Shape Of Molecules Research Articles

The Trifluorooxygenate Anion [OF3]-: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species.

Experimental evidence for hypervalent compounds of second-row elements is still scarce in literature. Here, we present the first report of the long-sought binary hypervalent trifluorooxygenate anion [OF3]-. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M = Li-Cs). As predicted by VSEPR theory and calculations at the CCSD(T) level, and confirmed by FTIR spectroscopy as well as isotopic labeling, [OF3]- exhibits a C2v-symmetric T-shaped structure with one short and two long O-F bond distances. Analysis of the natural local molecular orbitals shows the presence of 2c-2e bond and one 3c-4e bond. Natural resonance theory indicates the importance of the stability of [OF2]•- for the stability of [OF3]-. Although free [OF2]•- was not detected, the species MOF2 (M = Na-Cs) could be observed in the same experiments, which are best described as contact ion pairs of M+[OF2]•-.

The Trifluorooxygenate Anion [OF3]−: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species

Experimental evidence for hypervalent compounds of second‐row elements is still scarce in literature. Here, we present the first report of the long‐sought binary hypervalent trifluorooxygenate anion [OF3]−. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M = Li–Cs). As predicted by VSEPR theory and calculations at the CCSD(T) level, and confirmed by FTIR spectroscopy as well as isotopic labeling, [OF3]− exhibits a C2v‐symmetric T‐shaped structure with one short and two long O‐F bond distances. Analysis of the natural local molecular orbitals shows the presence of 2c‐2e bond and one 3c‐4e bond. Natural resonance theory indicates the importance of the stability of [OF2]•− for the stability of [OF3]−. Although free [OF2]•− was not detected, the species MOF2 (M = Na–Cs) could be observed in the same experiments, which are best described as contact ion pairs of M+[OF2]•−.

New Solutions of Lorentz Transformation IV

This paper is the fourth part of a hypothesis originally based on the basic assumptions of Lorentz transformation and has various implications. In the first part of the hypothesis [1], I calculated the wave function from the general assumptions of the Lorentz transformation. This wave function describes spacetime deformations and entirely replaces the original Lorentz solution used in special relativity. Importantly, each new solution, for both time and space deformation, has two possible solutions that are equally probable. Therefore, I have used these equations for further calculations, which already have a quantum nature. In the second part of my hypothesis [1], I converted this equation into an electromagnetic one and used it to calculate interference and diffraction. Thus, the resulting equation is not based on complex functions, as in standard calculations. We can further investigate this equation, for example, in the context of electron levels in an atom, as interference and diffraction are phenomena related to Young's experiment, and the wave properties of electrons have been demonstrated. In the third part of my hypothesis [1], I applied the calculations to atomic relations and outlined possible solutions for atomic orbitals. This outline of the potential arrangement of energies in the atomic model arose from the fact that some molecules, such as CH4, have the shape of a Platonic solid tetrahedron, which I consider pivotal within the framework of the VSEPR theory.

PENGEMBANGAN MEDIA BERBASIS KOMPUTER UNTUK PEMBELAJARAN KIMIA KELAS XI PADA SEKOLAH MENENGAH ATAS

Difficulty learning abstract consepts in material forms of the molecule based on the theory of electron domain and molecular hybridization in the formation of simple covalent coumpounds involving electron is verry small in size. With conventional learning to use the media shaped balloons and images/charta make their experience misconceptions. Make use of computer assisted animations media adobeflash program. The program is able to help students discover and explore the concepts of learning materials to animate the process of formation of the molecules of the compound geometry. The program is easy to obtain and can be used on all computers. Material forms of molecules according to VSEPR theory (valence shell electron pair repulsion) and Hybridization theory contained in the computer based media is aimed at helping students learn to achieve mastery of core competencies which are already contained in the syllabus set by time. Products are developed in accordance with the educational technology area abstract include students in determining the geometry of the steps forming the molecules of the compound. The stages are carried out in the development of media, namely: design learning, create computer based animation media, validate products with product testing. Advice of expert material/content, media expert, design expert, and data from trials of the target group to be enter performance improvement products. Based on the results of the expert validation and testing of the target group can be concluded that the computer –based instructional media products on the molecular forms of material at Senior High School chemistry in particular at ninth grade IPA (Natural Sciences). With regard to these results the school, especially Senior High School 8 Batanghari media products in order to incorporate this learning into the school website that can be accessed by the wider media users for further development. Keyword: Development, Computer based Media, Molecular Forms.

