THE CONCEPT OF VALENCE IN GENERAL CHEMISTRY TEXTBOOKS FROM THE 1890s TO THE 1940s. This paper aims to investigate the presentation of the concept of valence in college-level, general chemistry textbooks published in the USA between the 1890s and the 1940s. The delimited period covers the emergence of theories about atomic structure, electronic distribution and chemical bonding. Transition from the classical concept of valence (as the combining power of a chemical element), which resulted from either the analysis of formulas of compounds or experimental results, into the concept related to the electronic structure of elements, according to which the valence is determined by the number of electrons in the last shell, was observed. In general, valence was presented in textbooks in order to serve as an instrument for the writing of formulas of compounds, and historical approaches to the construction of the concept were not contemplated by the authors.

BETWEEN TYPES AND RADICALS: THE CONSTRUCTION OF THE CONCEPT OF VALENCE. This paper presents a historical case study regarding the development of the concept of valence in late nineteenth and early twentieth centuries. The case study focuses on Edward Frankland's contribution to the process which lead to the convergence of two theories about the combination of the elements: the theory of types and the theory of radicals. Results show how such process involved many other scientists from various countries and how the concept of valence related to studies on bonding, periodicity and chemical structure. Changes in the nomenclature and notation were also observed. In the beginning of the twentieth century, the empirical concept of valence received theoretical explanations under the light of the then new theories on electronic structure of atoms. Thus, this case study exemplifies the complexity of the process of development of a scientific concept and, in particular, shows the multiplicity of connections of the concept of valence in the body of chemical knowledge. Keywords: valence; history of chemistry; theory of types; theory of radicals; chemical bonding; Edward Frankland. This is an open-access article distributed under the terms of the Creative Commons Attribution License.

NOGUEIRA, H. S. A. The concept of valence in university-level General Chemistry textbooks in the first decades of the twentieth century. ix+86 p. Master thesis.