Atom Free Electrons . The copper atom, shown above, has 29 protons in its nucleus and 29 electrons orbiting its nucleus. The electrons which are not attached to the nucleus of a atom and free to move when external energy is applied are called free electrons. In some materials like copper, the outer electrons are so loosely held by the atom and so. Free electrons take part in heat and … Valence electrons are responsible for the chemical reactions and chemical bonding of atoms.