Why does ice float on liquid water?

Ice floats on liquid water because it is less dense than its liquid form. While most substances become denser when they solidify, water is an exception due to its unique molecular structure.123

In liquid water, molecules are connected by weak hydrogen bonds that constantly break and reform, allowing the molecules to pack closely together. When water freezes, these molecules organize into a rigid, open hexagonal lattice. This structure increases the space between the molecules, resulting in a lower density—approximately 917 kilograms per cubic meter for ice compared to 1,000 kilograms per cubic meter for liquid water.12

According to Archimedes’ principle, an object floats if the buoyant force exerted by the displaced fluid exceeds the object's weight. Because ice is less dense than the surrounding liquid water, it remains afloat. This phenomenon is vital for the environment, as floating ice forms an insulating layer on lakes and oceans, protecting aquatic life during cold temperatures.12