  | ||
|
|
Science and Scientists The Atomic Theory of Matter The Science 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 chemistry and established the basis for quantitative chemistry. The Scientists John Dalton (1766-1844), English chemist and meteorologist Thomas Thomson (1773-1852), Scottish chemist and medical doctor Antoine-Laurent Lavoisier (1743-1794), French chemist Joseph Louis Proust (1755-1826), French chemist Jons Jakob Berzelius (1779-1848), Swedish chemist Joseph Louis Gay-Lussac (1778-1850), French chemist and physicist Atomic Weights 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 the principle that particles of different mass can combine chemically. It also led him to assume, incorrectly, 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 Gay-Lussac showed that two atoms of hydrogen combines with oxygen to form water, which required a change in Dalton's table of atomic weights. Since Dalton was a very independent scientist who feared that others might misguide him in his research, he was reluctant to accept the findings of Gay-Lussac. Dalton continued the development of his atomic theory of matter in a series of lectures which he presented in London in 1803, in Manchester, England, in 1805, and in Edinburgh, Scotland, in 1807. The motivation that led Dalton to his atomic theory was discovered by chemist Henry Roscoe after Dalton's death. Roscoe carefully studied Dalton's lab notebooks and concluded that Dalton had formulated his atomic theory of matter from his observations that gases with different densities mix together instead of separating into layers. It was also motivated by an idea proposed by Joseph Proust in 1800 that elements combine in definite proportions to form compounds. Proust's concept enabled Dalton to associate the idea of an atom with the concept of an element. Although Dalton's scientific experiments were carried out with crude, homemade experimental equipment that produced rather imprecise data, they were of high enough quality to provide the necessary clues that Dalton's creative mind needed to formulate the explanation for the observed data. However, because of the many revisions that Dalton made in his lab notebooks, as well as the lack of dates on many of the pages, it is almost impossible to determine the exact time when he formulated the atomic theory of matter. Five Basic Principles In 1808, Dalton published the details of his atomic theory in New System of Chemical Philosophy. His atomic theory can be summarized by five basic statements: (1) All matter is composed of small particles called atoms. (2) Atoms are the smallest entities that make up matter. They cannot be subdivided, created, or destroyed. (3) The atoms of a specific element are identical in size, mass, and all other properties. The atoms that make up different elements differ in size, mass, and other properties. (4) The atoms of different elements can combine in simple, whole-number ratios to form chemical compounds. (5) Atoms are combined, separated, or rearranged in chemical reactions. Dalton defined an element to be 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 of elements. He used letters and symbols arranged inside of circles for his scheme. Later, Jons Jakob Berzelius pointed out that the circles were not needed and recommended the one- or two-letter symbols currently used in the periodic table of elements. Useful Explanations Although Dalton's atomic theory did not initially attract much attention from other scientists, his publication of New System of Chemical Philosophy (1808), along with Thomas Thomson's A System of Chemistry (1807), 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 be created nor destroyed in chemical or physical reactions. This is known as the law of conservation of mass, a principle first discovered by Antoine Lavoisier around 1789. Dalton's theory also explained the law of definite proportions, which states that every chemical compound has a definite composition by mass. The amounts of products and reactants in any particular chemical reaction always occur in the same definite proportions by volume of gases or by numbers of molecules. In the latter part of 1808, Dalton once again concentrated his efforts on meteorological research and associated investigations. He also frequently defended his atomic theory of matter in private conversations and in scientific meetings. Since he pictured atoms as hard, indivisible spheres, his theory provided no insight into the structure of atom or its components; consequently, the theory cast no light on the way atoms of different elements can bond together. Dalton's theory, however, laid the foundation for other scientists to pursue and eventually explain these phenomena. Impact John Dalton is referred to as the Father of Modern Atomic Theory. Until Dalton proposed the atomic theory of matter, the concept of atoms that was originally stated by Leucippus and Democritus in the fourth century B.C.E. remained a very simplistic idea. Dalton's atomic theory provided chemists with a new, enormously fruitful model of reality. It led to two fundamental laws of nature--the law of conservation of mass and the law of definite composition--which eventually led to the periodic table of elements. In addition, his theory of the existence of atoms led to the explanation of many confirmed experimental results. Nevertheless, Dalton's theory is still used to explain the properties of many chemicals and compounds today. His theory has 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. Because Dalton's theory formed the foundation for the science of chemistry, Dalton is also known as the Father of Modern Chemistry. His atomic theory has led to many 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. See Also Atomic Nucleus; Atomic Structure; Chemical Proportions; Isotopes; Periodic Table of Elements. Further Reading McDonnell, John James. The Concept of an Atom from Democritus to John Dalton. Lewiston, N.Y.: Edwin Mellen Press, 1991. Smyth, Albert Leslie. John Dalton, 1766-1844. Aldershot, England: Ashgate, 1998. Tillery, Bill W., Eldon D. Enger, and Frederick C. Ross. Integrated Science. New York: McGraw-Hill, 2001. Whiting, Jim, and Marylou Morano Kjelle. John Dalton and the Atomic Theory. Hockessin, Dela.: Mitchell Lane, 2004. Alvin K. Benson |
If you need help with products and ordering, setting up a new account or working with this website, call or email us:
 |
SALEM PRESS, INC. · 131 North El Molino Avenue · Pasadena · CA 91101 © Salem Press, Inc. All Rights Reserved. |