A solid forms from a liquid when the molecules no longer have enough kinetic energy to overcome:

1. Cooling a liquid removes kinetic energy from its molecules. 2. Compressing it pushes those molecules closer, strengthening their mutual attraction. 3. If the temperature of a liquid becomes sufficiently low, or the pressure becomes sufficiently high, the molecules no longer have enough kinetic energy to overcome the intermolecular forces between them. 4. At that point a solid forms. 5. Forces inside the molecules are covalent bonds, which are untouched by freezing. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 10 'Liquids and Solids', sections 10.1-10.6_