1. Chapter 8
Covalent bonding

2. Molecular Compounds… Are held together by covalent bonds
Are compounds composed of molecules
Are also known as Covalent Compounds
Are held together by covalent bonds
Covalent Bond :
atoms held together by the SHARING of electrons

3. Diatomic Molecules Molecules that contain 2 of the same atom
There are 7 diatomic molecules:
H2, O2, F2, Br2, I2, N2, Cl2
Ways to remember:
Make the shape of a seven on the periodic table
Excluding HYDROGEN!
Name: H-O-F Br-I-N-Cl

4. Comparing Ionic & Covalent Compounds
Ionic Compounds
Covalent Compounds
Complete transfer of electrons
Cation + Anion
Metal present
Have to look at charges
Electrons shared
Nonmetal + Nonmetal
No metals! No ions!
Have to look at valence electrons
Example:
Example:
K1+Cl1- O H

5. Properties of Covalent Bonds
Electrons are shared so that the atoms can attain the electron configuration of noble gases.
Weak inter-particle forces in contrast to ionic compounds.
Many are liquids or gases at room temperature, but some are solids (i.e. sugar).
Have low melting and boiling points compared to ionic compounds.
Do not conduct electricity.
Less soluble in water than ionic compounds, in general.

6. MUST OBEY THE OCTET RULE
Sharing of Electrons
H H
Single Covalent Bond
One shared pair of electrons
Represented by two dots or one line
H - H
MUST OBEY THE OCTET RULE
Double Covalent Bond
Two shared pairs of electrons
Represented by four dots or two lines
O = O
O O
Triple Covalent Bond
Three shared pairs of electrons
Represented by six dots or three lines
N N
N Ξ N

7. How to show a covalent bond…
Example: HCN
Draw Lewis dot structure for each atom
based on how many valence electrons the atom has.
2. Share only between electrons that are not paired
3. Make sure each atom obeys the octet rule after sharing. N H C C H N
Triple Covalent Bond
Single Covalent Bond C H N
2 e-
8 e-
8 e-

8. H Cl Cl Cl H N H H PRACTICE:
Did you check to make sure they obey the octet rule? Cl Cl H N H H

9. O C O N N MORE PRACTICE: C + 2 O  N + N  Double Covalent Bonds
Carbon Dioxide: CO2
Double Covalent Bonds N N
Nitrogen Gas: N2
Triple Covalent Bond

10. Exceptions to the Octet Rule
The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number.
The octet rule cannot be satisfied in molecules in which an atom has fewer, or more than a complete octet of valence electrons.
What does this mean?!
Let’s take a closer look…

11. 1. Odd number of TOTAL valence electrons…
NO2 – 17 total electrons
N – 5 valence electrons
O – 6 valence electrons (x 2) = 12 valence electrons
Count the total electrons around each atom…
Resonance Structure: structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion.

12. 2. less than a complete octet…
BF3
Count the valence electrons around each atom…
Boron is the exception
It is missing 2 electrons
Why? Because it only has 3 electrons to share!

13. 2. More than a complete octet…
SF6
Count the valence electrons around each atom… S
Original Lewis Structure
Sulfur has more than 8 valence
This is an expanded octet
Each of sulfur’s unshared pairs were split apart

14. What have you learned so far?
Quick review of Ionic, Metallic, & Covalent Bonds
What have you learned so far?

15. Ionic, Metallic, or Covalent?
Two non metals
Transfer of electrons
Metal and nonmetal
Two metals
Crystal Structure
Sharing of electrons
Conducts electricity without being melted
High melting point
Solid at room temperature
Sea of electrons
Covalent
Ionic
Metallic
Ionic & Metallic
QUESTION
ANSWER

16. Ionic, Metallic, or Covalent?
Brittle
Conducts electricity after being melted or dissolved in water
Strong inter-particle forces
Forms molecules
Low melting point
Does not conduct electricity
Liquid or gas at room temperature
Ionic
Covalent
QUESTION
ANSWER

17. Review: Naming Ionic Compounds
Name of cation followed by name of anion
Anion - change ending of nonmetal to -ide
Use a roman numeral to represent the charge for a cation ONLY if it is a transition metal
Transition metal with a specific charge:
Ag1+, Zn2+, Cd2+
Do NOT need roman numeral in the name!

18. Naming Covalent Compounds
In order to name molecular compounds, a different naming system is required.
WHY?
How else would we differentiate between CO & CO2?
Still follow the same naming rules, but add PREFIXES to distinguish how many atoms of each element are in the compound.

19. Prefixes – need to memorize
1 = mono
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca

20. Naming Covalent Compounds
Write the name of the first element.
Add a prefix if there is more than one of that first atom.
Write the name of the second element and change the ending to –ide
Add a prefix to the second atom even if there is only one!
If “ao” or “oo” appears in the name, remove the first “a” or “o”

21. H2O – dihydrogen monoxide N2O3 – dinitrogen trioxide
Examples:
H2O – dihydrogen monoxide
N2O3 – dinitrogen trioxide
BI3 – boron triiodide

22. N2O NO P3N2 P2S5 SO3 Practice: Dinitrogen monoxide Nitrogen monoxide
Triphosphorus dinitride
Diphosphorus pentasulfide
Sulfur trioxide

23. Naming Diatomic Molecules
7 diatomic elements:
H2, O2, F2, Br2, I2, N2, Cl2
You will name the molecule the same as the element!
H2 = hydrogen or hydrogen gas