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$$\Large\color{#D73D75}{Surface\ Tension\ Of\ Liquids}$$

An important property of liquids is surface tension.

What is it?

• It is the ability of liquids to resist spreading outward while lowering the surface area.

Why does it occur?:

• Molecules in a liquid experience Van der Waal's forces.

• The molecules' arrangements differ depending on if they are on the surface or not.

• The molecules in the inner part of the liquid experience maximum intermolecular forces because they are surrounded by other molecules.

• Molecules on the surface experience fewer intermolecular forces because fewer molecules are nearby.

• Liquids will minimize the number of molecules at the surface which minimizes the surface area.

Differences in surface tension:

• The number and strength of the intermolecular forces increase surface tension.

• The liquid with the highest surface tension is elemental mercury. Why? It's held together by metallic bonds. The sea of electrons creates a very strong electrostatic attraction with the nuclei.

• Water's surface tension is also quite strong. It is the second strongest liquid because of its hydrogen bonding.

• There are liquids that only experience dipole-dipole or dispersion forces. But, they have very small surface tensions.

• As a liquid's temperature increases, the surface tension decreases. Why? The kinetic energy of the molecules increases. So they begin to move more, allowing them to overcome any intermolecular forces. Often this is accompanied by a phase change to the gas phase. So, it is also responsible for some colligative properties, like vapor pressure elevation.

• Adding a solute lowers the surface tension. The ion-dipole interactions disrupt the attraction between the surface molecules. This also explains freezing point depression and boiling point elevation.

Surface Tension Examples

Surface tension can be seen in various examples:

• Water forms beads when in contact with other surfaces, especially wax. If you look at a waxed car or waxy leaf, water will form beads.

• A oil and water mixture will form rounded blobs. Oil and water do not mix and the two different surface tensions create suspended blobs.

• Water bugs or water striders are able to move on the surface of water due to surface tension.

(Video) Surface Tension of Water, Capillary Action, Cohesive and Adhesive Forces - Work & Potential Energy

by The Organic Chemistry Tutor

In this video, The Organic Chemistry Tutor illustrates surface tension. He starts by explaining how Van der Waal's forces create surface tension. This is particularly true in water because of its hydrogen bonding. Then he demonstrates a surface tension practice problem. Last, he explains the connection between surface tension and cohesive and adhesive forces. If you want a better understanding of surface tension, this video is for you!

(Video) What is Surface Tension? | Richard Hammond's Invisible Worlds | Earth Lab

by BBC Earth Lab

This isn't a chemistry video. But it has great slow-motion images of surface tension. You'll get to see a water strider moving across the water. I learned that they move two meters per second! That's crazy! Do you want a great visual of how surface tension works? Watch this short video!