Polar Bonds and Molecules (8.4)

• Bond Polarity• Bond polarity has to do with unequal

distribution of shared electrons• This causes one end of the bond to have a

“partial positive” (δ+) charge and the other to have a “partial negative” (δ-)charge

• These types of bonds are called polar covalent bonds and are said to possess a dipole moment

What causes bond polarity?

• A polar bond results from a difference in electronegativity between the bonded atoms

• The greater the difference, the more polar the bond is

• The degree of polarity depends upon the difference in electronegativity

Electronegativity Differences and Bond Types (Bond Character)

Difference in Electronegativity

Bond Character Example

0.0-0.4 Nonpolar covalent H-H (0.0)

> 0.4-1.0 Moderately polar H-Cl (0.9)

1.0-2.0 Very polar H-F (1.9)

≥ 2.0 Ionic Na+ Cl- (2.1)

Effect of Bond Polarity on Molecules

• Polar bonds may result in polar molecules• Bond character (nonpolar, polar, ionic) affects– How molecules interact with one another– Physical properties of substances

Polarity of Molecules

• A molecule as a whole has a dipole depending upon

• The presence of polar bond(s)• The geometry of a molecule• Examples:– CH4

– CO2

– H2O