Intermolecular Forces 11.4

• Surface tension is the energy required to increase the surface area of a liquid by a unit amount.
• The key principle is that the more intermolecular forces experienced by a molecule the lower its potential energy.
• Molecules in the interior of a liquid have a lower potential energy than those on the surface because they experience more intermolecular forces.
• In general, the stronger the intermolecular attractive forces, the greater the surface tension.
• Viscosity is a measure of a liquid's resistance to flow, occurring because the intermolecular attractive forces within a liquid prevent its molecules from moving around as freely as they could in the absence of those forces.
• Molecules that are large and complex tend to become entangled, contributing to the increased energy at higher temperatures that enables them to flow around each other more easily, which is why viscosity generally decreases with increasing temperature.
• Capillary action is the spontaneous rising of a liquid against the pull of gravity through a narrow tube.
• Capillary action is a result of the interplay between cohesive forces, the intermolecular attractions within a liquid, and adhesive forces, the intermolecular attractions between liquid molecules and the walls of the tube.
• Adhesive forces attract the surface molecules, causing them to move up the wall of the tube.
• If liquid mercury is placed in a glass tube, it displays a convex meniscus.