Water has an unusually high surface tension
The surface tension of water is the highest of all non-metallic liquids.
Scientific Explanation
Surface tension is the force that holds a liquid’s surface together, acting like an invisible skin. At 72.8 millinewtons per meter at 20 degrees Celsius, water has the highest surface tension of all non-metallic liquids. Only mercury and a few other liquid metals surpass this value.
For comparison, ethanol measures just 22.1 and acetone 25.2 millinewtons per meter. Water’s surface tension is thus roughly three times higher than that of these organic solvents.
The cause is the strong network of hydrogen bonds. At the surface, water molecules lack bonding partners on the air side. The remaining molecules in the interior pull the surface molecules inward, creating a strong surface tension. The stronger the intermolecular attraction, the greater the surface tension — and the hydrogen bonds in water are especially strong.
Step by Step
Water Molecules
We observe a group of water molecules. Each molecule consists of one oxygen atom (large, blue) and two hydrogen atoms (small). The molecules move freely within the liquid.
Hydrogen Bond Network
The molecules form a network of hydrogen bonds. Each molecule can build up to four bonds. This network holds the liquid together -- more strongly than in almost any other non-metallic liquid.
Surface vs. Bulk
At the surface, molecules lack bonding partners on the air side. The interior molecules pull the surface molecules inward. This unbalanced force creates the surface tension.
The Floating Needle
The surface tension is strong enough to support a needle. The water surface bends slightly under the weight without breaking -- like an invisible skin.
Everyday Relevance
Water’s high surface tension is visible everywhere in daily life. Water striders can walk on the surface because the tension supports their weight. Raindrops assume a nearly spherical shape. A carefully placed paperclip floats on water even though metal is heavier than water.
In the plant world, surface tension is crucial for capillary action: water rises through the fine vessels of plants to supply leaves with moisture. Surface tension also matters in washing — soap reduces it so that water can better wet and dissolve dirt.