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Bond Typesand Lewis Dot Structures
ChemistrySection 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
The electronegativity values are called Paulings (scale 0-4)
Pauling
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 Bond1.7 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 The weaker atom will
become + charged
The stronger atom will become - charged
This is also called a dipole molecule
Identifying a Polar Covalent Bond
H2O
2.2 3.4
1.2
Ionic 1.7 4.0Polar Covalent 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 HyrocarbonsBr2 N2 Butane C4H8
O2 Cl2 Octane C8H16
F2 H2
I2
Identifying NonPolar Covalent Bonds
N2
3.0 3.0
0.0
Ionic 1.7 4.0PC 0.3 1.7NPC 0.0 0.3
NonpolarCovalent
Characteristics of Bond TypesIonic 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
Li = 1.0, Br = 2.8, diff = 1.8, bond = I C + O
C = 2.5, O = 3.5, diff = 1.0, bond = PC C + Cl
C = 2.5, Cl = 3.0, diff = 0.5, bond = PC K + O
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
H
H
O
Lewis Dot Structure Practice
H2
H2O H = 1 valence e- O = 6 valence e-
H
H—H
H—O—H
H
ClC ClCl
More practice… CCl4
C has 4 valence e- Cl has 7 valence e-
ClCl
Cl—C—Cl
Cl
Steps for Lewis Dot Structures
1. Determine the number of valence electrons for each element
2. Determine the central atom (atom with lowest electronegativity value)
3. Write the central atom and valence electron dots
4. 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