Why is copper blue when it is oxidized?

[cmersits]

Why does copper turn blue when it is oxidized (rusted)? Does it have to do with the arrangement of electrons? Anyone help would be greatly appreciated.

[RyanJ]

Why does copper turn blue when it is oxidized (rusted)? Does it have to do with the arrangement of electrons? Anyone help would be greatly appreciated.

 

Welcome to SFN! hope you enjoy your time here with us :_-)

 

Are you shure you mean Blue? Copper(II) oxide is black and Copper(I) oxide is red. Maybe you mean copper sulphate?

 

Anyway, yes it is to do with electrons - the varying electron configurations absorb different wavelengths of light each giving a different colour (Realating to the varying energy levels of the electrons). Copper forms some interesting colours in aqueous chemistry too but vanadium is sweet also, have a look at this.

 

Actually this whole section may interest

 

Back on topic lookup chromatics at Wikipedia for more information

 

Cheers,

 

Ryan Jones

[jdurg]

Plutonium and Iridium also have a multitude of colors in their various oxidation states. Sadly, plutonium is a bit radioactive and iridium is quite a bit pricey so you really won't come across it on a routine basis.

[woelen]

When copper is oxidized by a combination of air, humid and finely divided acid and salts in the air, then a so-called patina of copper is formed. This is a basic copper (II) carbonate/sulfate mix, which has a cyan color.

 

The reason that the color changes is that a chemical compound of copper is formed. Copper itself is a metallic element. Compounds of elements can have totally different properties than the elements themselves (e.g. look at hydrogen and oxygen, these are gasses at room temperature, while the compound water, made of both elements is a liquid at room temperature).

 

A similar thing you see with iron. When iron is oxidized, then rust is formed, which is brown. This is a mixed oxide/hydroxide of iron (III).

[YT2095]

also it`s down to the particular Size and Shape of these molecules and how they interact with light which determines their color, many Copper molecules of copper compounds tend to reflect light in the Green/Blue area of the spectrum.

a good example how size/shape and density come into play with Light is petrol on water, you`ll see all the colors in the rainbow from such a set up because it`s uneven in reflection, whereas Copper salts are more Uniform in makeup

 

I`m sure one of the Physics Lads or lasses will be able to explain in much better detail than this though.

[Tartaglia]

It is due to d-d splitting of an incomplete d shell. When an electron is promoted from an occupied to an unoccupied orbital it will absorb light with photon energy equal to the diiference in energy of the two states. You will see the complementary colour.

 

The energy splitting will depend on the metal, its oxidation state the ligand and whether it is a pi donor or pi acceptor etc etc, but the symmetry has a major effect too. [Cu(H2O)6]2+ is roughly octahedral (Oh) but since Cu2+ is d9 it will suffer a Jahn Teller distortion which lowers the symmetry to D4h. This will lower the degeneracy of some of the d orbitals

[Daecon]

I always thought rusty copper was green.

[RyanJ]

I always thought rusty copper was green.

 

I can't remember exactly what it is (copper carbonate hydroxide or the like maybe?) but Copper(II) oxide is black and Copper(I) oxide is red.

 

Maybe impurities also so it...

 

@jdurg: Ihave never seen experiments with either of those, do you have any pictures?

 

Cheers,

 

Ryan Jones

[woelen]

When copper rusts, then no copper oxide is formed, but a basic copper carbonate and/or a basic copper sulfate (depending on the precise nature of pollutants of the air).

 

This mix of basic copper salts indeed is green with a somewhat blue hue (green/cyan). It is the well know copper patina.

 

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I do not have any experience with plutonium (my sample did not yet arrive ), but I do have experience with iridium salts. I ordered 3 grams of "IrCl4" and I will soon make a page about the different colors of solutions of Ir-salts.

 

One thing I can say already, the number of colors, which can be made with solutions of iridium salts really is great and the colors are very intense. IrCl4 certainly is as intense as KMnO4 when it is dissolved in water and gives a dull purple color to the solution (not the bright purple of KMnO4). On standing this solution turns brown.

 

When the solution is acidified and a reductor is added, then the solution turns yellow (color of iridium (III) ???). When an oxidizer is added in the presence of hydrochloric acid to this yellow solution, then it becomes dark red (like red wine, but a brighter color).

 

The colors are a mystery to me, I need more research and I'll try to find out more about that. There unfortunately is only little literature about this.

Also, the "IrCl4" has net formula IrCl4, but it is not simply iridium (IV) chloride (according to many textbooks, that compound is of doubtfull existence). Probably "IrCl4" is some complex compound, with Ir and Cl atoms in it at a ratio 1 : 4.

[RyanJ]

The colors are a mystery to me' date=' I need more research and I'll try to find out more about that. There unfortunately is only little literature about this.

Also, the "IrCl4" has net formula IrCl4, but it is not simply iridium (IV) chloride (according to many textbooks, that compound is of doubtfull existence). Probably "IrCl4" is some complex compound, with Ir and Cl atoms in it at a ratio 1 : 4.[/quote']

 

There is a little about them in Chemistry Of The Elements pages 1121+

 

Not a great deal though but its a start

 

Cheers,

 

Ryan Jones

[Tartaglia]

Iridium has been extensively studied particularly low oxidation state iridium complexes such as Vaskas complex. This is largely because many of its compound undergo oxidative addition reactions which were of tremendous interest due to their similarity to Wilkinson's catalyst.

Higher oxidation "Werner type" complexes were almost certainly studied in the early part of the 20th century and probably revisited later when spectroscopic methods became much more sophisticated in the 1960's and 1970's. One name springs to mind - "Kurt Dehnicke". He is the sort of chemist who looked at all sorts of high oxidation type metal complexes and has just published his 1250th paper

 

One point to note is that in colours of transition metal complexes the strict d-d transition is formally quantum mechanically forbidden. This however is relaxed often due to slight lowering of symmetry. Thus really intense colours are not generally due to d-d transitions, but to charge transfer bands which have much higher extinction coefficients

[woelen]

Can you provide some online pointers to this kind of information? That would be very interesting. I, unfortunately, have no means of accessing all those paid subscriptions of papers. If you happen to know some freely accessible papers on this subject (especially, Werner's work on Iridium compounds), then I would be very pleased.

 

I know of Werner's work on the carbonate/ammine/cobalt complexes, but I did not know that he also published work on iridium complexes.

[RyanJ]

Can you provide some online pointers to this kind of information? That would be very interesting. I' date=' unfortunately, have no means of accessing all those paid subscriptions of papers. If you happen to know some freely accessible papers on this subject (especially, Werner's work on Iridium compounds), then I would be very pleased.

 

I know of Werner's work on the carbonate/ammine/cobalt complexes, but I did not know that he also published work on iridium complexes.[/quote']

 

I did a quich search, been having computer problems and am working from the library right now but I could not find much of use. Will continue looking all the same

 

Cheers,

 

Ryan Jones