Polarity
Polarity: Separation of charge by a distance.
Molecular Polarity: Net imbalance of charge in a molecule
(separation of + and – charge by a distance.) Molecule will have
a partial + side and a partial – side.
1. If molecule has only 2 atoms: The polarity of the molecule is the
same as the bond polarity.
2. If molecule has more that 2 atoms, molecular polarity is
determined by:
A. Bond Polarity
Molecule must have at least 1 polar bond to be a polar
molecule. Otherwise, it is nonpolar. (ex- Cl2)
If there is at least 1 polar bond , must also consider the
molecular shape.
B. Molecular Shape
1. If Shape is symmetrical (all e- groups around central
atom have the same electronegativity) then bond polarities
cancel out, and molecule is NON Polar.
Examples:
Ex: HCl has a polar bond, is a polar molecule.
Ex: Cl2 has a nonpolar bond, is a nonpolar molecule.
2. If shape is asymmetrical (e- groups around central
atom are not all the same (electro negativities do not cancel out)
then molecule is polar.
Examples:
CCl4 – Molecule is nonpolar. Although it has slightly polar
bonds, the molecule is symmetrical.
CHCl3 – Molecule is polar. Asymmetrical electronegativity
differences.
NH3 – Molecule is polar. The lone pair makes it asymmetrical.
H2O – Molecule is polar. 2 lone pairs make it polar.