Lining Up

At the molecular level, water freezes when its thermal energy decreases to the point where hydrogen bonding becomes the dominant force over kinetic energy.

Below 0°C at 1 atm pressure, the motion of water molecules slows, allowing them to arrange into a hexagonal crystal lattice.

Each water molecule, with its bent structure and polar nature, forms four hydrogen bonds—two through its hydrogen atoms and two through its lone electron pairs—creating a tetrahedral geometry.

This lattice is characterized by significant open spaces between molecules, as the hydrogen bonds keep them at a fixed distance.

These spaces explain why ice is less dense than liquid water, allowing it to float.

As water transitions from liquid to solid, the latent heat of fusion (approximately 334 J/g) is released, which must be removed for freezing to continue.