This work aims to assess the difficulties encountered by students of the Ecole Normale Superieure of Kouba (Algeria) intending to teach physical science in the integration of the hybridization of atomic orbitals. It is a concept that they should use in describing the formation of molecular orbitals (s and p) in organic chemistry and gaps in the mastery of these concepts may represent an obstacle for the interpretation of the reactivity of organic compounds. Several studies have noted that the concept of hybridization is among one of the most difficult to understand for students at all levels of learning chemistry. In this work we try to analyze the alternative conceptions that students have constructed and how they have brought together in a conceptual structure the various concepts related to hybridization. The analysis of responses to a written questionnaire and exchanges between students in group activities sequences shows that for most students, the hybridization is not assimilated correctly. It seems that many students can speak about hybridization only once the bonds are formed and there is confusion between the formation of hybrid orbitals and the formation of molecular orbitals. Moreover, various alternative conceptions for the hybridization and the meaning of the designation of hybrid orbitals (sp, sp 2 , sp 3 ) appear. Finally, from the reasoning used by students in achieving the proposed tasks, we inferred a knowledge structure of their possible integration of the concept of hybridization.

The concept of covalent bonding is characterized by an interconnected knowledge framework based on Lewis and quantum models of atoms and molecules. Several research studies have shown that students at all levels of chemistry learning find the quantum model to be one of the most difficult subjects to understand. We have tried in this paper to analyze the extent to which Algerian students, at the end of their training, have integrated the covalent bonding theories based on the quantum model of atom theory and are able to interpret Lewis structures using the quantum model. The analysis of the responses to a written questionnaire showed that this integration was not achieved by our students and that they are not able to correctly describe covalent bonds in a Lewis structure using the concepts of the quantum model. They have a “quantum box” conception of atomic or hybrid orbitals. This conception acts as a “pedagogical learning impediment” to the integration of the geometrical representations of atomic and hybrid orbitals, the conditions of their overlapping to give bonds and consequently the description of covalent bonds using the quantum model. So, the students use an alternative conceptual framework based on the use of Lewis model paired valence electrons to form covalent bonds that we have named the: “electrons pair framework”. Furthermore, the students restricted the denomination of a covalent bond to the sharing of one electron (either s or p but not spn) from each atom to give one “electron pair σ”, and thought that σ bonds are only formed in single bonds.

In this study we tried to analyse how future teachers of Ecole Normale Supérieure (ENS) school who are at the end of education have integrated the specifications of covalent bonds in the different bond orders in terms of symmetry, stability, length, localisation (in the case of structures of ethane, ethylene and acetylene) or delocalisation of electrons (case of benzene). The analysis of responses to a written questionnaire shows that the majority of students have only integrated some knowledge, which may be termed as procedural, on the structural elements of molecules such as stability and the length of bonds. Although possessing some conceptual knowledge, students tend to use an alternative way of reasoning arising from the mental representation that single and multiple bonds are independent entities: the single bond is a “σ bond” while the double bond is considered only as a “π bond”.