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I have a questionor 2or 3.

  1. Aug 25, 2005 #1
    Hello. I just have a few questions about random stuff, and I feel that this section of the forums is appropriate to place it.

    1. Whats the deal with glass. So all I know about glass is that you melt sand into a liquid, let it cool down to a certain temperature, and it becomes solid glass. What I don't understand is how the glass(sand I guess) becomes transparent. Do the atoms become transparent or something?

    2.Do atoms ever stop vibrating? What happens to the motion of atoms at say absoulte zero?

    3. Why absolute zero? Is 0 K the coldest temperature attainable or something?

    4. How do atoms bond? I can't imagine there being a line between them like O-O So I know they like share electrons or something, but don't electrons follow a path around the nucleus? How would they do that if the electrons are connected? Why do they bond in the first place if they both are negatively charged wouldn't they repel each other or something?

    5. Does light have mass? If so how can it go through glass, and stuff like that?

    Thanks, Ill be back with more questions soon enough.
     
  2. jcsd
  3. Aug 25, 2005 #2
    1. Nothing happens to the atoms. Transparent materials are poor at absorbing visible light so that we just see right through them. But everything is transparent to some part of the EM-spectrum.
    2. At 0K yes.
    3. 0K is the coldest temperature but it's unattainable.
    4. The orbit model is incorrect. In a crude and short manner electrons are just "all over the atom" as probability clouds and in bonding the electrons have a great probability of being in a position so that they bind the nuclei together. Look up hyperphysics or some other place for introductory quantum mechanics.
    5. It does have mass in the sense that the photons that constitute light have energy. Why would that stop them? You can punch through a piece of paper, can't you?
     
  4. Aug 25, 2005 #3
    I still don't understand why glass or plastic is transparent. If they are poor at absorbing visible light wouldn't they just reflect the light and we'd see a white surface?

    As for photons travelling through glass. Are you saying they actually penetrate the glass? Do they damage it on a super microscopic scale? Or do they squeeze through gaps?

    As for Atoms not vibrating at 0 k thats pretty cool.

    Atomic bonding seems to be something very complicated that I'll have to read into to get a basic understanding.

    I have a few other questions. If you put a gas in a closed chamber and decreased the volume of the chamber constantly would the atoms condense until they became liquid, and then solid?

    I just saw a model for an atom and it mentioned there was a shell. Do atoms actually have a shell which has the nucleus and electrons within?
     
    Last edited: Aug 25, 2005
  5. Aug 25, 2005 #4
    Glass is transparant because its bandgap energy (solid state physics: energy difference between the top of the valence & the bottom of the conduction band, erergy levels for electrons between are not allowed) is too large to absorb visible light. If a 'visible' photon passes through the glass, you'd think it could excite electrons from the valence band, but since the absorbtion of a photon would get the electron in a state that is forbidden (want to know much more, Brillouin zone might be a good place to start). So excitation doesn't take place, the photon is not absorbed and comes out the other end.
     
    Last edited: Aug 25, 2005
  6. Aug 25, 2005 #5

    Claude Bile

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    For some combinations of atoms, their energy is minimised if they share electrons (this is the origin of covalent bonding).

    For an O2 bond, let us first consider a single O atom. The single O atom has a series of discrete energy levels. If we then bring a second O atom near the original O atom, we cannot regard each atom seperately we must treat both atoms as a single quantum mechanical system (i.e. a molecule).

    The energy levels of the molecule are slightly different to that of the original O atoms. In place of each original energy level are TWO energy levels, one with LESS energy that the original energy level (the bonding orbital) and one with GREATER energy than the original level (the anti-bonding orbital).

    If MORE electrons occupy bonding orbitals that anti-bonding orbitals (e.g. for the O2 case), then the molecule has less energy than the two isolated atoms, hence the molecule is stable (i.e. the atoms 'stick').

    If there are equal numbers of electrons in bonding and anti-bonding orbitals (e.g. in the case of He2), then the energy of the molecule is not reduced and hence the bond is unstable. This is why we don't observe He2 atoms in their ground state.

    Yes, if you increase the pressure in a gas eventually it will become solid (but it may bypass the liquid stage depending on the temperature).

    In an atom, the electrons form the 'shell' in the sense that they completely envelop the nucleus (well, at least the S orbital does).

    Claude.
     
  7. Aug 27, 2005 #6
    Transparent matter issue:

    So...the atoms in glass have electrons that are in a too high energy orbit to be energized anymore by visible light radiation? So when the photons pass through the atoms they are unable to energize them even more or something? Thats what I am getting from what you said. Man this is confusing....Now I don't understand why we can see plastic or glass if no light is being relfected to our eyes. Is the light still being reflected? If it was all being reflected I would think we would see the plastic as white since stuff that is white reflects all light. Does this mean no light is being reflected and the photons are just all passing through...yes that must be it. Hmm why do i see glares on windows and plastic then? Damn this is confusing.

    Bonding issue:
    ..So covalent bonding occurs because the atoms want to reduce their energy to be stable?

    ..when the atoms merge they create twice as many orbitals? Are the atoms intertwining or something? When you said,

    "The energy levels of the molecule are slightly different to that of the original O atoms. In place of each original energy level are TWO energy levels, one with LESS energy that the original energy level (the bonding orbital) and one with GREATER energy than the original level (the anti-bonding orbital)"

    The only thing I can imagine now is a line on a paper and then drawing 2 lines parallel to the original line. One will be higher and one will be lower than the original line. Now I erase the original line and the 2 new lines are my new orbitals. Does that have any relation to it?

    A few questions:

    Can electrons ever collide with each other during orbit? If so what happens?

    Do electrons orbit around the nucleus at the speed of light?

    Do electrons revolve as they orbit around the nucleus?

    Whats the importance of neutrons?

    Absolute zero issuge: Is it really unatainable? What is the closest temperature you can get to 0 k?
     
  8. Aug 28, 2005 #7
    The planetary model is not correct. Electrons do not behave like planets. I think you should google "introduction to quantum mechanics" or something like that to get the real picture of what's going on in atoms. So the answer to question 2 is no.

    Electrons do have a property called spin but it has nothing to do with spinning around an axis like the earth does.

    We can get really really close to 0K but not all the way there.
     
  9. Aug 28, 2005 #8

    Claude Bile

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    Yes.
    This is exactly how I visualise it. When you have two or more levels you can get situations where both bonding orbitals are lower than the two anti-bonding orbitals, meaning the electrons will fill up the two bonding orbitals first. This is the origin of double (and triple) bonds.

    The orbitals themselves do intertwine (some of them, not all) in the sense than some orbitals do not 'belong' to a parent atom.
    No, see below.
    Think of electrons as standing waves, not discrete paticles. The mass and charge of the electron are spread through space, but do not vary with time. This is why we do not observe atoms to radiate continuously.
    Not in any classical sense.
    Neutrons stabilise atom nucleii by providing addtional atomic 'glue'. All proton nucleii do not ordinarily occur due to the EM repulsion between protons (which gets greater, the more protons you add) overcoming the strong nulcear bonds. The presence of neutrons enables the protons to bind more readily via the Strong Nuclear force, without adding any additional EM repulsion, thus stabilising the nucleus.
    The 3rd law of thermodynamics says 0K is unattainable. The coldest temperature on record is something like 1x10^-9 K.

    Claude.
     
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