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A Pedantic Question

Discussion in 'Members Lounge' started by jpanhalt, Aug 6, 2013.

  1. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Ratch,

    Well from what you say it sounds like you are not being pedantic you are simply making an error in judgment. Being pedantic is when we argue a point more insignificant about something, but that argument is TRUE even though it is a tiny point which does not affect anything in most real life cases. So for example if we read a page of important text on a new theory of matter and then state that the writer forgot to dot the "i" in line number 22. The argument is certainly true but it has little bearing on such an important topic like that.

    In the case of the 'free' electron, i believe you are judging the use of the word 'free' to be of global significance when really we are using it as a local comparative. You are saying that we cant or should not use the word 'free' because there are OTHER materials that have more free electrons (which might be totally free), but the word as used in the context of a SINGLE material is such that it is comparing the bound electrons to the non bound electrons, and instead of calling them non bound electrons we simply call them 'free' electrons. It's that simple.

    It's also a matter of language. People tend to use the simplest words to describe the situation and that is partly because they remember them better. There was a simple experiment done about this where a professor gave his students words (nouns) to remember that were not from any known language that renamed common objects we all know. It turns out that when tested there was a trend where they all remembered some words and not others. So he started giving the words they thought were the correct ones even though they were wrong to the next group of students, and they got some wrong and some right also, and the ones they got wrong he started using those words for the next group, and so on. By the time he got through several rounds of this they were remembering almost all of the words! The words were conditioned by the people themselves and that made them easier to remember. Pretty amazing i think.
    So the words we use are not always the most technically correct but they allow us to think about a situation more easily and also remember what they stand for.

    I'd like to call the electrons the 'electroduckies' but no one else does so it wont work (just kidding of course).
     
  2. Ratchit

    Ratchit Well-Known Member

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    MrAl,

    I don't think that judgment (The act or process of judging; the formation of an opinion after consideration or deliberation. 2.a. The mental ability to perceive and distinguish relationships; discernment) is a factor in this case.

    Well, lightly bound electrons versus free electrons do have global significance, because they are one of the distinguishing factors between a conductor and a semiconductor. If that is unimportant or insignificant, the the word "semiconductor" should be abolished.

    Another example of interpret what I really mean, not what I say. The study you cited is not applicable because I am not arguing the meaning of the words, but whether they apply to the subject under discussion.

    Ratch
     
  3. steveB

    steveB Well-Known Member Most Helpful Member

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    MrAl and Ratch,

    I'm really confused by the conversation here. My understanding is that metallic conductors do indeed have truly free electrons without the need for excitation. A conductor has overlap between the conduction and valance bands, meaning that some electrons are not bound to any atom, but are bound to the solid at large. There is a work function for removing electrons off the solid surface to the vacuum, but within the conductor there are some free electrons. We sometimes hear the term "electron gas" applied.

    Even if somehow we thought that there is a gap between the valance and conduction band (as in an intrinsic semiconductor) a small gap would still allow excitation by the thermal energy KT, hence creating free electrons.

    Am I misunderstanding what was said?
     
  4. dave

    Dave New Member

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  5. Ratchit

    Ratchit Well-Known Member

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    steveB,

    In a pure metallic element, each valance electron will stay with its individual atom on a statistical basis, unless there is an excitation. A N-type semiconductor is composed of two elements, one of which contains 4 valance electrons and the other 5 valance electrons. That is a total 9 valance electrons, of which only 8 are needed to make a strong bond. The remaining 1 electron is free to wander around the crystal structure assigned to no particular atom. It is a prime candidate to diffuse into any P-type semiconductor in contact with the N-type, and fill the holes there while forming a depletion region. This diffusion happens without any voltage being applied until equilibrium is reached. This process will not happen without voltage being applied if a metal is bonded to a P-type semiconductor, because the metallic atoms keep their bound electrons.

    Ratch
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,

    Steve:
    Yes, but the motion they make actually helps to inhibit the 'free' electrons i am talking about, ie inhibit current flow. So that would be a different kind of 'free' i think. Feel free to comment though.

