3 ms·

You are correct, the Bohr model has been obsolete for almost a century. It continues to get trotted out because the more accurate model is quite unapproachable

You are correct, the Bohr model has been obsolete for almost a century. It continues to get trotted out because the more accurate model is quite unapproachable without a lot of math and study. When someone says "revolves around something" they are mentally projecting a whole sequences of measurements of the electron's position, one after another, that trace out a path. We are evolved to regard the path as a natural thing as opposed to focusing on the measurements. But we can't do that for electrons orbiting an atom, since measuring them involves wacking them with photons or something that bounce off in some direction so we can see that deflection. So all we get to talk about is the result of a measurement. When someone says "it's in this orbital," that's a statement about the values of energy and angular momentum a measurement will produce. What measurements actually produce those? Ones that involve absorbing or emitting photons, mostly, and we measure those by the energy of the photon absorbed or emitted, and those don't give us information about the position of the electron. You may think that we could put an electron into a very high orbit and then try to triangulate where it was when it emitted the photon based on the angle...but then you have to know where the atom is precisely, which means another measurement, which means some unknown momentum imparted, which means the energy spectrum of the photon we're trying to measure gets smeared... Meanwhile, if we measure position precisely, then we impart some new momentum vector to the electron. What the momentum vector would have been measured to be before that wasn't known, and so we have no idea how we have kicked it and the orbital (energy and angular momentum) can have various values if we measure them afterwards even if they would have always had a single value beforehand.

yomly 6y ago
I can't disagree with most of what you've said and it gives quite a classical intuition to the problem but it's still very classically grounded.
- madhadron 6y ago
  You're right, it is, despite my care to only speak of the result of measurements, not properties of the state we measure.
vertbhrtn 6y ago
Is the accurate model that complex, though? An electron is a standing wave: one could show the first two standing waves on a drum and say these are the lowest two electron energy levels. Higher levels create more sophisticated waves, and non-flat potential adds more complexity, but the idea remains the same.
- corty 6y ago
  Yes, you are right, standing waves is the exact model that is used. All the measurement problems with e.g. location are just a consequences of that, some properties of a standing wave may be "smeared all over" the wave, like its location. And some interactions with the wave will change it. Quantized things are just standing waves of different order or "frequency" in a confined system. You just understood 80% if quantum mechanics.
- madhadron 6y ago
  An electron isn't a standing wave, so apparently it is that complex. :(
  - vertbhrtn 6y ago
    What is it then?
    - madhadron 6y ago
      It's own thing, and thinking of it as a classical wave or a classical particle isn't accurate. You go through the math and the experiments and try to build and intuition for what it is in its own right without reference to classical analogies.
corty 6y ago
Electrons occupying their orbital can be precisely measured in some aspects. Energy most prominently: An atom does have distinct energy levels for its electrons and an electron changing between two of those levels absorbs or emits the precise energy difference between those levels. Thats how emission and absorption lines come to be. Thats what is called quantized. So if I see a certain emitted photon I can know precisely what the energy levels and angular momentum of the photon were before and after the emission. But I do not know its position or momentum.

yomly 6y ago

I can't disagree with most of what you've said and it gives quite a classical intuition to the problem but it's still very classically grounded.

madhadron 6y ago
You're right, it is, despite my care to only speak of the result of measurements, not properties of the state we measure.

vertbhrtn 6y ago

Is the accurate model that complex, though? An electron is a standing wave: one could show the first two standing waves on a drum and say these are the lowest two electron energy levels. Higher levels create more sophisticated waves, and non-flat potential adds more complexity, but the idea remains the same.

corty 6y ago
Yes, you are right, standing waves is the exact model that is used. All the measurement problems with e.g. location are just a consequences of that, some properties of a standing wave may be "smeared all over" the wave, like its location. And some interactions with the wave will change it. Quantized things are just standing waves of different order or "frequency" in a confined system. You just understood 80% if quantum mechanics.
madhadron 6y ago
An electron isn't a standing wave, so apparently it is that complex. :(
- vertbhrtn 6y ago
  What is it then?
  - madhadron 6y ago
    It's own thing, and thinking of it as a classical wave or a classical particle isn't accurate. You go through the math and the experiments and try to build and intuition for what it is in its own right without reference to classical analogies.

corty 6y ago

Electrons occupying their orbital can be precisely measured in some aspects. Energy most prominently: An atom does have distinct energy levels for its electrons and an electron changing between two of those levels absorbs or emits the precise energy difference between those levels. Thats how emission and absorption lines come to be. Thats what is called quantized. So if I see a certain emitted photon I can know precisely what the energy levels and angular momentum of the photon were before and after the emission. But I do not know its position or momentum.