1. 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

2. 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

3. Electronegativity Differences and Bond Types (Bond Character) Difference in Electronegativity Bond CharacterExample 0.0-0.4Nonpolar covalentH-H (0.0) > 0.4-1.0Moderately polarH-Cl (0.9) 1.0-2.0Very polarH-F (1.9) ≥ 2.0IonicNa + Cl - (2.1)

4. 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

5. 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: – CH 4 – CO 2 –H2O–H2O