ABSTRACT RESUMO Este trabalho busca oferecer uma breve revisão da literatura acerca da utilização... more ABSTRACT RESUMO Este trabalho busca oferecer uma breve revisão da literatura acerca da utilização de softwares de modelagem molecular no ensino de química nos últimos dez anos, promovendo uma reflexão sobre as possibilidades de utilização destas ferramentas nos currículos de química. Foram pesquisados os termos “modelagem molecular”, “molecular modeling” e “modelaje molecular” nos títulos e resumos dos principais periódicos especializados em ensino de química do Brasil, da América Latina, dos Estados Unidos e da Europa. A modelagem molecular a partir do uso de softwares tem se tornado ferramenta importante para a química profissional, bem como facilitadora na compreensão das propriedades de átomos e moléculas. No entanto, apesar dos esforços de pesquisadores e de fomento governamental, existem muito poucas publicações em pesquisa em educação química sobre modelagem molecular, que possam contribuir para a formação inicial e continuada de professores de química, assim como demais profissionais da área.
O objetivo deste trabalho é mostrar evidências da aquisição de novas representações e de novos ... more O objetivo deste trabalho é mostrar evidências da aquisição de novas representações e de novos drivers por parte de estudantes de química quando utilizam software de modelagem molecular. Neste trabalho, utilizamos referenciais inéditos na educação química: o referencial teórico da Teoria da Mediação Cognitiva em Rede (TMC) e a metodologia de combinar análise de discurso e análise gestual. Os registros usados são os testes escritos (pré e pós) e os vídeos gravados durante entrevista semiestruturada conforme protocolo Report Aloud. Desses vídeos, extraímos os gestos (discurso não verbal), que foram avaliados por análise gestual, e o discurso verbal, que foi avaliado por análise de discurso. Ao final deste recorte, conseguimos mostrar, tanto nos gestos quanto no discurso verbal e na escrita, os indícios da presença dessas novas representações e dos novos drivers que foram construídos a partir da mediação por computador. Por isso, os estudantes demonstraram ter criado uma comp...
Science learning still is, to a great extent, mechanical; and Chemistry learning does not constit... more Science learning still is, to a great extent, mechanical; and Chemistry learning does not constitute a counter example of this undesirable situation. Many reforms recently proposed of re-structuring chemistry curriculum ponder that in order to have a more meaning learning the student must be able to see chemistry as a predictive science made upon a structural analysis of chemical compounds and also to be able to understand chemistry phenomena within the framework of the concept of energy. Hence, the goal of this work is to propose the usage of a didactic sequence, based on using Molecular Modeling techniques and built with Moreira’s model of PMTU for teaching cis/trans stereochemistry. The activity has the objective of performing the conformational analysis of n-butane and the cis/trans isomers of 2-butene. Thus, its intended to offer the opportunity for the student to understand two fundamental concepts: a) that the energy of a molecule is determined by the structure that it assumes in space, and the molecule will assume the structure which has a minimum of energy and b) in case of double bonds, there is a potential barrier which prevents the spontaneous rotation around the double bond, without breaking it. Therefore, we employ the theoretical perspective of Ausubel of a potentially meaningful teaching by means of the integralizating concept of molecular energy of the cis/trans confomers, with such energy obtained by means of molecular modeling. Exploratory results seem to indicate that, if the student is already able to visualize microscopically chemical species, it is possible to reorder his conceptual structure in the field of isomerism by means of a combinatory meaningful learning around the concept of energy.
ABSTRACT This paper is based on the Cognitive Mediation Networks Theory and aims to describe the ... more ABSTRACT This paper is based on the Cognitive Mediation Networks Theory and aims to describe the results of an exploratory experiment in computational chemistry and molecular modeling. Six High School Chemistry students were used as sample and participated in all stages of the research, in which molecular modeling software was used as an external information processing mechanism so that the student can internalize the contents of simulation, the chemical representations shown and acquire new knowledge. In this sense, we aim to answer the following research question: what specific “drivers” are originated by the molecular visualization or by the molecular modeling? The full experimental design included: individual pre-test; individual pre-test interview; computational molecular modeling performed in pairs and approaching conformational analysis of the n-butane molecule and cis/trans stereochemistry from the analysis of the energy involved in the double bonding torsion of cis-2-butene; individual post-test and post test individual interview. The pre and post test interviews were conducted according to the Think Aloud Protocol. All the steps were registered in video. The analysis of the videos were done in order to obtain information about the mental images from gestures. In this paper, we focused in the conformational analysis. In general, it is possible to talk about sensible gains when students appropriate themselves of new ways of representing chemical information after using the software and can relate them to the properties of molecules. From there, the student naturally connects chemical compounds, their properties and the general concept of Energy.
