Ice Structure
Ice is a crystal. On a molecular level, all crystals are structured in a lattice form, with molecules bonded together in regular patterns. In ice, every water molecule is bonded to four other molecules by hydrogen "bridges."
Melting Process
ScienceDaily explains that when ice is heated above 32 degrees Fahrenheit, its molecules begin to vibrate back and forth quickly. When they reach their maximum vibration energy, they begin to spin. As they spin, they break their hydrogen bonds and lose their crystalline structure. Eventually, the molecules move more slowly and freely in a liquid state.
Fun Fact
The melting process begins at isolated spots in the ice crystal. Once one spot loses its structure, the surrounding areas become increasingly vulnerable, and eventually collapse as well.