Despite the growing importance of science and technology in society, school students consider these subjects irrelevant and hard to learn. Teachers must therefore know how to teach science in ways that enhance students’ understanding and interest. This thesis explores various aspects of the teaching and learning of chemical bonding, an important topic in school chemistry that is primarily taught using models. Research has shown that students find chemical bonding difficult to understand, and that the use of models in science education contributes to this difficulty. I therefore investigated teachers’ knowledge of how to teach chemical bonding and ways of developing it to improve students’ understanding. To this end, I analysed chemistry textbooks and teachers’ lesson plans, and conducted semi-structured interviews with teachers about their teaching of chemical bonding. This revealed that the representations of chemical bonding used in textbooks and by teachers can cause students difficulties. The teachers were generally unaware of how these representations might affect students’ understanding, implying that their pedagogical content knowledge (PCK) could be improved. To explore ways of incorporating research findings into teaching practice and developing teachers’ PCK, I conducted a learning study in which three secondary science teachers together explored and reflected on their own teaching practice. CoRe, a method for creating detailed descriptions of what, how, and why specific content is taught, was used to enhance the reflections and make the teachers’ PCK explicit. As a result, the teachers developed their representations of chemical bonding, became more aware of students’ understanding, and were better able to motivate their actions and choices of content and strategies. This thesis shows how professional development can bridge the gap between research and teaching practice, and how teachers’ PCK can be developed to improve students’ understanding. / Many complex real-world phenomena can only be understood using models that make the abstract visible and provide explanations, predictions, descriptions, or simplifications. However, research has shown that students have difficulties understanding models used in science education in general, and particularly chemical bonding models. This thesis examines various aspects of the teaching and learning of chemical bonding, and its presentation in textbooks and by teachers. It is shown that the representations used by teachers and in textbooks can cause students to have difficulties in understanding, which teachers were generally unaware of. Teachers rarely justify their choices specifically to overcome students’ difficulties, suggesting that their knowledge of how to teach chemical bonding could be improved. A learning study in which teachers collaboratively explored and reflected on their own teaching practice significantly improved their presentation of chemical bonding, their awareness of students’ understanding, and their ability to justify their choices. Overall, this work shows that there is a gap between research and teaching practice, and that effective ways of incorporating research results into teaching practice are needed to improve teaching and learning in chemistry.

Interactions between electrons determine the structure and properties of matter from molecules to solids. Therefore, the understanding of the electronic structure of molecules will enable us to extract relevant chemical information. In the first part of this thesis, we focus our attention on the analysis of chemical bonding by means of the Electron Localization Function (ELF) and the Domain-Averaged Fermi Hole analysis (DAFH). In the second part, we assess the performance of some indicators of aromaticity by analyzing their advantages and drawbacks. We propose a series of tests based on well-known aromaticity trends that can be applied to evaluate the aromaticity of current and future indicators of aromaticity in both organic and inorganic species. Moreover, we investigate the nature of electron delocalization in both aromatic and antiaromatic systems in the light of Hückel’s (4n + 2) rule. Finally, we analyze the phenomenon of multiple aromaticity in all-metal clusters. / Les interaccions entre electrons determinen l’estructura i propietats de la matèria. Per tant, la comprensió de l’estructura electrònica de les molècules ens permetrà extreure informació química rellevant. En la primera part d’aquesta tesi, centrem la nostra atenció en l’anàlisi de l’enllaç químic per mitjà de la funció de localització electrònica (ELF) i l’anàlisi dels anomenats domain averaged Fermi holes (DAFH). En la segona part, s’avalua el comportament d’alguns indicadors d’aromaticitat analitzant els seus avantatges i inconvenients. Al llarg d’aquesta part, es proposen una sèrie de tests basats en tendències d’aromaticitat conegudes que es poden aplicar per avaluar el comportament dels indicadors actuals en espècies tan orgàniques com inorgàniques. A més a més, s’investiga la naturalesa de la deslocalització d’electrons en sistemes aromàtics i antiaromàtics que segueixen la regla 4n+2 que proposà Hückel. Finalment, analitzem el fenomen de l’aromaticitat múltiple en sistemes metàl•lics

