Emitted vs. Observed Colors

[justadream]

As TBR puts it, for emitted colors, "what you see is what you get". Thus, if you see red light, then red light is being admitted.

For reflected colors, you see the COMPLEMENTARY color of the color that is absorbed most.

Okay those seem pretty straightforward.

TBR GenChem page 142 Passage reads

"With transition metals, the color emitted by the flame is often the color of the light absorbed when the cation in solution is exposed to white light. The color of the aqueous solution that is detected by the eye is the complementary color of the color absorbed"

Is there an intuitive reason between this relationship between the color emitted and the color observed when light is absorbed?

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[Czarcasm]

As TBR puts it, for emitted colors, "what you see is what you get". Thus, if you see red light, then red light is being admitted.

For reflected colors, you see the COMPLEMENTARY color of the color that is absorbed most.

Okay those seem pretty straightforward.

TBR GenChem page 142 Passage reads

"With transition metals, the color emitted by the flame is often the color of the light absorbed when the cation in solution is exposed to white light. The color of the aqueous solution that is detected by the eye is the complementary color of the color absorbed"

Is there an intuitive reason between this relationship between the color emitted and the color observed when light is absorbed?

Just ask yourself, can you see it in a dark room? If yes, then the color observed is the actual photon being emitted. Otherwise, it's the complementary color.

Fireworks, TV, Fluorescence, etc. all occur due to photons being emmited. A red shirt is red because the absorbed photon (blue) reflects all the other photons of white light not absorbed (and appears red as a result).

 

[justadream]

@Czarcasm

Right, I get when you see emitted light.

My question was more to do with:

Why is the color that a transition metal EMITS when you use a flame the same that is ABSORBED when you place incident white light on it.

For example, copper EMITS orange when you use a flame. According to the TBR passage, copper also ABSORBS orange when you shine white light on it. Thus, you would observe the complementary color of orange (Blue I think) after you have shown white light on it.

Is there some relationship underlying this phenomenon?

 

[Czarcasm]

@Czarcasm

Right, I get when you see emitted light.

My question was more to do with:

Why is the color that a transition metal EMITS when you use a flame the same that is ABSORBED when you place incident white light on it.

For example, copper EMITS orange when you use a flame. According to the TBR passage, copper also ABSORBS orange when you shine white light on it. Thus, you would observe the complementary color of orange (Blue I think) after you have shown white light on it.

Is there some relationship underlying this phenomenon?

That's weird. I don't know how to explain that. I mean, I do know transition metals are capable of producing color, because when they absorb light, I vaguely recall something along the lines of their d-orbitals occupy different transition energies when they emit light (not 100%); before absorption d-orbitals were degenerate (equal in energy). Maybe that has something to do with it? I'd be interested in hearing what others have to say, although it's not on the outline so can't be too important. Would probs be explained in a passage since that's very low-yield info.

 

[justadream]

@Czarcasm

Yeah in the passage TBR never asked a question explicitly about this but I was like....weird..when I read it.

Yes, the passage talks about it being caused by d-orbital electronic transitions. Why is that? I thought the s-electrons were in the outer-shell and should be more responsible for "chemical stuff"?

 

[Cawolf]

It may be similar to how electrons are at discrete energy levels - so only discrete wavelengths are absorbed to move to the next energy level, while a photon emitted will be for the reverse energy level transition.

This is what is observed in, for example, a hydrogen lamp.

 

[type12]

Cation vs atom. What's different?

 

[techfan]

From what I understand, when you flame a transition metal it is in its ground state (regular atom) and so it emits a certain color, but when you add the metal to a compound the bonds cause some of the electrons to move to different d orbitals and when you add light it emits a different color.

Cations act differently than the atom in the ground state since there are fewer electrons and as such adding light produces a different color.