atoms their "normal" number of bonds, they should all have formal charges of zero
If you have a structure that satisfies the octet rule and all atoms have a zero formal charge, it is usually the best, or one of the best possible structures.
You can always examine isomers based on the position of the hydrogens . . .
. . . but resulting structures are
often worse on formal charges

25. CH4O H H C O H H 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
14 / 2 = 7 e pairs
4 bonded to H
4) Complete octets using e pairs and bonds to H H
5) Create multiple bonds to finish all octets H C O H H
6) Calculate formal charges to get best structure

26. Check for Understanding 4
HNO2
Make both isomers based on bonding to hydrogen
Calculate formal charge to find the best structure

27. CO3‒2 O C 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
24 / 2 = 12 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H O C
5) Create multiple bonds to finish all octets

28. If asked, be sure to show resonance structures
CO3‒2
1) Add up all electrons
2) Arrange all non-H atoms
4 + 3(6) + 2 = 40 e
3) Connect all non-H atoms using e pairs
24 / 2 = 12 e pairs
0 bonded to H ‒1
4) Complete octets using e pairs and bonds to H O C
5) Create multiple bonds to finish all octets
6) Calculate formal charges to get best structure
If asked, be sure to show resonance structures

29. Check for Understanding 5
NH4+1
NO3‒1

30. COCl2 Cl C O Cl 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
24 / 2 = 12 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H Cl B
5) Create multiple bonds to finish all octets C O A Cl

31. O C Cl O C Cl O C Cl 6) Calculate formal charges to get best structure‒1 +1 O C Cl B O C Cl B
6) Calculate formal charges to get best structure A O C Cl A

32. Check for Understanding 6
CNO‒1 (N in center)

33. BF3 F B 1) Add up all electrons 2) Arrange all non-H atoms
3) Connect all non-H atoms using e pairs
24 / 2 = 12 e pairs
0 bonded to H
4) Complete octets using e pairs and bonds to H F B
5) Create multiple bonds to finish all octets

34. Is there a structure with better formal charges?
BF3
1) Add up all electrons
2) Arrange all non-H atoms
3 + 3(7) = 24 e
3) Connect all non-H atoms using e pairs
24 / 2 = 12 e pairs
0 bonded to H +1 ‒1
4) Complete octets using e pairs and bonds to H F B
5) Create multiple bonds to finish all octets
6) Calculate formal charges to get best structure
Is there a structure with better formal charges?

35. The structure with the suboctet is actually preferred
BF3
3 + 3(7) = 24 e
24 / 2 = 12 e pairs
0 bonded to H +1 ‒1 F B F B
The structure with the suboctet is actually preferred

36. Check for Understanding 7
BeCl2
AlH3

37. Homework
In SO4‒2, S is the central atom and all O's are bonded directly to it.
Draw the Lewis dot structure where all atoms get an octet
Compute the formal charge
Explore expanded octets and their formal charges to find the best structure
Draw line and composite resonance structures of the best structure

38. The second part of this lesson can be broken off to replace octet rule violators. The current octet rule violators was not well understood.
Use the benefits of the formal charge to show why the suboctet and expanded octet exist.
CO2 could have a triple bond between oxygen and carbon, but formal charges show it will not be favored.

39. Do Now
Below is step 5 of the easy method for CO2. Shown are two ways to finish the octet on C. Which is the better structure and why?
CO2
4 + 2(6) = 16 e
16 / 2 = 8 e pairs O C O C O C
Structure B
Structure A

40. O C O C O C Structure B Structure A‒1 +1 O C
Structure B
Structure A
Structure A is better. All atoms in structure A have formal charges of 0. In structure B, two atoms have formal charges that are not 0, including a +1 formal charge on highly electronegative oxygen.

41. Test 7 - Covalent Bonding
Honors Test: 25 questions, 9 pages
Chemistry Test: 17 questions, 6 pages
This is a hard test
Period
Cold Call Date
Test Date 3
Wed, Apr 27
Fri, Apr 29 4
Thu, Apr 28 6
Mon, May 2 7

42. CBr4