60 Atoms
chemical combinations. Dalton had no experience or training in chemistry. Still, he plowed
confidently into his studies.
By this time almost 50 chemical elements had been discovered—metals, gasses, and
nonmetals. But scientists studying chemistry were blocked by a fundamental question they
couldn’t answer: How did elements actually combine to form the thousands of compounds
that could be found on Earth? For example, how did hydrogen (a gas) combine with oxygen
(another gas) to form water (a liquid)? Further, why did exactly one gram of hydrogen always combine with exactly eight grams of oxygen to make water—never more, never less?
Dalton studied all of the chemical reactions he could find (or create), trying to develop
a general theory for how the fundamental particle of each element behaved. He compared
the weights of each chemical and the likely atomic structure of each element in each compound. After a year of study, Dalton decided that these compounds were defined by simple
numerical ratios by weight. This decision allowed him to deduce the number of particles of
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