Ice is less dense than water because
- it forms an open hydrogen-bonded net- work that prevents the molecules from pack- ing as tightly as they might otherwise.
- repulsive dipole-dipole interactions keep the water molecules apart.
- it weighs less.
- air is trapped in the ice, reducing its
- van der Waals interactions between water molecules are weak.
number 1. Molecules are pushed farther apart than in water