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Atomic structure

  1. Oct 16, 2011 #1
    I got a question :

    Why is the nucleon of Chlorine 35.5 ? Why is is not a whole number ?
     
  2. jcsd
  3. Oct 16, 2011 #2

    Borek

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    35.5 is not an atomic mass, it is atomic weight of the element.
     
  4. Oct 16, 2011 #3
    What's the difference between atomic mass and atomic weight of an element ?
     
  5. Oct 16, 2011 #4

    Borek

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    Have you ever heard about google and wikipedia?
     
  6. Oct 16, 2011 #5
    Yeah, I searched in Wikipedia.
     
  7. Oct 17, 2011 #6

    Borek

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    And you still don't know what is a difference between the two? Can you quote or write - in your own words - one line definitions of both?
     
  8. Oct 17, 2011 #7
    Atomic mass is the mass of 1 atom comprising of its protons, neutrons and electrons.

    Atomic weight is the average mass of all the atoms of an element that exist to 1/12 of the mass of an atom of Carbon - 12.

    Am I right here ?

    Wikipedia says this:

    "The atomic mass is the total mass of protons, neutrons and electrons in a single atom (when the atom is motionless)"

    Why does it specify when the atom is motionless ? Does it make a difference if its in motion ?

    "Atomic weight (symbol: Ar) is a dimensionless physical quantity,..."

    What is a dimensionless physical quantity ?
     
    Last edited: Oct 17, 2011
  9. Oct 17, 2011 #8

    Borek

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    Yes.

    Now, get back to your question and see if you can answer it.

    Yes - moving objects get heavier (although for the effect to be observable their speed must be real high). Google for "relativistic mass".

    One that has no units. Mass has units of kg (pound, stone...), length has units of m (feet, cable...), atomic weight has no units.
     
  10. Oct 17, 2011 #9
    Now I got the answer to my question. It is not a whole number because it is the average mass of the element. When making averages, we often encounter decimals.
     
  11. Oct 17, 2011 #10

    Borek

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    Wasn't that hard :smile:
     
  12. Oct 17, 2011 #11
    Yeah, thanks to you:smile:
     
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