Physical Properties of Liquids
. D. Surface Tension Liquids behave as though they have a delicate skin on their surface. This property is called surface tension. In rain droplets, surface tension acts like a thin balloon, holding the water molecules together in each droplet. Water-strider bugs take advantage of surface tension by flitting across the surfaces of ponds without falling through the surface. Surface tension results from the intermolecular forces of attraction in a liquid. A water molecule deep inside a droplet experiences attractive forces in all directions from other molecules in the drop. The sum of these forces is zero, leaving no net force on the molecule. A molecule that is close to the surface, however, has more neighboring molecules inside the drop than it has near the surface. The forces pulling the molecule toward the center of the drop are stronger than those at the surface, so the molecule sticks to the drop instead of falling away. Intermolecular forces of attraction make liquids pull togethe