Repulsion Theory Research Articles

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.

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.

Investigation of Three Migration Periods of Roman Elites in the Formation and Survival of the Jundishapur Scientific Center Applying the Theory of migration by Everett S. Lee

Jundishapur has been one of the oldest scientific and educational centers in Iran. A civil and intellectual field that emerged from the time of Sassanid Shapur (I), and gradually a scientific center emerged, especially in the medicine field. The splendor of the scientific center and the city of Jundishapur has been deeply correlated with the phenomenon of migration of Roman (Syriac-Nestorian) elites. Therefore, the causation and explanation of these migrations on the formation, life, and continuity of scientific center are significant to study. The present article attempted to investigate the dimensions of this issue from the perspective of historical sociology, relying on the theory of attraction and repulsion of Everett Lee. Thus, the present study tries to analyze three periods of elite migration from Rome to Jundishapur by using a descriptive-analytical method and relying on library resources and answer question of whether these migrations can be explained using the theory of attraction and repulsion? Findings indicate that in all three periods of the main migration of Roman elites to Jundishapur, Roman repulsions against Sassanid attractions have been very effective in the issue of residence and migration of elites. Religion has also been a crucial factor in the convergence and divergence of elites to migrate from Rome to Iran. The city of Jundishapur developed certain Syrian-Christian scientific and cultural features since its establishment. According to Everett Lee's migration theory, these characteristics had eliminated or downplayed the negative interventionist barriers and distance dilemma of elite migration from Rome to Jundishapur. Furthermore, the migration of elites from Rome to Jundishapur has been very effective in the survival of the city and the scientific center of Jundishapur.

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

FORMATION OF NANOCLUSTERS IN THE TRANSITION OF CARBON DIOXIDE TO THE SUPERCRITICAL STATE

Supercritical fluid extraction (SFE) with CO2 is widely used to extract biological materials, metal complexes and their isotopes. Supercritical CO2 (SC-CO2) is an environmentally friendly, efficient, and affordable solvent. However, the change in the chemical and physical properties of CO2 in the transition to the supercritical (SC) state has not been studied so far. The paper proposes to consider such a change as a result of the formation of elementary linear, flat or volumetric nanoclusters, from which large nanoclusters can also be formed. Based on the theory of repulsion of valence electron pairs, the geometry of the arrangement of atoms in elementary nanoclusters is described. The change in the chemical and physical properties of CO2 is confirmed by absorption spectra in the IR range for wavelengths of 4.2…4.4 μm in sub- and SC-CO2.

Vegetables for building molecular models

An exciting classroom activity involving the construction of molecular models and building hybrid orbitals is presented in this paper. Basic molecular geometries were built by connecting different types of vegetables using bamboo skewers. Vegetable of different shapes were used to describe the hybridization of atomic orbitals. This exercise is suitable for high school and undergraduate chemistry students. The activity helps students to apply Valence Shell Electron Pair Repulsion (VSEPR) theory to envisage the basic shapes of molecules and to conceptualize the hybridization of the atomic orbitals

Pre-Operative Motion Planner for Steerable Needles Using Cost Map Based on Repulsive Field and Empirical Model of Needle Deflection

Abstract Needle insertion is a common procedure in percutaneous puncture. A motion planner for a steerable needle that considers the risk level of the path in anatomical environment and the actual deflection of clinical needle is necessary. A novel pre-operative motion planner for a steerable needle controlled by robot is proposed. Our method utilizes sampling-based planner to compute candidate path in the reachable region, and the path solutions are optimized by calculating the cost of a path based on a cost map. The cost map, which is built based on repulsive field theory from CT image, encodes the information of the obstacle locations and the criticality of the anatomical environment. The empirical formula that can predict needle trajectory is obtained by insertion experiments. Experiments show that under the guidance of our planner, the positioning error in phantom made with gelatin and three-dimensional (3D) printed models is less than 1.1 mm. Comparing with the straight-line insertion method in the same phantom, the positioning error was reduced by 80%. The results indicate that the motion planner has the potential to provide effective guidance for robot-assisted puncture surgery while enhancing the position precision and patient safety.

An efficient QCA-based full adder design with power dissipation analysis

ABSTRACT Quantum Dot-Cellular automata (QCA) is a developing technology that is considered as the best viable alternate solution for CMOS technology which has short-channel effects. QCA is a transistor-free technology, and the information is distributed formulated on the charge of the electron and by Columbic repulsion theory. In this paper, an optimal adder circuit is proposed using QCA technology which consist only 14 cells. The proposed adder circuit is further utilised for designing of 4-bit adder design efficiently. Simulations results, are obtained precisely using QCADesigner software version 2.0.3., confirm that the proposed circuits work well. Moreover, the energy dissipations of the proposed adder circuit design is estimated using QCAPro tool. The performance of the proposed design was compared with the existing ones which shows better performance in terms of cell count, area, and latency. Suggested 1-bit and 4-bit QCA adders exhibit a delay of 0.5 and 1.25 clock cycle, occupy an active area of 0.01 and 0.1 and μm2, and use 14 and 84 QCA cells, respectively.

Spherical Nucleic Acids: Integrating Nanotechnology Concepts into General Chemistry Curricula.

