Beginners query about atomic model

Discussion in 'Physics' started by Tanya, Jan 22, 2011.

  1. Tanya

    Thread Starter New Member

    Jan 22, 2011
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    I do get the idea that electron shows wave particle duality and that it has unique quantum numbers.

    but this still does not explain that why does it not keep losing energy and collide into the nucleus..

    Please clarify my doubt.... I have only read the first chapter and am stuck here!!

    :confused:
     
  2. logicman112

    Active Member

    Dec 27, 2008
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    What follows is according to the classical theory of electro magnetics. When a charged particle moves and has acceleration it starts generating electromagnetic wave into the space. If i want to explain how an electron rotates around a nucleolus by the classic theory, it means that the electron is losing energy all the time because it has an accelerated circular motion around proton.
    The total energy of the electron is: E=1/2mv^2-ke^2/r
    When E is reduced , one possible scenario is that r becomes smaller so the potential energy diminishes while the other energy have to increase, it means that electron is always becoming closer to the proton while it rotates more quickly. The net result is that electron has to fall on proton!
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    You are thinking the electron is like a ball, it isn't. It is a particle. It obeys a different set of laws (which is why the duality of its nature, that of particle and wave exist). To the world of electrons there is only energy levels. These levels are fixed, they can not vary. The outside electron has some freedom of it's energy level, but each level on an atom is still fixed. The structure of metal is such electrons (the outside ones) are not tightly fastened down, so they can float within a mass of metal. This is conduction. Other materials the electrons are tightly fastened down, including the outside ones, these are insulators. The world of quantum physics and the world we live in are pretty different. We are seeing the averaging of those really small laws, and it hides things pretty well.

    When an electron absorbs a photon whose energy level matches its it jumps a level. When an electron emits a photon that photon will be of a precise energy level, and the electron jumps down an energy level. This is the nature of how lasers work. It also allows us to identify what kind of elements are present in glowing plasma.

    The old illustration of an atom of a ball of little spheres circled by little moons is pretty far off, and getting worst all the time. It is used as an anology, something we do in electronics all the time to get an idea across to beginners. Each one of those "spheres" is actually made of 3 sub atomic particles, including electrons. Last I heard they were debating whether those subatomic particles could be divided even further. It can make a persons head hurt.

    Matter, all matter, is mostly empty space. To say this casually understates the case. The reason our hands don't go through walls is more a matter of natural force fields. Solidity is an illusion.

    So basically the subject can't be explained in a couple of paragraphs, possibly not even a couple of books. To come close to understand it requires a lot of reading. Some cases Wikipedia is your friend, but be skeptical as well as open minded, the facts are not all in, not even close.

    BTW Tanya, Welcome to AAC! Another girl (judging from the name) has fallen amongst the geeks. This means you are going to be popular! :D
     
    Last edited: Jan 22, 2011
  4. Tanya

    Thread Starter New Member

    Jan 22, 2011
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    @Logicman : Thanks.... but that is exacltly what i want to know...that why does that not happen???

    @ Bill Marsden : Thanks for welcoming me.... I have never been a part of any forum.... but its good to know that people are so active here.......and by d way..I believe I will be more unpopular for my stupid questions since I am only an ammeture in this field. ;)

    Thanks for giving me the bigger picture. But to go step by step, I still don't understand what it means exactly by wave particle duality.

    We say that it behaves like a wave at times and as particles at times. But is it that what way it will behave is only predicted by experiments?? how do we know analytically that while revolving around nucleus it will not lose energy as electromagnetic radiation..??
     
  5. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Welcome aboard Tanya !! :D

    Please don't beat yourself up..........we all started out as noobs, and the only s-question is the one you don't ask......some others here have a different bend on this, tho' we try to be as helpful as possible. I think the E-books are really helpful, we have some really sharp people writing...........

    It's best to post questions with a schematic or drawing when possible.

    Keep coming back !:)
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Welcome to the forum.
    If you have any questions, start asking.
    We will be happy to answer the questions.

    There is also the eBook, see the tabs on the top of the page.
    The eBook can be downloaded using the PDF sign at the right top on the index page of a volume.
    Did you also look at the useful websites thread:
    Useful websites for electronics (Ver. 2)
    Or the RF related links thread:
    RF related links

    The links on this page of the EDUCYPEDIA will probably be of any help to you:
    http://www.educypedia.be/education/physicsbytopic.htm

    Bertus
     
  7. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Hello Tanya, you say you understand the idea of wave / particle duality so here goes.

    There is a theorem in structural engineering called "the shakedown theorem"

    This theorem basically says (in very posh structural language) that a structure will react to load in the strongest possible way.

    There are lots of equivalent theorems in physics which basically say that nature can choose or take the best or most convenient option for itself.

    In terms of wave / particle duality this means that nature can behave as a wave or as a particle to suit itself.

    Now I have sketched models of the atom both as a wave and as a planetary particle system.

    In the particle model the charge is localised and subject to the classical physics laws that require it to radiate energy.

