CHAPTER OUTLINE
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Electronegativity
Polarity & Electronegativity
Lewis Structures
Molecular Shapes
1
ELECTRONEGATIVITY
 Electronegativity
Linus Pauling derived
(E.N.)a is
relative
the ability of an
atom involved in aScale
covalent
bond
to attract
Electronegativity
based
on Bond
Energies.
the bonding electrons to itself.
Cs
F
0.7
4.0
Least
electronegative
Most
electronegative
2
ELECTRONEGATIVITY
3
BOND POLARITY &
ELECTRONEGATIVITY
Polarity is a measure of the inequality in the sharing
of bonding electrons
The more
different the
electronegativity
of the elements
forming the
bond
The larger the
electronegativity
difference
(EN)
The more
polar the
bond
formed
4
POLARITY &
ELECTRONEGATIVITY
As difference in
electronegativity
increases
Least
polar
Most
polar
Bond polarity
increases
5
POLARITY &
ELECTRONEGATIVITY
Electronegativity
difference
Bond Type
EN = 0
Non-polar covalent
0 < EN <1.7
Polar covalent
1.7 < EN
Ionic
6
POLARITY &
ELECTRONEGATIVITY
The molecule is
nonpolar covalent
Electronegativity
2.20
H
H
EN = 0
Electronegativity
2.20
Hydrogen Molecule
7
POLARITY &
ELECTRONEGATIVITY
The molecule is
polar covalent
+
-
H
Electronegativity
2.20
Cl
EN = 0.96
Electronegativity
3.16
Hydrogen Chloride Molecule
8
POLARITY &
ELECTRONEGATIVITY
No molecule exists
The bond is ionic
Na+
Electronegativity
0.93
ClEN =
2.23
Electronegativity
3.16
Sodium Chloride
9
SUMMARY
OF BONDING
EN > 1.7
Ionic Bond
(large EN)
Non-polar
(similar electronegativities)
EN = 0
Polar
(moderate EN)
Covalent Bond
(small to moderate EN)
0 < EN < 1.7
10
COMPARING PROPERTIES
OF IONIC & COVALENT
COMPOUNDS
Ionic
Covalent
Structural Unit
Ions
Molecules
Melting Point
High
Low
Boiling Point
High
Low
Solubility in H2O
High
Low or None
Electrical Cond.
Examples
High
NaCl, AgBr
None
H2, H2O
11
LEWIS
STRUCTURES
 Lewis
In Lewis
structures
symbols
symbols,
foruse
valence
theLewis
firstelectrons
3symbols
periodsfor
toofshow
each
valence electrons
representative
element
are shown
elements
inas
molecules
a dot.
are shown
and ions
below:
of
compounds.
12
LEWIS
STRUCTURES
 In a Lewis structure, a shared
electron pair is indicated by
two dots between the atoms, or
by a dash connecting them.
 Unshared pairs of valence
electrons (called lone pairs) are
shown as belonging to
individual atoms or ions.
13
LEWIS
STRUCTURES
 Writing correct Lewis structures for covalent
compounds requires an understanding of the
number of bonds normally formed by common
nonmetals.
14
LEWIS
STRUCTURES
 Structures
Covalent molecules
must satisfy
are octet
best represented
rule (8 electrons
with
around
electron-dot
each or
atom).
Lewis structures.
 Hydrogen is one of the few exceptions and forms
a doublet (2 electrons).
15
LEWIS
STRUCTURES
 Bonding
Non-bonding
electrons
electrons
can be
must
displayed
be displayed
by a dashed
as
dots.
line.
16
LEWIS
STRUCTURES
 More complex Lewis structures can be drawn
by following a stepwise method:
1. Count the number of electrons in the structure.
2. Draw a skeleton structure.
3. Connect atoms by bonds (dashes or dots).
4. Distribute electrons to achieve Octet rule.
5. Form multiple bonds if necessary.
17
Example 1:
Write Lewis structure for H2O
Step 1:
H2O
= 8 electrons
Step 2:

H
Step 3:
Step 4:
2 (1) + 6 = 8
O

H
Skeleton
Hydrogen
structure
has doublet
4 electrons used
Octet rule is satisfied should be
4 electrons remaining
symmetrical
18
Example 2:
Write Lewis structure for CO2
Step 1:
CO2
= 16
electrons
4 + 2(6) = 16
Step 2:

Step 3:
Step 4:
Step 5:


O


C
O



Skeleton
structure
Octet
10
4 electrons
rule is NOT
used
Octet rule is satisfied should be
6 electrons
12satisfied
electrons
remaining
symmetrical
remaining
19
Example 3:
Write Lewis structure for CO32Step 1:
CO32-
= 24
electrons
4+3(6)+2 = 24
Step 2:



O
O




Step 5:
C

Step 4:
O

Step 3:
12
18
06 electrons
electrons
remaining
Octet
Octetrule
ruleisissatisfied
NOT
satisfied
20
Example 4:
Write Lewis structure for NH3
Step 1:
NH3
= 8 electrons
Step 2:
Step 3:
Step 4:
5 + 3(1) = 8

H
N
H
H
Octet rule is satisfied
21
Example 5:
Write Lewis structure for ClO3
Step 1:
ClO3
= 26
electrons
7+3(6)+1 = 26
Step 2:


Cl
O
O

14
20
028 electrons
electrons
remaining




Step 4:
O

Step 3:


Octet rule is satisfied
22
EVALUATING LEWIS
STRUCTURES
 When evaluating Lewis structures for correctness,
two points must be considered:
1. Are the correct number of electrons present in
the structure?
2. Is octet rule satisfied for all elements?
(Hydrogen is an exception)
23
Example 1:
Determine if each of the following Lewis structures
are correct or incorrect. If incorrect, rewrite the
correct structure.
2(1)Octet
+ 4 + is
6 = 12
incomplete
Octet is complete
Doubletsisare
Structure
complete
incorrect
24
Example 2:
Determine if each of the following Lewis structures
are correct or incorrect. If incorrect, rewrite the
correct structure.
Structure
has
14
electrons
Only+124(1)
electrons
2(5)
= 14
shown
2
4
2
2
2
Structure is
incorrect
Octets are complete
25
MOLECULAR
SHAPES
 The
A very
three-dimensional
simple model , VSEPR
shape of(Valence
the molecules
Shell
is an important
Electron
Pair Repulsion)
feature inTheory,
understanding
has beentheir
properties by
developed
andchemists
interactions.
to predict the shape of
molecules
basedhave
on their
Lewis
 large
All binary
molecules
a linear
shape since
structures.
they only contain two atoms.
 More complex molecules can have various
shapes (linear, bent, etc.) and need to be
predicted based on their Lewis structures.
26
MOLECULAR
SHAPES
 Based on VSEPR, the electron pair groups in a
molecule will repel one another and seek to
minimize their repulsion by arranging
themselves around the central atom as far
apart as possible.
 Electron pair groups can be defined as any one
of the following:
bonding pairs
non-bonding pairs
multiple bonds
27
SUMMARY OF
VSEPR SHAPES
Number of electron
pair groups around
central atom
Molecular
Shape
Bond
Angle
Example
s
Bonding
Non-bonding
2
0
Linear
180
CO2
3
0
Trigonal
planar
120
BF3
2
1
Bent
120
SO2
4
0
Tetrahedral
109.5
CH4
3
1
Pyramidal
109.5
NH3
2
2
Bent
109.5
H2O
28