Electron Orbits and Nuclei 2- Rotation vs Orbital Motion

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Discussion Overview

The discussion revolves around the nature of electron behavior in relation to atomic nuclei, specifically addressing whether electrons orbit the nucleus, the distinction between rotation and orbit, and the concept of angular momentum in quantum mechanics. It encompasses theoretical aspects of quantum mechanics and the implications of these theories on our understanding of atomic structure.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that electrons do not orbit the nucleus in the classical sense, as the term "orbit" implies a defined path through space, which is not applicable in standard quantum mechanics (QM).
  • Others argue that angular momentum exists for electrons despite their lack of classical orbits, attributing this to the rotational invariance of the system and the nature of wavefunctions in QM.
  • There is a discussion about the difference between rotation (spinning around an axis) and orbit (revolving around another object), with examples provided to illustrate these concepts.
  • Some participants question the source of energy that allows electrons to remain near the nucleus without falling into it, with references to quantum mechanics and the uncertainty principle offered as explanations.
  • Concerns are raised about the vagueness of modern explanations compared to historical views that suggested electrons orbiting the nucleus.
  • Participants express a desire for further resources and clarification on angular momentum and its implications in quantum mechanics.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the interpretation of electron behavior and the implications of angular momentum. There is no consensus on whether the classical concept of orbit applies to electrons, and various viewpoints on the nature of angular momentum and energy stability are presented.

Contextual Notes

Limitations in understanding arise from the complexity of quantum mechanics and the differing interpretations of foundational concepts such as angular momentum and electron stability. Some responses reference established theories without resolving the underlying questions.

Karrar
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1-is electron orbit about the nucleus ?
2-is there is different between rotation and orbit?


thanks in advance
 
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Karrar said:
1-is electron orbit about the nucleus ?
2-is there is different between rotation and orbit?

1. No, in physics we don't say that "electrons orbit the nucleus." The word "orbit" implies following a path through space, and electrons don't do that in standard QM.

2. Yes, something can rotate even when no forces are applied (imagine throwing a stick in outer space and having it flip around and rotate as it travels away). Orbits require an external attractive force to make the thing which is orbiting stay bound to the thing it is orbiting around.
 
Civilized said:
1. No, in physics we don't say that "electrons orbit the nucleus." The word "orbit" implies following a path through space, and electrons don't do that in standard QM.

2. Yes, something can rotate even when no forces are applied (imagine throwing a stick in outer space and having it flip around and rotate as it travels away). Orbits require an external attractive force to make the thing which is orbiting stay bound to the thing it is orbiting around.

Well if it doesn't orbit the nucleus,then how come electron has angular momentum?
 
mccoy1 said:
Well if it doesn't orbit the nucleus,then how come electron has angular momentum?

Angular Momentum is due to rotational invariance of a system, so when we speak of angular momentum in QM (standard QM - Copenhagen interpretation) it reflects the shapes of the probability distribution functions.
 
Karrar said:
1-is electron orbit about the nucleus ?

I was taught that they did, but that was a loooong time ago. Modern explanations are vague, but http://en.wikipedia.org/wiki/Atomic_orbital" is good "information".
 
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StandardsGuy said:
I was taught that they did, but that was a loooong time ago. Modern explanations are vague, but http://en.wikipedia.org/wiki/Atomic_orbital" is good "information".

vague?
 
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mccoy1 said:
Well if it doesn't orbit the nucleus,then how come electron has angular momentum?

You can read about the quantum mechanical treatment of the Hydrogen atom http://en.wikipedia.org/wiki/Hydrogen-like_atom"

If you already know QM, then you know that the Hamiltonian for an electron in a spherically symmetric potential commutes with the angular momentum operator, and so the stationary states of definite energy have definite angular momentum as well.
 
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3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?
4- is electron rotate about it self(spin) ?
 
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Karrar said:
3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?
4- is electron rotate about it self(spin) ?

I need appointment to disscus on line by mail these questions
posters email

3. I told you, in standard QM it means rotation symmetry (under SO(3))of the systems solutions (wavefunctions)

4. Is and Is.. it has intrinsic angular momentum but that is again in standard QM just a property of its wavefunction under a rotation group (SU(2) in this case)

much of this is covered in standard intro QM texts, I can give you some links to free pdf's if you want, it is not so efficient for us to give a full blown course here at the forum but rather discuss real specific issues.

Don't give your email here, the discussion will take place at the forum - what we write here is meant for others to read and be learned from so that we don't have to consider the same questions again again and again (compare with using a textbook)
 
  • #10
if you has the text.pdf supply me please
 
  • #11
Karrar said:
1-is electron orbit about the nucleus ?

Not in the same way that the Earth orbits the sun. It was believed before the 20th Century that electrons *did* orbit this way. We know now that these theories are incorrect, but they are still taught because they are easy to understand and are a useful stepping stone to the modern theory.
2-is there is different between rotation and orbit?

