Final answer:
When ice melts to form water, the hydrogen bonds in the open lattice structure break due to increased molecular motion and thermal energy, causing the inherently spacious arrangement to collapse into a denser liquid form.
Step-by-step explanation:
When ice turns to water, the open lattice structure, characterized by its hydrogen-bonded network, collapses. In the solid form, water molecules are arranged in a fixed structure where each molecule is bonded to four others in a tetrahedral fashion, creating an open, cage-like structure with plenty of space in between. This arrangement is due to hydrogen bonds that form at low temperatures when molecular motion is limited.
As the temperature increases and ice melts, there is more thermal energy available, which leads to increased molecular motion. This additional energy allows the hydrogen bonds to break more frequently, making the structural arrangement of water molecules closer and more disordered. Consequently, the holes in the original lattice structure close up, resulting in liquid water being denser than ice.