Surface Tension The surface of any liquid behaves as if it was a stretched membrane. This phenomenon is known as surface tension Surface tension is caused by intermolecular forces at the liquid’s interface with a gas or a solid. Surface tension depends on the nature of the liquid, the surrounding media and temperature. Liquids that have strong intermolecular forces will have higher values of surface tension than liquids that have weak intermolecular forces.

and the liquid to shrink to the smallest possible surface area. A water molecule deep within the liquid is pulled equally from all sides A water molecule at the surface lacks neighbouring water molecules (toward the interface) net force is not zero! net force = zero when all hydrogen bonds can be fulfilled cohesion takes place=stable state This unequal attraction causes the water at the air-water interface to act as a cohesive surface. and the liquid to shrink to the smallest possible surface area.

Surface Tension A molecules in the interior of a liquid is under attractive force in all direction. However, a molecule at the surface of a liquid is acted on by a net inward cohesive force that is perpendicular to the surface. Hence it requires work to move molecules to the surface against this opposing force and surface molecules have more energy than interior ones Higher forces of attraction at surface Creates a “stretched membrane effect”

14:07 Surface Tension Liquid droplets behave like small spherical balloons filled with liquid, and the surface of the liquid acts like a stretched elastic membrane under tension. The pulling force that causes this is due to the attractive forces between molecules called surface tension ss. Attractive force on surface molecule is not symmetric. Repulsive forces from interior molecules causes the liquid to minimize its surface area and attain a spherical shape.

Drops of liquid in a state of weightlessness takes the form of sphere

Dependence of surface tension on temperature The surface tension of most liquids decreases with increasing temperature

Surface Tension

Surface Tension

Surface Tension

Surface Tension

Surface Tension

Surface Tension

Surface Tension

Surface Tension

Surface Tension

A drop forms when liquid is forced out of a small tube. The shape of the drop is determined by a balance of pressure, gravity, and surface tension forces.

Surface Tension A molecule in the center of a liquid drop experiences forces in all directions from other molecules. A molecule on the surface, however, experiences a net force toward the drop. This pulls the surface inward so that its area is a minimum. Since there are forces tending to keep the surface area at a minimum, it tends to act somewhat like a spring – the surface acts as though it were elastic.