It is said that the internal periodic electric field of the ions of the crystal lattice affects the distribution of electrons over the energy levels in solids. We make a rough calculation of the effect on the electron in the conduction band of the charge of the nucleus of the atom (ion) and the electron of the atomic core on the outer shell of the ion. Let the distance between atoms be 4 angstroms, and between the outer electron of the core and the conduction electron of 0.25 angstrom, then multiply 0.25 by 4 to give unity to the force and find an element with atomic number 64 whose charge of the nucleus acts on the conduction electron with the by force. Gadolinium. For elements with atomic numbers greater than 64, the main influence will be exerted by the periodic field of ions, while for elements with atomic numbers less than 64 the periodic field of the outer electrons of the atomic core will be decisive. Roughly, of course, nevertheless the band theory needs to be reviewed.