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What is special about the Avogadro's Constant ?

  1. Feb 16, 2012 #1
    What is special about the Avogadro's Constant ??

    6.0221367x10^23 is the avogrado's constant. Does this amount of substances just mean that 6.0221367x10^23 molecules or atoms in gaseous state arrangement will occupy a constant volume provided they are under the same condition(same temperature and pressure) ??
    Is it true that the avogadro's constant also imply that with this amount of atoms of same element, they could contribute a mass(g) of exactly a whole number ??
     
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  3. Feb 16, 2012 #2

    Borek

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    Re: What is special about the Avogadro's Constant ??

    No. It will be a mass in g identical to the average atom mass in amu. The latter is a whole number only for a 12C isotope.
     
    Last edited: Feb 16, 2012
  4. Feb 16, 2012 #3
    Re: What is special about the Avogadro's Constant ??

    sorry why it will not be a whole number ? wasn't chemist found that 6.02^23 hydrogen atoms will make up 1 g ? so for the atoms of other element which is n times heavier than one-twelfth of the mass of a carbon-12 isotope(or the mass of a hydrogen-1 atom = 1.66 x 10^-27 kg) supposed to have a mass of (n x no. of times heavier than 1/12 of a carbon-12 isotope ) right ? ?
     
  5. Feb 16, 2012 #4

    Borek

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    Re: What is special about the Avogadro's Constant ??

    Because real elements are mixtures of isotopes, and because of the mass deficit (AKA binding energy) which makes even "perfect" isotopes like 16O to have mass different from exactly 16 amu.
     
  6. Feb 17, 2012 #5
    Re: What is special about the Avogadro's Constant ??

    The mol is really just a proportionality constant to convert amu to grams.
     
  7. Feb 17, 2012 #6
    Re: What is special about the Avogadro's Constant ??

    But It looks like Borek already answered that, sorry didn't see your posts, computer page redirected me to advanced reply.
     
  8. Feb 18, 2012 #7
    Re: What is special about the Avogadro's Constant ??

    may i ask what does it means by the mass deficit ? and you mentioned that oxygen-16 isotope has a mass different from exactly 16 a.m.u. but i think oxygen-16 isotope should have a mass of exactly equal to 16.a.m.u. Could you please refer to the attachment i posted and help me to mark my calculation? thanks sir!
     

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  9. Feb 18, 2012 #8

    Borek

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  10. Feb 19, 2012 #9
    Re: What is special about the Avogadro's Constant ??

    a new question, is it true that the mass of an atom(atomic mass) is equal to the total mass of of all the protons, neutrons and electrons in that atom ?? and is that the mass of a atom is always constant ??
     
  11. Feb 19, 2012 #10

    Borek

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    Re: What is special about the Avogadro's Constant ??

    No, because of the mass deficit. If you will continue to ignore information you are given nobody will be willing to help you.
     
  12. Mar 5, 2012 #11
    Re: What is special about the Avogadro's Constant ??

    im sorry about that because frankly im a A-level student. I have been studying the piece of information that you gave me . Up to this stage i can almost understand the mass defect. But i am still not satisfied with the statement"No other nuclides other than the carbon-12 isotopes have exactly a whole number relative isotopic mass in the scale taking 1/12 of the mass of a carbon-12 isotopes as a standard. ". Because i found that since the relative isotopic mass of nuclides of different isotopes is just a ratio compared to 1u, then there will be other nuclides having a whole number OR non-whole number relative isotopic mass.For example the mass of an oxygen-16 isotope is exactly 16 times greater than 1u. I have showed some evidence by myself. Could you please help me to verify my attachment? Moreover i think that the rest mass of protons,neutron and electron are always constant while static but while moving as in real word the mass decreases. My question is what is the extent the mass will drop to and will it be fluctuating with time ??? i realy need your help
     
  13. Mar 8, 2012 #12

    Redbelly98

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    Re: What is special about the Avogadro's Constant ??

    According to the links below, the mass of O-16 is 15.9949 u. Close to 16 u, but not exactly.

    http://www.wolframalpha.com/entities/isotopes/oxygen_16/5x/ju/gs/ [Broken]
    http://en.wikipedia.org/wiki/Oxygen-16#Table

    It is not simply a matter of adding the masses of the protons, neutrons, and electrons. There is an energy change when these particles are combined vs. when they are isolated. The energy change will contribute to the mass of the atom, via the famous relation E=mc2.

    If not for this mass-energy equivalence, there would be no energy given off in nuclear reactions.
     
    Last edited by a moderator: May 5, 2017
  14. Mar 11, 2012 #13
    Re: What is special about the Avogadro's Constant ??

    Thanks so much for your explanation. But could i say that my above attachment is only correct when both the carbon-12 isotope and oxygen-16 isotope are under the same condition, for example both are in isolated form, same temperature and all other possible factors that affects the mass? And one more question, since you said that mass of the atoms are different when in different forms, because of this the unified atomic mass units is apparently a constant but precisely it is a value that keeps on fluctuating at but only at the position of the uncertainties. the same things for the relative isotopic mass of every isotope. They are always fluctuating but only with an extremely minute deficit, is it true??
     
    Last edited: Mar 11, 2012
  15. Mar 11, 2012 #14
    Re: What is special about the Avogadro's Constant ??

    Can anyone please show me the working on calculation of relative isotopic mass of any isotope?? thanks a lot!!
     
  16. Mar 11, 2012 #15

    Borek

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    Re: What is special about the Avogadro's Constant ??

    Please start a new thread.
     
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