模型素材差异对初中生“分子和原子”概念认知水平影响的观测工具设计

模型是为了理解事物而对事物做出的一种抽象，不同模型对学生关于同一概念的认知理解会产生不同的影响。以初三化学“分子和原子”章节为载体，设计了可以观测模型素材差异对初中生“分子和原子”概念认知水平影响的3份工具。     

模型素材差异对初中生“分子和原子”概念认知水平的影响

以“分子和原子”3堂同课异构课为载体,阐述了模型素材差异对学生概念认知水平的影响。通过控制变量法以及采用“前测问卷-课堂授课-课后测试-访谈问卷”的研究方法,得出以下结论:(1)教师采用教育的类比模型进行教学更有利于学生对“分子”“原子”概念的建构,采用图像和符号模型进行教学更有利于学生“从微观角度解释物理变化、化学变化”概念的建构。(2)从知识来看,使用图像和符号模型组织教学整体来说能帮助学生对“分子和原子”的概念建构到更高水平。从建模能力来看,使用图像与符号模型教学更能培养学生的图像识别与描述能力,使用教育的类比模型教学更能培养学生的动手能力和空间建模能力。(3)同时使用2种模型进行教学时学生对概念建构的程度最好,概念建构所达到的水平也更高。同时,研究对教材的编写、教师的教以及学生的学提出了一些建议。     

用活动表现评价深化学生对分子和原子概念的认识

活动表现评价是通过学生在一个真实的活动情境中的行为表现,对学生在知识、技能、过程、方法、情感、态度及价值观等方面的水平做出评判的评价方法。在“分子和原子”教学过程中,依据教学目标运用实验探究、模型分析或图示表达等多种活动表现评价方法,深化学生对分子原子概念的认识。     

“基于尺度再探原子结构”的教学设计与实施*

教学设计阶段首先进行原子结构学科理解研究,通过阐释如何基于原子核认识原子的构成,如何基于核外电子运动认识原子的结构这2个本原性问题,对主题大概念原子结构模型进行本原性、结构化地理解。继而从教学目标和教学思路设计、教学实施过程、学生收获、教师反思及专家评价等方面,系统地呈现了基于学科理解的“素养为本”“基于尺度再探原子结构”课堂教学的研究过程。     

对结晶化学教学中某些常见问题的讨论

结晶化学主要涉及晶体在原子水平上的结构理论,它研究晶体的组成、结构、性能及其相互关系和规律。晶体结构的教学是结晶化学教学中的主要任务之一,它对于培养学生灵活运用化学知识的能力极为重要。鉴于目前某些教科书或文章中的一些提法不太确切,加之学生学习这部分内容时对某些概念的理解颇感困难,本文拟对下面二个问题作一粗浅讨论。一、NaCl晶体结构是否可看成由一套Na+的面心立方点阵和一套Cl-的面心立方点阵互相穿插组合向成。产生这个问题的原因在于对晶体的点阵概念认识模糊。晶体是原子、离子或分子在三维空间周期地重复排列构成的。     

基于认识模型建构的“元素周期律·表”教学研究

在梳理已有研究并明确学生关于元素周期律·表学习问题的基础上,挖掘学生问题产生的根源,将元素周期律·表的教学定位于促进学生对于元素及物质的认识发展,并进一步提出了中学生对于元素及物质的认识发展层级,通过在高中化学必修2进行元素周期律·表复习课的教学设计与实践,提出了中学生关于元素及物质的认识模型,从单元整体设计、教学策略选择、教学主要环节的梳理与改进、教学效果的检验4个方面,进一步论证了中学阶段关于元素及物质的认识模型对帮助学生进行系统思维,促进学生认识发展所起的作用。     

有机链状分子的定域分子轨道的研究

利用Foster-Boys定域化程序和STO-3G ab initio方法,对含有C、H、O、N原子的100多个有机链状分子进行了研究,得到定域分子轨道能量及其相互作用参数。应用这些参数和定域分子轨道模型,对于众多的含有C、H、O、N原子的有机链状分子,可得到相应的正则分子轨道能量及其与定域分子轨道的关系。以此预测它们的电离能,结果与实验值符合较好。     

高中生“芳香烃”心智模型的测评及其教学启示*

采用二阶式纸笔测验以及半结构化访谈法对高中生持有的“芳香烃”心智模型进行测评,并重点分析了学生建构的与“芳香烃和苯的同系物的概念”“芳香烃的结构”“苯及其同系物的化学性质”等概念群相关的缺陷模型。研究发现学生建构的有关“芳香烃”缺陷模型包括3大类共计11种;学生对有机物空间结构的想象力和建构能力较为薄弱;学生对“有机化合物结构内基团之间相互作用对其化学性质的影响”认识不足,“性质结构”模型不完善;学生建构的有机化学的心智模型尚不具备整体性。     

