Final answer:
The structure of water changes between liquid and solid states (ice) due to the stability of hydrogen bonds. Ice forms a hexagonal lattice which is less dense than liquid water, allowing it to float and protect aquatic life in winter by insulating the water beneath.
Step-by-step explanation:
The water structure differs in ice and water because of the way hydrogen bonding occurs between water molecules. In the liquid state, hydrogen bonds are constantly breaking and reforming due to the motion of the molecules. However, as water cools and begins to freeze, these bonds become more permanent, creating a rigid, open, and hexagonal lattice structure that is less dense than the liquid form. This unique property of water, resulting in ice being less dense than liquid water, leads to ice floating on water and has significant ecological implications.
Each water molecule can both accept and donate hydrogen bonds, resulting in an intricate network. When water molecules are in their solid state (ice), they form a cage-like structure due to stable hydrogen bonds holding the molecules apart in a fixed pattern, whereas liquid water has a more jumbled structure with transient bonds because of higher thermal energy. The expansion of water when it freezes is also why ice is less dense, prompting important survival mechanisms in nature such as insulation of bodies of water, which allows aquatic life to survive through winter.