Atoms are in-dividuals, they follow own rules, and unify how (1) and when (2) they want.
Sometimes they loose their individuality, and behave like one, big atom (3).
The idea and the picture are courtesy of “Science”.
(1) Atom form chemical compounds, i.e. molecules, following precise proportions, i.e. stoichiometry. Only some compounds are stable; it means that this given combination of atoms stuck together have a lower energy than single atoms separately.
(2) The stoichiometry is not enough: to synthesize a given compound a specific path of reaction must be followed. In Physics it means that some activation barrier is needed to obtain the minimum of energy characterizing the molecule.
(3) Atoms are always in movement, i.e. from quantum mechanics point of view are waves. At very low temperatures (below microkelvins, when their de Broglie’s wavelength is long, similar to their interactomic distances) a herd of atoms can undergo Bose-Einstein condensation – all of them get described by the same quantum state.
There is no place for individuals any more – they loose their individuality, like soldiers in the army.