Construire une catégorie grâce à une analogie : cas du concept d'élément chimique / Building up a category using an analogy : case of the chemical element

Building up a category using an analogy : case of the chemical element . This research validates the use of an analogy introduced to build up the concept of chemical element viewed as a category. Such a teaching sequence involves experiments and discussions. The concept of chemical element, in the strict meaning of IUPAC, is discussed from previous work. On the basis of the property of conservation, a property that characterises the category students must make meaning with, the teaching sequence resorts to analogy to have students confront a contradiction due to the polysemy of the word copper. For students, this word means both copper metal and copper the chemical element. The way students solve the contradiction reveals an interesting students’ point of view about chemical transformations. The analysis of the way three teachers use contraction and analogy shows the benefit and the difficulties of the teaching sequence. The generalisation of the concept of chemical element then appears as a two step process :(i) the copper chemical element is conserved in all transformation : (ii) all chemical elements are conserved in all transformations.