What things don't dissolve in water?

Why Certain Substances Refuse to Dissolve in Water

If you have ever tried mixing olive oil into a glass of water, you already know the result: no matter how vigorously you stir, the two liquids quickly separate. This everyday phenomenon comes down to basic chemistry and a concept known as molecular polarity.

Water is composed of polar molecules, meaning it has distinct regions of partial positive and partial negative charges. Because of these charges, water molecules act like tiny magnets. They easily attract other polar substances—such as salt or sugar—surrounding their individual ions or molecules to form hydration shells and dissolve them completely.

However, substances like fats, oils, and waxes consist of nonpolar molecules. These molecules share their electrons evenly, resulting in a balanced charge with no positive or negative poles. Because nonpolar molecules lack charged regions, they experience no electrostatic attraction to water molecules and cannot form hydration shells.

Rather than mixing, water molecules prefer to stick to one another, effectively squeezing the nonpolar molecules out. This natural repulsion is why nonpolar substances are described as hydrophobic, or water-fearing, and why oil will always sit separately on top of water.