1. Covalent Bonding
Write down the information on these slides so that we can move through them quickly tomorrow.

2. Covalent Compounds Homework List
Copy these down , including the numbers and formulas.
Chlorine Cl2
Water H2O
Ammonia NH3
carbon tetrachloride CCl4
hydrogen peroxide H2O2
hydrogen sulfide H2S
Phosphine PH3
Hydrazine N2H4
Oxygen O2
carbon dioxide CO2
Nitrogen N2
carbon monoxide CO
Ethane C2H6
Ethene C2H4
Ethyne C2H2

3. Covalent Compounds Homework List
sulfur dioxide
ozone
sulfur trioxide
N2O4
AlI3
BeCl2
sulfur hexafluoride
phosphorus pentachloride
nitrate ion
nitrite ion
sulfate ion
phosphate ion
chlorate ion
carbonate ion
ammonium ion
hydronium ion

4. Covalent Bonding 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

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

6. Different Formulas for Covalent Compounds
Molecular Formula
Not necessarily the same as Empirical Formula
Shows element symbols and # atoms in molecule
Lewis Dot Formula
All bonding pairs are shown as dots
All non-bonding electrons shown as dots
Lewis Structure
Use dash to represent bonding pairs
Structural Formula
A dash (-) is used to represent bonding pair
No non-bonding electrons shown

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

8. When writing Lewis Dot Formulas:
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

9. Steps for writing Lewis Dot Formulas
Find the total number of valence electrons
Place a pair of electrons between each atom
Generally least electronegative atom goes in center
Add electron dots until every atom has enough electrons
(H=2; Everything else =8)

10. Count up electrons
If you have the same # as you calculated in step 1 you are finished
If you have more, you likely have a multiple bond
If you have an ion, put brackets around the structure and denote the charge

11. Example: Cl2 Cl Cl Valence Electrons = 7 + 7 = 14 e-
2. Add a pair of e- between each atom (single bond)
3. Give every atom full valence electrons
4. Count up electrons
14 e- This matches #1. You’re finished.
Cl Cl

12. Show as a Lewis Structure
Show as a Structural Formula

13. STOP Homework For Numbers 1-15, draw the following:
Molecular formula (Given)
Lewis dot formula
Lewis structure
Structural formula
STOP

14. What happens if you have too 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

15. C2H4 Valence Electrons = 4+4+1+1+1+1= 12
Add a single bond between each atom:
Give every atom full valence:
Count up electrons: 14  12  add double bond and recount

16. C2H4
Spread electron regions apart from each other.

17. Lewis Structure Practice
CH3I
SO4-2
CO2H

18. 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

19. 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

20. 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.

21. 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

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

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

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

25. 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

26. 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

27. 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

28. 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.

29. Assigning Oxidation Numbers
UF6
H2SO4
ClO3-