Re: Why is glass transparent? (telling me its a liquid doesn't help!)

hi Paul,

Let me extend your question a little. Why is anything transparent?

When light encounters a material, it can interact with it in several different ways. These interactions depend on the nature of the light (its wavelength, frequency, energy etc.) and the nature of the material (how closely packed its atoms or molecules are, whether those atoms or molecules are ordered, whether the electron orbitals are spaced such that they absorb light of certain frequencies and so on).

For instance, light falling onto a leaf encounters a number of pigment molecules, predominantly chlorophyll. These molecules absorb light from the red and blue ends of the visible spectrum. The remaining light is scattered back because molecules in a leaf are quite tightly packed and so we see a green leaf.

When light falls onto a block of metal, it encounters atoms that are tightly packed in a regular lattice and a "sea" of electrons moving between the atoms. Most of the light is scattered back from this kind of material, which is why we see a shiny metal surface.

Glass is often referred to as a liquid, but really it has properties of both a solid (its molecules don't move very much) and a liquid (the molecules are not arranged in any kind of ordered way). Molecules in glass are not packed into a tight lattice and unless tinted, it doesn't contain molecules that capture light with a particular energy. So when light encounters glass, most of it passes straight through. Hence, it is transparent.

Hope this helped answer your question,
Neil