Influence of the use of 3D printing technology for teaching chemistry in STEM disciplines

AbstractTeachers can create engaging learning environments in engineering courses through pedagogical innovation using Information and Communication Technologies (ICT). Introductory chemistry courses in Science, Technology, Engineering and Mathematics (STEM) disciplines typically include the study of molecular models and periodic properties, which are inherently visual concepts. Unfortunately, these concepts are often taught using two‐dimensional drawings, although three‐dimensional (3D) printing offers an engaging approach to learning chemistry in these disciplines. Undergraduate engineering students are provided with modelling software and a 3D printer, allowing them to construct 3D models of basic Valence Shell Electron Pair Repulsion theory shapes using polylactic acid. The results of this research showed that the average score of the students in the control group was lower than that of the students in the 3D technology group. This research has found that the learning curve for modelling and the time required for printing are high, limiting the practical application of this exercise in student laboratory classes. However, in an appropriate environment, 3D printing technology has the potential to be a valuable tool for teaching and learning molecular models and periodic properties of chemistry courses in STEM disciplines.

Elaborating the Link Between VSEPR and Orbital Hybridization

Many undergraduate chemistry textbooks discuss both the VSEPR (valence-shell electron-pair repulsion) and hybridization (the mixing of atomic orbitals to form new directional orbitals) models of molecular structure as separate topics and fail to mention Bent’s rule (the more electronegative ligand uses the hybrid bonding orbital with the greatest p-character). In this paper, important, but neglected, correlations among these three topics are explored. In addition, it is shown how a consideration of these correlations makes each of the topics more understandable to students.

Reconstructing perspectives: investigating how molecular geometry cards (MGCards) and molecular model building (MMB) disrupt students' alternative notions of molecular structure – a qualitative study

The range of abstract concepts encountered when learning chemistry and the inability of students to make connections between the macroscopic, sub-microscopic, and symbolic representations, used in chemistry teaching, are believed to be the main reasons for students’ difficulty when learning chemistry. Prediction and determination of molecular geometry using the theory of valence shell electron pair repulsion (VSEPR) is a sample of the abstract concept that is hard to understand by students who learn chemistry. Students may comprehend these ideas better if the learning process is supplemented with cutting-edge, interactive learning aids. To address the conceptual difficulties that students encounter when learning how to predict the shapes of molecules, a card game (MGCards) has been developed which is supported by simple molecular model building (MMB). The card game allows students to work through the steps required to predict the shape of a molecule in an engaging format. The student learning process is supported by feedback at all stages (if students make a mistake, they receive hints that will help them in the next step of the game). Action research with qualitative methods has been used to design, develop, and evaluate the MGCards. The MGCards and MMB were piloted at the University of Leicester with year one Natural Sciences students and modified based on the feedback received. Both MGCards and MMB were then used as part of the first-year chemistry education programme at Tanjungpura University in Indonesia. The findings of students’ answer analysis (pre- and post-test) in both cycles showed that students had a better understanding after learning with MGCards and MMB. The positive feedback for MGCards and MMB confirmed that these resources were effective in delivering an engaging learning experience. The results suggest that MGCards and MMB play a significant role in enhancing students’ understanding while also keeping them engaged.

Ligand-enforced geometric constraints and associated reactivity in p-block compounds.

The geometry at an element centre can generally be predicted based on the number of electron pairs around it using valence shell electron pair repulsion (VSEPR) theory. Strategies to distort p-block compounds away from these predicted geometries have gained considerable interest due to the unique structural outcomes, spectroscopic properties or reactivity patterns engendered by such distortion. This review presents an up-to-date group-wise summary of this exciting and rapidly growing field with a focus on understanding how the ligand employed unlocks structural features, which in turn influences the associated reactivity. Relevant geometrically constrained compounds from groups 13-16 are discussed, along with selected stoichiometric and catalytic reactions. Several areas for advancement in this field are also discussed. Collectively, this review advances the notion of geometric tuning as an important lever, alongside electronic and steric tuning, in controlling bonding and reactivity at p-block centres.

High-pressure stabilization of open-shell bromine fluorides.

