M Modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic fractionation. The difference between the atomic mass of the element in such specimens and that given in the table may exceed the stated uncertainty. G Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. вЂ Commercially available Li materials have atomic weights that range between 6.939 and 6.996 if a more accurate value is required, it must be determined for the specific material. However, three such elements (Th, Pa, and U) have a characteristic terrestrial isotopic composition, and for these an atomic mass is tabulated. Table 17.1 The Basics of the Elements of the Periodic Table Name The web offers many interactive periodic table resources. Some elements, such as lithium, can have varying atomic masses depending on how their isotopes are isolated. The atomic masses of other elements, especially radioactive elements, are not known as precisely. The atomic masses of some elements are known very precisely, to a large number of decimal places. The atomic masses in Table 17.1 'The Basics of the Elements of the Periodic Table' represent the number of decimal places recognized by the International Union of Pure and Applied Chemistry, the worldwide body that develops standards for chemistry. However, some applications (especially nuclear chemistry see Chapter 15 'Nuclear Chemistry') require more decimal places. For many applications, only one or two decimal places are necessary for the atomic mass. One item on most periodic tables is the atomic mass of each element. The Internet is a great place to find periodic tables that contain additional information. What follows here is a more complex version of the periodic table than what was presented in Chapter 3 'Atoms, Molecules, and Ions'. Periodic tables are available with a variety of chemical and physical properties listed in each elementвЂ™s box. Many of the physical and chemical properties of the elements are either known or understood based on their positions on the periodic table. The periodic table is arguably the best tool in all of science no other branch of science can summarize its fundamental constituents in such a concise and useful way. The periodic table, introduced in Chapter 3 'Atoms, Molecules, and Ions', lists all the known chemical elements, arranged by atomic number (that is, the number of protons in the nucleus). In this chapter, we present some data on the chemical elements. В© 2004 Wiley Periodicals, Inc.Chapter 17 Appendix: Periodic Table of the Elements It is concluded that the development of the periodic table went through a continual critical appraisal (conflict and controversy), in which scientists presented various tentative theoretical ideas to understand the observed phenomena. The textbook approach of emphasizing that the development of the periodic table was an inductive generalization, and that Mendeleev had no model or theory, does not facilitate the spirit of critical inquiry that led the scientists to grapple with alternative interpretations, conflicts, and controversies. The development of the periodic table as a sequence of heuristic principles in the form of a convincing argument has been ignored. Few textbooks have attempted to explore the possible cause of periodicity in the table and very few textbooks have explored the nature of Mendeleev's contribution. The relative importance of accommodation and prediction within an HPS framework is generally ignored. Accommodation of the elements according to their physicochemical properties is considered to be the major contribution of the periodic table by all textbooks, followed by contrapredictions of previously unknown elements (30 textbooks), and novel predictions (corrections of atomic mass) of known elements (10 textbooks).

There is considerable controversy with respect to the nature of Mendeleev's contribution, and various alternatives are discussed: ordered domain empirical law and a theory with limited explanatory power. The historical reconstruction of the periodic table showed that the periodicity of the elements could be construed as an inductive generalization or as a function of the atomic theory. The objectives of this study are: (a) elaboration of a history and philosophy of science (HPS) framework based on a reconstruction of the development of the periodic table (b) formulation of seven criteria based on the framework and (c) evaluation of 57 freshman college-level general chemistry textbooks with respect to the presentation of the periodic table.

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