Not a physicist, but I think temperature lives in motion of particles, let it be electrons, the nucleus, whole atoms, or otherwise. Because electrons shroud the nucleus and have much less mass, they are more prone with external interactions where they can change momentum by absorbing and releasing energy. The nucleus is not exempt from this, but takes a not more energy to change their momentum. That being said, "temperature" as we are accustomed to, is more like a statistical average of the total motion of all particles in the system.