Argumentar para aprender ligações químicas: contribuições de uma atividade investigativa

A utilização de regras para explicar a formação das ligações químicas em detrimento de uma abordagem em termos energéticos tem sido identificada no ensino e em muitos livros didáticos. Tal fato dificulta o entendimento desse tema, pois não fornece uma justificativa satisfatória para a formação e estabilidade das substâncias. Uma proposta de atividade investigativa é apresentada e discutida neste trabalho tendo em vista esse aspecto do Ensino de Química e as possíveis contribuições da argumentação para a aprendizagem do conteúdo e de processos da ciência. Esta atividade visa favorecer o entendimento das ligações químicas a partir de aspectos energéticos envolvidos na formação de substâncias e associados à estabilidade destas em relação aos átomos isolados porque contribui para a integração entre os níveis macroscópico e submicroscópico da matéria. A atividade possibilita aos alunos, além de aprender o conteúdo mencionado, elaborar argumentos, contrapor e avaliar os pontos de vista que emergem ao longo da mesma e trabalhar com justificativas e evidências, bem como diferenciá-los num argument

Elucidating the Influence of the Activation Energy on Reaction Rates by Simulations Based on a Simple Particle Model

An application for visualizing the dynamic properties of an equimolar binary mixture of isotropic reactive particles is presented. By introducing a user selectable choice for the activation energy, the application is useful to demonstrate qualitatively that the reaction rate depends on the above choice and on temperature. The application is based on a 2D realistic dynamic model where atoms move because of their thermal energies and the trajectories are determined by solving numerically Newton’s laws according to a Molecular Dynamics (MD) scheme. Collisions are monitored as time progresses, and every time the collision energy is larger than the selected activation energy, a reactive event occurs. By examining the time evolution of the configurations, it is possible to observe that the number of reactive collisions is always smaller than the total number of collisions. However, the number of reactive events increases on raising the temperature and/or by decreasing the activation energy. The above observations, as well as more quantitative analyses of the simulation data, are useful in elucidating the connections existing among particle kinetic energy, temperature, and activation energy of the reaction. The application can be used at different levels of detail and in different instruction levels. Qualitative visual observations of the progress of the reaction are suitable at all levels of instruction. Systematic investigations on the effect of changes of temperature and activation energy, suitable for senior high school and college courses and useful to gain insight into kinetic models and Arrhenius’ law, are also reported

Phylogenomics reveals the history of host use in mosquitoes

Mosquitoes have profoundly affected human history and continue to threaten human health through the transmission of a diverse array of pathogens. The phylogeny of mosquitoes has remained poorly characterized due to difficulty in taxonomic sampling and limited availability of genomic data beyond the most important vector species. Here, we used phylogenomic analysis of 709 single copy ortholog groups from 256 mosquito species to produce a strongly supported phylogeny that resolves the position of the major disease vector species and the major mosquito lineages. Our analyses support an origin of mosquitoes in the early Triassic (217 MYA [highest posterior density region: 188–250 MYA]), considerably older than previous estimates. Moreover, we utilize an extensive database of host associations for mosquitoes to show that mosquitoes have shifted to feeding upon the blood of mammals numerous times, and that mosquito diversification and host-use patterns within major lineages appear to coincide in earth history both with major continental drift events and with the diversification of vertebrate classes. © 2023, Springer Nature Limited