Why are some materials (glass) transparent but others not?

Someone got to tell me. Is it related to the structure of the material? Help me please. :shock:

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"Things" are transparent because they do not interact with light photons. Most items aren't transparent, because they scatter light in one way or another.

For example, http://www.coorstek.com/products/foodbev.asp notice the picture at the top of the page of the High Alumina (Al2O3) parts. They are white, and definitly not transparent.

However, Rubies and other gemstones based on Al2O3 clearly are. The product is actually composed of millions of tiny crystals, where the interface (known as grain boundarys) between these acts to scatter light photons. If you heated the piece up enough, and grew those tiny crystals to larger and larger crystals, the part would eventually become transparent. Rubies are a single crystal, with no boundarys or porosity (trapped air bubbles) so they do not scatter light.

The same thing goes with glass. If you grind up glass to a powder, then cook the particles together, the piece would not be transparent. Again, if you melt the particles together long enough to get rid of porosity and grain boundarys, it would be transparent.

Now, transparency also relates to the actual material and the photons which can be absorbed by the crystals. Metals absorb most incident light-radiation because their electrons easily absorb this energy (why most metals are a "metallic gray").

Germanium is added to fiber optic glasses, because Ge does not interact with Infared photons to the extent Si does. More Infared photons are transmitted as a result....so yes structure/bonding nature does play an important role however, its also dependant upon processing/impurities/surface finish. Anything can be transparent if made thin enough (hold a CD up to a light, as you should be able to see through the aluminum foil).

Re: Why are some materials (glass) transparent but others no

[quote="knight2004"]Someone got to tell me. Is it related to the structure of the material? Help me please.[/quote]

Electrons in solids occupy so called bands. Usually there are many bands, sometimes they are separated by a gap. Electron occuping the band has some eergy. It can move to other band absorbing (or loosing) energy amount equal to band gap. If the band gap size is in the same range as energy of photons of visible light, such photons are absorbed by electrons so they can't pass through the solid. Such solid is not transparent. If the band gap is smaller or larger, visible light can go through the solid not absorbed and the solid is transparent.

smarkotan oz gluthozmaz

How do the electrons "interact" with photons? I am 15 and studying basic chemistry and physics only. I only know that photons are basic unit of light radiation.

Photons occupy space but has no mass. However, they could "kick" the electrons to move. This is the way of which solar cells generate electricity. In return, electrons can also "kick" photons.

An addendum: I'm only 14, also from Hong Kong.

[quote="Deryck"]Photons occupy space but has no mass. However, they could "kick" the electrons to move. This is the way of which solar cells generate electricity. In return, electrons can also "kick" photons.

An addendum: I'm only 14, also from Hong Kong.[/quote]
Same with Photosynthesis.

Thanks. I've been wondering since yesterday if photosynthesis works the same way.

However there's a difference.

Photosynthesis is restricted to breaking down water to hydrogen and oxygen while solar cells have the energy collected in form of electricity.

I'm referring to the fact that in photosynthesis, a photon excites an electron that is rapidly moved across a molecular system, faster than the time for it to relax back to the ground state - thus there is electron movement, which is essentially electricity.

But no, it does not produce electricity. Just has a similar initial stage in the process.

But by what means it breaks down water?

I don't think we covered that.

Some Radical process, perhaps?
Or the promoted electron changes the oxidation state of some atom in there which goes on to cause the breakdown of water?

It is very interesting, if you look into it.
I love biological chemistry, but I've never been any good at holding onto the knowledge. It's a case of 'that is really, REALLY interesting...then 5 minutes later 'what was that again?'
:?

I can ask 'what was that again' just 1 minute after I was told.

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