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Impact of concepts on Atomic Theory

  1. Feb 28, 2005 #1
    During most of the 19th Century physicists believed that atoms were the smallest particles of matter and thus couldn’t be further subdivided. With such characteristics, an atom of one element obviously couldn’t become an atom of another element – a process they labeled “alchemy”.

    J. J. Thomson forced a change in this concept of the atom in 1897 when he showed that atoms actually consisted of smaller charged particles( negatively charged electrons, positively charged protons and neutrons with a neutral charge). This concept made possible his subsequent discovery that atoms could actually lose protons allowing an atom of one element to become an element of another element – a process called fission.

    Subsequent investigations indicated that Thomson’s particles were themselves composed of even smaller “particles”, or maybe “wavelets”.

    Thomson initially conceived of all of these particles as being distributed evenly within the atom. Ernest Rutherford introduced the concept that the protons and neutrons were concentrated in a nucleus with the electrons orbiting the nucleus like planets orbiting the sun. Physicists no longer compare electrons to the planets, but the basic concept of a nucleus surrounded by electrons is still use. Many physicists still believe that electrons go around the nucleus.

    This concept made possible a major new concept developed by Niels Bohr. During the 19th Century physicists believed that the absorption of specific wavelengths of light by atoms resulted in them becoming hotter because there wasn’t any other aspect of the atoms that could change. In 1913 Bohr reported that the process of absorbing specific wavelengths of light actually involved a change in the energy level of the electrons in atoms. Rather than continuously absorbing radiation, the electrons would switch to a higher energy state when they absorbed radiation and then back to a lower level when they emitted that radiation. Electrons had to emit radiation before absorbing any new radiation. Bohr provided the concept of electrons being in “shells”.

    The concept of atoms as particles didn’t adequately explain how atoms could combine to form molecules. The concept of atoms comprised of smaller particles provides a mechanism for atoms to join together. The “shells” Bohr suggested needed to have a certain number of electrons. Sharing electrons allowed atoms to fill those “shells” with one electron in effect becoming part of two different atoms. Having moving electrons in atoms would complicate such sharing. How would electrons move around multiple atoms? Another problem of moving electrons would be keeping them from colliding or being thrown out of the atom by the repulsive effect of their negative charges.

    If electrons maintained fixed positions within atoms they could easily be shared by two atoms. Fixed positions could explain the need for specific numbers of electrons. The electrons negative charges would repel each other. The positive charge of the nucleus would tend to draw them to the nucleus. Electrons could form a sphere around the nucleus. The electrons could not move closer to the nucleus because the repulsive force of their charges would prevent them from getting close enough to each other to move closer to the nucleus. The force keeping the electrons in position might prevent a determination of their exact position by creating an energy field. Fixed positions would allow atoms to share electrons by positioning themselves so that an electron could hold a fixed position in both atoms.
     
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  3. Feb 28, 2005 #2

    dextercioby

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    So what is the conclusion (if there is one) of your lengthy post...?

    Daniel.
     
  4. Feb 28, 2005 #3

    ZapperZ

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    May I suggest, if you care to debunk your own picture here, that you pick up a solid state physics text and study it? The field of condensed matter/solid state physics (y'know, the one responsible for all the materials that you are using in your modern electronics) deals primarily with what happens when atoms get too close to each other to form a bunch of structures. What you are trying to explain, is nothing new and has been studied, and studied extensively. It is best that you figure out what has already been known.

    Zz.
     
  5. Mar 1, 2005 #4
    This is part of a longer piece I'm working on dealing with the role that the way physicists conceptualize reality impacts theory development and subsequently the usefulness of theories. The piece is getting too long so I'm breaking it up into posts dealing with specific subject matter.

    The thread probably would be more appropriate in the Theory Development sub forum, but threads cannot be started there.

    The above discussion should have been preceded by the following, but I forgot to include it.

    The way physicists conceptualize reality can have a significant impact on theory development. Physicists can see what water waves look like but they cannot actually see the structure of light waves. Perhaps light isn’t a wave, or maybe light is a wave but differs in some way from water waves. One of my interests in is to look at the role of concepts and how effectively they can explain physical reality.

    Physicists can easily see how billiard balls react to physical stimulus but cannot directly see how molecules react or what they look like. Physicists cannot see subatomic particles like quarks or the elusive neutrino, whatever it is. Maybe quarks are really little “wavelets” rather than ”particles”. Maybe quarks are something that do not correspond to physical entities we can see.

    The natural tendency is to apply concepts based on what we see to those physical entities and processes that cannot be seen even though the unseen may not really resemble what can be seen.
     
