Molecules with nonpolar bonds can repel water molecules.
A non-polar bond is a covalent bond between atoms in which electrons are shared equally between the atoms. Equal sharing of electrons results in the formation of a nonpolar molecule that has no electrical dipole moment, or electrical charge separation. Two identical atoms will form a nonpolar bond because they have the same electronegativities.
A common example of non-polar bonding can be found in diatomic oxygen. Each oxygen atom has six electrons in its outer shell, needing two more to achieve the stable eight-electron noble gas configuration. In the oxygen molecule, atoms share a set of four electrons equally in double bonds, satisfying each atom’s need for two extra electrons. Each of these bonds would be considered a non-polar bond.
Lipids like olive oil are not polar, so the oil doesn’t mix with vinegar, which is mostly water.
Nonpolar covalent bonds tend to be found in diatomic molecules, where two identical atoms are bonded together. This includes iodine, hydrogen and nitrogen. The general polarity of a molecule should not be confused with the polarity of its bonds. It is possible for a molecule to be nonpolar as a whole, even when its atoms are not linked by a nonpolar bond. This occurs when polar covalent bonds cancel each other’s charge due to molecular structure.
In methane, carbon is bonded to hydrogen in slightly polar bonds, involving a somewhat unequal sharing of electrons. The tetrahedral structure of the molecule causes these charges to cancel, resulting in a molecule that is nonpolar. Even if the atoms are not linked by non-polar bonds, the molecule behaves in a non-polar way.
This global non-polar interaction between hydrogen and carbon atoms makes organic compounds hydrophobic, meaning they cannot interact with water to form hydrogen bonds. When interacting with polar molecules, water forms hydrogen bonds between its own positively charged hydrogen atoms and an electronegative atom of another molecule. Non-polar compounds cannot perform this interaction because they have no charge separation in their structure and therefore no place to attract a charge.
The hydrophobic behavior can be observed in household products, such as vegetable oil, which visibly separates from water. The non-polarity of hydrophobic substances is also an important factor in the functioning of living organisms. Lipids, which occur in cellular structures, prevent water from mixing with internal structures and separating fluids. As with other organic compounds, these molecules consist of bonds that are almost, but not entirely, nonpolar: their bonding structure causes their polarity to be cancelled.
Carbon dioxide is another example of a nonpolar molecule with polar bonds. The structure of this molecule is linear, with two oxygen atoms doubly bonded to a central carbon atom. These bonds are polar covalent, but because they are exactly symmetrical, their charges cancel each other out, creating a nonpolar molecule.