针对高中生有关物质结构的前科学概念的探查研究

1　引言现代化学教育的着眼点不是看学生学会了哪些化学知识 ,而是帮助学生理解化学的核心概念 ,形成化学认识 ,发展对物质及其变化的解释力。化学概念众多 ,哪些是核心概念呢 ?目前普遍认为化学核心概念至少包括以下几类 :(1)微粒———原子、分子、离子 ;(2 )微粒间的作用———化学键 ;(3)分子构型———三维化学 ;(4)动力学理论 ;(5 )化学反应 ;(6 )现代化学的新进展。这 6类概念均与对物质结构的微观认识相联系 ,可见使学生形成正确的物质结构微观认识是很重要的任务。然而 ,由于微观世界看不到 ,摸不着 ,学生对微观世界的认识也就形式…     

高中生化学可逆反应心智模式的诊断和分析

提出完整的可逆反应心智模式分析框架,通过纸笔测验诊断高二理科实验班、理科平行班、文科班共369名学生在高一化学必修模块建立的可逆反应心智模式。研究发现,3个学生群体均主要具有可逆反应是双向变化的心智模式,出现多种不完善、不科学的心智模式,对可逆反应具有科学的综合认识的学生比例不高。最后,对研究结果进行讨论,对教学实践和后续研究提出建议。     

The Atom in the Chemistry Curriculum: Fundamental Concept, Teaching Model or Epistemological Obstacle?

Research into learners' ideas aboutscience suggests that school and collegestudents often hold alternative conceptionsabout `the atom'. This paper discusses whylearners acquire ideas about atoms which areincompatible with the modern scientificunderstanding. It is suggested that learners'alternative ideas derive – at least in part –from the way ideas about atoms are presented inthe school and college curriculum. Inparticular, it is argued that the atomicconcept met in science education is anincoherent hybrid of historical models, andthat this explains why learners commonlyattribute to atoms properties (such as beingthe constituent particles of all substances, orof being indivisible and conserved inreactions) that more correctly belong to otherentities (such as molecules or sub-atomicparticles). Bachelard suggested that archaicscientific ideas act as `epistemologicalobstacles', and here it is argued thatanachronistic notions of the atom survive inthe chemistry curriculum. These conceptualfossils encourage learners to develop an`atomic ontology' (granting atoms `ontologicalpriority' in the molecular model of matter); tomake the `assumption of initial atomicity' whenconsidering chemical reactions; and to developan explanatory framework to rationalisechemical reactions which is based on thedesirability of full electron shells. Theseideas then act as impediments to thedevelopment of a modern chemical perspective onthe structure of matter, and an appreciation ofthe nature of chemical changes at the molecularlevel.     

Sun Exposure at School

There is strong evidence that sun exposure during childhood and adolescence plays an important role in the etiology of skin cancer, in particular cutaneous melanoma. Between the age of 6 and 18, most children and adolescents will spend around 200 days per year at school and may receive a substantial fraction of their daily total solar ultraviolet radiation (UVR) exposure while at school. This study estimated the average daily erythemally effective dose of 70 grade 8 students from a high school in Townsville during 5 school days in July 1998. Through UV measurements of shade locations at the school and a combination of frequency counts and a questionnaire of grade 8 students, it was possible to determine the fraction of solar UVR reaching under the shade structures during lunch breaks and routine outdoor activities. Also, a routinely operating UV-Biometer provided the annual variation of the daily dose that was used to calculate exposure levels for the 70 students. Our results suggest that up to 47% of the daily total dose fell within the time periods where students were outdoors during school hours. For students not seeking shade structures during the breaks (which usually was the case when involved in sport activities such as basketball or soccer), the average daily dose could have been as high as 14 SED (standard erythemal dose). Using results from the questionnaire of 70 grade 8 students, their average annual dose while at school was 414 SED or 2 SED per school day. However, the distribution of average daily erythemal effective dose per grade 8 student over the whole year showed that on 31% of all school days in 1998, this dose was exceeded. Because most previous attempts to change arguably poor sun-protective behavior of young Australian children and adolescents at school showed little success, one way of decreasing the amount of harmful UVR reaching unprotected skin is the more careful design of shade structures at schools.     

Minimalist explicit solvation models for surface loops in proteins

We have performed molecular dynamics simulations of protein surface loops solvated by explicit water, where a prime focus of the study is the small numbers (e.g., ~100) of explicit water molecules employed. The models include only part of the protein (typically 500 - 1000 atoms), and the water molecules are restricted to a region surrounding the loop. In this study, the number of water molecules (N(w)) is systematically varied, and convergence with large N(w) is monitored to reveal N(w)(min), the minimum number required for the loop to exhibit realistic (fully hydrated) behavior. We have also studied protein surface coverage, as well as diffusion and residence times for water molecules as a function of N(w). A number of other modeling parameters are also tested. These include the number of environmental protein atoms explicitly considered in the model, as well as two ways to constrain the water molecules to the vicinity of the loop (where we find one of these methods to perform better when N(w) is small). The results (for RMSD and its fluctuations for four loops) are further compared to much larger, fully solvated systems (using ~10,000 water molecules under periodic boundary conditions and Ewald electrostatics), and to results for the GBSA implicit solvation model. We find that the loop backbone can stabilize with a surprisingly small number of water molecules (as low as 5 molecules per amino acid residue). The side chains of the loop require somewhat larger N(w), where the atomic fluctuations become too small if N(w) is further reduced. Thus, in general, we find adequate hydration to occur at roughly 12 water molecules per residue. This is an important result, because at this hydration level, computational times are comparable to those required for GBSA. Therefore these "minimalist explicit models" can provide a viable and potentially more accurate alternative. The importance of protein loop modeling is discussed in the context of these, and other, loop models, along with other challenges including the relevance of appropriate free energy simulation methodology for assessment of conformational stability.     

