To understand the principle of atomic spectrometry you have to know something about my structure. Over the centuries there have been many scientist who discovered interesting things related to atomic structure. They also created models to explain their discoveries. The best known model is the planetary model which describes me as a nucleus surrounded by one or more electrons. Although there were many people who knew that the planetary model is too simplistic, Bohr conceived the next acceptable model.
According to Bohr you may consider me as a hotel for electrons. I have some double rooms called orbitals, but they can be used by a single electron as well. My orbitals are also called energy levels because, in order to enter a room, an electron must have a certain energy. An inner orbital reqires a lower energy than an outer one. Just like the rooms in a hotel are grouped on different floors the orbitals are further organized in shells - one shell contains one or more orbitals.
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