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Esta dissertação faz uma análise da abordagem do conceito de valência em livros didáticos de química geral para nível superior publicados nos EUA ao longo das primeiras décadas do século XX. Para tanto, foi feito um estudo de caso histórico a respeito do desenvolvimento do conceito de valência no final do século XIX e início do século XX, no qual se observou a influência de duas teorias sobre a combinação dos elementos: a teoria dos tipos e a teoria dos radicais. Outros pontos de destaque no caso histórico foram o envolvimento de vários cientistas, de vários países, e a relação do conceito de valência com os estudos sobre ligação, periodicidade e estrutura química, além de mudanças na nomenclatura e notação utilizadas. Num segundo momento, investigou-se a presença do conceito de valência nos livros didáticos selecionados, buscando uma análise qualitativa do material, tendo como referencial a análise textual discursiva. Os critérios de análise incluem: localização do assunto no livro, a nomenclatura e a notação utilizada, a definição fornecida e se ela está atrelada a alguma determinação histórica, matemática ou experimental, a presença do contexto histórico e do desenvolvimento do conceito ao longo dos anos, quais assuntos se apresentam correlacionados e quais os usos e aplicações dados à valência. Observou-se nos livros: a ausência de discussões mais aprofundadas a respeito da história da ciência; a grande importância dada pelos autores ao conceito de valência; a existência de um período de transição entre o conceito clássico e o eletrônico, ocorrido pouco tempo depois da construção do conceito eletrônico pelos cientistas; e uma mudança no enfoque da ciência química apresentada nos livros, os quais gradativamente deixam de reconhecer a existência de incertezas e lacunas no conhecimento químico. / This dissertation analyzes the approaches to the concept of valence in university-level general chemistry textbooks published in the USA throughout the first decades of the twentieth century. A historical case study about the development of the concept of valence in late nineteenth and early twentieth century is presented. It is shown that the concept of valence emerged from two theories on the combination of elements: the theory of types and the theory of radicals. Other important points from the historical case study were the involvement of several scientists from various countries and the relationship between the concept of valence and studies on chemical bonding, periodicity and chemical structure. Changes in nomenclature and notation for valence were also noted. In a second moment, the presence of the concept of valence in selected textbooks was investigated, by means of a qualitative analysis based on discursive textual analysis. The criteria for analysis included: location of the subject in the textbook; nomenclature and notation used; definition provided and whether it is linked to some historical, mathematical or experimental method of determination; presence of the historical context and the development of the concept over the years; which subjects are related to valence; and which uses and applications were given to valence in the textbooks. The main results of such analysis include: the absence of in-depth discussions about the history of science; the importance given to the concept of valence by the authors; the existence of a transition period from the classical to the electronic concept of valence, which occurred shortly after the construction of the electronic concept by scientists; and a shift in the focus of chemical science presented in the textbooks, which gradually fail to recognize the existence of uncertainties and gaps in chemical knowledge.

Esta dissertação faz uma análise da abordagem do conceito de valência em livros didáticos de química geral para nível superior publicados nos EUA ao longo das primeiras décadas do século XX. Para tanto, foi feito um estudo de caso histórico a respeito do desenvolvimento do conceito de valência no final do século XIX e início do século XX, no qual se observou a influência de duas teorias sobre a combinação dos elementos: a teoria dos tipos e a teoria dos radicais. Outros pontos de destaque no caso histórico foram o envolvimento de vários cientistas, de vários países, e a relação do conceito de valência com os estudos sobre ligação, periodicidade e estrutura química, além de mudanças na nomenclatura e notação utilizadas. Num segundo momento, investigou-se a presença do conceito de valência nos livros didáticos selecionados, buscando uma análise qualitativa do material, tendo como referencial a análise textual discursiva. Os critérios de análise incluem: localização do assunto no livro, a nomenclatura e a notação utilizada, a definição fornecida e se ela está atrelada a alguma determinação histórica, matemática ou experimental, a presença do contexto histórico e do desenvolvimento do conceito ao longo dos anos, quais assuntos se apresentam correlacionados e quais os usos e aplicações dados à valência. Observou-se nos livros: a ausência de discussões mais aprofundadas a respeito da história da ciência; a grande importância dada pelos autores ao conceito de valência; a existência de um período de transição entre o conceito clássico e o eletrônico, ocorrido pouco tempo depois da construção do conceito eletrônico pelos cientistas; e uma mudança no enfoque da ciência química apresentada nos livros, os quais gradativamente deixam de reconhecer a existência de incertezas e lacunas no conhecimento químico. / This dissertation analyzes the approaches to the concept of valence in university-level general chemistry textbooks published in the USA throughout the first decades of the twentieth century. A historical case study about the development of the concept of valence in late nineteenth and early twentieth century is presented. It is shown that the concept of valence emerged from two theories on the combination of elements: the theory of types and the theory of radicals. Other important points from the historical case study were the involvement of several scientists from various countries and the relationship between the concept of valence and studies on chemical bonding, periodicity and chemical structure. Changes in nomenclature and notation for valence were also noted. In a second moment, the presence of the concept of valence in selected textbooks was investigated, by means of a qualitative analysis based on discursive textual analysis. The criteria for analysis included: location of the subject in the textbook; nomenclature and notation used; definition provided and whether it is linked to some historical, mathematical or experimental method of determination; presence of the historical context and the development of the concept over the years; which subjects are related to valence; and which uses and applications were given to valence in the textbooks. The main results of such analysis include: the absence of in-depth discussions about the history of science; the importance given to the concept of valence by the authors; the existence of a transition period from the classical to the electronic concept of valence, which occurred shortly after the construction of the electronic concept by scientists; and a shift in the focus of chemical science presented in the textbooks, which gradually fail to recognize the existence of uncertainties and gaps in chemical knowledge.

