The basics of electronic conductivity can be explained without inciting quantum mechanics or brillouin zone- simply by virtue of outermost free electrons of metallic elements (from electronic configuration) and overlapping of energy bands as many metal atoms come close to one another. The similar approach for electrical conductivity does not apply too good for ceramics, because it is nearly impossible to explain delocalized electrons in ionic/covalent bonded material in terms of basic chemistry (say 10th to 12th grade level) without inciting QM, VBT-MOT and Brillouin zone; and it is hopeless task to locate position of electronic band for ceramics with simple Bohr theory of Atom (e.g. Rydberg ionization equation).

So, How can I preliminarily explain electrical (both ionic and electronic) conductivity of ceramics in a language familiar with (preliminary) origin of band structure in metals? I do not want deep Quantum Mechanics or Brillouin Zone explanation at this level.