great comment on the page:
"trivia: molecules have no color"
They don't? Then where does color come from?
Why wouldn't gold atoms be golden?
i'm hoping the guy was being sarcastic but...
i'm hoping the guy was being sarcastic but...
Molecules have no color because they are smaller then the shortest length wave of light you and I can see.
Think about dropping a stone in a quiet pond. Think of the waves that are created. If they bump into a large obstacle they are reflected back. If they hit a tiny one, like a thin blade of grass sticking out of the water, they just flow around.
Gold is golden because a whole lot of gold atoms bunched together reflect a yellowish range of light. Gold the material is gold colored. A single gold atom does not have color.
It seems to me it's an argument about semantics, not physics.
A single atom has very specific set of electron energies as a consequence of the electrons being confined to the area around the nucleus. This means that it can only absorb or emit photons with energies corresponding to the spacings between any two energy levels (and the absorption/emission must be accompanied by a jump/fall of an electron between corresponding energy levels. Any type of atom will thus have a secific pattern of absorption/emission peaks, this is incidentally how we can tell the composition of stars and dust clouds in distant galaxies.
For a lump of metal, a good approximation is to consider the electrons as being able to freely roam throughout the entire crystal. As a consequence, when they are excited by an incoming photon (of any energy), they immediately relax back to their original state, emitting the photon again at the same energy. This is why metal films act as mirrors and why metals in general are shiny. As for the goldish color of Gold, that has to do with some relativistic effects which I don't understand (yet ;-) ). I believe the same is true for Copper.