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The realisation that the atom was divisible, and thus that elements were not the "fundamental building blocks" arguably began around 1897 with J. J. Thomson's discovery of the electron and proceeded through the early 20C to Rutherford's experiments with hydrogen nuclei, described as the discovery of the proton (although William Prout [ibid] had suggested that all atoms were composed of hydrogen atoms as early as 1815).

From this Wiki page, Robert Boyle proposed the idea that matter was made of irreducible atoms in 1661, rejecting earlier ideas of "the elements", and in 1789, Antoine Lavoisier published a list of 33 elements (although some were questionable). By 1818, atomic weights were known for 45 of the 49 accepted elements; in 1869, Mendeleev had 66 elements in his periodic table; and by 1900, all but three of the naturally occurring stable elements had been discovered.

So the question is: as the number of known elements grew (see graph here), did anyone (ideally with at least some degree of credibility) use what might be termed a more "philosophic" argument to question the fundamental nature of elements and atoms, based on the idea that there were "too many" elements for them to be "fundamental"?

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The "thought process" (not necessarily "logical objection") that I was wondering whether anyone had gone through was along the lines of:

"So, we've now got 50 [or however many] fundamental particles, with more being found every year... maybe they are not quite so fundamental as we thought... maybe there is something else [protons / neutrons / electrons in the first descent] going-on underneath?"

There is, I suppose, no intrinsic reason why there couldn't be a large / infinite number of "fundamental particles", and possibly such a situation only "feels wrong" to me because of the knowledge that atoms aren't fundamental. In essence, the question is about whether anyone else "felt this was wrong" before it was known that atoms were not fundamental. I'm suspecting the answer is "no".

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    $\begingroup$ Never heard about it. There were few scientist that speculated about an inner structure of an atom just a bit earlier than J. J. Thomson discovered an electron and suggested that atoms were divisible. For instance, George Johnstone Stoney developed his model (started in 1868) in which atoms still were indivisible but had some moving parts (which he called electrons). But all these attempts were made to explain the characteristic emission spectra and were not caused by the use of the "philosophic" argument you proposed. $\endgroup$ – Wildcat Jul 7 '15 at 10:12
  • $\begingroup$ Huh, Occam's Razor would have been useful in this case :) $\endgroup$ – Mithoron Jul 7 '15 at 10:27
  • $\begingroup$ @Wildcat Thanks for the reference: Stoney doesn't sound like who I'm after, but I'll check his bio. I wasn't so much proposing this as an argument, more wondering if someone else had (although, in an even more hand-wavy way, I [as a relative layman] kind of have this sort of misgiving about the Standard Model ... it "feels" like it's got too complicated to be truly fundamental). $\endgroup$ – TripeHound Jul 7 '15 at 12:45
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There were both historical and experimental reasons for maintaining indivisibility of atoms in chemistry despite large number of elements. What confirmed compositeness of molecules were transformations of compounds into each other in chemical reactions. Analogous idea for atoms suggested transmutation of elements, which was not observed. In particular, it resembled the alchemic idea of transmuting metals into gold, many metals were elements and alchemists failed to transmute them for centuries. Only at the start of 19th century chemistry fully freed itself from alchemic mentality and notation and became an established science, scientific chemists had no appetite for going back.

So ideas that led to the discovery of atomic structure came from different quarters. In 1845 Fechner suggested that electric currents were composed of small electric charges, named electrons by Stoney in 1891, that moved in opposite directions. Weber in 1846 developed the first theory of them, as did Stoney and Clausius later. The most successful electron theory was proposed in 1892 by Lorentz, who combined it with Maxwell's electrodynamics and explained many observed electric properties of matter based on it. Lorentz imagined a gas of electrons filling material bodies, but the question remained as to where electrons came from, and how they fit together with atoms and molecules. This is what prompted Thomson's experiments in 1897, who then proposed the first model of composite atom with electrons as negatively charged raisins stuck in a positively charged pudding (his analogy), but occasionally break out and form Lorentz's gas. See Whittaker's History of the Theories of Aether and Electricity.

This is not to say that there weren't philosophical objections to atoms, but they did not concern the large number of elements. They had more to do with the rise of philosophical empiricism, and a preference for phenomenological theories over mechanistic ones like atomism. The most prominent opponents, Mach and Ostwald, denied reality of atoms altogether. They considered them theoretical fictions only useful in organizing calculations of observable quantities like energy, entropy, etc. Mach stopped mentioning atoms in his works in 1863, and openly attacked them in his 1872 book. Ostwald, a very influential chemist in his time, published a chemistry textbook with no mention of atoms in 1892. The chief defender of atomic theory was not a chemist but Boltzmann, the founder of the kinetic theory of gases, who engaged both of them in public debates in 1890s. Interestingly, he considered atoms changeable and perishable, but without suggesting a specific mechanism. See Blackmore's note.

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  • $\begingroup$ A great answer and some good links to follow-up when I get a chance. Thanks. $\endgroup$ – TripeHound Jul 9 '15 at 8:23
  • $\begingroup$ I do not follow the chronology in the first paragraph of your answer. You write about “maintaining indivisibility of atoms in chemistry despite large number of elements” until the “start of 19th century chemistry”. Who “maintained” this? After the demise of ancient Epicurianism only a small number of people in Europe believed in atomism of any sort (a rare example being Gassendi in the 16th century). Modern atominsm begins with Dalton in the early 19th century. $\endgroup$ – fdb Jul 9 '15 at 17:34
  • $\begingroup$ @fdb No, after the start of 19th century. Before that alchemic belief in Aristotle's 4 elements made the issue moot. But that belief eroded over the course of 18th century with the rise of experimental chemistry. $\endgroup$ – Conifold Jul 10 '15 at 20:29
  • $\begingroup$ What do "Aristotle's 4 elements" (five actually) have to do with atoms? $\endgroup$ – fdb Jul 11 '15 at 8:19
  • $\begingroup$ @fdb In alchemy material compounds were believed to be assembled from them somehow, just as later from "elements" in chemistry in a precise sense. The fifth "element" (ether) does not occur in the sublunar sphere according to Aristotle, so it was not relevant. $\endgroup$ – Conifold Jul 13 '15 at 22:16
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The idea that matter consists of indivisible atoms was first proposed by Democritus and Leucippus in the 5th century BC. In fact, the word “atomos” means “un-cut”. And Democritus at least seems to have believed that there is an infinite number of types of atoms. I do not see any logical objection against indivisibility on the basis of there being “too many” elements. In any case, it does not seem that anyone has ever raised that particular objection.

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