SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
John Dalton's table of atomic weights and the symbols he used for a number of "elements". Compiled in 1808, some of the 20 substances included in the table are compounds & not pure elements: lime, for example. Dalton calculated the weight of each substance relative to hydrogen, the lightest, ending his list with mercury, to which he had incorrectly assigned a greater atomic weight than for lead. Dalton's view of each element consisting of a unique type of indivisible atom was consistent with contemporary observations & "laws" concerning the combination of elements to form compounds.
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