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The aim of this study was to investigate how an experienced chemistry teacher gains and refines her pedagogical content knowledge (PCK) by cooperating with two grade 12 students (age 18) as coteachers while teaching chemical bonding in a grade 10 Upper secondary class. The study has been conducted from a sociocultural perspective, especially Vygotsky’s zone of proximal development (ZPD) (Vygotsky, 1978). Other theoretical concepts and models that has framed this study are Shulman´s Pedagogical content knowledge (PCK) and Pedagogical reasoning and action model (Shulman, 1986, 1987). When analysing the data, Magnusson, Krajcik, and Borko´s (1999) model of PCK and the 2017 Refined consensus model of PCK (Carlson, Daehler, et al., in press) was used. Empirical data was collected by video- and audio recorded lessons, coreflection sessions, coplanning sessions and interviews. During 10 weeks, about 28 hours of video and audio recordings was collected. Selected parts of the material were transcribed and analysed in order to answer two questions: (1) How can chemistry teachers refine their PCK when coteaching together with senior students in an Upper secondary science class? (2) How do Upper secondary senior student coteachers´ conceptual knowledge of representations and chemical bonding shape a teacher’s foundation of personal PCK (pPCK) when teaching chemical bonding in an Upper secondary science class? The results relating to research question one indicates that the coteachers contributed with their own learning experiences to help the teacher understand how students perceive difficult concepts. The coteachers were mediating between the teacher and the students, thus bridging the gap between the teacher and the students’ frames of references. The experienced chemistry teacher improved her understanding of students´ thinking about themselves as learners of chemical bonding. Regarding the second research question, the findings showed that the creative process of reconstructing concepts of chemical bonding in the coplanning sessions meant that these were a useful tool for developing new teaching strategies and to further develop representations such as drama to illustrate chemical bonding. Together, the teacher and student coteachers, constructed a new representation that better illustrated polar covalent bonding. Taken together, these results provide important insights into how the chemistry teacher´s pPCK was refined and how the coteachers contributed to improve instructional strategies.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.

Teaching of chemistry at secondary school level is not always carried out in the most effective way and this is often because teachers do not realise the difficulties experienced by pupils while studying a conceptually challenging topic. The development of a teaching strategy to assist teachers is thus of value. The research questions:  Do focussed intervention questions followed by rapid feedback to pupils foster sound concept formation in chemical bonding?  Is this new teaching method more effective than traditional methods? In this study I have examined the effect of a novel teaching method (referred to as the Targeted Intervention Questioning process) on concept formation during the study of chemical bonding. This study involves action research in secondary school classrooms. The findings from the study are being used to further inform current teaching practice. The teaching method is a set of focused intervention questions administered at relevant stages during the teaching of the topic. Pupils answer these questions with the help of their learning material and are given rapid feedback with an evaluation of their answers. This questioning process is designed to focus pupils’ attention on the relevant concepts and the feedback is to inform pupils of their progress in mastering the topic. The effectiveness of the method was measured using a concept development test. The learning gain in a test group was compared to that of a control group in a quasi-experimental study. This research involves action research as findings will inform practice and practice will change in line with the research findings. Data gathering to ascertain the effectiveness of the teaching method will be through quantitative methods in a quasi-experimental setup. The sample size was approximately 80 learners, divided into the four classes. All teachers use the methods and techniques that they normally use. The learning gain was determined through the use of a concept development test developed by the author (referred to as the Conceptual Test tool). This test tool contained a set of 25 conceptual questions, either requiring selection of a correct answer from a multiple choice selection or requiring a free response answer. The testing tool was piloted using a group of Grade 11 pupils in 2010. The test was then refined and used to measure the effectiveness of the intervention questioning process in 2011. A second run of the intervention process was carried out in 2012 using a slightly modified testing tool. The result of the test group was compared to that of the control group. A Correlation analysis and a Rasch analysis determined the validity of the testing tool. Results from both runs of the intervention process show that the test group has a statistically significant greater learning gain (LG) over the control group. Analysis of answers given by pupils to the intervention questions provided insight into the learning process that was happening. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Science, Mathematics and Technology Education / unrestricted

Chemistry is the study of materials and the changes that materials undergo. One can tune the properties of the known materials and design the novel materials with desired properties knowing what is responsible for the chemical reactivity, structure, and stability of those materials. The unified chemical bonding theory could address all these questions, but we do not have one available yet. The most accepted general theory of chemical bonding was proposed by Lewis in 1916, though Lewis’s theory fails to explain the bonding in materials with delocalized electron density such as sub-nano and nanoclusters, as well as aromatic organic and organometallic molecules. The dissertation presents a set of projects that can be considered the steps towards the development of the unified chemical bonding theory by extending the ideas of Lewis. The dissertation also presents the studies of the properties of multiply charged anions, which tend to undergo Coulomb explosion in the isolated state and release the excess energy stored in them. It is shown how the properties of multiply charged anions can be tuned upon changing the chemical identity of the species or interaction with solvent molecules. Our findings led to the discovery of a new long-lived triply charged anionic species, whose metastability was explained by the existence of a repulsive Coulomb barrier. We also proposed two ways to restore high symmetry of compounds by suppression of the pseudo Jahn-Teller effect, which could lead to the design of new materials with the restored symmetry and therefore the novel properties.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24634号 / 工博第5140号 / 新制||工||1982(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 佐藤 啓文, 教授 佐藤 徹, 教授 松田 建児 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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In this work, chemical bonding models are developed and extended by the aid of the quantum-chemical position-space analysis. The chemical bonding models are then utilized to rationalize and predict the structure and conducting properties of MgAgAs-type and other intermetallic compounds. Additionally, new position-space bonding indicators are developed.