Water Facts: Why Water Behaves So Unusually

Water facts start with a simple idea: this everyday substance behaves in ways that most common materials do not. Its polarity and strong hydrogen bonding explain why it can be solid, liquid, and gas in normal terrestrial conditions, and why it has such unusual physical and chemical properties.

Why is water so unusual?

Water is a polar molecule whose strong intermolecular hydrogen bonding is a major reason for its unusual behavior. The water molecule is bent, with the hydrogen atoms forming a 104.5 degree angle around the oxygen atom. Because of that shape and polarity, water can form up to four hydrogen bonds with neighboring molecules in its liquid or solid state.

Those bonds are powerful. Water has a much higher melting and boiling point than similar compounds because its hydrogen bonds are about ten times as strong as van der Waals forces. That same bonding is also why water can exist as a supercritical fluid above its critical point of 647.096 K and 22.064 megapascals.

How does water behave when it freezes?

Water is one of the few common substances that expands as it cools, and it is the only known naturally occurring substance that does so while liquid. When water freezes, it expands by about nine percent, which can burst pipes and crack rocks.

The freezing point of water is zero degrees Celsius at one atmosphere, and the boiling point is one hundred degrees Celsius. Water is also the only common substance that exists as a solid, liquid, and gas in normal terrestrial conditions.

Its density behavior is just as striking. Water reaches its maximum density at three point nine eight degrees Celsius. At four degrees Celsius, water sinks in lakes and oceans while ice floats on top, insulating the water below. That floating ice layer helps preserve liquid water underneath.

Why does water matter so much for life and climate?

Water's polarity makes it a good solvent for salts, sugars, ethanol, oxygen, and carbon dioxide. That ability helps it interact with a wide range of substances in living systems and in nature. Pure water has a low electrical conductivity, but it increases when a small amount of ionic material is dissolved in it.

Water also has a high specific heat capacity, heat of fusion, and heat of vaporization. Those properties help moderate Earth's climate by storing and transporting heat. Water is a diamagnetic material, adding another unusual physical trait to its profile.

The combination of bonding, polarity, and thermal behavior gives water its place as one of chemistry's most distinctive molecules. It can carry heat, dissolve many substances, freeze into an expanding solid, and still move between solid, liquid, and gas under normal conditions.

What are the key water facts to remember?

Water is a polar molecule with a bent shape and a 104.5 degree bond angle. It can form up to four hydrogen bonds, reaches maximum density at 3.98 degrees Celsius, and expands by about nine percent when it freezes. It also has a freezing point of 0 degrees Celsius, a boiling point of 100 degrees Celsius, and a critical point where it becomes a supercritical fluid.

Those are the core water facts that explain why ice floats, pipes burst, lakes layer by temperature, and Earth keeps a remarkably balanced flow of heat.

Test what you learned in the quiz below.