What happens to water's density as it freezes?

When water freezes, its density decreases, which allows ice to float. This phenomenon occurs due to the unique molecular structure of water. As water cools and approaches its freezing point, the molecules begin to slow down and arrange themselves into a crystalline structure. This structure is held together by hydrogen bonds, which are responsible for the spacious arrangement of the molecules in ice.

In the solid state, water molecules are spaced further apart than they are in the liquid state. As a result, ice has a lower density than liquid water, typically around 0.92 g/cm³ compared to liquid water's average density of about 1 g/cm³ at 4°C. This lower density is the reason that ice floats on water.

Understanding this property is significant in various environmental and scientific contexts, such as the insulation of aquatic ecosystems during winter, where ice cover protects the water beneath it.