Why is ice less dense than liquid water?

Ice is less dense than liquid water primarily due to the unique structure of ice. When water freezes, the molecules arrange themselves in a hexagonal lattice formation, which maximizes the number of hydrogen bonds between water molecules. This specific arrangement creates an open structure that occupies a larger volume compared to liquid water, where the molecules are in closer contact and can move more freely.

In liquid water, molecules are constantly moving and can come closer together, which increases the density. However, during freezing, the formation of these hexagonal structures forces the molecules apart, leading to an increase in volume and a corresponding decrease in density. As a result, ice floats on water. This property is critical for aquatic life, especially in climates where bodies of water freeze over, as it insulates the water below and helps maintain a stable environment.