An orbit (or revolution) is when one object walks around another in an ellipse. A rotation is when an object spins around its own center. The Earth rotates, and because of it we have night and day. The Earth also revolves around the sun, and because of this, we have spring and winter.

Karrar said:
3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?

Angular momentum is a property of a physical system. It has two different, but historically related meanings.

The first is classical angular momentum. A system with angular momentum rotates or revolves about an axis, and can be calculated by the position and velocities of all the masses involved. It is conserved. Because of this, things that rotate or revolve tend to continue rotating or revolving.
4- is electron rotate about it self(spin) ?

The second meaning of angular momentum is a quantum phenomenon. It is called spin. It gets its name because it produces effects similar to what would happen if an electron rotated ("spun") around its own axis. However, this is just an analogy, and shouldn't be taken literally. It is treated as a quantum property and we usually only experience its effects in indirect ways (such as permanent magnets).

A very intriguing idea behind angular momentum is that its units: [tex]\frac{kg m^2}{s}[/tex] are the same units as action, an extremely important quantity in physics. Action is what you get when you add up the kinetic energy minus the potential energy of a system at every instant of time. When the universe chooses a path that a particle takes, it always chooses the path which costs the least amount of action. This is called the Principle of Least Action, and among many, many other things, it explains why and how light bends when it goes between air and water.
 
  • #12
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  • #13
5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?
 
  • #14
Karrar said:
5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

There is no need for a "source" of energy to hold the electron in place. An electron around a nucleus is a stable system. It doesn't consume energy, nor does it produce it.

The reason the electron doesn't fall into the nucleus is because it's magic. If it did fall in, the universe would blow up. But we see a universe that hasn't blown up, so we know it doesn't fall in.

More precisely, it's because of the nature of quantum mechanics. A rough argument of why this happens goes like this. The uncertainty principle says there is a lower limit to how well defined a particle's momentum and position can be. If you know where a particle is, it's momentum becomes almost random. If you know a particle's momentum, it's location is almost random.

If we try squeezing an electron to the size of the nucleus, we know its position very well. By the uncertainty principle, it's momentum becomes randomized. Very soon afterwards, it will end up (by simple chance) with a very high momentum, allowing it to break free of the electric field.
 
  • #15
Karrar said:
5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

You may have a problem with understanding the responses being posted on here, at least based on how you are writing your questions.

Please start by reading the FAQ thread in the General Physics forum. Some of the posts there may have already addressed a few of your questions.

Zz.
 
  • #16
malawi_glenn said:
Angular Momentum is due to rotational invariance of a system, so when we speak of angular momentum in QM (standard QM - Copenhagen interpretation) it reflects the shapes of the probability distribution functions.

Hi malawi_glenn,
Yes I understand that, but what business do electrons get upto really inside the atom? The n(quantum number) fits itself around the nucleus of the atom and there the electrons oscillate,rotate etc, right? If so, do they oscillate at fixed points or around the nucleus as they move?
Cheers
 
  • #17
mccoy1 said:
what business do electrons get upto really inside the atom?

There is no generally accepted answer to this question. The mathematics of QM allows us to calculate the probabilities of getting various values for physical quantities when we measure/observe them, but it does not address the question of what is "really going on" when we don't measure/observe them. This is the subject of interpretations of QM, about which people argue vigorously (in this forum and elsewhere). We cannot as yet distinguish between these interpretations experimentally, even in principle, as far as I can tell.
 
  • #18
Tac-Tics said:
More precisely, it's because of the nature of quantum mechanics. A rough argument of why this happens goes like this. The uncertainty principle says there is a lower limit to how well defined a particle's momentum and position can be. If you know where a particle is, it's momentum becomes almost random. If you know a particle's momentum, it's location is almost random.

If we try squeezing an electron to the size of the nucleus, we know its position very well. By the uncertainty principle, it's momentum becomes randomized. Very soon afterwards, it will end up (by simple chance) with a very high momentum, allowing it to break free of the electric field.

I have never heard of HUP being applied as the reason electrons do not physically interact with the nucleus. This may be my oversight. I'd like to ask for independent clarification.
 
  • #19
Karrar said:
5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?
In other word,it's like asking why atom doesn't collapse.okay according to intro chemistry,when you have say 5 electrons atom,no more than two electrons can share a 'spot',so the filling will be 1s^2 2s^2 2p^1.lowest energy orbitals get filled first and the next electrons move to the next orbitals(i.e no one electron sitting on top of other electron).I guess this makes the atom 'stable'.I may be wrong!
 
  • #20
malawi_glenn said:
vague?

Yes. Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.
 
  • #21
jtbell said:
There is no generally accepted answer to this question. The mathematics of QM allows us to calculate the probabilities of getting various values for physical quantities when we measure/observe them, but it does not address the question of what is "really going on" when we don't measure/observe them. This is the subject of interpretations of QM, about which people argue vigorously (in this forum and elsewhere). We cannot as yet distinguish between these interpretations experimentally, even in principle, as far as I can tell.

