Polar Molecule Definition
A polar molecule is a molecule containing polar bonds where the sum of all the bond's dipole moments is not zero. Polar bonds form when there is a difference between the electronegativity values of the atoms participating in a bond. Polar molecules also form when the spatial arrangement of chemical bonds leads to more positive charge on one side of the molecule than the other.
Examples of Polar Molecules
- Water (H2O) is a polar molecule. The bonds between hydrogen and oxygen are distributed so that the hydrogen atoms are both on one side of the oxygen atom, rather than evenly spaced. The oxygen side of the molecule has a slight negative charge, while the side with the hydrogen atoms has a slight positive charge.
- Ethanol is polar because the oxygen atoms attract electrons because of their higher electronegativity than other atoms in the molecule. Thus the -OH group in ethanol has a slight negative charge.
- Ammonia (NH3) is polar.
- Sulfur dioxide (SO2) is polar.
- Hydrogen sulfide (H2S) is polar.
Carbon dioxide is made up of polar bonds, but the dipole moments cancel each other out and therefore is not a polar molecule.
Predicting Polarity and Nonpolarity
Whether a molecule is polar or nonpolar is a matter of its geometry. If one end of the molecule has a positive charge, while the other end has a negative charge, the molecule is polar. If a charge is evenly distributed around a central atom, the molecule is nonpolar.