The quantization of electronic energy levels in atoms is foundational to a mechanistic explanation of the periodicity of elemental properties and behavior. This paper presents a hands-on, guided inquiry approach to teaching this concept as part of a broader treatment of quantum mechanics, and as a foundation for an understanding of chemical behavior. The approach is centered around two laboratory experiments in which students use light emitting diodes (LEDs) to test hypotheses related to the quantization of energy levels. In the first experiment, students determine the relationship between the voltage required to light a series of LEDs and the wavelength of the light emitted. In the second experiment, they determine the relationship between the intensity and wavelength of a series of LEDs to the intensity of the glow produced by a piece of phosphorescent material exposed to those LEDs. From the experiments and guided discussion, the students can build a solid understanding of the quantization of energy levels and transitions in atoms. This can provide them with a firm foundation on which to build their understandings of quantum mechanics and chemical behavior in general. (Contains 3 figures.)