Editing History of atomic theory (section)

==Isomerism==
Scientists discovered some substances have the exact same chemical content but different properties. For instance, in 1827, [[Friedrich Wöhler]] discovered that [[silver fulminate]] and [[silver cyanate]] are both 107 parts silver, 12 parts carbon, 14 parts nitrogen, and 16 parts oxygen (we now know their formulas as both AgCNO). In 1830 [[Jöns Jacob Berzelius]] introduced the term ''isomerism'' to describe the phenomenon. In 1860, [[Louis Pasteur]] hypothesized that the molecules of isomers might have the same set of atoms but in different arrangements.<ref>[[#refPullman1998|Pullman (1998). ''The Atom in the History of Human Thought'', p. 230]]</ref>

In 1874, [[Jacobus Henricus van 't Hoff]] proposed that the carbon atom bonds to other atoms in a tetrahedral arrangement. Working from this, he explained the structures of organic molecules in such a way that he could predict how many isomers a compound could have. Consider, for example, [[pentane]] (C<sub>5</sub>H<sub>12</sub>). In van 't Hoff's way of modelling molecules, there are three possible configurations for pentane, and scientists did go on to discover three and only three isomers of pentane.<ref>[[#refMelsen1952|Melsen (1952). ''From Atomos to Atom'', pp. 147–148]]</ref><ref>Henry Enfield Roscoe, Carl Schorlemmer (1895). [https://books.google.com/books?id=JU1KAAAAYAAJ&pg=PA121 ''A Treatise on Chemistry'', Volume 3, Part 1, pp. 121–122]</ref>

{{multiple image
 | align = center
 | total_width = 600
 | footer =  [[Jacobus Henricus van 't Hoff]]'s way of modelling molecular structures correctly predicted the three isomers of [[pentane]] (C<sub>5</sub>H<sub>12</sub>).
 | image1 = Pentane-3D-balls.png
 | alt1 =
 | caption1 = [[n-pentane]]
 | image2 = Isopentane-3D-balls.png
 | alt2 =
 | caption2 = [[isopentane]]
 | image3 = Neopentane-3D-balls.png
 | caption3 = [[neopentane]]
}}

Isomerism was not something that could be fully explained by alternative theories to atomic theory, such as [[radical theory]] and the theory of types.<ref>Henry Enfield Roscoe, Carl Schorlemmer (1895). [https://books.google.com/books?id=JU1KAAAAYAAJ&pg=PA121 ''A Treatise on Chemistry'', Volume 3, Part 1, pp. 121]: "The radical theory and the theory of types are capable of explaining many cases of isomerism, but it was not until the doctrine of the linking of atoms was established that a clear light was thrown on this subject."</ref><ref>[https://books.google.com/books?id=vTY6AAAAMAAJ&pg=PA291 Adolphe Wurtz (1880). ''The Atomic Theory'', p. 291]: "It is in this manner that the theory of atomicity predicts, interprets, and limits the number of isomers; it has furnished the elements of one of the greatest advances which science has accomplished in the last twenty years. [...] The theory of atomicity has successfully attacked the problem by introducing into the discussion exact data, which have been in a great number of cases confirmed by experiment."</ref>