THE ATOM AND ATOMIC SPECTROSCOPY The science of atomic spectroscopy has yielded three techniques for analytical atomic emission, atomic absorption, and atomic fluorescence. In order to un derstand the relationship of these techniques to each other, it is necessary to have an understanding of the atom itself and of the atomic process involved in each technique The atom is made up of a nucleus surrounded by electrons. Every element has a specific number of electrons which are associated with the atomic nucleus in an orbital structure which is unique to each element. The electrons occupy orbital po- sitions in an orderly and predictable way. The lowest energy, most stable electronic configuration of an atom, known as the"ground state is the normal orbital con figuration for an atom. If energy of the right magnitude is applied to an atom, the energy will be absorbed by the atom, and an outer electron will be promoted to a less stable configuration or"excited state". As this state is unstable, the atom will immediately and spontaneously return to its ground state configuration. The elec- tron will return to its initial, stable orbital position, and radiant energy equivalent to the amount ofenergy initially absorbed in the excitation process will be emitted. The process is illustrated in Figure 1-1. Note that in Step of the process, the ex- citation is forced by supplying energy. The decay process in Step 2, involving the emission of light, occurs spontaneously.