    The argument i am making is that we can call the outer electrons 'free' because they are the ones that are free to take part in conduction of the metal. And we call them simply 'free' because there are other electrons that are bound ie not free. So 'free' is a comparative comparing some electrons in the SAME metal to other electrons in that same metal.

    The argument Ratchit seems to be making is that we should not call these electrons 'free' (the electrons i am talking about as above) because there are other materials that have electrons that are even more free as compared to those i mentioned.

    So we have my 'free' which we might call free1, and Ratchit's free which we might call free2, and now your free which we might call free3.

    But the reason the rest of the world usually says free1 electrons are simply 'free' is because they are free to move under the influence of an external field. If they were not free, then they would not be able to move.

    And this 'free1' definition can be found in many articles where the context is a SINGLE metal, not a set of materials that might include semiconductors. So i believe it is definitely a valid description.

    Ratchit:
    You seem to want to reinvent the entire nomenclature of electronics sometimes :)
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Al,

    This is the description I was taught, long before doped semiconductor devices were commonly used.

    I can see no purpose in Ratch's alternative descriptions other than to continue this unhelpful discussion that I am sure is causing some confusion amongst wannabes who read these posts.

    Eric
     
  8. steveB

    steveB Well-Known Member Most Helpful Member

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    OK, let's focus on the metal part, and not the semiconductor part. My issue was not with the semiconductor statement but the implication that metals don't have conduction band electrons without (voltage) excitation.

    Here, all you did is restate what you said before, but do you have a reference to back this up? The band theory for metals is a long standing theory in which it is stated that conduction electrons are established in the solid material at large. These electrons are often referred to as free electrons or an electron gas. I have never heard a modern theory of solid metals claim that all electrons are valance electrons, and voltage excitation creates free electrons. Again, can you provide a reference for this viewpoint?

    One ambiguity in your above statement (as compared to before) is that here you just say "excitation" but above you say excitation by voltage ("easily dislodged by a small voltage"). Well, if you are now broadening the meaning of excitation to include thermal excitation, I'll go along with you a little more easily, if we consider absolute zero. But, is it reasonable to be talking about absolute zero effects among engineers? Anyway, if that's the point then please clarify it.

    Certainly a room temperature metal (and much colder too) has those free electrons bouncing around randomly, so to speak. They are bound to the solid at large, but not bound to any one atom. The applied voltage is then needed to create a drift motion that gives rise to current, not to create the free electron.

    I'll just point to a few online references to give an idea of what I mean. Nowhere in any of these does it mention that a voltage is needed to excite the electrons into the conduction band.


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

    "In conductors, such as metals, that have many free electrons under normal circumstances, the conduction band overlaps with the valence band--there is no band gap."

    http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html

    "In terms of the band theory of solids, metals are unique as good conductors of electricity. This can be seen to be a result of their valence electrons being essentially free. In the band theory, this is depicted as an overlap of the valence band and the conduction band so that at least a fraction of the valence electrons can move through the material."
     
  9. Ratchit

    Ratchit Well-Known Member

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    steveB,

    No matter what the band theory says, for all practical purposes, each metallic atom has a valance electron. A electron might be a valance electron to many different atoms while if moves around, but it does not go off by itself unless can displace another valance electron. A small or overlapping band gap just means that the displacement can occur easily and often. You can call the available electrons a gas, or a sea of electrons. In a metal there are many, many more available electons than in a semiconductor. In a metal, conduction is by drift displacement caused by a voltage, not free electrons. In a semiconductor, conduction can occur by diffusion caused by truly free electrons migrating to where they are attracted, even when there is no voltage. All material is affected by thermal energy, but that does not directly support conduction in metals.

    Thermal effects are small compared to drift caused by voltage. If I want to put a current through a wire, I apply a voltage across it, not a blowtorch.

    If those so called "free" electrons cannot diffuse, then they are not truly free. Drift motion in metals is a chain displacement, not an independent movement of electrons such as occurs in semiconductors.

