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Will a single atom of an element with greater atomic mass than the H2O molecule sink in a cup of water?

A single atom or molecule of a substance is placed in a cup of water. Because of its specific gravity, I suppose it should sink. However, I have never heard about a colloidal system with a single molecule or element.

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    $\begingroup$ Brownian motion will work against such settling. $\endgroup$
    – David White
    Commented Mar 1, 2020 at 18:17
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    $\begingroup$ Not a single atom, but say you dissolve a bunch of really large, non-polar particles like Xenon, then they might aggregate and sink due to the hydrophobic effect. $\endgroup$
    – H2Forge
    Commented Mar 1, 2020 at 19:04

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Like dissolving cesium bromide in water? Entropy (the larger number of accessible microstates) makes atoms in a crystal on the bottom go in solution.

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  • $\begingroup$ Why are there more microstates with the heavy atom at the bottom? $\endgroup$
    – Superfast Jellyfish
    Commented Mar 1, 2020 at 19:37
  • $\begingroup$ @FellowTraveller There are more microstates (possible positions) for an atom in solution than the position in the crystal. So a CsBr crystal will sink and then dissolve. $\endgroup$
    – user137289
    Commented Mar 1, 2020 at 20:01
  • $\begingroup$ I get why it’ll dissolve. But not why it will sink. $\endgroup$
    – Superfast Jellyfish
    Commented Mar 1, 2020 at 21:22
  • $\begingroup$ @FellowTraveller The CsBr crystal has much higher density than water. So crystals sink, but independent heavy atoms will be evenly distributed in the whole volume. $\endgroup$
    – user137289
    Commented Mar 1, 2020 at 21:46

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