I am a newbie to the forum and impressed by the breadth and depth of the material here. After searching I am unable to answer a question that I have been pondering. One of my brightest students asked whether electrons other than the valence electrons were involved in the emission spectra of complex atoms. Research in my own texts didn't reveal an answer, nor did research here or on the net. The closest I got suggests that spectra are usually but not always generated by transitions of the valence electrons. http://www.daviddarling.info/encyclopedia/E/energy_level.html http://www.800mainstreet.com/spect/spectrum.html Can anyone confirm that spectra are generated by electrons other than the valence electrons? Any net references would also be appreciated.