    I already explained the a small or overlapping bandgap only means it is easier to move electrons. It does not prove your assertion that conduction does not occur by chain displacement. In a semiconductor, drift is very small component of current compared to diffusion.

    In conclusion, I maintain that if metals contained free electrons, they would support diffusion like semiconductors do.

    Ratch
     
  10. steveB

    steveB Well-Known Member Most Helpful Member

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    Ratch,

    So you still provide no references? You just make statements without support. "No matter what the band theory says ... X must be true". This is unscientific debating. If you are going to refute accepted theories, cite references, or publish a paper in a scientific journal that gives it credence.

    Your comment about thermal effects makes no sense. Thermal excitation can raise electrons to higher energy levels. This can also be viewed as phonon (not photon) interactions. So, what is all the talk about direct band gap and indirect band gap semiconductors. Phonons (lattice vibrations due to thermal energy) do not matter because you say so?

    So, all I asked was for you to provide a reference. I'll ask again, can you provide one that supports your assertion (quoted below) that a small voltage is needed to free the electrons.

    A simplified description of some of the theory developments are given here to again give some justification for why I am questioning your wording above.

    http://encyclopedia2.thefreedictionary.com/free-electron+theory+of+metals
     
    Last edited: Aug 13, 2013
  11. Ratchit

    Ratchit Well-Known Member

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    SteveB,

    No one provides references for everything they say provided it is common knowledge. No one publishes a paper on common knowledge referenced in textbooks. If you have a problem with what I said, ask for clarification.

    What is there about thermal energy I said you do not agree with? Metals conduct all the way from absolute zero to their melting point. They already have a sea of electrons at all temperatures available to support conduction. Semiconductors rely on thermal energy to ionize their dopant sites and release electrons. From absolute 0 to 100°K, a semiconductor will not work anymore due to a low concentration of electrons caused by reduced ionization.

    I believe you are having a problem with the above paragraph saying that no free electrons are available in metals. I expounded on that statement previously when I pointed out that electrons in metals do not diffuse, whereas in semiconductors they do. If the electrons in metals were free, they would diffuse and we could make semiconductors out of metal instead of Si or Ge. Do you doubt what I said about diffusion? Any good textbook on semiconductor physics will explain diffusion. Do I have to quote chapter and page of a particular textbook on this?

    Ratch
     
  12. steveB

    steveB Well-Known Member Most Helpful Member

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    The point i'm making is that what you said strikes me as not being common knowledge. If anyone else thinks your statement is common knowledge, I hope they please post here and tell me I've somehow missed that day of class.

    You said, "The metallic plate of a cap has no free electrons when it is not energized. Each electron is bound and assigned to a metallic ion to make a electrically neutral material. A good conductor like a metal has its valance electrons very loosely bound, so they can be easily dislodged by a small voltage."

    Honestly, I have never heard this before. So, exactly what voltage will dislodge the electron. What order of magnitude? Can you give a number of gold, silver, copper etc. ?
     
  13. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Actually there is a much simpler way to explain what we call the 'free' electron.

    A copper atom has 29 electrons. 28 can not take part in conduction, 1 can. That one electron we call free. It doesnt matter how it got into a state where it could take part, but in any case it can take part while the others can not take part in conduction. So we call it 'free' like it or not. That makes it easy to distinguish from the other 28 that can not take part. That's also why i brought up that study of words used by humans to describe things because we tend to like simple descriptions.

    So it's that 1 out of 29 that we call free. It's that simple. If someone doesnt like calling it that then they will have trouble reading material written on subjects involving current and the like.
     
  14. Ratchit

    Ratchit Well-Known Member

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    SteveB,

    I believe it is for students of physics.

    Yes, I did.

    Good question. Here is the answer. Look at page 17 of this link. http://books.google.com/books?id=Ty...nce electrons electrical conductivity&f=false .

