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A History of Chemistry – Part 2

May 6, 2020

Article

This article is Part 2 of a series.

The return to atomism and the rise of modern chemistry

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John Dalton

In 1808, John Dalton (1766–1844) published his book entitled «A New System of Chemical Philosophy» – a work which marked the birth of modern chemistry. In his theories, Dalton took up Democritus’ conception of atomism. He postulated that atoms were the smallest constituents of matter, and that they could not be divided further, nor created or destroyed in chemical reactions. According to Dalton, all atoms of the same element are identical, but differ from the atoms of other elements. In chemical reactions, atoms combine to form compounds, are separated from one another, or are rearranged relative to other atoms. Because atoms are indivisible according to this model, and therefore only whole atoms can react with one another, Dalton concluded that the elements in a compound are always present in whole-number ratios.

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In his atomic theory, Dalton made many hypotheses which have been pivotal to our understanding of chemistry even up to the present day. Some of the premises of his theory are not yet conclusive. For example, Dalton believed that an atom of one element only reacts with exactly one atom of another element. He only deviated from this hypothesis in cases where experimental observations made it absolutely necessary. For instance, he therefore theorized that the composition of water was H-O, meaning that he made subsequent errors, particularly when determining relative atomic masses.

Nevertheless, his atomic theory put chemistry firmly on the right track. From this point onwards, scientific discoveries in chemistry became much more frequent.