Simple bond length dependence: a correspondence between reactive fluid theories

Two elementary models of reactive fluids are examined, the first being a standard construction assuming molecular dissociation at infinite separation; the second is an open mixture of nondissociative molecules and free atoms in which the densities of free atoms and molecules are coupled. An approximation to the density of molecules, to low order in site density, is derived in terms of the classical associating fluid theory variously described by Wertheim [J. Chem. Phys. 87, 7323 (1987)] and Stell [Physica A 231, 1 (1996)]. The results are derived for a fluid of dimerizing hard spheres, and predict dependence of the molecular density on the total site density, the hard sphere diameter, and the bond length of the dimer. The results for the two reactive models are shown to be qualitatively similar, and lead to equivalent predictions of the molecular density for the infinitely short and infinitely long bond lengths.     

Influence of confinement on atomic and molecular reactivity indicators in DFT

Spatial confinement of atoms and molecules influences electronic structures, energy spectra, and chemical reactivity. A simple potential barrier approach involving a single parameter is used to study confinement in both atoms and molecules, focusing on the reactivity of the systems through the HOMO-LUMO gap, which is linked to the global chemical hardness. Both atoms and molecules are shown to respond with an increase in hardness when confined. The results suggest that previous observations of a HOMO-LUMO gap decrease for guest molecules in zeolites cannot be assigned exclusively to electron confinement.     

Modeling of isospecific Ti sites in MgCl2 supported heterogeneous Ziegler-Natta catalysts

New models for the steric environment of Ti isospecific polymerization sites for poly(propylene) on MgCl₂ microcrystals are proposed. They directly involve a donor molecule in order to obtain isospecific activable Ti atoms otherwise belonging to isolated adsorbed TiCl₄ molecules or Ti₂Cl₈ dimers which are lacking of the required chirality for stereocontrol. The donor molecules able to attain at best this effect keep to some peculiar conformational rules settled by the authors in a previous theoretical-correlative study on highly active Lewis bases. The new 1,3-dimethoxypropane series suggested by the authors and recently patented by Montell has been examined in detail. Essentially three different types of closeness between Ti atoms and donor molecules can take place, in which different moieties of the diether compound help to build the ‘right’ steric environment in the site's neighbouring. In the three proposed models S1, S2, S3 the stereocontrol is attained through, respectively, one of the methoxy moieties, one of the methyls, and one of the central carbon atom substituents. New hypotheses on the role of Lewis bases in the preparation of isospecific heterogeneous Ziegler-Natta catalysts are discussed.     

Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

The kinetic energy is the center of a controversy between two opposite points of view about its role in the formation of a chemical bond. One school states that a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism of covalent bonding. In contrast, the opposite school holds that a chemical bond is formed by a decrease in the potential energy due to a concentration of electron density within the binding region. In this work, a topographic analysis of the Hamiltonian Kinetic Energy Density (KED) and its laplacian is presented to gain more insight into the role of the kinetic energy within chemical interactions. This study is focused on atoms, diatomic and organic molecules, along with their dimers. In addition, it is shown that the laplacian of the Hamiltonian KED exhibits a shell structure in atoms and that their outermost shell merge when a molecule is formed. A covalent bond is characterized by a concentration of kinetic energy, potential energy and electron densities along the internuclear axis, whereas a charge-shift bond is characterized by a fusion of external concentration shells and a depletion in the bonding region. In the case of weak intermolecular interactions, the external shell of the molecules merge into each other resulting in an intermolecular surface comparable to that obtained by the Non-covalent interaction (NCI) analysis.     

A practical procedure for the determination of electrostatic charges of large molecules

Summary A practical procedure for the precise determination of electrostatic charges, which are evaluated by fitting the rigorous quantum mechanical molecular electrostatic potential to a monopole-monopole expression, is presented. The proposal of this procedure arises from the study of the minimum requirements necessary to obtain reliable electrostatic charges. Such a study is focused on: (i) the dependence of the electrostatic charges on the set of points where the quantum mechanical and the monopole-monopole molecular electrostatic potentials are fitted; thus, both the influence of the number of points and their distribution in layers located out of the van der Waals radii of the atoms are examined, and (ii) the reliability of the use of fractional models for the evaluation of electrostatic charges of large molecules. Results point out that the optimum number of points is defined by a density of points ranging from 0.45 to 0.60 points/Ų when four layers (separated by 0.2 Å) are considered. Nevertheless, the use of only two layers (separated by 0.4 Å) for large molecules is recommended, thus enabling one to obtain reliable charges at a reduced computational cost. Moreover, results justify the use of fractional models for the determination of electrostatic charges of extremely large molecules, even when aromatic structures exist.