1. SCH3U: Chemical Bonding
Q: what did the bartender say when oxygen, hydrogen, sulphur, sodium and phosphorous walked into the room?
A: OH SNaP!

2. Agenda Questions from Last Class? Ionic, Covalent and Metallic Bonding
Lewis Diagram
Single Atoms; hints for drawing Lewis diagrams
Compounds
Total Valence Electrons
Steps to draw Lewis Diagram for compounds
Practice Questions
Reminder (Homework; Quiz; Gizmo)

3. Ionic bonding (Li + Cl) Li + Cl  [Li]+[Cl]–
Ionic bonding (stealing/transfer of electrons)
Li + Cl  [Li]+[Cl]–
Chemical Formula
Rutherford Diagram
3p+
4n0
2e-
17p+
18n0
8e-8e-2e
3p+
4n0
2e-1e-
17p+
18n0
7e- 8e- 2e-
1e- Li Cl
[ Cl ]–
[Li]+
Lewis Diagram

4. Ionic bonding (Mg + O) Mg + O  [Mg]2+[O]2– O Mg [ O ]2– [Mg]2+ 1e-
Chemical Formula
12p+
12n0
2e- 8e- 2e-
6e- 2e-
8n0
8p+
8e- 2e-
8n0
8p+
1e-
12p+
12n0
2e- 8e-
1e-
Rutherford Diagram O Mg
[ O ]2–
[Mg]2+
Lewis Diagram

5. Ionic bonding: Li + O 2Li + O [Li]2+[O]2– or 4Li + O2 2[Li]2+[ O]2–
3p+
4n0
2e-1e-
8e- 2e-
8n0
8p+
3p+
4n0
2e-
1e-
6e- 2e-
8n0
8p+
3p+
4n0
2e-1e-
1e- O Li
[ O ]2–
[Li]2+

6. Ionic vs. Covalent

7. Types of Covalent Bonds
a. non Polar Covalent Bond: When EN difference is zero. Equal sharing of electrons.
b. Polar Covalent Bond: When EN difference is >0 and <1.7. Results in unequal sharing of electrons, one atom has a higher affinity for the electrons.

8. Polar Covalent Bonds

9. Metallic Bond (neither ionic or covalent)
Occurs between two metal atoms.
Valence electrons are released into a sea of electrons.
Atoms release their electrons in a shared pool leads to stronger metallic bonds.
Electrons are free to move and are not held together by a lattice formation (like that of ionic bonds
That is why pure metals such as copper, sodium and gold are soft elements

10. Metallic Bonds

11. Chemical Bonding
Lewis Structures

12. Lewis Diagram
Single Atom: the chemical symbol and dots indicating the number of electrons in the valence energy level
Compound: representation of covalent bonding based on Lewis symbols; Shared electrons are shown as lines and lone pairs as dots

13. To Write Lewis Diagrams
1. Write the element symbol. Around this, draw dots one for each valence electron.
2. The dots should be spread over four sides. Dots are not paired until all sides have at least one dot.
3. It does not matter on which side dots are placed. For example, hydrogen can be drawn four ways:
4. The number of valence electrons is equal to the group number. For example, hydrogen is in group IA (group 1) and it has one valence electron. Neon is in 0 (group 8) and it has 8 valence electrons. The only exception is He which is in group 8 but has 2 valence electrons.

18. As Br Br Br Example: AsBr3
STEP 1:place the single atom in the center and other atoms around it evenly spaced As Br Br Br

19. STEP 2: count the total # of valence e- for all atoms involved in the bonding
Arsenic: 1 Arsenic with
5 valence
electrons (1x5) = 5
AsBr3
5+21 =26
Bromine: 3 bromine
with 7 valence
electrons (3x7) = 21

20. STEP 3: place the electrons in pairs between the central atom and each non-central atomAs Br Br Br

21. As Br Br Br STEP 4: place the remaining
electrons around the non-central atom until each has 8 electrons (H atoms have only 2e-)
Ex: AsBr3
5 + (7x3) = 26
= 20 As Br Br Br

22. STEP 5: if electrons remain they are placed in pairs around
the central atom
Ex: AsBr3
5 + (7x3) = 26
= 2 As Br
Structural Formula As Br Br Br

23. Exception: if the central atom is in
group 14, 15, 16, 17 or 18, the octet rule must be satisfied by moving electron pairs from non-central atoms, creating multiple bonds.
Ex: SO2
6 +(6x2)
=18 O O S - O S = O
Structural Formula

24. Resonance Structure EX) CO3
When several structures with different electron distributions among the bonds are possible, all the structures contribute to the electronic structure of the molecule. These structures are called resonance structures
EX) CO3
When considering the resonance structure…
Formal charge closest to zero is favoured
Negative formal charges on the more negative elements are favoured

25. Summary
STEP 1:place the single atom in the center and other atoms around it evenly spaced
STEP 2: count the total # of valence e- for all atoms involved in the bonding
STEP 3: place the electrons in pairs between the central atom and each non-central atom
STEP 4: place the remaining electrons around the non-central atom until each has 8 electrons (H atoms have only 2e-)
STEP 5: if electrons remain they are placed in pairs around the central atom
Exception: if the central atom is in group 14, 15, 16, 17 or 18, the octet rule must be satisfied by moving electron pairs from non-central atoms, creating multiple bonds

26. Summary / Hints When drawing Lewis Diagrams…
Symmetrical arrangements are favoured
Hydrogen is never a central atom
The least electronegative element is usually the central atom
When considering the resonance structure…
Formal charge closest to zero is favoured
Negative formal charges on the more negative elements are favoured

27. Practice Questions
Draw Lewis Structure/ Structural Formula for the following compounds
CCl4
HCl
NH3
H2O OH H2

28. Reminder Do the practice problems and assigned homework
Gizmo activity is due this Thursday!