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Seicair t1_je2cmmp wrote

Reply to comment by forte2718 in Is NaCl relatively common in the galaxy/universe? by PHealthy

> The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars.

I’d like to point out for any chemistry enthusiasts not well versed in astronomy. In astronomy, it’s hydrogen, helium, or metal.

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Beer_in_an_esky t1_je2vjad wrote

Astronomy, the field where Oxygen is a metal, and four orders of magnitude can be a rounding error. Love it.

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SkoomaDentist t1_je2utiy wrote

Out of curiosity, why this divide? Is it just because hydrogen and helium constitute such large part of all matter that it makes no sense to divide the tiny remaining part further?

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D180 t1_je4o60e wrote

That's the most important part I think, hydrogen and helium make up 98% of the universe as they were produced immediately after the big bang, all other elements matter much less.

There's also the fact that the chemical behaviour of an element does not matter much at the temperatures encountered in stars - the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together. If you heat up iron to 3000°C it stops being a metal and just behaves like any other dense, hot gas. But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures (for example, they rise to the surface of a star)

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Seicair t1_je691wn wrote

> the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together.[...] But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures

Hey, that makes sense, thanks for the explanation. I've kinda wondered why they use the terminology myself since I learned it. My specialty is organic chemistry.

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