Not all substances are made up of molecules, but sometimes chemists act as if.... Definetly, things are not easy ! In metals and salts, the atoms are stacked regularly. Molecules cannot be identified, but we recognize "structural units" which are reproduced regularly. - In the lattice of common salt the structural unit is formed by one atom of sodium and one atom of chlorine:
Lattice of common salt (sodium chloride NaCl)
- In the lattice of iron the structural unit is formed by one atom of iron (Fe)
Lattice of iron