    A partial quote from this book is "In metals, the energy bands of the valence electrons and conduction electrons overlap, or the highest energy of the valence electgrons is equal to the lowest energy of conduction electrons. This means that valence and conduction electrons are indistinguishable and even a small external electric force may accelerate the electrons which are located near the upper "border" of the valence band in the metal in the direction of the force. A general expression for electrical conductivity, sigma, is sigma = n times e times mu, where n is the number of conductin electrons in unit volume, e is the electron charge, and mu is the mobility of the electron current carriers ... ."

    In other words, if one knows the mobility of the material and its conduction electrons per unit volume, then the conductivity of the material can be calculated. Then, once the dimensions of the material are known, the current can be figured out from the conductivity and the applied voltage.

    Ratch
     
    Last edited: Aug 13, 2013
  15. steveB

    steveB Well-Known Member Most Helpful Member

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    Ratch,

    The reference you quoted exactly conforms to my long standing understanding and does not support the statement you made. It mentions thermal excitation of valance electrons into the conduction band, not the voltage (or applied electric fields) as the excitation.

    Your view that the voltage (even a small one) is what frees the electron is incorrect and would result in an offset nonlinearity between current and voltage, and would violate Ohm's law.

    There is mention of all valance levels being filled at 0 K, and that conduction electrons (free electrons) exist at higher temperature.

    The reference you provided is common knowledge, your statement I quoted from you is not, and is incorrect.

    Steve
     
  16. Ratchit

    Ratchit Well-Known Member

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    SteveB,

    If you are referring to metals, it says that the energy bands overlap, so no thermal excitation is needed to provide conduction electrons. I am glad you understand that a metal is conductive from absolute zero to its melting temperature and beyond.


    Where did I say that a voltage frees electrons? I said that a voltage moves electrons by shifting them from one atom to another in a drift operation. During that time, the electrons are available to shift to a different atom, but they are not unassigned like they are in a semiconductor. If electrons are not fed into one end of the wire, nothing will come out the other end. A PN junction will support charge flow for a period of time even if no voltage is applied to the junction. That tells me that there are truly free electrons in a semiconductor, but not in a wire.

    The reference says, "At any temperature, including very low, metals have a large number of electrons which are able to participate in electric current.

    I believe my statement is correct, but your interpretation of my statement is not.

    Ratch
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again Ratch,

    Yes but when we say 'free' we are talking about what happens in ONE wire, not in ALL materials on earth. As i said before, we are using the word 'free' locally but you want to use it globally, and in doing so you want to inhibit our use in our own context as well. It's ok if you want to use it globally, but you should not try to insist that we can not use it
    locally in a more confined context. Dont you get that simple concept?

    Also a correction on my part one of my posts said the thermal agitated electrons can impede the current flow, it's actually the ions, sorry about that.
     
  18. steveB

    steveB Well-Known Member Most Helpful Member

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    Yes, that is probably the case. Usually disagreements are based on miscommunications. So, I'll just post my interpretation of your quote and then explain why my interpretation of what you said is incorrect. You are then free to post your intended meaning.

    The original statement I took a stance against is as follows.

    Here you say there are no free electrons when not energized. Every description I've ever learned says there are free conduction electrons available. They have kinetic energy from thermal excitation and behave as free charges that can move (drift slowly in one direction on average around the high speed from random thermal motion) at the slightest application of voltage. Ohm's law is an end result of this behavior.

    Here you say each electron is bound and assigned to an ion, but all modern descriptions say that the conduction electrons are bound to the solid at large. This can crudely be thought of as the crystal structure forming a molecule and those conduction electrons are bound to the molecule, and not individual ions. One can even study the quantum mechanical solutions to this using a periodic lattice potential function. The result indicated free unbound solutions for conduction electrons.

    The last sentence of your statement is misleading. The valance electrons are bound, but it is the free conduction electrons that participate in the conduction, not the valance electrons. Your first sentence says there are no free electrons, so conduction must be coming from these bound valence electrons by your description. You have basically defined a threshold voltage and given the value as "small" without in any way quantifying what small means. You have now invalidated Ohm's law theory for metals. For voltages below this threshold, you will have a different resistance than for voltage above this threshold. I expect that's not what you mean, but that is what you are implying.

