By now, we already know that all matter is made up of atoms, but what is an atom made out of? Chemists describe the structure of atoms using models. In this tutorial, we will look at the Bohr model, photoelectric effect, absorption and emission spectra, quantum numbers, and electron configurations. We will discuss light and other forms of electromagnetic radiation and how they are related to the electronic structure of atoms. We will also see how this radiation can be used to identify elements, even from thousands of light years away.