1. Ionic Bonding Test Scale

2. Covalent Bonding

3. Covalent Bonding Review
A sharing of electrons
Polarity of bond refers to how equally electrons are shared
Bonding Pair/s: The shared electrons
Non-Bonding Pair/s: The electrons that do not participate in bonding

4. Lewis Dot Diagrams
Element symbol X
Insert S-sublevel electrons first

5. Lewis Dot Formulas F F
Non-Bonding
Pair
Bonding Pair

6. Different Formulas Molecular Formula Structural Formula
Not the same as Empirical Formula
Structural Formula
A dash (-) is used to represent bonding pair
No non-bonding electrons shown
Lewis Dot Formula
Use dash to represent bonding pairs
All non-bonding electrons shown

7. When writing Lewis Structures:
ALL valence electrons must be shown for ALL atoms present
Atoms that are bonded share one or more pairs of electrons
All atoms must have 8 electrons*
*Exception Hydrogen (2 electrons)
*Exceptions to Octet Rule

8. Steps for writing Lewis Dot Formulas
Find the total number of valence electrons
Draw a dash between each atom
Generally least electronegative atom goes in center
Add electron dots until every atom has enough electrons
(H=2; Everything else =8)
Count up electrons
If you have the same # as you calculated in step 1 you are finished
If you have more  you have a multiple bond
If you have an ion, put brackets around the structure and denote the charge

9. Cl2 Cl Cl Cl Cl Valence Electrons = 7 + 7 = 14 e-
2. Add a dash between each atom (single bond)
3. Give every atom full valence electrons
4. Count up Electrons
Cl Cl
Cl Cl

10. What happens if you have to many Electrons?
Compound has a multiple bond
Single bond – 1 bonding pair
Double bond – 2 bonding pairs
Triple bond – 3 bonding pairs
C, N, O, and S may have multiple bonds

11. C2H4 C C C C C C H H H H H H H H H H H H H H H
Valence Electrons = = 12
Add a single bond between each atom:
Give every atom full valence:
Count up electrons: 14  12  add double bond and recount H H H H
C C H H H H H
C C H H H H
C C H H

12. Lewis Structure Practice
CH3I
SO4-2
CO2H

13. SO2 O S O O S O O S O O S O # V.E. = 6+6+6= 18
Single Bonds between atoms and fill valence
Add a double bond
But ... We can write two different structures. Which one is right?
O S O
O S O
O S O
O S O

14. Bond Energies and Bond Length
What do we know about bond energy and strength of a bond?
Bond energy = energy required to break a bond
Higher bond energy  Higher bond strength
We can also relate Bond energy/strength and Bond length
Bond
Length (pm)
Energy (kJ/mol)
C-C
154
348
C=C
134
614
CC
120
839

15. Resonance X-Ray diffraction can be use to determine bond lengths
For SO2 we would expect to observe different bond lengths
But… Both bonds have the same length?
Resonance is the bonding in molecules or ions that cannot be correctly represented by one Lewis structure.

16. Resonance and SO2 O S O O S O O S O O S O
NOT the correct structure
NOT the correct structure
Correct structure is an average of the 2
Correct Lewis Structure is represented like this:
O S O
O S O

17. Resonance Practice:
Draw the Lewis Structure for 03 (include all resonance structures)

18. Exceptions to Octet Rule
Some Group II and Group III that bond covalently can have less than 8 electrons (Be, B)
Example BF3
BeCl2

19. Exceptions to the Octet Rule
Some nonmetals may have more than 8 electrons (expanded octet)
Only row 3 and greater nonmetals
SF6
PCl5

20. Oxidation Numbers
Oxidation numbers also called oxidation states, indicate the general distribution of electrons among the bonded atoms in a molecular compound or polyatomic ion
Have no physical meaning
Arbitrary
But… can be very useful in naming, writing formulas and balancing chemical equations

21. Assigning Oxidation Numbers
An atom in its elemental state has an oxidation number of zero
The oxidation number of a monoatomic ion is considered to be equal to the charge on the ion.
The oxidation of Fluorine in a compound is always -1
Group 1 elements (except H) in compounds are assigned oxidation numbers of +1
Group 2 elements are assigned an oxidation number of +2

22. Assigning Oxidation Numbers
6. The elements of group 17 are assigned a charge of -1, when combined with less electronegative atoms
7. Oxygen is assigned an oxidation number of -2 except:
When paired with fluorine OF2 (oxygen +2)
In peroxides O2-2 (each oxygen is -1)
In superoxide O2- (each oxygen is -1/2)
8. For Hydrogen:
If in a compound with more electronegative elements
Charge is +1
In compounds with metals, (less electronegative)
Charge is -1

23. Assigning Oxidation Numbers
9.The sum of oxidation numbers for neutral compounds must equal 0.The sum of oxidation numbers of polyatomic ions must equal the ions overall charge.

24. Assigning Oxidation Numbers
UF6
H2SO4
ClO3-