Are atomic elements still viewed as “atomic” in the ancient sense? As I understand it, the idea “atomic” meant that everyone of the element everywhere always is the “same” and that it cannot be broken down further. The second clearly is not true, so is anything “atomic”? But I’m also wondering if the first is true: is helium, or whatever, the same everywhere and always?
Thanks.
The chemical properties of deuterium, as opposed to neutron-less hydrogen, are somewhat different in that the chemical reaction times can be changed due to the mass. It’s probably the same w/r/t other elemental isotopes but I’d wager not that noticable except in the case of hydrogen.
Couple of points: what Ludovic says about deuterium is also true for tritium (H-3) and tralphium (He-3) – they have slightly different physical properties, which results in slightly different chemical behavior, owing to the difference in mass from the predominant isotope. While this is probably true for any two isotopes, it’s noticeably true only in those two elements because only there is the mass difference between isotopes a significant percentage of their overall mass. Deuterium:Hydrogen is a 2:1 difference, tritium a 3:1, tralphium:helium-4 is a 3:4. Contrast that with uranium, where actinouranium (U-235) to normal U-238 is 235:238, a very miniscule proportion of the overall weight.
There are, however, significant differences in isotopic concentration in nature for several elements where one isotope (or more) is at the foot of a radioactive decay series. Natural deposits of lead ores may vary significantly in isotopic composition depending on whether they result from “primordial” lead (present as lead since the planet’s crust first cooled) or in part from uranium or thorium decay. There are a couple of other examples of this, not quite as common or as startling a difference, in the lanthanides.
And (and here I’m reporting from memory and would like to see it confirmed or corrected), the reason for the overwhelming dominance of isotope 40 in terrestrial argon (e.g., in the atmosphere) is owing to K-40 breakdown. Spectroscopic observations of cosmic gas with a composition including significant quantities of argon do not have the same isotopic ratio as does terrestrial argon.
But the cosmological principle (borne out to the extent we can observe to test for it) does say that in general what is true here and now is true there and then, including the physical and chemical properties of elements. The above are “exceptions that prove the rule” – cases where the same physical laws that call for isotopes of the same element to usually be in the same relative concentrations and usually behave virtually identically chemically, call for somewhat different behavior owing to circumstances.
It is likely that there are isotopic differences between parts of the galaxy. Our solar system formed out of the remnants of a supernova - this fixes the isotopic ratios for the entire system. Some isotopic pairings are stable, and some are not, but have very long halflives. By (large scale) analysis, you could create an isotopic signature that is unique for the supernova that our solar system was formed out of. This signature would be unique, and could identify sister systems formed of the same source.
This was an element of a sci-fi novel (whose name and author escape me now) about people tracking down the alien civilization that had destroyed the earth with von-neumann style harvesting machines. They eventually identified their targets by isotopic ratios.
But as PolyCarp said - the chemical properties are the same, even if the isotopic ratios are slightly different.
Si