Some of Dalton's contemporaries saw these assumptions as arbitrary. One assumption was that if two elements formed only one compound, that compound consisted of a single atom of each element (for example, water would be HO and ammonia NH). The table was based on chemical analyses and on certain assumptions about what we would call molecular formulas. When Dalton set out his atomic hypothesis, he included a table of atomic weights relative to hydrogen = 1. He also seems to have believed that they were indestructible. Dalton believed that atoms of the same element were identical. As valuable and fruitful as Dalton's work certainly was, it was mistaken in several details. The fruitfulness of Dalton's theory can be seen in the research on combining masses and relative masses of the elements and their compounds that followed it. Dalton focused on properties of atoms that were amenable to empirical investigation, namely their relative masses. The laws of definite proportions and multiple proportions follow naturally from such an atomistic view of chemical combination. His theory pictured chemical compounds much as we do today, as atoms of different elements bound together. Notes: John Dalton (1766-1844) is best known for formulating an atomic theory that proved to be enormously fruitful, even though it turned out to be incorrect in several important details. Reference: John Dalton, A New System of Chemical Philosophy, Part I, (Manchester, 1808, 1810) Dalton atomic weights: teaching notes Dalton atomic weights Content: composition, formulas, stoichiometry
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