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The Atomic Emission Spectrum: an explanationAn atomic emission spectrum is the opposite of an atomic absorption spectrum. While an absorption spectrum has parts missing from the rainbow, the emission spectrum is made up only of a few lines of colour. They are the SAME lines of colour that would be missing in the absorption spectrum for the same sample you test. How do we get an emission spectrum?The process of obtaining an emission spectrum is slightly different to that for the atomic absorption spectrum. A sample of an element or compound is made into a gas and heated. As it gets hotter, the atoms absorb the energy. When the flame is turned off and the gas is allowed to cool, the atoms release the energy as light. Here’s a picture summary of the process:
What’s happening with the atoms?When the atoms are heated the electrons take some energy and jump to a higher orbit; these are the bands missing in the absorption spectrum. When the heat is turned off, those electrons let go of the energy and drop back down to their original orbit; that energy is released is light.
Here is what the absorption and emission spectra for the same sample look like. Note the perfect match: |