Halogen fluorides are textbook examples of how fundamental chemical concepts, such as molecular orbital theory or the valence-shell electron-repulsion (VSEPR) model, can be used to understand the geometry and properties of compounds. However, it is still an open question whether these notions are applicable to matter subject to high pressure (>1 GPa). In an attempt to gain insight into this phenomenon, we present a computational study on the phase transitions and reactivity of bromine fluorides at pressures of up to 100 GPa (≈106 atm). We predict that at a moderately high pressure of 15 GPa, the bonding preference in the Br/F system should change considerably with BrF3 becoming thermodynamically unstable and two novel compounds emerging as stable species: BrF2 and BrF6. Calculations indicate that both these compounds contain radical molecules while being non-metallic. We propose a synthetic route for obtaining BrF2 which does not require the use of highly reactive elemental fluorine. Finally, we show how molecular orbital diagrams and the VSEPR model can be used to explain the properties of compressed bromine fluorides.

Resources for reasoning of chemistry concepts: multimodal molecular geometry

Central to conceptual understanding of STEM disciplines is visuospatial processing. Despite its acknowledged role in assuring learners’ success, less is known about the underlying reasoning students must employ when solving 3-D problems and the ways in which gaining an understanding of this can inform formative assessment and learning in STEM education. Chemists must utilise their spatial understanding when visualising 3-D structures and processes from 2-D representations and so this exploratory practitioner-researcher study sought to identify the ways in which secondary school chemistry students reason when explaining their predictions about molecular geometry, and how the use of certain modalities was linked to assessed accuracy. Coding of students’ verbal and written responses to the research task revealed that students employed multiple reasoning strategies and conceptual resources to facilitate use of analytical heuristics and imagistic reasoning. Analysis of students’ verbal responses and spontaneous gestures provided insight into the extent of imagistic vs. analytical reasoning and the finer-grained conditions which promoted their use. Importantly, it was observed that despite being instructed on the use of VSEPR theory to find analytical solutions, some students exhibited preference for alternative reasoning strategies drawing upon imagistic reasoning; showing more nuanced and varying degrees of accuracy through their verbal responses and representations gestured in 3D space. This work has pedagogical implications as use of specific reasoning strategies and the identification of key conceptual resources is not readily promoted as classroom practice for learning or assessment. This study therefore raises questions and contributes to the evidence base for attending to learners’ visuospatial thinking, as revealed through the multiple modalities they may use to assist and communicate their understanding, and highlights the significance of this to formative assessment in Chemistry and STEM Education.

Shortcomings of the VSEPR Model for Hypercoordinate Species and Its Presentation in General Chemistry

Shortcomings of the VSEPR Model for Hypercoordinate Species and Its Presentation in General Chemistry

More than Marshmallows: Implementation and Assessment of an Interactive In-Class Activity for Learning VSEPR Theory

More than Marshmallows: Implementation and Assessment of an Interactive In-Class Activity for Learning VSEPR Theory

Chemistry Students’ Understanding of Lewis Structure, VSEPR Theory, Molecular Geometry, and Symmetry: A Cross-Sectional Study

Most chemical concepts are abstract, hierarchical, and constructed from basic to complex concepts. Lewis structure, VSEPR theory, molecular geometry, and molecular symmetry have hierarchical idea. This study attempted to characterize and determine the relationship between students’ knowledge of Lewis structure, VSEPR theory, molecular geometry, and molecular symmetry of the 1st, 2nd, and 3rd-year chemistry students at a public university. This study involved 88 students in total selected using proportionate stratified random sampling. The instrument was a relevant short-answer question on the three topics. The data were measured using nonparametric statistics, especially the Kruskal-Wallis difference and Spearman Rank correlation tests. This study’s results show differences in understanding of Lewis structure, molecular geometry, and symmetry between the 1st, 2nd, and 3rd-years students. The 3rd-year students always performed better than the 1st and 2nd-year students for all topics. The test result confirms a positive and strong relationship between students’ understanding of Lewis structure and molecular geometry for the three groups of students with ρ values of 0.979, 0.979, and 0.966 (< 0.01) for 1st, 2nd, and 3rd-year students, respectively.

Development of Android-based E-Modules on Molecular Shape Materials of VSEPR Theory

The use of teaching materials in online learning during the Covid-19 pandemic results in a lack of students' understanding of the molecular shape material of the VSEPR theory leading to learning objectives not being achieved. So the researchers make an Android-based e-module as a teaching material as a solution so that students better understand the material of molecular shapes in online learning. This study aims to determine the feasibility of an android-based e-module on the molecular shape material of the VSEPR theory. This research used a research and development (R&D) method which is based on the ADDIE model. The android-based e-module on the molecular shape material of the VSEPR theory was validated by an expert or validator which included the feasibility of the material, language, and graphics. The results show that the android-based e-module developed is categorized as very feasible to use. This Feasibility is reviewed from the results of the validation of the feasibility of the material which obtain a validity score of 92.69% showing that the e-emodule made has fulfilled the Feasibility aspects including the suitability of the material and basic competence, the accuracy of the material, the updating of the material, and encouraging curiosity. Language Feasibility validation with a validity score of 92.69% shows the module made has fulfilled the Feasibility aspects of being straightforward, communicative, conformity with the development of students, and conformity with the correct rules of the Indonesian language. Graphic feasibility validation with a feasibility percentage of 91.66% with very decent criteria shows that the e-module has met the qualifications from the aspect of measurement, cover design, and cover body design. The feasibility research results obtained will be applied as a reference in the manufacturee-mode android based, so the e-modules that are suitable for use can be used in further research

