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What do we mean by the fact that energy levels are quantized?

aspiringmedic178

Help would be really appreciated because I am slightly confused with the answers I have found online.

Reply 1

Oxazole

Original post by natalia.medicine

Help would be really appreciated because I am slightly confused with the answers I have found online.

It just means that electrons (or any other quantum particles) can only take on certain discrete values of energy.

Reply 2

aspiringmedic178

Original post by Oxazole

It just means that electrons (or any other quantum particles) can only take on certain discrete values of energy.

Thank you very much! :smile:

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Reply 3

alow

Original post by Oxazole

It just means that electrons (or any other quantum particles) can only take on certain discrete values of energy.

It's more like their energies have a distribution that has huge peaks at discrete values. If it was actually a discrete value we would not be able to see absorption lines in absorption spectra.

Reply 4

KombatWombat

Original post by alow

It's more like their energies have a distribution that has huge peaks at discrete values. If it was actually a discrete value we would not be able to see absorption lines in absorption spectra.

What do you mean by a distribution of energies? If there was a distribution there'd be no lines, the absorption spectra would be continuous…

Reply 5

alow

Original post by KombatWombat

What do you mean by a distribution of energies? If there was a distribution there'd be no lines, the absorption spectra would be continuous…

A distribution with very sharp peaks (so there is only a very small probability of a particle having an energy with more than a very small difference from the absorption line is very low). If there was no small variance in energy we would not see the lines as they would be infinitesimally narrow.

Reply 6

Oxazole

Original post by alow

It's more like their energies have a distribution that has huge peaks at discrete values. If it was actually a discrete value we would not be able to see absorption lines in absorption spectra.

I didn't say 'a discrete value', I said 'discrete values', which is consistent with a non-continuous energy distribution.

Reply 7

alow

Original post by Oxazole

I didn't say 'a discrete value', I said 'discrete values', which is consistent with a non-continuous energy distribution.

You're misunderstanding what I said.

Reply 8

richpanda

alow is right. They have to be relative to something else (as in sharp peaks vs negligible parts) otherwise they'd be infinitely small lines?

Reply 9

Oxazole

Original post by alow

You're misunderstanding what I said.

Are you referring to the variance of energy 'around' the discrete energies of electronic states due to different vibrational modes, rotational modes, etc?

Reply 10

alow

Original post by Oxazole

Are you referring to the variance of energy 'around' the discrete energies of electronic states due to different vibrational modes, rotational modes, etc?

Yes.

Reply 11

Oxazole

Original post by alow

Yes.

In fairness even vibrational and rotational energy levels have a discrete distribution, it's just that the peaks appear 'smeared' on the specturm due to the large number of possible modes and limitations with the resolution of the instrument.

Reply 12

KombatWombat

Original post by alow

Yes.

Ultimately the energy levels are entirely discrete, even if there's lots of them bunched up due to rotational, vibrational states. High resolution can pick these up, and then any broadening is due to HUP/Doppler/pressure, but this doesn't mean energy levels aren't quantised, just that the energy of the emitted photons isn't quantised.