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Why the chemical elements are found together in nature

  1. Jul 23, 2015 #1
    I've often wondered, but have never found a solid explanation for, why the chemical elements are found together in nature? Why aren't atoms all in a somewhat homogenous mix? Why are X atoms found with other X atoms?

    And why are isotopes found together, such as Uranium 235 and the far more common Uranium 238? They aren't even formed in the same decay chains. Does it simply have to do with atomic mass, or is there some other reason?
     
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  3. Jul 23, 2015 #2
    I'm not a geologist, but I imagine density is the main factor. When the Earth's crust formed, it congealed from a molten mixture of many types of rock and metals. Rocks and metals of similar density and composition would tend to cool at the same rate, and separate out together. Overtime most of the earth's crust has been recycled, but those rock and metals would still tend to end up in similar places due to their similar density and thermodynamic properties.
     
  4. Jul 23, 2015 #3

    SteamKing

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    It's not clear what you mean here. Some elements are found together because they reacted with one another and formed chemical compounds. As to any other mixtures, I'm afraid you'll need to provide some specific examples.

    I'm afraid you've got things backwards. U-235 and U-238 are not formed by radioactive decay; each isotope however does decay radioactively into lighter elements, albeit over much different time scales.

    Since isotopes behave identically chemically, it stands to reason that you would find different isotopes of the same element as part of a deposit of the compounds of that element.
     
  5. Jul 23, 2015 #4
  6. Jul 24, 2015 #5
    Ok, as an example, why is there such a thing as a vein of gold or silver? I'm not talking about different elements reacting, but the same elements, not chemically bonded, just in the same geographical location.

    Uranium-235 is formed from the decay of Protactinium-235(-B), Neptunium-235 (EC), and Plutonium-239.

    Uranium-238 is formed from the decay of Plutonium-232 (a) and Protactinium-238 (-b).
     
  7. Jul 24, 2015 #6

    SteamKing

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    Just because U-235 and U-238 show up in the decay chain of another element does not necessarily imply that these isotopes were originally formed from that element.

    https://en.wikipedia.org/wiki/Primordial_nuclide
     
  8. Jul 24, 2015 #7

    SteamKing

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    You can read up on the hypothesized origins of gold an silver deposits:

    https://en.wikipedia.org/wiki/Gold

    https://en.wikipedia.org/wiki/Silver
     
  9. Jul 24, 2015 #8

    Bystander

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    Paraphrasing, "Why aren't all A-B interaction energies equal to all A-A and all B-B interaction energies (zero)?" The cold oatmeal universe bored itself out of existence picoseconds after the original "big splat," and was replaced with something having a little more variety --- fusion reactions, a periodic table, individual elemental chemistries .....
     
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