Ice is less dense than water because of the way water molecules arrange themselves when they freeze. In liquid water, molecules are constantly moving and can pack closely together, but as water freezes, hydrogen bonds form a crystalline lattice structure that holds the molecules further apart. This open lattice creates more space between molecules, increasing the volume and thus lowering the density of ice compared to liquid water. Because density is mass divided by volume, the increase in volume with the same mass results in ice being less dense and able to float on water. This phenomenon is due to hydrogen bonding between water molecules, which becomes more structured in ice, forcing the molecules into a fixed, ordered pattern with gaps that make the solid less dense than its liquid form. This unique property of water is crucial for aquatic life, as the ice layer insulates the water below and prevents entire bodies of water from freezing solid.
