Chemical Polarity - Polarity of Molecules - Nonpolar Molecules

Nonpolar Molecules

A molecule may be nonpolar either because there is (almost) no polarity in the bonds (when there is an equal sharing of electrons between two different atoms) or because of the symmetrical arrangement of polar bonds.

Examples of household nonpolar compounds include fats, oil, and petrol/gasoline. Therefore (per the "oil and water" rule of thumb), most nonpolar molecules are water-insoluble (hydrophobic) at room temperature. However, many nonpolar organic solvents, such as turpentine, are able to dissolve polar substances. When comparing a polar and nonpolar molecule with similar molar masses, the polar molecule in general has a higher boiling point, because of the dipole–dipole interaction between their molecules. The most common form of such an interaction is the hydrogen bond, which is also known as the H-bond.

• Example 3. In the methane molecule (CH₄) the four C–H bonds are arranged tetrahedrally around the carbon atom. Each bond has polarity (though not very strong). However, the bonds are arranged symmetrically so there is no overall dipole in the molecule.

• Example 4. The boron trifluoride molecule (BF₃) has a trigonal planar arrangement of three polar bonds at 120°. This results in no overall dipole in the molecule.

• Example 5. The oxygen molecule (O₂) does not have polarity in the covalent bond because of equal electronegativity, hence there is no polarity in the molecule.

• Methane: the bonds are arranged symmetrically so there is no overall dipole

• Boron trifluoride: trigonal planar arrangement of three polar bonds results in no overall dipole