Bond Types
and Lewis Dot Structures
Chemistry
Section 9.5
Bond Types
 Three
types of chemical bonds:
Ionic – electrons are transferred
 Polar Covalent – uneven sharing of electrons
 Nonpolar Covalent – evenly shared electrons

Electronegativities



Definition: ability of an atom to attract electrons in a
bond
Used to determine bond type by calculating the
difference in electronegativities of atoms in the bond
Use Period Table of Electronegativities
Pauling
The electronegativity
values are called
Paulings (scale 0-4)
Electronegativity Table
Determining Bond Type

Ionic (I): 1.7 – 4.0, large difference indicates a transfer of
electrons

Polar Covalent (PC): 0.3 – 1.7, difference is not strong
enough to transfer electrons, share electrons unequally,
electrons spend more time around the more
electronegative atom

Nonpolar Covalent (NPC): 0 – 0.3, atoms are
approximately equal in electronegativities, common in
diatomic molecules and hydrocarbons
Types of Chemical Bonds - Ionic



The type of chemical bond can be predicted using the
differences between the electronegativities of the
elements that are bonded
An electronegativity difference between 1.7 and 4.0 is
considered to be an ionic bond
Large differences between the electronegativities of two
atoms indicate that an electron has been transferred from
one atom to another
Ionic
Determining Electronegativity Differences
NaCl
0.9
3.2
2.3
Ionic Bond
1.7  4.0
Types of Chemical Bonds – Polar Covalent




If the electronegativity difference is between 0.3 and 1.7,
the bond is generally considered to be polar covalent
With polar covalent bonding, the electronegativity
difference is not strong enough to transfer and electron.
So, instead, the electrons are shared.
The sharing is not always equal because one atom will
have a stronger electronegativity than the other.
When the electrons of one atom are pulled closer to the
other atom, the molecule becomes polar covalent
This is also called
a dipole
molecule
The stronger atom
will become charged
The weaker atom will
become + charged
Identifying a Polar Covalent Bond
H2O
2.2 3.4
1.2
Ionic
Polar Covalent
1.7  4.0
0.3  1.7
Polar
Covalent
Types of Chemical Bonds – Nonpolar Covalent



If the electronegativity difference is between 0 and 0.3, the bond
type is nonpolar covalent
In this type of bond, both atoms are approximately equal in their
electronegativities
This type of bond is most common in diatomic molecules and
hydrocarbons
Diatomic Molecules Hyrocarbons
Br2
N2
Butane
C4H8
O2
F2
I2
Cl2
H2
Octane
C8H16
Identifying NonPolar Covalent Bonds
N2
3.0
3.0
0.0
Ionic
PC
NPC
1.7  4.0
0.3  1.7
0.0  0.3
Nonpolar
Covalent
Characteristics of Bond Types
Ionic
Polar Covalent
Nonpolar Covalent
1.7  4.0
0.3  1.7
0.0  0.3
High Melting Point
Low Melting Point
Low Melting Point
Solids
Solids and Liquids
Liquids and Gases
No Dipoles
Dipoles
No Dipoles
Dissolves in PC
Does Not Dissolve in NPC
Does Not Dissolve in PC
Determining Bond Type Examples

Li + Br


C+O


C = 2.5, Cl = 3.0, diff = 0.5, bond = PC
K+O


C = 2.5, O = 3.5, diff = 1.0, bond = PC
C + Cl


Li = 1.0, Br = 2.8, diff = 1.8, bond = I
K = 0.8, O = 3.5, diff = 2.7, bond = I
C+I

C = 2.5, I = 2.5, diff = 0, bond NPC
Bond Type Exercise
Bond Type Exercise Continued
“Like Dissolves Like”



Substances with like (similar) properties will dissolve in
each other
Substances with unlike (dissimilar) properties will NOT
dissolve in each other
Ionic and Polar compounds have charges while Nonpolar
compounds have no charge
“Like Dissolves Like” Examples


NaCl (I, 2.1) dissolves in
H2O (PC, 1.4)
Oil (NPC) will not
dissolve in H2O
“Like Dissolves Like” Table
Substance 1
Substance 2
Solubility??
Ionic
Polar Covalent
Soluble
Ionic
Nonpolar Covalent
Not Soluble
Polar Covalent
Polar Covalent
Soluble
Polar Covalent
Nonpolar Covalent
Not Soluble
Nonpolar Covalent
Nonpolar Covalent
Soluble
Lewis Dot Structures




Used to predict and show structural arrangements of
molecules
Shows how electrons are being shared in covalent bonds
Follows Octet Rule
Example
Lewis Dot Structures, continued


can substitute lines for pairs of shared electrons
examples
Lewis Dot Structure Practice

H2

H2O


H H H—H
H = 1 valence eO = 6 valence e-
H O H
H—O—H

More practice…
CCl4


C has 4 valence eCl has 7 valence e-
Cl
Cl C Cl
Cl
Cl
Cl—C—Cl
Cl
Steps for Lewis Dot Structures
1.
2.
3.
4.
Determine the number of valence
electrons for each element
Determine the central atom (atom
with lowest electronegativity value)
Write the central atom and valence
electron dots
Fill in the remaining elements with
their valence electron dots
Lewis Dot Structure Practice

Draw Lewis Dot Structures for the following compounds:
CF4
CH4
Cl2
NF3
H2
PCl3