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Chapter 10
Basic Concepts of Chemical
Bonding
I. Covalent Bonds and Lewis Bonding Theory
A. Lewis Symbols, the Octet Rule and
Covalent Bonding
B. Other Types of Covalent Bonds
1. Multiple Covalent Bonds
2. Coordinate Covalent Bonds
C. Sharing of Electrons in Covalent Bonds
1. Electronegativity
2. Bond Polarity
II. Molecular Compounds and Lewis
Structures in Detail
A. Drawing Lewis Structures
1. Formal Charge
2. Exceptions to the Octet Rule
3. Resonance Structures
III. Molecular Shapes and Polarity
A. VSEPR Theory
B. Polarity of Molecules
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http://media1.shmoop.com/images/chemistry/chembook_bonds_graphik_5.png, http://www.worldsurfleague.com/posts/198463/2016-tag-heuer-biggest-wavewinner#
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I. Covalent Bonds and Lewis Bonding
Theory
Types of Compounds
1. Ionic Compounds
Ionic Bonds - transfer of electrons
between atoms
metal
-
non-metal
2. Molecular Compounds
Covalent Bonds -
non-metal -
sharing of
electrons
between atoms
non-metal
CH3COOH
https://s-media-cache-ak0.pinimg.com/600x315/a0/13/69/a013699d6436b8672a6c90e3158b56f6.jpg,
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A. Lewis Symbols, the Octet Rule and
Covalent Bonding
How do atoms interact?
-they share electrons
Which electrons can be shared?
-valence electrons (outer s & p e-)
Lewis Bonding Theory
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
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Main group elements and valence eGroup
Element
E.C.
Lewis
Symbol
1
H
1s1
H
13
B
1s22s22p1
B
15
P
[Ne]3s23p3
P
17
Br
[Ar] 3d104s24p5
Br
Covalent Bonding, Lewis Symbols and Lewis Structures
Covalent Bond
- involves the sharing of electrons between two
atoms
Lewis Structure
- structure obtained by combining Lewis
symbols to create covalent bonds
http://ammoniabmp.colostate.edu/images/peeingcow
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B. Other Types of Covalent Bonds
1. Coordinate Covalent Bonds
-
covalent bond in which both e- of the
shared pair are donated by one atom
Example
http://www.comsol.com/blogs/wp-content/uploads/2014/05/Ammonia-small.png
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2. Multiple Covalent Bonds
-
covalent bond formed by the sharing of
more than 2 electrons (in multiples of 2)
Type of e shared Example Length Strength
Bond
Single
Double
Triple
Examples of Lewis Structures with Multiple Bonds
http://www.everstring.com/wp-content/uploads/2015/11/James-Bond.jpg
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C. Sharing of Electrons in Covalent Bonds
1. Electronegativity
- Are the electrons shared equally between
the two N atoms?
- Are the electrons shared equally between the
C and the O atoms?
How can we predict the equality of sharing?
Which atoms want electrons the most?
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2. Bond Polarity
measure of how well atoms share e- in a
bond
- calculated using electronegativity
Determining Bond Polarity
-
∆e.n. = e.n. of atom w/ largest e.n. - e.n. of atom with smallest e.n.
Approximations
1. Δe.n. below ~ 0.5
2. Δe.n. between ~0.5
and~2
3. Δe.n. above ~2
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Examples
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II. Molecular Compounds and 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 (many
exceptions)
4. Trends
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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
CO32-
CH3CH2OH
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A. Writing Lewis Structures
Plan of Attack
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 (a single bond) for
each connecting bond. (If there is a central
atom it is usually written first in the formula
and usually has the lowest e.n.)
3. Determine the amount of electrons used and
the number of electrons left over
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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
Qualitative Approach
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1. Formal Charge (a quantitative approach)
Formal Charge – The hypothetical charge on an
atom in a molecule assuming
equal sharing of the bonding
electrons
1


F.C.  # valence e  lone e  (shared e- )
2


-
Rules
1. formal charges of all atoms in molecule must
add up to the charge of the molecule or ion
2. For non-equivalent Lewis Structures, in the
best structure …
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Example
Which is the best Structure?
:O C N¨ :
¨
or
A.
¨ C N : or
:O
¨
B.
Formal Charges
A.
B.
O = 6 –[4 + ½(4)] = 0
C = 4 –[0 + ½(8)] = 0
N = 5 –[4 + ½(4)] = -1
C.
O = 6 –[6 + ½(2)] = -1
C = 4 –[0 + ½(8)] = 0
N = 5 –[2 + ½(6)] = 0
¨ C N:
:O
¨
C.
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Lewis Structure Example
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2. Exceptions to the Octet Rule
a. Odd #’s of electrons
b. Less than an octet
c. More than an octet
a. Odd #’s of Electrons
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b. Less than an Octet
c. More than an Octet (Most common)
Experimental – central atoms with more than octet
Explanation
Period 1:
Period 2:
Period 3:
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Example
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3. Resonance Structures
What happens if there are multiple equally likely Lewis
Structures possible?