How does light interact, and travel through Solid matter as matter gets thicker, in w

Jan 2016
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How does light interact, and travel through Solid matter as matter gets thicker, in width.?

In the absorption, and emission process of light, hitting electrons, I do not really understand that much, about electron energy levels, and how they change when a lot of atoms become molecules, and them those molecules become solid matter.
I think eV levels for electrons change when single atoms become molecules, and matter.
I need to get a idea of how eV changes in electrons, as atoms come together in groups in molecules, and solid matter.
so if you have a single atom, then add more atoms in a line up to a micron in width, then add more atoms up to a millimeter.
How is light going to behave as more and more atoms are added in a line, then becoming a molecules, and then solid matter, and how do the electrons eV levels change as more atoms are added.
Thank you for your help, anything helps even a few words.