I'm somewhat confused about the emission of photons when electrons go down an energy level. What sentence could I use to help me comprehend this process? This is what I was thinking: When electrons absorb photons from electromagnetic radiation, the electrons have more energy and thus it moves to a higher energy level. After a while the electrons lose this energy and eventually returns to ground-state energy. Electrons lose this energy by emitting photons that correspond the the difference of the energy levels. (I would like a better setence to replace my last sentence. Why do the electrons lose the photon energy? Does this mean that every time something loses energy (even humans?) they give off photons?? I know that everything has both a wave and particle nature. So does that mean we absorb photons and give them off too? So basically, in order for an electron to emit photons or go down an enery level, it must have already absorbed a photon and its energy before? I don't get why the energy levels are negative (-eV). Is it because it is somewhat like a workfunction and how it acts like a deficit of energy that the electron needs to absorb in order to free itself from the atom? Does the electron free itself from the atom after it reaches over the maximum energy level (the one closest to zero)? Thanks for your help in adv.!