![]() This process is experimental and the keywords may be updated as the learning algorithm improves. These keywords were added by machine and not by the authors. This period of the history of structure of the atom has been the subject of considerable debate and controversy in the history and philosophy of science literature (Achinstein, 1991 Falconer, 1987 Heilbron, 1985 Heilbron & Kuhn, 1969 Hettema, 1995 Holton, 1986, 1993 Jammer, 1966 Kuhn, 1984 Lakatos, 1970 Popper, 1965). Bohr evolved in quick succession and had to contend with competing models based on rival research programs. The history of the structure of the atom since the late nineteenth and early twentieth centuries shows that the models of J.J. This reminds us that almost 45 years ago we ignored Schwab's (1962) advice that science cannot be taught as an “unmitigated rhetoric of conclusions in which the current and temporary constructions of scientific knowledge are conveyed as empirical, literal, and irrevocable truths” (p. In contrast, most textbooks consider Bohr's major contribution to be the explanation of the Balmer and Paschen series of the hydrogen line spectrum (i.e., experimental findings). In the case of Bohr's research program, Lakatos (1970) considers Bohr's explanation of the paradoxical stability of the Rutherford atom as the heuristic principle. This rationale, which helped Thomson to identify cathode rays as ions or universal charged particles (rival hypotheses), precisely constitutes the “heuristic principle.” In a recent study, Blanco and Niaz (1997b) have shown how both students and teachers understand Thomson's experiments as a series of conclusions based on empirical findings (truths). Although the experimental details are important we cannot ignore the rationale behind Thomson's determination of the charge to mass ratio of cathode rays. ![]() Thomson's experimental work with cathode rays. ![]() Isotopes of an element contain different numbers of neutrons. Each element has its own atomic number, which is equal to the number of protons in its nucleus. Atoms themselves are composed of protons, neutrons, and electrons. To understand the function of “heuristic principles” let us consider J.J. Chemistry is based on the modern atomic theory, which states that all matter is composed of atoms. ![]() Matthews (1994) emphasized the importance of heuristic principles in scientific inquiry and science education in similar terms. Monk and Osborne (1997) pointed out how many science curricula have forgotten Schwab's important epistemological distinction between the methodological (experimental data) and interpretative (heuristic principles) components. It tells us what meaning to assign these facts” (Schwab, 1974, p. In other words: “A fresh line of scientific research has its origins not in objective facts alone, but in a conception, a deliberate construction of the mind … this conception … tells us what facts to look for in the research. Atoms of one element differ in properties from atoms of all other elements.According to Schwab (1974) scientific inquiry tends to look for patterns of change and relationships which constitute the heuristic (explanatory) principles of our knowledge.The right image calls out an area of one of the pennies, which is made up of many sphere-shaped copper atoms. (credit: modification of work by “slgckgc”/Flickr) The left image shows a photograph of a stack of pennies. Chemistry is based on the modern atomic theory, which states that all matter is composed of atoms. This page titled 3.2: Summary of Atomic Theory and the Construction of Atoms is shared under a mixed license and was authored, remixed, and/or curated by Anonymous. Define isotopes and give examples for several elements. Describe the three subatomic particles that compose atoms. Summarize and interpret the results of the experiments of Thomson, Millikan, and Rutherford. \): A pre-1982 copper penny (left) contains approximately 3 \(\times\) 10 22 copper atoms (several dozen are represented as brown spheres at the right), each of which has the same chemical properties. Ions form when atoms lose or gain electrons. By the end of this section, you will be able to: Outline milestones in the development of modern atomic theory.
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