Ronald James Gillespie. 21 August 1924—26 February 2021

Ron Gillespie moved in 1958 from a lectureship at University College London to McMaster University, Hamilton, Canada, where he spent all his subsequent career. He was a distinguished inorganic chemist who made major discoveries in the fields of acids and super-acids, the generation and study of new inorganic species particularly polyatomic cations, the cations of noble gas compounds and the development of the Valence Shell Electron Pair Repulsion and the Ligand Close Packing models for understanding molecular structures. Ron was active in reforming the teaching of introductory chemistry, avoiding if possible descriptions that relied on thermodynamics or quantum mechanics, and instead presenting qualitative non-mathematical models.

The Teaching Blind Spot and Practice Optimization of Valence Shell Electron Pair Repulsion Theory

The Teaching Blind Spot and Practice Optimization of Valence Shell Electron Pair Repulsion Theory

Enhancement of Indonesian High School Student Conceptual Mastery on VSEPR Topic Using Virtual Simulation of Molecule Shapes: A Case Study of Quasi-Experimental Evidence

The Valence Shell Electron Pair Repulsion (VSEPR) is an essential topic for high school student’s fundamental understanding of 3D shapes of chemical compounds. Due to the spatial aspect of the topic, the students were forced to imagine the geometry of the molecule by predicting the free or bonded electron pair repulsion. Suitable learning media to accommodate those features should be precisely selected to help students properly understand the geometry of the molecule based on the VSEPR topic. This study compared the significant difference in the application of two media of animation video and interactive simulation toward the control and experimental groups, respectively, to enhance conceptual mastery of the VSEPR topic. This study was a statistical quasi-experiment study with two classes of control (animation video) and experimental (interactive simulation) groups. The results of the significant difference test of the groups showed that the distribution of the experimental and control groups was not normal (significantly different) and normal (not significantly different), respectively. Analysis results using Mann-Whitney for the non-parametric free two samples comparative test with a 95% confidence level showed that the application of virtual simulation on the experimental group impacted more in improving the conceptual mastery of the VSEPR topic. Furthermore, there was an identified significant improvement in sub-concepts of the VSEPR topic in binding pair, molecular shape, and electron repulsion. These findings could support the teachers in designing lesson plans for students to master the VSEPR topic.

Reminiscing about Ron Gillespie

The interactions between Ronald J. Gillespie (1924–2021), the initiator of the VSEPR model of molecular geometry, and the author started in the early 1970s and culminated in a joint book about the model in 1991, republished in 2012. In 1998, they recorded a conversation about Gillespie’s life and career, which he augmented by his thoughts about the similarities between his demeanor as a scientist and that of Charles Darwin.

Hints for a formal language inspired by Lewis structures

SummaryIn this work we elaborate on the idea of a formal theory for a limited but important part of structural chemistry, that described by Lewis’ methods and VSEPR (Valence Shell Electron Pair Repulsion). For this purpose, recursive functions and propositional functions are defined, that apply to formal expressions of the structure, based on a finite set of symbols. This approach allows for the expression of numerous questions of chemical interest. The formalization of basic structural chemistry based on Lewis/VSEPR method is potentially useful for the automation of the related procedures, but possibly also of some use as complementary material in teaching and as a heuristic tool in structural chemistry.

New Directions in Teaching Introductory and Organic Chemistry

<p>To resolve several problems that arise in the teaching of hybrid atomic orbitals (HAO) and the valence-shell electron-pair repulsion (VSEPR) model, we propose an original way to present molecular structures, beginning with an analysis of the teaching of lone pairs without HAO and VSEPR. Our purpose in eliminating completely the HAO and VSEPR models from introductory and organic chemistry is to avoid erroneous concepts about the distributions of electronic charge within molecules. We provide a general design to teach the basic curriculum of chemistry in the future without HAO and VSEPR.</p><div> </div>