  6. Mar 1, 2005 #5

    dextercioby

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    I think this is worthy of being moved back and forth between phylosophy and TD...

    You're not saying anything new or captivating...Sorry,but that's the truth.

    Daniel.
     
  7. Mar 1, 2005 #6
    One of the reasons I'm writing about this subject is that I recently read a short article in the journal Science indicating that the writer still basically viewed the atom as being somewhat analogous to the model of the sun and planets. I have only a limited amount of time for examining currernt physics concepts, so I don't know whether that writer's view is common or not.

    One of the disadvantages of the explosion of knowledge in the physical sciences in general, is that scientists become compartmentized in a narrow specialty and aren't aware of what is going on in even closely related. Field. Scientists are humans and thus can have the same difficulty accepting new ideas that humans often have.

    I don't have time right now to investigate the current state of knowledge in this particular field. Are you suggesting that the idea of the electron going around the nucleus is or isn't commonly accepted today?
     
  8. Mar 1, 2005 #7

    ZapperZ

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    Whenever you are refering to another article, it is CRUCIAL that you make an exact citation to that paper. Tell me who the author is, the volume and page number, and the year. I read Science every week, and I do not recall coming across something like this. If you do not make an exact citation, there is no way to know if you read the article correctly, or if you misinterpret what is being presented.

    If that is true, then there cannot be any expansion of the boundary of our knowledge, because "scientists" are, based on your observation, having some difficulty in accepting new ideas. So my question is, how valid is your observation based on the "explosion of knowledge in the physical sciences"? By the very nature of an "explosion" of knowledge means that we ARE expanding the boundary of knowlege and learning NEW things and accepting new ideas! It appears that you are contradicting yourself in just that one paragraph.

    Zz.
     
  9. Mar 1, 2005 #8

    dextercioby

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    Me neither,but that doesn't put me in the position of making erroneous remarks... :rolleyes:

    The electron is there,around the nucleus.But the idea with planets and s*** is dead for over 90 years...

    Daniel.
     
  10. Mar 14, 2005 #9
    Does the discussion at the following site represent current thinking in physics?

    http://www.wag.caltech.edu/home/jang/genchem/infrared.htm

    The discussion seems to indicate that wavelength/frequency determines energy which would be impossible considering that the energy received by an object of specified size declines with the square of the distance from the source of the emission but wavelength/frequency do not(I'll ignore the suggested possibility that wavelength increases gradually over very long distances - red shift).

    The discussion may be confusing the photo electric effect with the process Bohr reported in for absorption of specific wavelengths of light. I thought they were different processes, but it's been some time since I read about the photo electric effect and my interest in Einstein was more in the area of space/time.

    I'm also skeptical of the model suggesting that the atoms in a molecule "spring" back in forth from each other upon absorbing/emitting radiation.
     
  11. Mar 14, 2005 #10

    ZapperZ

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    You need to be VERY clear that how atoms behave in isolation (such as in gaseous form) is VERY different than how they behave when they are in a solid structure. Atomic absorption is NOT the same as photoemission effects - the former is due to energy transition of the atomic energy levels, the latter is primarily due to a continuum of states in either the valence or conduction band (depending on the material).

    Because of that, solids have MANY differnt mechanisms to interact with light which are NOT available to an isolated atom. This includes various phonon modes (lattice vibrations) that is responsible for the optical properties of a material. I recommend you read a solid state physics text and see if what you read about molecules "spring" back and forth on that webpage makes any sense. Optical conductivity of solids is a HUGE field of study in condensed matter physics. It should not be trivially dismissed that way.

    Zz.
     
    Last edited: Mar 14, 2005
  12. Mar 14, 2005 #11

    jtbell

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    It looks reasonable to me, as an introductory-level presentation. Note that it's for an introductory chemistry course, not for an advanced physics course, so I wouldn't expect it to go deeply into the details of atomic physics.

    Planck's [itex]E=h \nu[/itex] applies to individual photons. A macroscopic light source emits bazillions and bazillions of photons, which travel outwards in all directions from the source. Because they "spread out" over a larger and larger area as they get further and further from the source, the number impinging on an object of fixed size decreases inversely with the square of distance. But each individual photon still has the same wavelength, frequency and energy.

    It's a very simplified model of the interactions between atoms in a molecule. To analyze molecular vibrations completely correctly, you have to use quantum mechanics, with a potential energy function that is different from that of a simple harmonic oscillator. Nevertheless, for small oscillations, most any potential energy function that has a minimum can be approximated by a simple harmonic oscillator for some range of amplitudes. A model that uses simple harmonic oscillators can convey some the main aspects of the dynamics of the system, at least approximately.
     
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