Dipole moment, static dipole polarizability and hyperpolarizability are calculated for MgH with h... more Dipole moment, static dipole polarizability and hyperpolarizability are calculated for MgH with high-order many-body perturbation theory and coupled-cluster methods using large basis sets. At the highest levels, CCSD(T), the calculated values are 0.533 a.u. (dipole moment), 65.3 a.u. (average polarizability), −10.3 a.u. (polarizability anisotropy) and 580.7 a.u. (first hyperpolarizability). The derivatives of the dipole moment and dipole polarizability with respect to the internuclear separation are also calculated. These gradients are used to predict the infrared absorption intensity. Raman scattering activity and Rayleigh and Raman depolarizations of light scattering by diatomic MgH. The cross section for Raman scattering is predicted. The degree of depolarization of the Raman scattered light is found to be very large for natural, planar and circular polarizations.
The ground state of CaC is determined from high-order coupled cluster calculations to be a 3Σ− st... more The ground state of CaC is determined from high-order coupled cluster calculations to be a 3Σ− state with a rotational constant of 9.94 GHz. This state lies close to a 5Σ− state.Lower-order calculations give the 5Σ− state below but at the highest level of calculation, CCSD(T), the 3Σ− state lies about 800 cm−1 below the 5Σ− state. This reproduces the situation of similar diatomics such as B2, BC+, BeC and MgC where similar competition between the 3Σ− and 5Σ− states has been solved in favor of 3Σ− as the ground state. High-order single and double excitations are crucial but further adding triple excitations is decisive to give the proper ordering of these two states. The use of the frozen core approximation does not change this qualitative pattern but gives bond distances that are too long making this approximation somewhat unreliable for predicting the microwave spectrum necessary for a proper identification of this astrophysically important carbide. A broken symmetry spin-contaminated triplet solution is found that lies lowest at every level of calculation considered.
The dipole moment, static dipole polarizability and hyperpolarizability of CaC are calculated usi... more The dipole moment, static dipole polarizability and hyperpolarizability of CaC are calculated using high-level many-body perturbation theory and coupled-cluster methods with large basis sets. These moments and the corresponding gradients are used to predict the Rayleigh and Raman activities. The effects of the electron correlation on the calculated properties are discussed. At the highest level, CCSD(T), the dipole moment is 1.6 a.u. (4.1 D), and the average dipole polarizability is 111.5 a.u. (16.52 Å3) with a large and negative anisotropy of 7.4 a.u. (1.1 Å3). The average dipole hyperpolarizability is 1720.0 a.u. (14.862×10−30 cm5 esu−1). Analysis of the polarizability gradient indicates a very large Raman depolarization of the light scattered by CaC with the depolarization being 96%, 93% and 77% for natural, planar and circular polarizations, respectively.
ABSTRACT RESUMO Este trabalho busca oferecer uma breve revisão da literatura acerca da utilização... more ABSTRACT RESUMO Este trabalho busca oferecer uma breve revisão da literatura acerca da utilização de softwares de modelagem molecular no ensino de química nos últimos dez anos, promovendo uma reflexão sobre as possibilidades de utilização destas ferramentas nos currículos de química. Foram pesquisados os termos “modelagem molecular”, “molecular modeling” e “modelaje molecular” nos títulos e resumos dos principais periódicos especializados em ensino de química do Brasil, da América Latina, dos Estados Unidos e da Europa. A modelagem molecular a partir do uso de softwares tem se tornado ferramenta importante para a química profissional, bem como facilitadora na compreensão das propriedades de átomos e moléculas. No entanto, apesar dos esforços de pesquisadores e de fomento governamental, existem muito poucas publicações em pesquisa em educação química sobre modelagem molecular, que possam contribuir para a formação inicial e continuada de professores de química, assim como demais profissionais da área.
O objetivo deste trabalho é mostrar evidências da aquisição de novas representações e de novos ... more O objetivo deste trabalho é mostrar evidências da aquisição de novas representações e de novos drivers por parte de estudantes de química quando utilizam software de modelagem molecular. Neste trabalho, utilizamos referenciais inéditos na educação química: o referencial teórico da Teoria da Mediação Cognitiva em Rede (TMC) e a metodologia de combinar análise de discurso e análise gestual. Os registros usados são os testes escritos (pré e pós) e os vídeos gravados durante entrevista semiestruturada conforme protocolo Report Aloud. Desses vídeos, extraímos os gestos (discurso não verbal), que foram avaliados por análise gestual, e o discurso verbal, que foi avaliado por análise de discurso. Ao final deste recorte, conseguimos mostrar, tanto nos gestos quanto no discurso verbal e na escrita, os indícios da presença dessas novas representações e dos novos drivers que foram construídos a partir da mediação por computador. Por isso, os estudantes demonstraram ter criado uma comp...
