system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What atomic properties determine the transparency of a material?
gpt
It has to do with the way that the electrons are arranged.

Electrons can also absorb photons to jump up energy levels - but only if there's the right amount of energy in the photon to do a complete jump. Electrons won't jump up anything but whole energy levels.

This means that there has to be the right amount of energy in the light in order for it to be absorbed. With light, energy is proportional to the frequency, which is inversely proportional to the wavelength. This means there's a direct relationship between wavelength and energy.

This is why glass, for example, is transparent. The amount of energy necessary to excite electrons in glass doesn't match the amount of energy that photons have when they're in the visible part of the spectrum, so the photons go whizzing on through without being absorbed.