Orientador: Jose de Alencar Simoni / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T19:19:13Z (GMT). No. of bitstreams: 1 Duarte_AlineEiras_M.pdf: 1068677 bytes, checksum: 59b0dbfa7366f507ed4f00586382d731 (MD5) Previous issue date: 2007 / Resumo: Este trabalho propõe possíveis alterações em procedimentos experimentais de química geral envolvendo mudanças de materiais, reagentes, quantidades e concentrações de soluções, para a redução de custos e resíduos produzidos em laboratórios de ensino. Os roteiros experimentais estudados fazem parte da disciplina de Química Geral Experimental (QG-102), ministrada no Instituto de Química da Universidade Estadual de Campinas (UNICAMP), no 2° semestre de 2005 e 1° semestre de 2006. Durante esses dois semestres os alunos foram observados no desenvolvimento de suas aulas.Diante das observações, modificações foram propostas em cinco dos doze experimentos trabalhados e novos materiais foram criados, na intenção de preservar ou melhorar os aspectos didáticos dos experimentos, os resultados obtidos e o processo de aprendizagem. Alguns dos experimentos modificados reduzem em até vinte vezes a quantidade de reagentes, a quantidade de resíduos produzidos, o tempo de realização do experimento, energia elétrica e água para a limpeza dos materiais, sem comprometer os objetivos didáticos e, em alguns casos, melhorando os resultados obtidos e a compreensão dos conceitos envolvidos no experimento. Os novos roteiros experimentais foram descritos neste trabalho e aplicados para alunos ingressantes no 1° semestre de 2007, na mesma disciplina, com sucesso. Embora não avaliadas sistematicamente, as modificações propostas agradaram aos alunos e demonstraram que a preocupação com a geração e tratamento de resíduos foi despertada nos mesmos. / Abstract: This work shows possible changes introduced in experiments procedures of general chemistry involving the modification of educational materials, reagents, and solutions amount and/or concentrations, in order to diminish cost and residues. The modified experimental procedures suggested for disciplines of Laboratory of General Chemistry at Campinas State University, were conceived by observing, during two semesters, the students' pratical work at the laboratory. The aim of this project is to create new educational materials that present the same didactic performance of the conventional experimental procedures. In many respects the utilization of these new educational materials or procedures lead to the achievement of better experimental results and improved the students learning process. The new experimental procedures reduced by 20 times the amount of used reagents, and also reduced the amount of generated residues as well as the cleaning materials and energy. This work also describes new experimental procedures that were already effectively applied during experimental classes. Experiments procedures reducing by 20 times the reagent amounts, classified as micro scale, resulted in short times to carry on the experimental work, allowing free time for experimental reports and theoretical studies. The modifications proposed did not show any loss regarding the didactics purposes of the experiments. Even though not systematically evaluated, the students appreciated the modifications proposed and were concerned residue generations and managements. / Mestrado / Físico-Química / Mestre em Química

Doctor Of Philosophy / Department of Chemistry / Christer Aakeröy / Crystal engineering, or non-covalent synthesis in the solid state, requires an understanding of intermolecular forces, and the hydrogen bond has become a reliable non-covalent tool in the construction of supramolecular architectures. In the same way that synthetic chemists refer to a “yield” to quantify a desired product, crystal engineers typically determine the successful formation of a supramolecular product according to the frequency or occurrence of preferred intermolecular interactions between molecules under certain reaction conditions, thus, the supramolecular yield. These non-covalent reactions can be effectively carried out using supramolecular reagents (SR’s). A family of ditopic bis-imidazol-1-yl/benzimidazol-1-yl compounds were synthesized and used as SR’s in combination with a variety of dicarboxylic acids to produce binary solids in 100% yield through the primary acid···imidazol-1-yl/benzimidazol-1-yl synthons even in the presence of potentially disruptive intermolecular interactions. We furthermore noted that secondary C–H···O interactions within and between 1-D chains were of equal structural importance based upon an analysis of the metrics displayed by these interactions. The use of these SR’s as ligands with neutrally charged metal complexes was also investigated. SR’s containing benzimidazol-1-yl and carboxamide moieties were synthesized and combined with two different carboxylic acids to make ternary solids through acid···benzimidazol-1-yl and carboxamide···acid hydrogen bonds using a hierarchical approach – the best donor-best acceptor, second best donor-second best acceptor guidelines. These SR’s were also employed as ligands for high-yielding syntheses of linear metal complexes where neighboring complexes are linked via carboxamide···carboxamide hydrogen bonds. Asymmetric SR’s possessing two different N-heterocycles were synthesized and employed in the construction of ternary supermolecules with a high degree of structural selectivity and specificity when introduced to two different carboxylic acids. The stronger acid interacts at the more basic site, while the weaker acid hydrogen-bonds with the less basic nitrogen atom. Finally, an SR containing three different binding sites was designed and synthesized with the aim of producing quaternary co-crystals.

