Relações históricas de precedência como orientações para o ensino médio de química: a noção clássica de valência e o livro didático de química

Abstract

The study develops a framework for examining the way the classic notion of valency is adapted by the secondary teaching chemistry curricula. The analysis is based upon twenty-seven new and old textbooks. The textbooks are divided in three categories: new Secondary Teaching (ensino médio), new Primary Teaching (ensino fundamental) and old Secondary Teaching (ensino secundário). For aiding the analysis of the textbooks in how they appropriate the history of the concept it is presented a rational reconstruction of the classic notion of valency. The methodological approach uses precedence matrices and conceptual maps to verify the use of a specific precedence relationship, characterized as [A, P, L], which refers to the themes: atomistics, chemical periodicity and chemical bonding. This precedence relationship composes what is called the "hard nucleus" of the didactic strategy addressed by the authors for learning the themes related to the structure of matter. A counterpoint to what is found in the current books is observed in the books of the old Secondary Teaching, in which precedence [A, P, L] is not observed. In that sense, it is considered that the material of Chemical Bond Approach Committee CBA was a strong influence for the implementation of that precedence. It is also noticed that there is a prevalence of using the history as an organizing axis in the presentation of the themes related to the quantum mechanics, but that most textbooks lacked a history precedence and did not deal with the conceptual understanding. As an alternative way to the predominant organization observed it is proposed a strategy based in the history of the classic notion of valency.