Atoms
Year of Discovery: 1802
What Is It? An atom is the smallest particle that can exist of any chemical
element.
Who Discovered It? John Dalton
Why Is This One of the 100 Greatest?
The modern worlds of chemistry and physics depend on knowing and studying the
universe of atoms. But no one could actually see an atom until the invention of the electron
microscope in 1938. Centuries before that, atoms were well known and were an important
part of chemistry and physics research. It was John Dalton who defined the atom, allowing
scientists to being serious study at the atomic level. An atom is the smallest particle of any
element and the basic building block of matter. All chemical compounds are built from
combinations of atoms.
Since atoms are the key to understanding chemistry and physics, Dalton’s discovery of
the atom ranks as one of the great turning points for science. Because of this discovery, Dalton is often called the father of modern physical science.
How Was It Discovered?
In the fifth century B.C., Leucippus of Miletus and Democritus of Abdera theorized
that each form of matter could be broken into smaller and smaller pieces. They called that
smallest particle that could no longer be broken into smaller pieces an atom. Galileo and
Newton both used the term atom in the same general way. Robert Boyle and Antoine
Lavoisier were the first to use the word element to describe one of the newly discovered
chemical substances. All of this work, however, was based on general philosophical theory,
not on scientific observation and evidence.
John Dalton was born in 1766 near Manchester, England, and received a strict Quaker
upbringing. With little formal education, he spent 20 years studying meteorology and
teaching at religious, college-level schools. Near the end of this period, Dalton joined, and
presented a variety of papers to, the Philosophical Society. These included papers on the barometer, the thermometer, the hygrometer, rainfall, the formation of clouds, evaporation,
atmospheric moisture, and dew point. Each paper presented new theories and advanced
research results.
Dalton quickly became famous for his innovative thinking and shifted to science research full time. In 1801 he turned his attention from the study of atmospheric gasses to
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