The ability of a material to conduct electricity depends on its atomic structure, specifically the presence of free electrons. In good conductors like metals, the outermost electrons in their atoms are not tightly bound to a single nucleus. Instead, they can move freely throughout the material, forming what is often called an "electron sea." When a voltage is applied, these free electrons are able to flow easily in a coordinated direction, creating an electric current. Materials that have many free electrons and a molecular structure that allows for easy electron movement are excellent conductors.