The stability of an electron is affected by electrostatic self-repulsion of the charge, attraction of opposite charge/s, Casimir effect, kinetic, and zero-point energies. Investigating the energy balance of these affects it can be shown that the point charge electron loses its stability at the Bohr`s radius and forms a static surface charge around the proton. First principle calculations also show that for individual atoms the formed surface charge around the nucleus is stable as long as the absorbed destabilizing energies are below the one-dimensional Casimir energy. Thus in neutral atoms the Casimir effect stabilizes the surface charge electron shell. For individual atoms the Casimir effect is active on the entire surface area of the electron shell. In this case the one-dimensional Casimir energy should be equivalent with the ionization energy. If the neighboring atoms shielding the Casimir effect then the energy required removing an electron should be reduced in proportion to the active surface area of the atom. On the surface of a metal about half of the atomic surface is shielded by the neighboring atoms. Thus the energy requiring removing an electron should be half of the ionization energy. In the bulk of the metal, where the Casimir effect is completely shielded by the neighboring atoms, the electron shell should be unstable. These predictions are consistent with experiments, since the ionization energy is the same as the one-dimensional Casimir energy, the measured energies of the work function are about half of the ionization energy, and the band gaps of metals are zero.