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Homework Help: Finding number of atoms and volume

  1. Sep 15, 2012 #1
    1. The problem statement, all variables and given/known data

    The mass of a copper atom is 5.30 10-25 kg, and the density of copper is 8 920 kg/m3 .
    (a) Determine the number of atoms in 1 cm3 of copper.


    (b) Visualize the one cubic centimeter as formed by stacking up identical cubes, with one copper atom at the center of each. Determine the volume of each cube.


    (c) Find the edge dimension of each cube, which represents an estimate for the spacing between atoms.


    2. Relevant equations


    3. The attempt at a solution

    Well, the book the book we are using for this class "Physics for Scientists and Engineers" by Serway has no right being used in an Introductory Physics class.

    I re-read the relevant chapter THREE times and still haven't figured out how to solve this.

    Therefore, I used my intuition alone.

    Using the info I have:

    3.06*10^(-25)kg= (8,920kg/m^3)*1cm^3 = M=D*V

    I cancelled the volumes but that won't left over any missing variables.

    I googled for alternatives and my textbook absolutely does not point us in any direction regarding this question. Please help.

    Thanks in advance.
  2. jcsd
  3. Sep 15, 2012 #2


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    Gold Member

    You need the answer from a) to do b) and c). So focus on that first. It is essentially a unit conversion problem.
  4. Sep 16, 2012 #3
    Yes, I just figured that this morning. Thanks.

    But now I am having trouble with that.

    I equated:


    Then 8920/m^3*1m/100*5.24*10^(-27)=Cu-atom/cm^3

    But now what? Does my setup even look right?
  5. Sep 16, 2012 #4


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    Not really. You need to inventory all of your unitary conversion factors and apply them correctly.
    1 = 1 Cu atom / 5.30 10-25 kg
    1 = 1m3 / 1x106 cm3
    1 = 8920 kg / 1m3

    You are trying to convert 1 cm3 [of Cu] to Cu atoms. If you had a unitary conversion factor
    in the form of:
    1 = X Cu atoms / Y cm3 you would be close to being finished with part a). Can you try this using the above unitary factors?
    Last edited: Sep 16, 2012
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