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Wednesday, 6 July 2011

17th century

17th century

The earliest views on the shapes and connectivity of atoms was that proposed by Leucippus, Democritus, and Epicurus who reasoned that the solidness of the material corresponded to the shape of the atoms involved. Thus, iron atoms are solid and strong with hooks that lock them into a solid; water atoms are smooth and slippery; salt atoms, because of their taste, are sharp and pointed; and air atoms are light and whirling, pervading all other materials. It was Democritus that was the main proponent of this view. Using analogies from our sense experiences, he gave a picture or an image of an atom in which atoms were distinguished from each other by their shape, their size, and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes others with balls and sockets.
A water molecule as Descartes' hook-and-eye model might have represented it. Note that at the time (c.1625) the composition of water was not known.
The atomic theory, curiously, was abandoned for nearly two millennia in favor of the various four element theories and later alchemical theories. The 17th century, however, saw a resurgence in the atomic theory primarily through the works of Descartes, Gassendi, and Newton. Using earlier Greek atomic theories to explain how the tiniest particles of matter bonded together, Descartes visualized that atoms were held together by microscopic hooks and barbsHe held that two atoms combined when the hook of one got caught in the eye of the other (see diagram):
By the mid 1770s, it was generally believed that any theory involving particles endowed with physical hooks was considered “Cartesian chemistry”.[4] Similar to Descartes, Gassendi, who had recently written a book on the life of Epicurus, reasoned that to account for the size and shape of atoms moving in a void could account for the properties of matter. Heat was due to small, round atoms; cold, to pyramidal atoms with sharp points, which accounted for the pricking sensation of severe cold; and solids were held together by interlacing hooks.
Newton, though he acknowledged the various atom attachment theories in vogue at the time, i.e. “hooked atoms”, “glued atoms” (bodies at rest), and the “stick together by conspiring motions” theory, rather believed, as famously stated in "Query 31" of his 1704 Opticks, that particles attract one another by some force, which “in immediate contact is extremely strong, at small distances performs the chemical operations, and reaches not far from particles with any sensible effect.”

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