3. Representation of body properties

3.1 Solid, liquid and gaseous phases

A pure substance can be in one or more of three phases: solid, liquid or gaseous. The solid state can even comprise several allotropic varieties, reflecting the different possible arrangements of the crystal lattice.

Microscopically, these three phases are distinguished by the intensity of intermolecular forces:

• in the solid state, these only allow atoms to oscillate around fixed positions of random or ordered distribution (crystals);

• their intensity diminishes in liquids, which have no form of their own, but remain weakly compressible. This is referred to as short-range order and long-range disorder;

• In a...