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Old Apr 16th 2014, 07:29 PM   #1
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Electron orbit

What kind of motion does electron have as it "orbits" a nucleus? I have heard its not a classical orbit as that would mean the electron would radiate energy as it spiraled into the nucleus. Does that mean it "jumps erratically" around the nucleus?
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Old Apr 17th 2014, 03:53 AM   #2
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Just My Opinion

I feel that ORBIT is a mis-interpretation based on simplified analogies
Similarly for describing an electron as a subatomic PARTICLE.

My personal interpretation is that the electron is quite literally a non-local phenomena.
The electron exists as a probability potential (whatever that is) as described by the Schrödinger equation.
The shape of the probability potential function depends on the energy levels of the electron (with respect to the rest of the atom).

The standard interpretation is the "don't worry, just calculate" interpretation.

Physicists can calculate the observed consequences of an electron with exquisite accuracy.
But there seems to be little or no interpretation of of what an electron actually is,
or what it might be upto when you are not looking at it...
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Old Apr 17th 2014, 03:20 PM   #3
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Ok, thats interesting. I was thinking in terms of what the electric field of the electron must be doing. Whether the electric field is erratically changing in direction while the electron "makes up its mind" where it is located.
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Old Apr 17th 2014, 03:51 PM   #4
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Making it up as I go along...

I am posting way outside my proper knowledge base here, but lets have a go anyway..

The electric field in an atom arises as a combination of the electric potentials of its component parts.
The electron "orbits" could be viewed as surfaces of constant electric-field strength
by which I mean surfaces where the combined effects of the electric potentials between the nucleus and the electron (and all the other electrons), is constant.

For a Hydrogen atom this would be a simple sphere, for more complex atoms the surface would have a more complex shape.

The electron could exist anywhere on this surface without changing the overall electric field.

ChipB or Topsquark or (i.e one of the proper physicists) will probably give us a better answer.

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Old Jun 21st 2014, 11:56 PM   #5
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Originally Posted by kiwiheretic View Post
What kind of motion does electron have as it "orbits" a nucleus? I have heard its not a classical orbit as that would mean the electron would radiate energy as it spiraled into the nucleus. Does that mean it "jumps erratically" around the nucleus?
In quantum mechanics one doesn't think of particles as moving per se. That is to say that we don't follow their motion as we would a particle on a classical trajectory. All that can be done is to determine the probability that an electron will be found in a certain region of space. For details see

http://en.wikipedia.org/wiki/Atomic_orbital

Last edited by Pmb; Jun 26th 2014 at 10:32 AM.
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Old Jun 22nd 2014, 04:34 AM   #6
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See this from the wiki atomic orbitals page that Pmb linked to:

"The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves."

Don't think of an electron as some tiny little particle going round a proton. Think of it as a smeared-out thing, more like Saturn's rings than our Moon. Only it's isn't a "ring", it can adopt one of many "shapes". Only it's quantum field theory, and the electron is just field.
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Old Jun 23rd 2014, 03:59 PM   #7
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I've had a bit of a think about this in conjunction with the wiki link of PMB.

The combination of properties of the electrons and nucleus of the atom affect the probability of finding the electron at any given location.
The probability of finding the electron at any position can be calculated from the probability density function.

This function can be integrated to define a volume within which the probability of finding the electron is higher than some figure (eg 99.9%).

The shape of this volume is the shape of the "orbital" of the electron.

Note that theoretically the electron can be miles (even parsecs) from the nucleus, but the probability falls off extremely sharply beyond a picometre or so.
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Old Jun 26th 2014, 10:35 AM   #8
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Originally Posted by Farsight
Think of it as a smeared-out thing, more like Saturn's rings than our Moon.
This is wrong. It gives a wrong picture of what's going on. All that the "standing wave" means is that the square of the magnitude of the wave has the physical meaning of a probability function which tells you what the probability of measuring a particle at a particular place is. The wave itself isn't really a physical entity.
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Old Jun 27th 2014, 07:17 AM   #9
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I'm afraid it is, Pete. You can diffract electrons.
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Old Jun 27th 2014, 11:50 AM   #10
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Originally Posted by Farsight
I'm afraid it is, Pete. You can diffract electrons.
Your fear is for not. I made no mistake whatsoever. Recall The Copenhagen interpretation (See http://en.wikipedia.org/wiki/Copenhagen_interpretation)
The Copenhagen interpretation is one of the earliest and most commonly taught interpretations of quantum mechanics. It holds that quantum mechanics does not yield a description of an objective reality but deals only with probabilities of observing, or measuring, various aspects of energy quanta, entities that fit neither the classical idea of particles nor the classical idea of waves.
....
The Copenhagen Interpretation denies that the wave function is anything more than a theoretical concept, or is at least non-committal about its being a discrete entity or a discernible component of some discrete entity.
...
Throughout much of the twentieth century the Copenhagen interpretation had overwhelming acceptance among physicists. Although astrophysicist and science writer John Gribbin described it as having fallen from primacy after the 1980s,[21] according to a poll conducted at a quantum mechanics conference in 1997,[22] the Copenhagen interpretation remained the most widely accepted specific interpretation of quantum mechanics among physicists. In more recent polls conducted at various quantum mechanics conferences, varying results have been found.
However you won't find a text that uses anything other than the Copenhagen interpretation.

The Copenhagen interpretation states the following
The probability of finding the particle in the interval dx = = |<x|Psi>|^2 = |Psi(x)|^2 dx
where the notation Psi(x) is defined as Psi(x) = <x|Psi>

In any case you're confusing the wave properties of electrons with a mathematical tool used to describe the probability density of finding the electron at a particular place in space. Watch the video at
http://physicsworld.com/cws/article/...n-a-real-thing

Just because I said that the wave function is not a real thing that has an existance which is measurable you can't logically take that to mean that wave phenomena doesn't exist. What you just said and what you're thinking is a very well-known and very common mistake made by amateurs and beginners. You should pick up and carefully rear a good textbook on quantum mechanics. E.g. the following textbook is used at MIT to teach QM - Introduction to Quantum Mechanics - Second Edition by David J. Griffiths, (2005).

Last edited by Pmb; Jun 27th 2014 at 06:40 PM.
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