1. Chapter
8
Covalent Bonding

2. Section 8.1
Molecular Compounds
OBJECTIVES:
• Distinguish between the melting points and boiling points of molecular compounds
and ionic compounds.
• Describe the information provided by a molecular formula.
Bonds are…
 Forces that hold groups of atoms together and make them function as a unit. Two
types:
1) Ionic bonds – transfer of electrons (gained or lost; makes formula unit)
2) Covalent bonds – ________________________ of electrons. The resulting
particle is called a ___________________________________
Covalent Bonds
• The word covalent is a combination of the prefix co- (from Latin com, meaning
“with” or “together”), and the verb valere, meaning “to be strong”.
• Two electrons shared together have the strength to hold two atoms together in a bond.
Molecules
• Many elements found in nature are in the form of molecules:
• a ______________________________________________________________ joined
together by covalent bonds.
• For example, air contains oxygen molecules, consisting of two oxygen atoms joined
covalently
• Called a “_______________________________________________________” (O2)
How does H2 form?
(diatomic hydrogen molecule)
• The nuclei repel each other, since they both have a positive charge (like charges
repel).

3. + +
+ +
• But, the nuclei are attracted to the electrons
• They _______________________ the electrons, and this is called a
“_____________________________________________”, and involves only
____________________________________
+ +
Covalent bonds
• Nonmetals hold on to their valence electrons.
• They can’t give away electrons to bond.
• But still want noble gas configuration.
• Get it by _______________________________________________with each other =
___________________________________________
• By sharing, both atoms get to count the electrons toward a noble gas configuration.
• Fluorine has seven valence electrons (but would like to have 8)
• A second atom also has seven
• By sharing electrons…
• …both end with full orbitals

4. Molecular Compounds
• Compounds that are bonded covalently (like in water, or carbon dioxide) are called
________________________________________________
• Molecular compounds tend to have relatively __________________________
melting and boiling points than ionic compounds – this is not as strong a bond as
ionic
• Thus, molecular compounds tend to be _____________________________________
at room temperature
• Ionic compounds were solids
• A molecular compound have a ___________________________________________
o Shows how many atoms of each element a molecule contains
• The formula for water is written as H2O
• The ___________________________________ behind hydrogen means there are 2
atoms of hydrogen; if there is only one atom, the subscript 1 is omitted
• Molecular formulas do not tell any information about the structure (the arrangement
of the various atoms).

5. Section 8.2
The Nature of Covalent Bonding
OBJECTIVES:
• Describe how electrons are shared to form covalent bonds, and identify
exceptions to the octet rule.
• Demonstrate how electron dot structures represent shared electrons.
• Describe how atoms form double or triple covalent bonds.
• Distinguish between a covalent bond and a coordinate covalent bond, and
describe how the strength of a covalent bond is related to its bond dissociation
energy.
• Describe how oxygen atoms are bonded in ozone.
A Single Covalent Bond is...
• A sharing of two valence electrons.
• Only _____________________________ and ____________________________
• Different from an ionic bond because they actually form molecules.
• Two specific atoms are joined.
• In an ionic solid, you can’t tell which atom the electrons moved from or to
How to show the formation…
• It’s like a jigsaw puzzle.
• You put the pieces together to end up with the right formula.
• Carbon is a special example - can it really share 4 electrons: 1s22s22p2?
o Yes, due to electron promotion!
• Another example: lets show how water is formed with covalent bonds, by using
an electron dot diagram
Water
 Each hydrogen has 1 valence electron
H
- Each hydrogen wants 1 more
 The oxygen has 6 valence electrons
- The oxygen wants 2 more
 They share to make each other complete
O

