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Thread: Atomic mass

  1. #1 Atomic mass 
    Forum Professor leohopkins's Avatar
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    If I had a sphere of uranium the size of a football and a sphere of say, iron, also the size of a football. Would the uranium weight more because it has more atomic mass ? (i.e more stuff in it)


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  3. #2  
    Forum Professor river_rat's Avatar
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    Not exactly - density matters at the macroscopic level and this has to do with the bonding structure of the material in question and the actual weight of the molecules making up the material. For example water has very different densities if it is liquid or ice, but both cases you have the same molecular weight.

    Now uranium as a metal as a density of around 18900 kg/m^3 while iron has a density of around 7000 kg/m^3 at 293 degrees kelvin so the ball of uranium would be more massive then the ball of iron. In case you are interested, the most dense elements known to man are osmium and iridium (with almost the same density) each with a density of 22600 kg/m^3. The densest thing we know of is a neutron (well thing with a measurable size that is) and it has a density of 10^18 kg/m^3!


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  4. #3  
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    Relative density of Iron is about 7gms/cc and I think uranium is around 20 so it's weight would be almost 3 times that of the Iron. (Water has a relative density of 1).

    If I had a football sized piece of Uranium - I'd drop it and run.
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  5. #4  
    Forum Senior silkworm's Avatar
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    Atomic mass is certainly part of what amounts to density, but also the volume that the atoms take up when they're combined. It really depends on the structure. Different allotropes have different densities. For example, graphite has a density of 2.09–2.23 g/mL and diamond has a density of 3.52 g/mL. They're both entirely composed of carbon, and their difference in densities is due to their different structures.
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  6. #5  
    Forum Sophomore Matt Lacey's Avatar
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    Yep - it's down to the packing of the individual atoms on the nanometer scale. The atoms that can most densely pack on the atomic scale will have the greatest density on the macroscopic scale - but yes, atomic weight is still a factor.
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  7. #6  
    New Member pwnzn00b's Avatar
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    If the volume is the same the element with the higher density would weigh more. Now if the two elements have the same mass there would be no difference (I find it fun to go up to people on the street and ask them, "What weighs more a pound of air or a pound of lead?" you would be suprised how many people answer lead and then try to defend their answer when I tell them they are wrong
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