Electrons are the principal charge carriers in metal wires because they are free to move within the metal, while protons are tightly bound to the atomic nuclei and cannot move freely. The outer electrons in metal atoms are loosely bound and can move through the metal lattice, allowing them to carry electrical charge when an electric field is applied. In contrast, protons remain fixed in the nuclei and do not contribute to electrical conduction. Metals have many free (delocalized) electrons that can move through the metal structure, creating electric current by drifting toward the positive terminal of an electrical source. This mobility of electrons makes metals good conductors of electricity, whereas the protons stay locked in the crystal lattice and do not move.