Why the chemical elements are found together in nature

[Keln]

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?

 

[dipole]

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.

 

[SteamKing]

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?

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.

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?

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.

 

[rootone]

Some types of atoms preferentially like to bond with others, some prefer not to bond at all.
This wiki article seems to be an accurate enough place to begin.
https://en.wikipedia.org/wiki/Valence_(chemistry)

 

[Keln]

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.

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.

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.

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).

 

[SteamKing]

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).

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

 

[SteamKing]

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.

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

 

[Bystander]

Why aren't atoms all in a somewhat homogenous mix?

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 ...