July 07, 2022, 03:06:25 AM
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Topic: Electron excitation + photon emission and the colours we see  (Read 325 times)

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Offline ovin8k

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When an electron absorbs a photon and is excited (not sure if thats the right phrase) so it enters a higher energy level; then when its relaxed returning back to ground level, is the colour we see corresponding to the wavelength caused by the photons energy = the energy it took for the electron to go from one energy level to the other.

Hence why some objects are one colour and other objects other colours, as theyre made from different atoms so the distance between energy levels is different requiring different energies to be absorbed? If yes what's a better way of explaining it, and if not what affects the wavelength caused by the photon energy emitted?

I'm not really sure how to phrase it, so i'm hoping someone will be able to get at what I mean.

Offline Corribus

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Re: Electron excitation + photon emission and the colours we see
« Reply #1 on: May 03, 2022, 11:47:02 PM »
Most of the colors you see are not caused by the kind of photon emission you are describing (what you might term fluorescence). Rather most colors you see are due to absorption and scatter events. A good example is a leaf. Sun light is (approximately) white, meaning in the visible range (about 400-700 nm), there are roughly equivalent* amounts of photons spanning wavelengths from 400 nm (blue, say) all the way to 700 nm (red). Leaves have a lot of chlorophyll, which is a molecular pigment that  pretty strongly absorbs photons ranging from 350-450 nm and from about 600-700 nm. So when white light falls on a leaf, most of the photons in those ranges are absorbed (where their energy contributes to photosynthesis) and the rest of them - from 450 nm to 600 nm - are scattered and reflected. Guess what color most photons in that range look like to your eye? Yeah, green. So, the color of MOST objects is due to what wavelengths are left over and scattered to your eye after molecules in the surface of the object absorb a selrct fraction of the white ambient light around you.

Keep in mind, though, that the perception of color depends not only on what energy photons reach your eye (which depends on how many of each wavelength started from the various light sources around and the number of photons that are absorbed/scattered by various surfaces) but also on how efficient your eye is as picking up the photons that make it through your lenses.

*let us pretend, anyway
« Last Edit: May 04, 2022, 12:31:51 AM by Corribus »
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Offline Borek

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Re: Electron excitation + photon emission and the colours we see
« Reply #2 on: May 04, 2022, 02:53:02 AM »
+1 to what Corribus wrote, although your thinking is not completely wrong - yes, color of the emitted light is a function of the energy level difference between orbitals occupied by the electron when excited/relaxed. What I would change in your post though is that these orbitals are not function of just "atoms" - when you deal with a molecule electrons occupy molecular orbitals. On some level they are conceptually not different from atomic orbitals, they are just characteristic for the molecule composed of many atoms.
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Offline ovin8k

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Re: Electron excitation + photon emission and the colours we see
« Reply #3 on: May 04, 2022, 01:36:44 PM »
Most of the colors you see are not caused by the kind of photon emission you are describing (what you might term fluorescence). Rather most colors you see are due to absorption and scatter events.

Are there any articles that I could read that you'd recommend?

Also when you burn metals, the flame appears as different colours. This is due to different wavelengths of light (from what I gathered). What causes the different wavelengths to be emitted during combustion for the different metals? What causes the different wavelengths so that aluminium is silver white, and boron is bright green?

Offline ovin8k

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Re: Electron excitation + photon emission and the colours we see
« Reply #4 on: May 04, 2022, 01:42:55 PM »
What I would change in your post though is that these orbitals are not function of just "atoms" - when you deal with a molecule electrons occupy molecular orbitals. On some level they are conceptually not different from atomic orbitals, they are just characteristic for the molecule composed of many atoms.

What's another way of thinking about this, I don't understand what you mean by orbitals not being functions of just "atoms". What do you mean by a function an an atom?

Offline Corribus

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Re: Electron excitation + photon emission and the colours we see
« Reply #5 on: May 04, 2022, 02:23:46 PM »
Are there any articles that I could read that you'd recommend?
You can just google "what causes color" and there are a lot of articles written in basic language. For instance, this one looks like it might be decent.

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Also when you burn metals, the flame appears as different colours. This is due to different wavelengths of light (from what I gathered). What causes the different wavelengths to be emitted during combustion for the different metals? What causes the different wavelengths so that aluminium is silver white, and boron is bright green?
Well, this *is* due to photon emission from excited states of different metal atoms and ions. The color of light emitted is characteristic of the energy level spacing, which depends on the electron configuration and nuclear core charge of different elements. It is how we determine what elements are in distant stars and also what elements are in environmental samples in the lab. You may find this article interesting.

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What's another way of thinking about this, I don't understand what you mean by orbitals not being functions of just "atoms". What do you mean by a function an an atom?
He means that most atoms combine to form molecules, so most colors you see come from light interaction with molecular orbitals, not atomic orbitals. (Although the case you mention above, a flame, light mostly does come from atomic orbitals, since the high energy of a flame "atomizes" a large portion of the substrate.)
« Last Edit: May 04, 2022, 03:16:57 PM by Corribus »
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