6. • Put the pieces together
• The first hydrogen is happy
• The oxygen still needs one more
• So, a second hydrogen attaches
• Every atom has full energy levels
Multiple Bonds
• Sometimes atoms share more than one pair of valence electrons.
• A ____________________________________________ is when atoms share
two pairs of electrons (4 total)
• A ____________________________________________ is when atoms share
three pairs of electrons (6 total)
• Table 8.1, p.222 - Know these 7 elements as _____________________________:
Dot diagram for Carbon dioxide
• CO2 - Carbon is central atom ( more metallic )
• Carbon has 4 valence electrons
• Wants 4 more
• Oxygen has 6 valence electrons
• Wants 2 more
C
O

7. Carbon dioxide
• Attaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 short
• Attaching the second oxygen leaves both of the oxygen 1 short, and the carbon 2
short
• The only solution is to share more
• Requires two double bonds
• Each atom can count all the electrons in the bond
How to draw them?
 Use these guidelines:
1) Add up all the valence electrons.
2) Count up the total number of electrons to make all atoms happy.
3) Subtract; then Divide by 2
4) Tells you how many bonds to draw
5) Fill in the rest of the valence electrons to fill atoms up.

8. Example
• NH3, which is ammonia
• N – central atom; has 5 valence electrons, wants 8
• H - has 1 (x3) valence electrons, wants 2 (x3)
• NH3 has 5+3 = _______
• NH3 wants 8+6 = 14
• (14-8)/2= ___________________
• 4 atoms with _________ bonds
• Draw in the bonds; start with singles
• All 8 electrons are accounted for
• Everything is full – done with this one
Example: HCN
• HCN: C is central atom
• N - has _____ valence electrons, wants _____
• C - has _____ valence electrons, wants _____
• H - has _____ valence electron, wants _____
• HCN has _____+_____+_____ = _____
• HCN wants _____+_____+_____=_____
• (_____-_____)/2= _____ bonds
• 3 atoms with _____ bonds – this will require multiple bonds - not to H however
HCN
• Put single bond between each atom
• Need to add 2 more bonds
• Must go between C and N (Hydrogen is full)

9. • Uses 8 electrons – need 2 more to equal the 10 it has
• Must go on the N to fill its octet
Another way of indicating bonds
• Often use a line to indicate a bond
• Called a ________________________________________________
• Each line is ________ valence electrons
Other Structural Examples
A Coordinate Covalent Bond...
• When one atom donates both electrons in a covalent bond.
• Carbon monoxide (CO) is a good example:

10. Coordinate covalent bond
• Most polyatomic cations and anions contain covalent and coordinate covalent
bonds
• Table 16.2, p.445
• Sample Problem 16.2, p.446
• The ammonium ion (NH41+) can be shown as another example
Bond Dissociation Energies...
• _________________________________________________________________
_________________________________________________________________
__
• High dissociation energy usually means the chemical is relatively
_________________________________, because it takes a lot of energy to break
it down.
Resonance is...
• When ____________________________________ valid dot diagram is possible.
• Consider the two ways to draw ozone (O3)
• Which one is it? Does it go back and forth?
• It is a hybrid of both, like a mule; and shown by a double-headed arrow
• found in double-bond structures!
Resonance in Ozone
• Neither structure is correct, it is actually a hybrid of the two. To show it, draw all
varieties possible, and join them with a double-headed arrow.
Resonance

11. • Occurs when more than one valid Lewis structure can be written for a particular
molecule (due to position of double bond)
• These are resonance structures of benzene.
• The actual structure is an average (or hybrid) of these structures.
The 3 Exceptions to Octet rule
• For some molecules, it is impossible to satisfy the octet rule
#1. usually when there is an ________________________________ of valence electrons
– NO2 has 17 valence electrons, because the N has 5, and each O contributes
6.
• It is impossible to satisfy octet rule, yet the stable molecule does exist
• Another exception: Boron
• Page 451 shows boron trifluoride, and note that one of the fluorides might
be able to make a coordinate covalent bond to fulfill the boron
#2 -But fluorine has a ________________________________________
(it is greedy), so this coordinate bond does not form
• #3 -Top page 229 examples exist because they are in period 3 or beyond