THE CONCEPT OF VALENCE AS A SOURCE OF APORIA IN TEACHING CHEMISTRY AT THE LEVEL OF BASIC SECONDARY EDUCATION

Abstract

Two current model curricula for the subject “Chemistry. Years 7–9”, developed in accordance with the new State Standard for Basic Secondary Education, as well as textbooks written in accordance with these curricula, were analysed in relation to the use of the scientific concepts. The attention is focused on the removal of the term “valency”, which has traditionally been among the cornerstone concepts of the school chemistry course, from one of the curricula. Out of related terms, only “oxidation degree” is used in the curriculum.The article examines contradictions (aporia) that arise during the teaching and learning of school chemistry courses and relate to the concept of valency. In particular, the appropriateness of applying the term “valency” to ionic compounds, examples of mismatch between valency (as the number of covalent bonds) of the atom in a compound and its oxidation state, violation of the octet rule, involvement or non-involvement of d-electrons (for d-block elements) in the formation of covalent bonds, formation of dative covalent bonds vs d-electron covalent bonds have been analysed and illustrated by examples. The definition of the valency concept in various Ukrainian and foreign textbooks is compared with the definition of the International Union of Pure and Applied Chemistry (IUPAC), and an analysis of domestic and foreign scientific and methodological literature on the use of this concept in school education is carried out. Based on the experience of the foreign school education systems and the understanding of covalent bonds in modern chemical science, the authors’ opinions on the inexpediency of using the concept of “valence” at the level of basic secondary education are substantiated and presented. The recommendations for textbook authors and teachers of general secondary education institutions (GSEI) regarding the removal of the concept of “valence” and its replacement with the concepts of “oxidation state”, “number of bonds” and “ionic charge” are formulated in the article. Opportunities are outlined for the development of skills belonging to the 4th group of mandatory learning outcomes of the natural science branch of the State Standard for Basic Secondary Education (“development of scientific thinking, gaining of experience in problem solving”). These skills can be achieved by introducing problematic issues related to the formation of covalent bonds into the lesson materials.