Chapter 12
CHEMICAL BONDING
Sharing
electrons
is fun!
H
F
Do you smell
what the Rock
is cooking?
I. Types of Chemical Bonds
A. Formation of Covalent Bonds
B. Lewis Symbols and Covalent Bonding
C. Other Types of Covalent Bonds
II. Molecular Compounds and Lewis
Structures
A. Drawing Lewis Structures
1.
Resonance Structures
2.
Exceptions to the Octet Rule
III. The Shapes of Molecules
A. VSEPR Theory
B. Bond Polarity and Molecular Polarity
1
I. Types of Chemical Bonds
Review of Ionic and Covalent Bonds
Ionic Compounds
Ionic Bonds - transfer of electrons
between atoms
metal
-
non-metal
Molecular Compounds
Covalent Bonds -
non-metal
Example
CH3CH2OH
-
sharing of
electrons
between atoms
non-metal
2
A. Covalent Bonding in more Detail
How do atoms interact?
- They share electrons
Which electrons can be shared?
- valence electrons (outer s & p orbitals)
Observations atoms react until they
obtain a noble gas core
Octet Rule 
most atoms share electrons
until they are surrounded
by 8 valence electrons
Duet Rule Hydrogen and Helium share
electrons until they are
surrounded by 2 electrons
Lewis Symbol  chemical symbol for
element + a dot for each
valence electron
Group Element
E.C.
1A
H
1s1
2A
Be
[He]2s2
3A
B
[He]2s22p1
4A
C
[He]2s22p2
5A
P
[Ne]3s23p3
6A
S
[He]2s22p4
7A
Br
[Ar] 4s23d104p5
8A
Kr
[Ar] 4s23d104p6
Valence
Lewis
Electrons Symbol
3
B. Lewis Symbols and Covalent
Bonds
Covalent Bond
- involves the sharing of electrons between
two atoms
Lewis Structure
- structure obtained by combining Lewis
symbols to create covalent bonds
Example  Lewis Structure for F2
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4
C.
Other Types of Covalent Bonds
Multiple Covalent Bonds
-
covalent bond formed by the sharing
of more than 2 electrons (in multiples
of 2)
Single bond –
Double bond –
Triple bond –
Example O2 and CO
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5
II. Lewis Structures in Detail
Requirements and Trends for L.S.
1. L.S. must include all valence e-
+ ion  subtract e-
-
- ion  add e-
2. Usually e- are paired
3. Octet rule is usually followed, most
notable exception  H (duet)
4. Trends
6
5. Skeletal Structure
- arrangement of atoms in molecule
Central atom  bonded 2 or more atoms
Terminal atom  bonded to 1 atom
-
H-atoms are always terminal
-
Carbon atoms are almost always
central atoms
-
central atoms generally have the
lowest electronegativity
-
More compact and symmetrical
the better
examples
CH3CH2OH
CO32-
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Electronegativity
7
A. Rules for Writing Lewis Structures
1. Sum all of the valence electrons from all
of the atoms
2. Draw the skeleton structure of the
molecule using one pair of electrons (=
one single bond) for each connecting
bond. (If there is a central atom it is
usually written first in the formula: CO2
 C is the central atom)
3. Determine the amount of electrons used
and the number of electrons left over
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8
4. Distribute the remaining
electrons to achieve a noble gas
configuration (octet) on each atom:
1) How many are needed?
2) How many are available?
-If needed = available distribute as lone pairs
-If needed > available make one additional
bond for every 2
electrons short and
distribute remaining
electrons as lone
pairs
Example:
Step 1
Sum the valence
electrons
Step 2
Draw the skeleton
using single bonds
Step 3
Determine the # of
electrons left
Need = avail. 
Need > avail. 
Step 4
Distribute remaining eto achieve noble gas
config. on each atom
Example:
Step 1
Sum the valence
electrons
Step 2
Draw the skeleton
using single bonds
Step 3
Determine the # of
electrons left
Need = avail. 
Need > avail. 
Example:
Step 1
Sum the valence
electrons
Step 2
Draw the skeleton
using single bonds
Step 3
Determine the # of
electrons left
Need = avail. 
Need > avail. 
Step 4
Distribute remaining eto achieve noble gas
config. on each atom
Example:
Step 1
Sum the valence
electrons
Step 2
Draw the skeleton
using single bonds
Step 3
Determine the # of
electrons left
Need = avail. 
Need > avail. 
Step 4
Distribute remaining eto achieve noble gas
config. on each atom
Example:
Step 1
Sum the valence
electrons
Step 2
Draw the skeleton
using single bonds
Step 3
Determine the # of
electrons left
Need = avail. 
Need > avail. 
Step 4
Distribute remaining eto achieve noble gas
config. on each atom