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Avogadro constant

  1. Jul 1, 2011 #1
    Hello, I read that equal volumes of different gas contain the same number of molecules so if I solidify that gases they will occupe different volumes?

    How do we know that for example H contain 1 electron 1 proton and 1 neutron, E contain 2 , Li 3, Be 4 and etc..?
    is it a consequence of a reasoning or they were counted sperimentally? how?

  2. jcsd
  3. Jul 4, 2011 #2
    Yes I believe you are correct. Correct me if I am wrong, but I think a mole or 6.02X10^23 molecules of CO2 gas at STP occupies 22.4 liters. A and a mole or 6.02x10^23 molecules of H2O gas also occupies 22.4liters. As you approach the freezing point of water, the volume decreases until around 4 Celsius, then it expands so as to take the shape of solid ice crystals. Carbon dioxide has a different behavior when it freezes, and since it freezes at a much lower freezing point I am guessing that it might even get a tiny fraction smaller in volume than it would if frozen by high pressure at 0C.
    For the second question, I think most H contains 1 electron and 1 proton.
    I think most He contains 2 protons and 2 neutrons, most Li contains 3 protons and 4 neutrons. I think we know this from a combination of reasoning with the data from experiments. But I am open to the idea that maybe words could not really describe what really exists. I think that we can use the ideas we have (right or wrong) to make airplanes fly, to make buildings tall, and make Bill Gates wealthy.
    Last edited: Jul 4, 2011
  4. Jul 4, 2011 #3


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    Staff: Mentor

    Water is not a gas at STP, so it doesn't occupy 22.4L. More like 18 mL.

    Also note that STP is ambiguous - see http://en.wikipedia.org/wiki/Standard_Temperature_and_Pressure

    Number of protons/neutrons in nucleons have been determined experimentally.
  5. Aug 1, 2011 #4
    what experiment was made to know the number of electrons exactly?

    thank you
  6. Aug 1, 2011 #5
    Photoelectron spectroscopy has been used to experimentally probe the electron configurations of the elements. I would suspect that the very fleeting heavy elements at the very edge of the known periodic table have probably not been quite as extensively studied as their lighter cousins, of course.
  7. Sep 20, 2011 #6
    Why are we sure that equal volumes of different gases at the same condition (pressure, temperature etc) contain exactly the same number of particles? How is it possible to prove this?
    thank you!
  8. Sep 20, 2011 #7


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    Staff: Mentor

    Stoichiometry (for example).
  9. Sep 30, 2011 #8
    There are no mathematical derivations for it ! The only thing you can do it is logically and theoretically think about it but it will not lead you to its proof. This is because it has been proved experimentally.

    Truly said : Chemistry is based on observations.

    Even Avogadro's constant is derived experimentally.
    6.023 x 1023
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