# 13.6: Surface Tension

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### How is this insect able to stand on water?

The next time you are by a still body of water, take a close look at the creatures scooting along on the surface. You may see insects seemingly floating on top of the water. These creatures are known by a variety of names including water skaters, water striders, and pond skaters. They take advantage of a property called surface tension to stay above the water and not sink. The force they exert downward is less than the forces exerted among the water molecules on the surface of the pond, so the insect does not penetrate the surface of the water.

## Surface Tension

Molecules within a liquid are pulled equally in all directions by intermolecular forces. However, molecules at the surface are pulled downwards and sideways by other liquid molecules, but not upwards away from the surface. The overall effect is that the surface molecules are pulled into the liquid, creating a surface that is tightened like a film (see A in the figure below). The surface tension of a liquid is a measure of the elastic force within the liquid's surface. Liquids that have strong intermolecular forces, like the hydrogen bonding in water, exhibit the greatest surface tension. Surface tension allows objects that are denser than water, such as the paper clip shown in B in the figure below, to nonetheless float on its surface. It is also responsible for the beading up of water droplets on a freshly waxed car because there are no attractions between the polar water molecules and the nonpolar wax.

Other liquids, such as diethyl ether, do not demonstrate strong surface tension interactions. The intermolecular forces for the ether are relatively weak dipole-dipole interactions that do not draw the molecules together as tightly as hydrogen bonds would.

##### Science Friday: Candy Corn in Space

Candy corn is a very tasty treat. In this video by Science Friday, astronaut Don Pettit uses Candy Corn to demonstrate the effects of hydrophobic and hydrophilic interactions.

## Summary

• The surface tension of a liquid is a measure of the elastic force in the liquid’s surface.
• Liquids with strong intermolecular forces have higher surface tensions than liquids with weaker forces.

## Review

1. Define surface tension.
2. What is responsible for the strong surface tension in water?
3. Does diethyl ether have a stronger or weaker surface tension than water?

13.6: Surface Tension is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.