bond types and lewis dot structures chemistry section 9.5

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