This study uses the ACS first-term general chemistry exam to determine if one curriculum approach is more effective in increasing student success than the other based on their performance on the ACS exam. Two chemistry curriculum approaches were evaluated in this study; the traditional curriculum (TC) and the Atoms First (AF) approach. The sample population was first-semester general chemistry students at Collin College in Frisco, TX. An independent sample t-test was used to determine if there were differences in overall performance between the two curriculum approaches on two different versions of the ACS exam. The results from this study show that AF approach may be a better alternative to the TC approach as they performed statistically significantly better on the 2005 exam version. Factor analysis was used to determine if there were differences between the two curriculum approaches by topic on the ACS exam. Eight different topics were chosen based on topics listed on the ACS Examinations Institute Website. The AF students performed better at a statistically significant level than the TC students on the topics of descriptive chemistry and periodicity, molecular structure, and stoichiometry. Item response theory was used to determine the chemistry content misconceptions held by the students taught under both curriculum approaches. It was determined that for both curriculum groups the same misconceptions as determined by the Zcrit values persisted.

<p>Student-centered pedagogies have become increasingly popular in higher education. Research on flipped learning, in particular, has shown that collaborative problem-solving environments are able to better support effective learning than lecture alone. However, the effects of this format on students’ interests and motivations in chemistry remain unknown. For this study, students and graduate teaching assistants who participated in a flipped learning, second-semester general chemistry course were selected to participate in a focus group discussion and individual interviews that explored their experiences and perceptions of the features of the course (affordances) that supported and thwarted their sense of motivation.</p><p>This phenomenographic study mapped eight students’ experiences of the course and used qualitative data from interviews with the graduate teaching assistants (TAs) to compare and contrast with students’ claims. Self-determination theory was used to frame these experiences and the results were discussed using other relevant theories of motivation, including, but not limited to expectancy-value theory and achievement goal theories.</p><p></p><p>It was found that there are several features of the course that support students’ motivations according to the basic psychological needs of relatedness, autonomy, and competency in self-determination theory. The study also revealed many features of the course that thwarted students’ motivations. Features that students described as motivating left them feeling connected to their peers and other agents in the course, capable of efficiently interacting with their environments as a result of the course tasks, and a sense that their performance was related to their efforts. Features that students’ described as demotivating left them feeling helpless, incompetent, alone, and without a sense of control over their performance in the course.</p><p>The results of this study shed light on students’ perceptions of the environment in a flipped learning chemistry course. These findings can be used to improve students’ experiences, and consequently their motivation when taking a flipped learning chemistry course. Specific assertions developed from these results and recommendations for these improvements are further discussed.</p>

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Improved metacognitive thinking can impact student’s success. A novel homework method called Solved Problem Analysis (SPA) was developed with the intent to foster metacognitive thinking. It was hypothesized that supporting metacognition would lead to increased performance on in-class exams and the ACS final exam. Results showed SPA was effective at increasing performance on both. In order to more directly measure student’s metacognitive thinking, a knowledge survey was implemented to measure the difference between student’s perceived understanding of the material and their actual performance. These knowledge surveys showed students were able to predict how much of the material they understood. Monitoring one’s thinking is an important part of metacognition. This cognitive monitoring can be mimicked in study group interactions. The effect of self-assembled study groups on student exam performance was also examined, where it was found that self-assembled study groups did not effectively increase exam performance.

The science-major General Chemistry sequence offered at the University of Houston has been investigated with respect to the effectiveness of recent incorporation of various levels of computer technology. As part of this investigation, questionnaire responses, student evaluations and grade averages and distributions from up to the last ten years have been analyzed and compared. Increased use of web-based material is both popular and effective, particularly with respect to providing extra information and supplemental questions. Instructor contact via e-mail is also well-received. Both uses of technology should be encouraged. In contrast, electronic classroom presentation is less popular. While initial use may lead to improved grades and retention, these levels decrease quickly, possibly due to a reduction in instructor spontaneity.