Great post. Enlightening and insightful. Had I seen this, I wouldn't have posted my previous one.
 
  • #22
sokrates said:
Yes. Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.

These things are not vague; they are exactly the opposite of vague.

You're up against something that needs a set of definitions beyond day-to-day language. In order to discuss these things meaningfully, you need to learn the language.

How do you suppose you would discuss the details of an integrated circuit with someone who thought that voltage and resistance were "buzzwords"?
 
  • #23
DaveC426913 said:
These things are not vague; they are exactly the opposite of vague.

You're up against something that needs a set of definitions beyond day-to-day language. In order to discuss these things meaningfully, you need to learn the language.

How do you suppose you would discuss the details of an integrated circuit with someone who thought that voltage and resistance were "buzzwords"?

No. That's what some brilliant people around here want to believe. They want to believe that QM is well-understood and Copenhagen is the way to go, although much of the interpretation is still vague. Worse yet, the understanding and the MACHINERY can change depending on the interpretation.

Voltage and Resistance can be physically defined in day-to-day language, I'll give you one if you want a layman explanation. And that's what makes Voltage and Resistance CLEAR - that they can be expressed simply.

Using rotational invariance to explain electron's angular momentum and pretending (or naively believing) that mathematics of it is the reason behind the physics is misleading.
and incorrect.
 
  • #24
sokrates said:
Using rotational invariance to explain electron's angular momentum and pretending (or naively believing) that mathematics of it is the reason behind the physics is misleading.
and incorrect.
Sure, that is arguably true. But nobody is pretending that.
 
  • #25
sokrates said:
They want to believe that QM is well-understood and Copenhagen is the way to go, although much of the interpretation is still vague. Worse yet, the understanding and the MACHINERY can change depending on the interpretation.
You claimed, or at least implied, that terms such as 'angular momentum' are buzzwords. They're not. I was arguing your complaint of unclear terminology, not unclear theories.

sokrates said:
Voltage and Resistance can be physically defined in day-to-day language, I'll give you one if you want a layman explanation. And that's what makes Voltage and Resistance CLEAR - that they can be expressed simply.
Nice try. The fact that something cannot be expressed simply does not invalidate it. It is a matter of the listener's level of competence in the subject. Good luck explaining how a computer works to a caveman - in a form he finds acceptable - while using only his own vocabulary. To understand QM, you need to understand the math.


sokrates said:
No. That's what some brilliant people around here want to believe.
Yeah, that attitude will go far... "I don't understand all this. Obviously, I'm smarter than the rest of you delusional ones..."
 
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  • #26
DaveC426913 said:
My argument was not about whether the theory was well-defined it was about whether the terminology was well-defined. You claimed, or at least implied, that terms such as 'angular momentum' are buzzwords. They're not.

No, I never implied terms "such as '''angular momentum''' are buzzwords" or not. I specifically criticized a specific post that attempted to explain the angular momentum of an electron with rotational invariance (which is not wrong) to a person who required physical intuition and visualization. If you had read what I wrote carefully, you'd have easily caught that. But since you are too busy posting and trying so hard to 'bust', I can see why...
DaveC426913 said:
To understand QM, you need to understand the math.

You don't understand QM, you write some equations and formulate the theory. Understanding and calculating are two different things. But I have a feeling that you feel better when you think you understand QM...

DaveC426913 said:
Yeah, that attitude will go far... "I don't understand all this. Obviously, I'm smarter than the rest of you delusional ones..."

It definitely goes further than yours. At least, I know what I don't understand about QM and I don't satisfy myself with half-baked
intuition gained from deep, solid mathematics. This is why, contrary to popular belief, great deal of research is being conducted to "understand" about things, you think, are clearly "established".

This is what distinguishes mediocre physicists from the precious few... Physics is about INTUITION and IDEAS, not just some extremely complicated mathematical construct.
 
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  • #27
sokrates said:
No, I never implied terms "such as '''angular momentum''' are buzzwords" or not.

You may not have intended to, but this is pretty implicative:
Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.

sokrates said:
I specifically criticized a specific post that attempted to explain the angular momentum of an electron with rotational invariance (which is not wrong). If you had read what I wrote carefully, you'd have caught that!
I read what you wrote. I caught it. I take issue with the implication.

Here is your opportunity to clarify your use of the term "buzzword".
 
  • #28
I'll give you a moment to finish retro-editing your posts...
 
  • #29
DaveC426913 said:
I'll give you a moment to finish retro-editing your posts...

I respect your "eager" wait for new material to debunk!

Coming, almost ready...
 
  • #30
sokrates said:
I respect your "eager" wait for new material to debunk!

Coming, almost ready...
Debunking? I'm not debunking anything. I'm taking issue with unsupported claims.

And I'm talking about editing posts that have already been in the discussion stream.
 

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