Liquid water is flexible
Molecules continually rearrange and can pack relatively closely.
Freezing organizes hydrogen bonds
The common ice lattice holds molecules in a more open arrangement.
Density falls
The same mass occupies more volume, which is why ice floats.
This matters in nature
Floating ice insulates water below and freeze-thaw cycles can affect rocks and structures.
This page explains scientific concepts for general learning. It does not replace laboratory safety procedures, professional engineering guidance, or individualized medical advice.