Question

Water beads up on the surface of a waterproof coat. What can you say about the bonds in the molecules on the surface of the coat?

Answer 1

Water beads because the coat surface is hydrophobic: the surface molecules are essentially nonpolar (lots of C–H bonds, hydrocarbon chains, or other nonpolar groups). Those molecules have strong covalent bonds internally but only weak intermolecular (van der Waals/London dispersion) forces between them and water, and they cannot form hydrogen bonds with water. As a result the cohesive hydrogen‑bonding forces within the water are stronger than the adhesive forces to the coat, so the water minimizes contact area and forms beads.