Absorbtion Spectrum: Atom Sublevels & Compounds

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    Absorbtion Spectrum
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Discussion Overview

The discussion revolves around the relationship between atomic sublevels and absorption spectra, particularly in the context of compounds. Participants explore how individual atoms and their bonding in compounds influence the absorption spectrum, addressing both theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Scott questions whether the sublevels of an atom dictate its absorption spectrum and why compounds can absorb the same spectrum at every point.
  • One participant explains that absorption spectra arise when atoms absorb incident light, with electrons transitioning to higher energy states at specific frequencies.
  • Another participant suggests that the formation of compounds involves overlapping orbitals, leading to new electronic configurations that affect absorption.
  • Scott seeks clarification on whether atoms can absorb any frequency and expresses confusion about the nature of spectral lines being unique to specific frequencies due to quantized energy levels.
  • Scott raises a point about the uniformity of absorption spectra in complex molecules like chlorophyll, questioning how this uniformity occurs despite some atoms not being directly bonded.
  • A participant notes that in complex compounds, different groups of bonds correspond to different spectral regions, implying a lack of uniformity in absorption across all atoms.
  • Scott references a discussion about resonance structures contributing to uniform absorption in chlorophyll and seeks further understanding.
  • Another participant mentions nuclear magnetic resonance but does not elaborate on its relevance to the absorption spectrum of chlorophyll.
  • Scott reiterates his question about the relationship between the spectral signatures of constituent atoms and the properties of the compound, suggesting that individual atomic characteristics may be lost in molecular formation.
  • A participant clarifies that molecular orbitals replace individual atomic orbitals in compounds, affecting the absorption spectrum, and emphasizes the statistical nature of absorption spectra across macroscopic samples.
  • Scott acknowledges the practical uniformity of absorption spectra but questions whether it can be determined without physical testing.

Areas of Agreement / Disagreement

Participants express differing views on the nature of absorption spectra in compounds, with some suggesting uniformity due to resonance and others emphasizing the complexity of molecular interactions. The discussion remains unresolved regarding the specifics of how absorption spectra are influenced by atomic and molecular structures.

Contextual Notes

Participants highlight the importance of resonance and molecular orbital theory in understanding absorption spectra, but there are unresolved questions about the implications of these concepts on the uniformity of spectra in compounds.

scott_alexsk
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Hello,
Am I correct in thinking that the sublevels of an atom dictate its absorption spectrum? Also why is that a compound can absorb the same spectrum at every point, rather than individual atoms absorbing their respective spectrums?
Thanks,
-Scott
 
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Am I correct in thinking that the sublevels of an atom dictate its absorption spectrum?
what do you mean by "sublevels dectate"? we get absorption spectrum when the atoms absorb some of the incident light..its because at these frequencies the electrons in the atom can be excited n reach higher states absorbing the radiation.

Also why is that a compound can absorb the same spectrum at every point, rather than individual atoms absorbing their respective spectrums?
A compound is formed when the orbitals of the individual atoms overlap, so there will be re-arrangement of electronic configuration when a compüound is formed. so it will absorb radiation depending on the new electronic energies rather than the individual atoms.

I hope it is clear from what I understood from your question.
 
Are you saying that atoms can absorb any frequency and they only generate specific frequencies in response to excitation by heat or other light?
-Scott
 
Are you saying that atoms can absorb any frequency
I didnt say it anywhere I think. These spectral lines are like finger prints of the atoms. Only certain frequencies can be absorbed and emitted, this from the fact that energy levels are quantized. The emitted or absorbed radiation is exactly the difference between the two energy levels involvedin the transition.
 
I thought you were saying something different last time, oh well. Alright so what allows for the transfer of this spectrum to all atoms within a compound. I mean it makes sense that the structure of the bonds will change the absorption spectrum, but what about the ones that are not directly bonded? I mean in certain complex molocuels like chlophyll, all points share the same absorption frequency, even though they are not bonded directly together.
-Scott
 
what allows for the transfer of this spectrum to all atoms within a compound.

I didnt get you saying transferring the spectrum,,if its a complex compound with many atoms, only some atoms will make bonds with some other depending on their orbital energies, so there are different groups of bonds corresponding to different regions of the spectrum.
 
Yeah orginally I thought that the distrubion would not be uniform, however when I was talking to someone about chlorpyll he said that because of resonance structure, it is uniform. I was wondering if anyone understood why this would be?
-Scott
 
I think he might be talking about the Nuclear Magnetic Resonence. I don't have idea about that,you must look into the absorption spectrum of clorophyl,,
 
scott_alexsk said:
Hello,
Am I correct in thinking that the sublevels of an atom dictate its absorption spectrum? Also why is that a compound can absorb the same spectrum at every point, rather than individual atoms absorbing their respective spectrums?
When a compound does not retain the physical or chemical properties of the constituent elements, why do you expect it to possesses the spectral signatures of the atoms that make up the molecule ?

The constituent atoms lose much of their individuality in a molecule. The excitation/emission spectrum of a compound are related to the molecular energy levels of the molecules that make up the compound. The only spectrum that will show some characteristics of the induvidual atoms will be the core excitation (x-ray) spectrum.
 
  • #10
Thanks for respoding Gukul. The reason I thought that is because in single atoms the excitation spectrum is determined by the difference in energy levels within the atom. It was described to me before that as a result of resonence and the merging of orbitals in bonding, a compound retains a uniform absorption spectrum even though its constituent atoms differ. Can you tell me what is wrong with this view?
-Scott
 
  • #11
scott_alexsk said:
Thanks for respoding Gukul. The reason I thought that is because in single atoms the excitation spectrum is determined by the difference in energy levels within the atom. It was described to me before that as a result of resonence and the merging of orbitals in bonding, a compound retains a uniform absorption spectrum even though its constituent atoms differ. Can you tell me what is wrong with this view?
-Scott
There's nothing wrong with it, though there are two problems in your understanding.

The individual atomic orbitals are no longer present; they are replaced by molecular orbitals formed by the superposition of the valence atomic orbitals. The valence energy levels are therefore those of the molecular orbitals.

Second, you must keep in mind that an absorption spectrum is a statistically generated plot, with data coming from a macroscopic number of molecules all over the sample. So, in that sense, it is meaningless to speak of a uniform spectrum (by which, I think you mean to say that the spectrum generated at one spot on the sample is identical to that generated from a different spot).

Describe to me, an experiment where you can generate different spectra to verify "uniformity" down to whatever level you desire, and then I'll try and explain why you see what you see.
 
  • #12
I suppose for all practical purposes the distrubtion is uniform, but as a result of resonence it is also uniform at the microscopic level. Is there a way to determine the absorption spectrum of a compound without physical testing?
Thanks,
-Scott
 

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