    Properties in any wave are delocalised ie spread out. Now it just so happens that the circumference of the particle orbit corresponds to a whole number of wavelengths (didn't I say nature could arrange things to suit itself) of a delocalised 'charge wave' corresponding the the matter wavelength proposed by De Broglie.
    So a standing wave will 'fit' around the nucleus just dandy. And a standing wave does not radiate energy..
    This is how the electron is confined to particular 'orbits' where it does not radiate energy.

    Of course there are yet more complicated models.

    Hope this helps.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    So, why do excited atoms radiate?

    Here's a description of how Bohr solved the problem:
    http://abyss.uoregon.edu/~js/glossary/bohr_atom.html

    John
     
  10. ELECTRONERD

    Senior Member

    May 26, 2009
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    I am not a physics expert, by any means, but I have read about it.

    No energy is lost in regards to electrons, but merely transferred into different states. One thing that was very peculiar for physics scientists and the like was the fact that electrons kept disappearing from one shell and immediately would arrive on some other shell. Now we know that the electron changes from actual matter to a pulse of energy and then into matter once again.

    It has been a while since I've read about this, though, if I'm wrong perhaps someone could affirm what is correct.
     
  11. studiot

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    Nov 9, 2007
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    electronerd has it.

    The radiation energy is the difference in energy between the excited state and the ground state.

    The model I offered is the simplest possible wave model.
    Of course, the circumference that holds a whole number of wavelengths is not unique, as is the number of wavelengths itself.

    It is this fact that leads to the excited states and thence to the taking up or shedding of the energy difference.
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    My point, perhaps I should have added a smiley, was to question this statement: "And a standing wave does not radiate energy."

    Or, to get back to Tanya's question (paraphrased), why don't atoms in their ground state decay to neutrons? Perhaps to take it a step further, why don't protons and neutrons collapse to points?

    John
     
  13. studiot

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    Wave motion is not dissipative of itself. That is why electromagnetic waves have been travelling across the universe since time began.

    Of course they spread out by the inverse square law, but that is a different thing.
     
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  14. Tanya

    Thread Starter New Member

    Jan 22, 2011
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    @studiot : yes it did help... but again ... is there a model to predict what nature will suit the electron......??
    is it just the fact that- " had electron behaved as a particle, it would have radiated energy and collapsed into the nucleus,....which does not happen" , the only proof that it actually behaves like a wave in this case.

    Or do we have a model ( a kind of entropy model) which says that it has to behave like this in order for the system to be feasible??

    I sound confused.. :rolleyes:

    but really.... it is only from the results that we are concluding here that it behaves like waves..... had we not known the results... and say we want to predict that how an electron will behave in some other hypothetical scenario........ then how will we do that???
     
  15. Tanya

    Thread Starter New Member

    Jan 22, 2011
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    Hi,... i believe when he said that standing wave does not radiate energy... he meant, a fixed energy is associated with a particular standing wave...

    when an electron jumps from one energy state to another( or a standing wave converts from one to another), the difference in the energies of the two standing waves is what is radiated.


    I am trying to comprehend it myself...

    @Studiot... is that right??
     
  16. studiot

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    Yup that's right, got it in one.

    Note I referenced 'wave motion' and the inverse square law. Travelling waves transfer energy from one location to another and are subject to the ISL. Standing waves do not transfer energy anywhere (that is why they are stationery or standing) and so are not subject to the ISL.

    Sorry but there is no easy answer to the question 'How do we predict wave v particulate behaviour?'
    That was the point about the earlier preamble. The electron can do pretty well what it wants.
    There are also further ways to look at it or ways it can behave to do with probability.

    What I have shown is the very simplest transition from classical to quantum mechanics.

    To do more we have to set up and solve some pretty fearsome equations which requires degree level maths.
     
    Last edited: Jan 23, 2011
  17. nsaspook

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    Aug 27, 2009
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    In someways it depends on if that electron is bound "to a atom" or free. A free traveling electron behaves as a wave.
    In a CRT the electrons behave as particles in the electron gun, travel as waves to the screen and behave as particles when they hit the screen phosphor.
     
    Last edited: Jan 22, 2011
  18. Tanya

    Thread Starter New Member

    Jan 22, 2011
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    Thankyou everyone.... I guess my doubts are pretty much cleared and now I can move on with my reading.......

    this forum is really fun!!

    Ill be back very soon with my next query.... :)
     
  19. studiot

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  20. thatoneguy

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    Feb 19, 2009
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    Electrons, they've decided to be a basic particle now(quark). They have a mini-chart similar to the Periodic Table but for quarks that shows which ones we know about, and what we expect to exist, currently it is "full" with 12 types of quarks, leptons, and bosons. Protons and Neutrons are still make of a few quarks each, and are a great deal larger than electrons.

    Minor correction that may be re-corrected once more is discovered, it may be obsolete once the LHC goes to full power. (The theory, not the electron)
     
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