Your questions seems to be in two parts, electron behavior and structural characteristics of compounds that account for light propagation properties. I will summarize basic electron behavior as it applies to absorption of light (Electromagnetic Radiation = EMR).
In the study of electron behavior, it has been determined that electrons can gain and release electromagnetic radiation (EMR light) as well as function as a particle with finite rest mass and dimensional properties. This is generally referred to as the 'Wave - Particle Duality of the Electron'. Using the Bohr 'Concentric Ring' Theory of the atom, it can be shown that when Hydrogen gas is confined inside of a glass tube fitted with metallic conductors at each end and connected to a transformer, the gas will have a lavender glow. When this lavender glowing is observed through a spectroscope or diffraction grating, one sees three bright color lines. (Actually there are 4 lines, but one is so close to the UV spectrum that it is difficult to see by most human eyes.) The question is, what causes the lines. Answer: electrons releasing all or part of absorbed EMR having very discrete energy values, frequencies and wavelengths. These 'discrete' EMR events are called 'energy packets, or photons'. Each photon has a specific energy, frequency and wavelength. The basic calculations for energy change, frequency and wavelength can be found in reviews on the Bohr Concentric Ring model of the atom. Considering the Hydrogen atom, as you may already know, the most abundant form of the element has one proton and one electron. When the hydrogen atom is considered with the electron in the 1st energy level (ring), it is said to be in its 'ground state'. However, due to the electrons wave-particle duality, absorption of EMR will cause the electron to leave the 1st energy level and move to a higher energy level (absorption spectrum). Assuming the electron does not completely leave the atomic environment (ionization), the electron then releases part or all of the absorbed EMR energy and falls back toward the nucleus. However, it is important to note that the electron can only fall (transition) between energy levels and does not stop in between energy levels. This results in a specific amount of energy being released and is referred to as a 'quantum' leap or jump. If the electron transitions from a higher energy level and stops in the 2nd energy level, the energy given off can be seen as a 'bright line spectrum'. All atoms have unique bright line spectra that can be used to identify the element. In the case of the Hydrogen atom, the spectrum consists of a Red Line, Green Line, Blue Line and Violet Line. The Red line is an n = 3 to 2 transition, Green is an n = 4 to 2 transition, Blue is an n = 5 to 2 transition and Violet is a n = 6 to 2 transition. Electrons that stop at n = 3 or n = 1 can not be seen with the human eye. Those stopping at n = 3 are Infrared Transitions and those stopping at n = 1 are Ultra Violet Transitions. Electrons are in constant motion by sweeping out designated orbitals based upon their energy content and proximity to the nucleus. It is interesting to note that electrons associated with the more complex elements do not collide with one another, but exist within their own 'energy window' that prevents any other electron from occupying the same space. (Pauli Exclusion Principle). I hope this helps a bit... I have posted summaries of how valence electrons undergo changes in energy content to form pre-bonding hybrid orbitals that account for the molecular geometry of substances. Such can be extended into chemical bonding and related to structural characteristics that give the compounds formed their chemical and physical properties. Again, I hope this helps. Doc