H-Bonding and the properties of water

Water molecules are very special.
Water (H2O) molecules are polar molecules. They have small charges on both ends that give them exceptional strength when it comes to attracting each other and other charged particles. Click to see a demonstration of the charged nature of water molecules.

Click to see what creates these charges on the water molecule.

This force of attraction that exists between water molecules is known as hydrogen bonding.

Click to see a demonstration of the charged nature of water molecules.

When cooled into a solid, water expands. This is why drink bottles left in the freezer will explode.

Ice is less dense than water and hence floats on the surface. Icebergs float, for this reason, and is why the Titanic came to its tragic end.

The reason why ice is less dense is outlined below.


You would have noticed the difference in density between ice and water. Every time ice blocks are placed in a glass of water they float. There is more space between the water molecules in ice than in water.

Water molecules are held close together by relatively strong hydrogen bonding. At room temperature hydrogen bonds are broken and reformed repeatedly as shown on the right.

When water molecules are cooled down hydrogen bonding traps the molecules into a rigid three dimensional structure that aligns water molecules in such a way as to create huge gaps between the molecules. This makes ice less dense than water.

Click to see how the water molecules are arranged in ice. Notice that there is more space between water molecules in ice than in the water.

The small charges on the surface of the water molecule help make water an excellent solvent. These charges attract charged particles and help dissolve solids such as salt and sugar.

Click to see an animation (source unknown)


Hydrogen bonding is also responsible for the high surface tension of water. Hydrogen bonding holds the water molecules tightly at the surface and is the reason why small insects and even dense paper clips, as shown on the right, can remain on the surface. Even the so called Jesus lizard, which can walk on water, owes its special skill to hydrogen bonding and the high surface tension of water.

Try placing a paper clip on the surface of cold and hot water. Is there a difference?


Some insects, like the pond skater pictured on the right, can land on the surface of the water and be supported by the surface tension of water.


Click to see the Jesus lizard move across the surface of water.

Why does the surface tension of water reduce when it is heated?

Explain how water is able to dissolve solids such as salt or sugar?

Why does ice float on the surface of water?

Continue with capillary action and hydrogen bonding

Related topics, emulsifiers, surfactants activity, new theory of liquid water.

Hydrogen bonding demonstration