Spectra and Atoms continued

• A given atom will Absorb and Emit the SAME frequencies of E-M radiation.
  • So a gas of hydrogen will produce an absorption line spectrum if it is between you (your spectrograph) and a continuum light source, and an emission line spectrum if viewed from a different angle.

  

• The E-M radiation frequencies absorbed/emitted map out the allowed energy levels in the atom.

• It turns out that the allowed energy levels in an atom depend mostly on the electric field configuration. So, Hydrogen, with one proton in the nucleus has a different field configuration than does Helium with two protons - this is why the two atoms have a different energy levels and different characteristic absorption and emission lines.