Sciencemadness Discussion Board

color of elementel cupper

emrebjk - 24-9-2007 at 06:49

why cupper is red? how can u explain that?

Slimz - 24-9-2007 at 06:55

This looks promising...
http://www.chemicalforums.com/index.php?topic=5836.msg25932

12AX7 - 24-9-2007 at 07:52

Plasma frequency, that is, the rate at which free (metallic) electrons can move. It just happens to be low in copper, gold and cesium, crossing the visible spectrum.

Tim

emrebjk - 25-9-2007 at 00:06

12AX7 can you explain your answer.

guy - 25-9-2007 at 01:44

The energy gap between the d and s orbitals of Cu is very small allowing visible light to excite an electron between orbitals.

The 3d is initially higher in energy than the 4s because of shielding. As the 3d orbital gets filled, its energy is lowered and eventually is lower than the 4s. At copper, the energy gap becomes small enough to absorb visible light.

[Edited on 9/25/2007 by guy]

12AX7 - 25-9-2007 at 03:06

http://mysite.du.edu/~jcalvert/phys/copper.htm#Copp
Quote:
Copper is often described as a "red" metal, though its actual color is an orange-red of lower intensity, not a bright signal red. It is not a spectral color by any means, but a particular impure one requiring its own name, such as "copper-red." The red color is produced by the density of electrons being insufficient to cause a high plasma frequency, so the shorter wavelengths are not reflected as efficiently as the longer, redder ones. The red color is unique to copper and its alloys.


As far as I know, plasma frequency is something to do with plasma physics, so it's something of an abstract concept as far as trying to associate chemical / quantum mechanical phenomena with it. It certainly is NOT due to spectral lines, like the small energy gap. The color is red in reflected light due to an abosrbance of higher energy radiation (green, blue, etc.) over, say, 1.5 or 2 eV, certainly not a small energy gap.

Most metals look "red", but only if you can see a spectrum shifted towards UV, because their plasma frequency is higher.

BTW, I don't really get his explanation, because other metals with less electron mobility (manganese, silicon, plutonium, etc.) are still silvery...

Tim

guy - 25-9-2007 at 13:50

http://en.wikipedia.org/wiki/Plasmon

This is the true explanation though I dont understand any of it :P
Copper and gold have a lower plasma frequency but it doesn't say why they do. I still suspect it has to do something with the small energy gap. I know pretty sure that a small energy gap due to relativistic effects in Gold is responsible for the color.

[Edited on 9/25/2007 by guy]

emrebjk - 26-9-2007 at 03:25

we have to find a review about the color of copper. I2m still searching.