to gain more knowledge

1. Polarity of Molecules

2. Electronegativity
 A numerical value that describes the ability
of atoms to attract shared electrons to itself
within a chemical bond
 Nonmetals are far more electronegative than
metals, as you might imagine
 Electronegativity increases towards the
upper right of the periodic table (excluding
noble gases)
 Look at chart on p. 263

3. Polar Covalent Bonds
 Most covalent bonds, even though electrons are
shared, still contain some difference in charge.
 Example: When Oxygen bonds with Hydrogen,
there is a difference in electronegativity between
Oxygen and Hydrogen which results in more of
the electrons surrounding the Oxygen more
frequently.
 This causes the Oxygen end of the bond to be
more negative and the Hydrogen end of the bond
to be more positive.

4. Polar Covalent Bonds
δ- O-H δ+
lower case Greek letter delta indicates charge
This bond contains a dipole, which merely
means a positive and a negative end.

5. Electronegativity difference
 In order to determine the polarity of a bond,
calculate the difference in electronegativity
Electronegativity
difference
Type of Bond
>1.7 Ionic
1.7-0.8 Polar Covalent
0.8-0.3 Weakly polar
<0.3 nonpolar

6. Polar molecules
 Bonds within a molecule can be polar
 Molecules themselves can be polar or nonpolar
 If the center of negative charge overlaps with the
center of positive charge within the molecule, the
molecule itself is nonpolar, e.g., methane (CH4),
CO2.
 If the centers of charge do not overlap, the
molecule contains a dipole, and is considered
polar, e.g, H2O, ammonia (NH3).

7. Polarity Model
δ-O-Hδ+ lower case Greek letter delta
indicates charge
↓ center of negative charge
δ-O Hδ+
x ← center of positive charge
Hδ+
The molecule has a dipole.

8. Polarity and Solubility
 “Like Dissolves Like”
 Polar solvents like water can dissolve ionic
and polar compounds
 The negative parts of the water molecule
attract the positive ions.
 Positive part of water can attract negative
ions
 Ionic solids are pulled apart and dissolved

9. Polarity and Solubility II
 Polarity explains why oil and water don’t
mix.
 An intermediate solvent like some alcohols
will mix with both water and nonpolar
solvents like gasoline
 Polar solvents have positive and negative
parts that do not overlap
 Nonpolar solvents do