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Unformatted text preview: Emission and Absorption Lines (cont) But why are there lines? Quantum theory explains that in an atom, the electron orbits the nucleus (which contains the protons and neutrons), but the orbit is not like the Earth around the Sun. The orbit can exist only in certain energy states. In those and no others. To go from a lower energy state to a higher energy state, the electron must absorb a photon. The energy of the photon must exactly equal the difference in energy between the two levels. Otherwise, no photon is absorbed. Electrons prefer to be in the lowest energy state, so an electron at a higher level (an excited energy state) will spontaneously decay to a lower state, giving off a photon of exactly the difference in energy between the two levels (to within a very small error) ....
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- Spring '06