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Can anyone explain energy levels of an Atom?

  1. Aug 8, 2011 #1
    Now, from what I understand, Bohr's model of the atom is outdated and flawed. But whenever I imagine energy levels, it is the Bohr's model that comes to mind. Do electrons really orbit around the nucleus? I would assume because of classical physics, even though the electron can be on any portion of the "sphere", it is always on that sphere because it does not lose or gain speed. Due to the acceleration from the centripetal force, it would be kept on an orbit, not the orbit like the planets, but I would call it a "mesh". From what I know, then the electron would "jump" to a higher energy level if a force acted upon the electron because its speed increases. Now, what makes it come back down? Is it the attraction from the proton? But that is centripetal force that keeps it at an "equilibrium" so the electron does not fly out. I understand that there is no force other than the centripetal acting upon the electron, it would keep moving at its same speed because of Newton's first law. If it somehow got to a lower level, that extra energy needs to be spit out as a photon. But what causes it to go to a lower level?

    Also, what determines energy levels? Why are there specific energy levels?

    Just saying, I am just a high school student, if I got the whole thing wrong because I am trying to used classical physics intuition while trying to understand quantum physics, no need to bash me.
  2. jcsd
  3. Aug 8, 2011 #2


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    Newton's Laws do not correctly describe interactions at the atomic level. Forces do not make sense at the quantum scale. Quantum mechanics correctly describes why electrons behave the way they do and why they have specific energy levels. It does not model atoms as electrons orbiting protons like the Earth orbits the Sun. Modeling like this results in contradictions that are not observed experimentally.

    The electron is modeled using a "wave function". What is it? Good question, call me when someone figures it out. However, using the wave function along with the formalism of quantum mechanics, you are able to correctly describe what we see with atoms.

    Also, Bohr is outdated and wrong, but it is MORE correct than classical mechanics.
  4. Aug 8, 2011 #3


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    I really recommend to forget about such mechanistical pictures of quantum objects (atoms). Electrons do not orbit for at least two reasons:
    1. (at least some of them) they have angular momentum equal to zero - so what direction they follow???
    2. it makes no sense to speak/think about electron position changing in time.
    "Electron position" makes sense only ot the very moment of its measurement, which influence further movement.

    Also, what determines energy levels? Why are there specific energy levels?
    I don't think that explanation would be quite satisfactory for you, but the most straightforward answer is that Schrödinger's equation for energy levels of electron in an atom has a discrete set of solutions... Or maybe we should think about it in an opposite way: Quantum Mechanics (and, especially Schrödinger's equation) had been created as a model explaining observed discrete energy levels of atoms?
  5. Aug 8, 2011 #4


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    You got the nail on the head.
    Some of the concepts of classical physics have an analogue (to a certain extent) in quantum physics. For example, when the electron has angular momentum around the nucleus, then the atom has a magnetic moment. (So this is similar to the classical picture). But there are other cases which make no sense to talk about with classical terms. For example, the intrinsic spin of an electron, which does not result from the electron physically spinning.
  6. Aug 8, 2011 #5
    How does the electron move around the nucleus?

    For a visual representation, see here:

    http://en.wikipedia.org/wiki/Atomic_...es_of_orbitals [Broken]

    Note that modern quantum theory discards ORBITS for ORBITALS ....smeared out cloud like probabilities of finding an electron.

    "Also, why does the proton not suck in the electron due to the magnetic attraction?"

    because the electron does not follow classical Maxwell electromagnetic behaviors....it does not radiate energy and fall in as expected classically. ...things in the subatomic realm follow quantum rules.....the electron is in a bound state and therefore quantized...

    Quantized energy levels result from the relation between a particle's energy and its wavelength. For a confined particle such as an electron in an atom, the wave function has the form of standing waves. Only stationary states with energies corresponding to integral numbers of wavelengths can exist; for other states the waves interfere destructively, resulting in zero probability density. Different stationary states result from different nuclear-electron interactions, like the number of protons.

    Elementary examples that show mathematically how energy levels come about are the particle in a box, a violin string, and the quantum harmonic oscillator.

    See here for illustrations of a quantum harmonic oscillator:


    The Pauli exclusion principle explains something about limitations of multiple electrons in a given orbital.

    Here is another discussion on your questions:
    Last edited by a moderator: May 5, 2017
  7. Aug 8, 2011 #6
    This is how I feel right now:

  8. Aug 9, 2011 #7


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    Someone (Feynman?) said something like "if you think you understand quantum mechanics, you don't". It makes EVERYONE's head hurt.
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