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Thread: Why does the electron orbit the nucleus?

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    Contributor skepticalbip's Avatar
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    Quote Originally Posted by James Brown View Post
    Why don't the electrons and the protons click together like all all things with opposite charges do?
    They would if they were little balls like is popularly imagined. The problem is that they are nothing like anything we would commonly be familiar with. There is no description of what they are as far as I am aware. There is only some understanding of the effects of their behavior under given conditions.

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    Quote Originally Posted by James Brown View Post
    Why don't the electrons and the protons click together like all all things with opposite charges do?
    The electron can only exist in quantized energy states within the potential well generated by the. nucleus. No zero energy state is allowed.

    In classical EM, an orbiting electron would emit radiation and it would spiral into the nucleus. That was one clue that modern physics needed to be invented to explain the structure of the atom.

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    Veteran Member Treedbear's Avatar
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    I don't feel so bad anymore about getting a C in high school chemistry after failing to make a model of an atom out of styrofoam balls.

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    Quote Originally Posted by Shadowy Man View Post
    The answer will depend on how deep down the physics rabbit holes you want to go.
    That's what tends to happen when you ask why about most anything in physics. It's rabbit holes inside rabbit holes until you either reach your limits, or his the limits of human knowledge.

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    Fair dinkum thinkum bilby's Avatar
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    Electrons and photons really aren't like anything in human experience at the macroscopic scale. People talk about 'particles' as though they were miniature billiard balls; Or 'waves', as though they were vibrations in a guitar string. But they're really neither of those, and it's not particularly better in most cases to say that they have characteristics of both. They are like neither; They are a thing unlike anything with which we are familiar, but they do obey very clear and (nowadays) well understood rules of behaviour. Some of those rules are probabilistic, but that's OK because for most applications, we deal with large numbers of these entities, and the probabilities cancel out into a single macroscopic behaviour which we call classical physics. If you are dealing with trillions of them, you usually don't need to know or understand how each individual is behaving in order to understand the behaviour of the collection.

    If you do need to deal with small numbers of subatomic particles, then it's easier not to try to make analogies with familiar macroscopic objects; Just "shut up and calculate", as David Mermin put it.

    Sadly, this approach is not considered viable for teaching schoolchildren, so they are given models that everyone knows are wrong, and then asked to unlearn those models (often more than once) as their education advances. Couple this with the authoritarian nature of most schooling, and you get students with little understanding of reality, and even less faith in the honesty of those who do have an understanding of it.

    I do wonder whether it might be better to start by saying that it's futile to attempt any analogy, and just give students the facts, and show them the experimental approaches that allowed us to determine what those facts are.

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    http://web.physics.ucsb.edu/~phys128...l-AP-8210A.pdf

    An updated version of the oil drop experiment.

    Milikan's apparatus was more primitive and took him years to gather all his data working nights. Not as well known, he was up there wit Einstein and others.

    There were competing theories to explain electric current. His won out.

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    Quote Originally Posted by James Brown View Post
    Why don't the electrons and the protons click together like all all things with opposite charges do?
    As long as you don't want to go very deep down the physics rabbit hole, the simple answer is that they have "angular momentum". The electron's angular momentum is the component of its velocity at right angles to the direction to the proton, multiplied by its mass, multiplied by its distance from the proton. Angular momentum is "conserved", i.e. it's a law of physics that you can't ever create or destroy angular momentum. Whenever you add some angular momentum to one thing you have to subtract an equal amount from something else, just like the conservation of energy. Because of this, whenever a spinning object shrinks, provided it doesn't bump into something else that it can transfer some angular momentum to, it has to spin faster, in order for the angular velocity times the distance to the center to stay the same. The standard example is a spinning figure skater -- when she pulls her arms in she spins faster. The point being, if an electron clicked together with a proton, the distance between it and the proton would go to zero, so its angular velocity would have to go to infinity. Since the electron can't speed up to infinity, it can't ever land on the proton.

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    Elder Contributor barbos's Avatar
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    Quote Originally Posted by Bomb#20 View Post
    Quote Originally Posted by James Brown View Post
    Why don't the electrons and the protons click together like all all things with opposite charges do?
    As long as you don't want to go very deep down the physics rabbit hole, the simple answer is that they have "angular momentum". The electron's angular momentum is the component of its velocity at right angles to the direction to the proton, multiplied by its mass, multiplied by its distance from the proton. Angular momentum is "conserved", i.e. it's a law of physics that you can't ever create or destroy angular momentum. Whenever you add some angular momentum to one thing you have to subtract an equal amount from something else, just like the conservation of energy. Because of this, whenever a spinning object shrinks, provided it doesn't bump into something else that it can transfer some angular momentum to, it has to spin faster, in order for the angular velocity times the distance to the center to stay the same. The standard example is a spinning figure skater -- when she pulls her arms in she spins faster. The point being, if an electron clicked together with a proton, the distance between it and the proton would go to zero, so its angular velocity would have to go to infinity. Since the electron can't speed up to infinity, it can't ever land on the proton.
    Well, it's a completely wrong theory as to why electron can't fall on nucleus.
    Electron change angular momentum when it emits radiation. Photons have angular momentum. So total angular momentum conserves.

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    Quote Originally Posted by barbos View Post
    Quote Originally Posted by Bomb#20 View Post
    As long as you don't want to go very deep down the physics rabbit hole, the simple answer is ...
    Well, it's a completely wrong theory as to why electron can't fall on nucleus.
    Electron change angular momentum when it emits radiation. Photons have angular momentum. So total angular momentum conserves.
    I.e., you can always go deeper down the rabbit hole; but the point is to provide an intuitive picture. Suppose light weren't quantized and the "ultraviolet catastrophe" were real -- how fast would an electron be going when it hit the nucleus?

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    Elder Contributor barbos's Avatar
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    Quote Originally Posted by Bomb#20 View Post
    Quote Originally Posted by barbos View Post
    Quote Originally Posted by Bomb#20 View Post
    As long as you don't want to go very deep down the physics rabbit hole, the simple answer is ...
    Well, it's a completely wrong theory as to why electron can't fall on nucleus.
    Electron change angular momentum when it emits radiation. Photons have angular momentum. So total angular momentum conserves.
    I.e., you can always go deeper down the rabbit hole; but the point is to provide an intuitive picture.
    There is no intuitive picture. And THAT's the point.
    Suppose light weren't quantized and the "ultraviolet catastrophe" were real -- how fast would an electron be going when it hit the nucleus?
    Does not matter, classical EM radiation still carry angular momentum. Also, ultraviolet catastrophe is a separate problem.

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