When water freezes to form ice, it becomes less dense than its liquid form, which is why ice floats. This phenomenon occurs due to the unique molecular structure of water. Water is made up of molecules that consist of one oxygen atom bonded to two hydrogen atoms (H2O).
As water cools down and approaches freezing, the molecules begin to move slower and arrange themselves into a crystalline structure. In this structure, each water molecule forms hydrogen bonds with four neighboring molecules, creating a spacious lattice. This configuration takes up more space than the same number of molecules in their liquid state, where they are more closely packed due to fluid motion.
Since density is defined as mass per unit volume, the lighter, more spacious structure of ice means that it is less dense than liquid water. Consequently, when ice is placed in water, it displaces a volume of water that weighs more than itself, allowing it to float. This unique property of water is crucial for aquatic life, as it insulates the water below and provides a habitat for various species even in cold environments.