Science learning still is, to a great extent, mechanical; and Chemistry learning does not constit... more Science learning still is, to a great extent, mechanical; and Chemistry learning does not constitute a counter example of this undesirable situation. Many reforms recently proposed of re-structuring chemistry curriculum ponder that in order to have a more meaning learning the student must be able to see chemistry as a predictive science made upon a structural analysis of chemical compounds and also to be able to understand chemistry phenomena within the framework of the concept of energy. Hence, the goal of this work is to propose the usage of a didactic sequence, based on using Molecular Modeling techniques and built with Moreira’s model of PMTU for teaching cis/trans stereochemistry. The activity has the objective of performing the conformational analysis of n-butane and the cis/trans isomers of 2-butene. Thus, its intended to offer the opportunity for the student to understand two fundamental concepts: a) that the energy of a molecule is determined by the structure that it assumes in space, and the molecule will assume the structure which has a minimum of energy and b) in case of double bonds, there is a potential barrier which prevents the spontaneous rotation around the double bond, without breaking it. Therefore, we employ the theoretical perspective of Ausubel of a potentially meaningful teaching by means of the integralizating concept of molecular energy of the cis/trans confomers, with such energy obtained by means of molecular modeling. Exploratory results seem to indicate that, if the student is already able to visualize microscopically chemical species, it is possible to reorder his conceptual structure in the field of isomerism by means of a combinatory meaningful learning around the concept of energy.
ABSTRACT This paper is based on the Cognitive Mediation Networks Theory and aims to describe the ... more ABSTRACT This paper is based on the Cognitive Mediation Networks Theory and aims to describe the results of an exploratory experiment in computational chemistry and molecular modeling. Six High School Chemistry students were used as sample and participated in all stages of the research, in which molecular modeling software was used as an external information processing mechanism so that the student can internalize the contents of simulation, the chemical representations shown and acquire new knowledge. In this sense, we aim to answer the following research question: what specific “drivers” are originated by the molecular visualization or by the molecular modeling? The full experimental design included: individual pre-test; individual pre-test interview; computational molecular modeling performed in pairs and approaching conformational analysis of the n-butane molecule and cis/trans stereochemistry from the analysis of the energy involved in the double bonding torsion of cis-2-butene; individual post-test and post test individual interview. The pre and post test interviews were conducted according to the Think Aloud Protocol. All the steps were registered in video. The analysis of the videos were done in order to obtain information about the mental images from gestures. In this paper, we focused in the conformational analysis. In general, it is possible to talk about sensible gains when students appropriate themselves of new ways of representing chemical information after using the software and can relate them to the properties of molecules. From there, the student naturally connects chemical compounds, their properties and the general concept of Energy.
Dipole moment, static dipole polarizability and hyperpolarizability are calculated for MgH with h... more Dipole moment, static dipole polarizability and hyperpolarizability are calculated for MgH with high-order many-body perturbation theory and coupled-cluster methods using large basis sets. At the highest levels, CCSD(T), the calculated values are 0.533 a.u. (dipole moment), 65.3 a.u. (average polarizability), −10.3 a.u. (polarizability anisotropy) and 580.7 a.u. (first hyperpolarizability). The derivatives of the dipole moment and dipole polarizability with respect to the internuclear separation are also calculated. These gradients are used to predict the infrared absorption intensity. Raman scattering activity and Rayleigh and Raman depolarizations of light scattering by diatomic MgH. The cross section for Raman scattering is predicted. The degree of depolarization of the Raman scattered light is found to be very large for natural, planar and circular polarizations.
The ground state of CaC is determined from high-order coupled cluster calculations to be a 3Σ− st... more The ground state of CaC is determined from high-order coupled cluster calculations to be a 3Σ− state with a rotational constant of 9.94 GHz. This state lies close to a 5Σ− state.Lower-order calculations give the 5Σ− state below but at the highest level of calculation, CCSD(T), the 3Σ− state lies about 800 cm−1 below the 5Σ− state. This reproduces the situation of similar diatomics such as B2, BC+, BeC and MgC where similar competition between the 3Σ− and 5Σ− states has been solved in favor of 3Σ− as the ground state. High-order single and double excitations are crucial but further adding triple excitations is decisive to give the proper ordering of these two states. The use of the frozen core approximation does not change this qualitative pattern but gives bond distances that are too long making this approximation somewhat unreliable for predicting the microwave spectrum necessary for a proper identification of this astrophysically important carbide. A broken symmetry spin-contaminated triplet solution is found that lies lowest at every level of calculation considered.
The dipole moment, static dipole polarizability and hyperpolarizability of CaC are calculated usi... more The dipole moment, static dipole polarizability and hyperpolarizability of CaC are calculated using high-level many-body perturbation theory and coupled-cluster methods with large basis sets. These moments and the corresponding gradients are used to predict the Rayleigh and Raman activities. The effects of the electron correlation on the calculated properties are discussed. At the highest level, CCSD(T), the dipole moment is 1.6 a.u. (4.1 D), and the average dipole polarizability is 111.5 a.u. (16.52 Å3) with a large and negative anisotropy of 7.4 a.u. (1.1 Å3). The average dipole hyperpolarizability is 1720.0 a.u. (14.862×10−30 cm5 esu−1). Analysis of the polarizability gradient indicates a very large Raman depolarization of the light scattered by CaC with the depolarization being 96%, 93% and 77% for natural, planar and circular polarizations, respectively.
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