4.2 Energy distribution
Atoms without much thermal energy will not be doing very much. Consider fifty million million million (50 × 1018) silicon atoms, bonded into a single massive network; I've chosen silicon, but any elemental solid would do. It will be a speck just large enough to be seen without a microscope. You know that if it is heated it will expand, at some stage it will melt and then eventually it will vaporise – that is because thermal energy effectively 'rattles it to bits'. Having thermal energy makes the atoms able to move. For them, the thermal energy is in part associated with energy of motion – kinetic energy. They may not be free to move far, however – not if the electrons have conspired to bond the atoms together. Within the constraints of being bound by the behaviour of the electrons, the atoms simply jiggle about, exchanging kinetic energy with each other.