1. Electronegativity and Polarity

2. Electronegativity
The ability of an atom to attract electrons when bonded
Nonmetals have high electronegativity
Metals have low electronegativity
Electronegativity increases across a period and decreases down a group

3. Nonpolar Covalent Bond
When electrons are shared between 2 atoms, a covalent bond is formed.
If the atoms are identical, e.g. Cl2, the electrons are shared equally (nonpolar)

4. Polar Covalent Bond
If the electrons are shared between 2 different atoms, e.g. HBr, the sharing is unequal
The bonding electrons spend more time near the more electronegative atom H Br

5. Electronegativity Differences
The absolute value of the difference in electronegativities of two bonded atoms provides a measure of polarity of a bond.
The greater the difference, the more polar the bond.
0 to 0.4
Nonpolar covalent
0.41 to 1.69
Polar covalent
> 1.7
Ionic
Electronegativity Difference

6. Polar Molecules
Note: Not all molecules with polar bonds are polar molecules