    So, what is the purpose of your very confusing words? I can read the reference you provided and make perfect sense of it, and be in perfect agreement. I've also read other books and listened to many professors and never had an issue understanding those. But, your words just confuse me and don't seem to make much sense. I suppose it could be me, but I've been around the block enough times to doubt that. Anyway, please clarify your intended meaning, and all will be OK.
     
    Last edited: Aug 14, 2013
  19. Ratchit

    Ratchit Well-Known Member

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    SteveB,

    The word choice is wrong, as is "current flow". The electrons are available, but they are not free to move anywhere without jumping from one atom to another. More on this later.

    There is a few bonds broken due to thermal agitation, but in metals that is small compared to drift. Otherwise, we would see a large change in conductivity when the temperature changes, which we do not.

    If you believe that Ohm's law is V=IR, then you have another argument from me.

    If electrons could go anywhere without utilizing the drift method, then a metal would contain bound ions with a positive charge. More on this later.

    Misunderstood perhaps, but not misleading. There are available electrons for drift conduction, but not free electrons that are not bound to any atom.

    I did not define a threshold voltage, I said small voltage. Actually it is energy supplied to the material by this small voltage that defines when an electron will hop to the next atom. The reference I gave earlier showed how to get the conductance. From the conductance, one can determine the voltage to make any charge flow rate happen. There is no threshold for this to happen.

    It is confusing because you believe that free electrons abound in a metal. If one electron did leave its atom, it would leave behind a bound positive ion. If a metal did support positive bound ions, it would support a hole. We know that metals do not support holes because the sea of available electrons would immediately annihilate it. Whichever electron filled the first ion vacancy would leave behind another vacancy and so on.

    Now, in a N-type semiconductor, the dopant atoms are thermally ionized at about 100°K, and full ionized at room temperature. The semiconductor supports a positive ion because the ion bonds nicely with the 4 valance electrons of Si or Ge atom, and does not want the extra electron very much. So the extra electron can wander around and not get grabbed by another atom. It can also participate in diffusion with P-type material to support conduction. None of the above in this paragraph happen in metals. So it boils down to conduction in metals is mostly by drift, and conduction in semiconductor is mostly by diffusion. Drift is a charge movement from one atom to another like marbles in a hose. Therefore the electrons that participate in this are not free, but available. Unless you believe that electrons shoot through a wire like an electron beam of a CRT.

    Ratch
     
  20. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Aw Ratchit...stop it.

    You drive me crazy. If I follow your posts for any longer....I will know less than I did when I started fixing TV's around 20 Years ago.

    Heck, I might even shock myself with you complicating everything.

    Please listen to your Peers that are trying to help you to stop being so damn stubborn with everything. And I refer specifically to steveB and Mr Al.

    Regards,
    tvtech
     
  21. steveB

    steveB Well-Known Member Most Helpful Member

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    Ratch,

    Thank you for clarifying your statement. If you are not implying a threshold (small value) voltage that "unbinds" the electron and creates the free electrons, then I'm satisfied. By Ohm's law I was just meaning the expected proportionality of voltage and current at a given constant temperature in metals (call that what you want). A threshold voltage for conduction would not reproduce this expected result from the application of both classical and quantum theory in conducting metals.

    I can't say I agree with the comments against the term "free electrons" when this literature is fully rampant with this phrase, but I know you disagree with many things that are traditionally accepted. So, that part is of minor concern to me. I never really worried too much about labels, and I'm quick to adapt to whatever the people around want to use.

    tvtech,

    The point of a forum is to discuss and learn. Opposing positions are an opportunity to learn and think. Just relax and don't get worked up. They are only opinions and words being thrown around: not sticks and stones. :)

    Often I get involved in these discussions so that a varied viewpoint is represented to students and others in the earlier phases of learning. But, I always walk away from any discussion more enlightened, even when my opinion is not changed. And, every once in a while, my opinion is changed, which makes the time and effort all the more worth while.
     
    Last edited: Aug 14, 2013

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