What makes glass transparent even though it’s in a solid state?
In: Physics
Atoms and molecules can only interact with light if that light has a very specific amount of energy per photon (which also determines its color). The colors they can interact with depend on the arrangement of the atoms and molecules within the material.
Basically, if an atom wants to interact with light, the light has to lift an electron from one energy level exactly to the next one, or it doesn’t do anything at all. Different molecules can alter this by changing how big that energy gap is. In the case of glass, all visible light simply has too little or too much energy for all the energy levels available in glass, so it all passes right through. UV-proof glass, on the other hand, absorbs UV light while letting visible light through; if you looked at that through a UV camera, it would look black. Likewise, black trash bags are opaque to visible light, but let infrared light through just fine.
FYI: Glass, is not actually a solid, nor a liquid. It is an amorphous solid—a state somewhere between those two states of matter.
But to answer your question, the electrons in the resulting compound of heating sand, limestone, and soda, don’t have much freedom within its crystalline structure, and thus are not very effective at absorbing light energy., so it passes thru them.
Edit to explain easier:
If a photon (a particle of light) traveling through a solid meets an electron with an energy gap of equal energy, it will be absorbed by that electron as it ‘jumps’ to a higher energy level. This means that very little light can travel through the material without being absorbed, thus making the material opaque. However, with transparent materials, the energy gap is larger, so that the photons cannot excite the electrons into a higher energy level. This allows the photons to pass through the material unaffected, making the material see-through. So in essence, the interaction between light and a material is based on the light wavelength and the nature of the material.
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