Atomic wire electronics are considered, where the band structure and the resultant Fermi energy are designed by manipulating the lattice constant. Using the tight-binding theory with universal parameters, it is shown that Si wires and arrays are metallic, Mg wires are insulating, and ME arrays have metallic and insulating phases for infinitely large, isolated cases. Structures are of finite size, and electrodes are necessary for the applications. The finite size brings about discrete electron energy levels, and electrodes will charge or discharge the structure, reflecting the work function difference, so that even the basic electronic properties may be altered. The electrodes will cause further complications such as the energy level broadening, the Coulomb interaction through an effective capacitance, or the mode-selection resistance. When the contact satisfies certain conditions, a metallic wire is predicted to show two distinct I-V patterns for small voltages. Depending on whether the highest occupied level is either partially or fully filled, the current starts to flow rapidly or does not flow until the voltage overcomes the next level, respectively.