John Dalton
Originator of Atomic Theory
Born to a Quaker family on September 6, 1766, in Eaglesfield, England, Dalton attended school until he was 12. At this young age, he became a teacher and taught for the rest of his life. By accident he discovered he was colorblind. This phenomenon fascinated him. In 1794 he published his first scientific paper on the subject. Colorblindness came to be called Daltonism because of his research.
A friend introduced him to meteorology, sparking his interest in the natural sciences. In 1787 Dalton began a daily record of weather observations that would eventually include over 200,000 items. As he became more involved with these observations, Dalton wondered about the atmosphere and its components.
Dalton recognized patterns in the interactions of atmospheric gases. In 1803 he published his law of partial pressures, now called Dalton’s Law. This law states that when different gases are combined the resulting pressure is the sum of what each gas exerts individually. He explored other characteristics of gases including solubility in water and how temperature affects volume.
These studies led Dalton to infer that gases must be made of small particles. Dalton expanded on the Greek Democritus’ idea that atoms could not be split and created a new atomic theory. He stated that all matter is composed of tiny, indivisible parts and that these atoms are indestructible and cannot be changed. Dalton also asserted that each element has a unique type of atom. For example, all gold atoms are alike but different from those of other elements. Additionally, each atom has a measurable weight that can be experimentally determined. He include in his 1808 publication, New System of Chemical Philosophy, a list of weights for certain elements. Dalton used the lowest density gas, hydrogen, as a basis for the comparative weights. In conjunction with his theory, he also discussed how atoms form compounds. Although he did not use the term molecule, Dalton hypothesized that atoms combine in certain proportions to become compound substances. Even though several of his measurements later proved incorrect, Dalton’s basic theory of matter and atoms was a tremendous achievement. He was awarded a Royal Medal in 1826 for his groundbreaking work.
Throughout his life Dalton supported himself by teaching; in later years, he spent less time on his scientific research. He continued to be recognized for his earlier work until he died on July 27, 1844, at his home in England.
John Dalton’s Legacy
Dalton’s atomic theory provided scientists with new ways of viewing the physical world. The concepts of atomic weights and fixed ratios of atoms within compounds challenged researchers to explore the chemical composition of matter further.
Dalton’s assertion that atomic weights could be experimentally determined provided scientists with a new key to studying various substances. New information on the atomic weights of elements later enabled Russian chemist DMITRY MENDELEYEV to create the periodic table of elements. This, in turn, sparked the discovery of new elements. Dalton also proposed symbols for the elements that could be used to represent combinations of atoms in compounds.
These were later changed to the abbreviations used today, but the initial idea for a consistent system was Dalton’s. And while Dalton’s theory was wellaccepted at the time, it also raised many new questions about the interactions of atoms. New ideas about the structure of atoms and how they interact helped to refine atomic theory.
During Dalton’s time, the division between physics and chemistry was just emerging. His theory helped clarify both disciplines. The atom is a cornerstone for understanding forces and matter in physics and chemistry, in particular in quantitative analysis, an aspect of chemistry that measures how much of a particular substance is present in a sample. Dalton’s physical view of the atom was later refined through the work of ERNEST RUTHERFORD, NIELS BOHR, and others. Nuclear energy and fusion research today are the progeny of Dalton’s theory. In chemistry, Dalton’s work provides a basis for stoichiometry (the study of the quantitative relationships between substances in chemical reactions), structural theory and how the arrangement of atoms influences properties, and other fields. His early models of compounds evolved into an understanding of the threedimensional quality of molecules and how structure affects properties. While Dalton’s theory contained inaccuracies, his atomic theory provided a foundation for later generations of scientists—a foundation that didn’t exist before Dalton.
John Dalton – 1766-1844