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Homework Help: Mass number

  1. Nov 10, 2011 #1
    1. The problem statement, all variables and given/known data
    My instructor give me a question:
    Mass number (number of protons and number of neutrons in an atom) is supposed to be a whole number for a particular atom, in reality IT IS NOT. Why is it so?

    2. Relevant equations

    3. The attempt at a solution
    Here, I am very sure that this question ask for mass number (nucleon number) not atomic weight. However, how can only a part of a proton or neutron exist in an atom if mass number are not a whole number?
    Last edited: Nov 10, 2011
  2. jcsd
  3. Nov 10, 2011 #2


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    Hint: Check out isotopes.
  4. Nov 10, 2011 #3
    you are absolutely correct. Mass number is the NUMBER of neutrons and protons (nucleons)
    This does not mean that the MASS is a whole number.
    Like steamking I suggest you look at isotopes to get the idea of mass
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