Therefore, electrons existing in the outermost shell of an atom are relatively loosely bound to the atom. For example, in the copper atom the most outer shell has one electron and when that electron gains sufficient thermal energy it can break away from the parent atom and become a free electron. In copper at room temperature, a large number of these free electrons are present that are not bound to any atom and are free to move. Free electrons make copper an excellent conductor and make electrical current possible. Other conductive materials may have similar characteristics but with different conductivity determined by their atom structure.