The formulation of the atomic theory of matter and the first tabulation of atomic weights by John Dalton had a profound effect on the development of both chemistry and physics. It established the basis for quantitative chemistry and provided a bridge across which chemistry and physics could relate to each other.
From the time he was a young boy, John Dalton showed a keen interest in scientific observations. A poor, mostly self-taught individual, Dalton developed an intuitive ability for formulating theories to explain collections of data. Between 1787 and 1844, he kept a daily record of the weather, recording more than 200,000 meteorological observations in his notebooks. This interest led him to investigate the composition and properties of gases in the atmosphere. He realized that water could exist as a gas that mixed with air and occupied the same space as air. In 1793, he published some of his findings in Meteorological Observations and Essays. From 1793 until 1799, he taught chemistry and some other scientific subjects at New College in Manchester, England, where he began his quest for an atomic theory of matter.
In 1803, John Dalton wrote a classic paper titled “The Absorption of Gases by Water and Other Liquids,” which was published in 1805. Near the end of the paper, he proposed an atomic theory of matter that also included the first published tabulation of atomic weights. His concept of atoms was directly related to the measurable property of mass. He had determined the relative weights of a number of atoms from chemical analyses that were available for water, ammonia, carbon dioxide, and a few other substances.
Dalton assumed that chemical combination always occurred in the simplest way possible with the smallest number of atoms. This insight led him to formulate the principle that particles of different mass can combine chemically. It also led him incorrectly to assume that only one atom of hydrogen combines with oxygen to form water. As a result, he concluded that oxygen atoms weighed eight times as much as hydrogen atoms. Experiments conducted later by Joseph-Louis Gay-Lussac
Dalton continued to develop an atomic theory of matter in a series of lectures that he presented in London in 1803, in Manchester in 1805, and in Edinburgh in 1807. Dalton’s primary impetus was discovered by chemist Henry Roscoe after Dalton’s death. Roscoe carefully studied Dalton’s lab notebooks and concluded that Dalton formulated his theory in response to his observation that gases with different densities mix together instead of separating into layers. The theory was also motivated by Joseph-Louis Proust’s
Dalton’s scientific experiments were carried out with crude, homemade experimental equipment that produced rather imprecise data. They were of sufficient quality, however, to provide the necessary clues that Dalton’s creative mind needed to formulate the probable explanation for the observed data. Because of the many revisions that Dalton made in his lab notebooks, as well as the lack of exact dates on many of the pages, it is almost impossible to determine the exact time when he formulated the atomic theory of matter.
In 1808, Dalton published the details of his atomic theory in the first part of his New System of Chemical Philosophy (1808-1827, 2 vols.). The second part of volume 1 was published in 1810. Dalton defined an element as a substance composed of only one kind of atom. His theory provided a natural way to represent chemical compounds. After inventing a set of elemental symbols, he used them to combine different elements to provide schematic representations of what he believed were the molecular structures of a variety of compounds. Dalton constructed the first periodic table
Although Dalton’s atomic theory did not initially attract much attention from other scientists, his publication of New System of Chemical Philosophy, along with Thomas Thomson’s
A System of Chemistry (1802), stirred great interest in Dalton’s theory. The atomic theory of matter allowed Dalton and others to explain many principles of chemistry with simplicity. Dalton’s theory explained the fact that mass can be neither created nor destroyed in chemical or physical reactions. This is known as the law of conservation of mass, a principle first discovered by Antoine-Laurent Lavoisier
Dalton’s theory also explained Proust’s
John Dalton has been called the founder of modern atomic theory. Until Dalton proposed the atomic theory of matter, the concept of atoms—which was originally stated by Leucippus
Dalton’s theory had significant explanatory power, leading him and his successors to develop explanations for many confirmed experimental results. Dalton’s theory is still used to explain the properties of many chemicals and compounds today. His theory has also been expanded to explain new observations, including the existence of elementary particles that make up the internal structure of atoms and the existence of isotopes of atoms. A variety of isotopes can be used to trace the various steps in chemical reactions and metabolic processes in the human body. Tracer techniques have proven invaluable in the clinical diagnosis of many disorders in the body.
Dalton’s theory formed the foundation for the science of chemistry. As a result, Dalton is known as the founder of modern chemistry. His atomic theory has led to myriad significant applications, including the development of the best model of the atom, the description of different phases of matter, the harnessing of atomic energy, the development of atomic weapons, the quantitative explanation of chemical reactions, and the chemistry of life. Dalton’s theory established the framework for the development of biochemistry and the understanding of the bonding of carbon atoms to form chains and branching structures that are essential in the formation of sugars, fatty acids, nucleic acids, carbohydrates, proteins, and other molecular structures on which life is based.
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McDonnell, John James. The Concept of an Atom from Democritus to John Dalton. Lewiston, N.Y.: Edwin Mellen Press, 1991. Historical development of ideas about the fundamental makeup of matter from Democritus (460-370 b.c.e. ) until Dalton’s proposed atomic theory. -
Smyth, A. L. John Dalton, 1766-1844: A Bibliography of Works by and About Him. Brookfield, Vt.: Ashgate, 1998. Contains a bibliography of works by Dalton and about Dalton, including an annotated list of his personal effects and experimental equipment that are still in existence. -
Tillery, Bill W., Eldon D. Enger, and Frederick C. Ross. Integrated Science. New York: McGraw-Hill, 2001. Discusses the history of Dalton’s formulation of the atomic theory and explains its importance in the context of chemistry and the other physical sciences. -
Whiting, Jim, and Marylou Morano Kjelle. John Dalton and the Atomic Theory. Hockessin, Del.: Mitchell Lane, 2004. An excellent treatise on John Dalton and the steps he took in developing the fundamental concepts for his atomic theory of matter.
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John Dalton; Joseph-Louis Gay-Lussac; Dmitry Ivanovich Mendeleyev.