Early Atomic Laws of Combination

The early understanding of the combination of atoms was shaky. Theories that would have progressed the understanding or at least pointed discussion in the right direction were ignored by key individuals and it potentially set back chemical understanding for decades. One of the first theories that developed about how atoms combine was published by Proust in 1808. The “law of constant proportions” was the result of Proust’s experimentation with copper carbonate in which he found that the composition, no matter how it was prepared or if it occurred naturally, was fixed. Proust’s idea seemed to hold true for simple compounds, but was ultimately disproven. Dalton assumed that a compound of 2 substances would contain one atom of each constituent. Eventually Dalton was able to develop the idea of “variability of chemical composition” in which most compounds were binary and were made in a one to one ratio, but some elements were allowed to form ternary compounds where one element connected two others. Following Dalton, the work of Berzelius became popular. He ultimately cemented the idea of the “law of multiple proportions”, or the theory that one atom might combine with a variable number of other atoms. Working on atomic theory around the same time as Berzelius was Avogadro. Avogadro came up with the theory that equal volumes of different gasses must contain the same number of particles. This idea allowed him to deduce that the ration of the densities of any two gasses is equal to the ration between the masses of their particles, ultimately giving rise to the idea of “atomic weights”. Avogadro also theorized that elements could bond with themselves. This idea was ultimately too far-fetched for Berzelius and was disregarded which, due to the influence Berzelius had on the chemistry world, meant that it was ignored by all. In 1815 and 1816 William Prout published two anonymous papers suggesting that atomic weights of many of the known elements were whole multiples of the atomic weight of hydrogen, which was unfortunately supported with inaccurate data. One of the last areas of discussion in the selection relates to the composition of acids. Lavoisier had assumed that all acids contained oxygen, even if in small amounts. This was ultimately disproven by Humphry Davy and a new understanding of acids was proposed by Liebig. Liebig began to assume that acids were not compounds of oxygen, but of hydrogen (1). The road to understanding the combination of atoms was a knot of theories that were often supported with research results, but sometimes inaccurate results were published and taken as truth. This act of unintentional misleading in conjunction with the complex nature of atomic interactions is responsible for the delayed acceptance of a unified atomic theory.

References

(1). H.M. Leicester. The Historical Background of Chemistry, Dover Publications, Inc., New York, USA, (1971) pp. 150-171.