[smghz]

Hi. I'm studying introductory chemistry and found a bit of challenge learning emission spectrum.

• Say it's H. I put some amount of energy and a red photon is released. Now I put that same amount and a bit more. I know the answer: a red photon will be emitted. But will it be of the same frequency? Because I know there will be excess. That's what I am trying to wrap my head around: how can a red photon be emitted despite the possibility of more and more energy being absorbed? What happens to the excess energy?
• I found this interesting statement by Zumdahl: When we study the photons of visible light emitted, we see only certain colors. That is, only certain types of photons are produced. We don’t see all colors, which would add up to give “white light”; we see only selected colors. This is a very significant result. Let’s discuss carefully what it means. What does he mean by white color? How can there be a white color made? I mean, it's just a spectrum of color based on frequency. And even if scientists before assumed that an atom can exist in any state of energy, what would be the use of a photon then??

Thank you so so much!

[Corribus]

1. Atoms absorb only certain frequencies as well. In an emission experiment (i.e., in an ICP-AES, or a star perhaps), the energy source incident to an atomized sample is generally a continuum. Excited atoms only emit certain ones, as do ground state atoms undergoing absorption events. It is possible to absorb a high energy photon and emit lower energy photons. This is more common in molecules, which convert some of the absorbed energy into heat, which accounts for the difference. In gas phase atoms, the absorbing and emitting states are more or less the same, as there is no significant structural relaxation in the excited state.

2. The point is that you don't see continuum emission (white light, or light of all wavelengths) from gas phase atoms, because electrons exist in discrete energy states. You can certainly generate a continuum of light - for example, the heated tungsten filament in a conventional light bulb does a reasonably good job of this - but the process of photon generation is completely different from what's going on in emission from a gas-phase sample of atoms.