Nanoscience and technology research offer exciting avenues to modernize undergraduate-level General Chemistry curricula. In particular, spherical nucleic acid (SNA) nanoconjugates, which behave as "programmable atom equivalents" (PAEs) in the context of colloidal crystals, are one system that one can use to reinforce foundational concepts in chemistry including matter and atoms, the Periodic Table, Lewis dot structures and the octet rule, valency and valence-shell electron-pair repulsion (VSEPR) theory, and Pauling's rules, ultimately leading to enriching discussions centered on materials chemistry and biochemistry with key implications in medicine, optics, catalysis, and other areas. These lessons connect historical and modern concepts in chemistry, relate course content to current professional and popular science topics, inspire critical and creative thinking, and spur some students to continue their science, technology, engineering, and mathematics (STEM) education and attain careers in STEM fields. Ultimately, and perhaps most importantly, these lessons may expand the pool of young students interested in chemistry by making connections to a broader group of contemporary concepts and technologies that impact their lives and enhance their view of the field. Herein, a way of teaching aspects of General Chemistry in the context of modern nanoscience concepts is introduced to instructors and curricula developers at research institutions, primarily undergraduate institutions, and community colleges worldwide.

TÜRKİYE'DEKİ AFGAN GÖÇMENLERİN FIRSAT VE ZORLUKLARINA YÖNELİK BİR ANALİZ

The history of population movements goes back to the history of humanity due to the desire of individuals and society to live better. Migration has been developed in different periods due to various reasons. The originality, war, democratic pressure, labor force and different pressure in space, attractiveness of the places have been the reasons for migration, respectivley. The purpose of writing this article is to show the migration of Afghans to Turkey by analyzing the situation for immigrants. Their opportunities and challenges during migration were examined by both descriptive and analytical methods. Its approach analysis is based on the usage of related immigration theories including ravenstein's theory of repulsion and gravity (new security theory), which has been used in immigration data collection from international immigration organizations and library in the field area. Afghanistan has been involved in war for a few decades, and thousands of Afghans have migrated to countries around the world especially European countries. Each year, thousands of refugees migrate to Turkey for spacial purposes. Turkey provides some opportunities and challenges for Afghans such as studying, employement and investment opportunities. However, working permission and health insurance with no kimlik (ID card) is not possible for them.

The role of visuospatial thinking in students’ predictions of molecular geometry

Visuospatial thinking is considered crucial for understanding of three-dimensional spatial concepts in STEM disciplines. Despite their importance, little is known about the underlying cognitive processing required to spatially reason and the varied strategies students may employ to solve visuospatial problems. This study seeks to identify and describe how and when students use imagistic or analytical reasoning when making pen-on-paper predictions about molecular geometry and if particular reasoning strategies are linked to greater accuracy of responses. Student reasoning was evidenced through pen-on-paper responses generated by high attaining, high school students (N = 10) studying Valence Shell Electron Pair Repulsion (VSEPR) Theory in their final year of chemistry. Through analysis and coding of students’ open-ended paper-based responses to an introductory task, results revealed that students employed multiple reasoning strategies, including analytical heuristics and the spontaneous construction of external diagrammatic representations to predict molecular geometry. 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 on prior knowledge and imagistic reasoning; showing greater accuracy with 3D diagrammatic representations than students who used the algorithmic method of instruction. This has implications for both research and practice as use of specific reasoning strategies are not readily promoted as a pedagogical approach nor are they given credit for in national examinations at school level.

Breakdown of Valence Shell Electron Pair Repulsion Theory in an H-Bond-Stabilized Linear sp-Hybridized Sulfur

Exploring the unusual orbital hybridization types of atoms and their new connection modes contributes to the development of chemical bond theory and can inspire compounds with unique molecular conf...

Understanding the Chemical Insights of Staple Motifs of Thiolate-Protected Gold Nanoclusters.

Improving the fundamental understanding of the basic structures of ligand-protected gold nanoclusters is essential to their bottom-up synthesis as well as their further application explorations. The thiolate ligands that cover the central metal core in staple motifs are vital for the stability of the gold clusters. However, the knowledge about the geometrical and bonding characters of the thiolate ligands has not been fully uncovered yet. In this work, density functional theory calculations and molecular orbital analysis are applied to show that the Au atoms in the thiolate ligands are hypervalent. The chemical insights of the linear SAuS configuration as well as the lengthened AuS bond by combining the 3-center 4-electron (3c-4e) model and the well-recognized valence shell electron pair repulsion theory are revealed. Valence bond formulations of the motifs are given to provide more chemical insights, for example, the resonant structures, to show how the thiolate motif forms one covalent bond and one dative covalent bond with the Au core. This work provides a thorough understanding of the structure and bonding pattern of thiolate ligands of Au nanoclusters, which is important for the rational design of ligands-protected Au nanoclusters.

Probe into the Issues about the Theory of Valence Shell Electron Pair Repulsion in Different Textbooks

Probe into the Issues about the Theory of Valence Shell Electron Pair Repulsion in Different Textbooks

Delocalized π36 bond in OX2 (X=halogen) molecules

OX2 (X=halogen) molecules was studied theoretically. Calculation results show that delocalized π36 bonds exist in their electronic structures and O atoms adopt the sp2 type of hybridization, which violates the prediction of the valence shell electron pair repulsion theory of sp3 type. Delocalization stabilization energy is proposed to measure the contribution of delocalized π36 bond to energy decrease and proves to bring extra-stability to the molecule. These phenomena can be summarized as a kind of coordinating effect.

Mixed Carboxyl and Hydrophobic Dendrimer Surface Inhibits Amyloid-β Fibrillation: New Insight from the Generation Number Effect.

Fibrillation of amyloid-β peptide (Aβ) is closely associated with the progression of Alzheimer's disease (AD), and so inhibition of Aβ fibrillation has been considered as one of the promising strategies for AD prevention and treatment. Our group has proposed the hydrophobic binding-electrostatic repulsion (HyBER) theory on inhibiting Aβ fibrillation by a surface with mixed negative charges and hydrophobic groups, which provides a new strategy for the design of potent amyloid inhibitors. Carboxyl-terminated polyamidoamine dendrimer (PAMAM) is a kind of biocompatible nanomaterial with only carboxyl groups on its surface, and its architecture and property vary with the generation number, low-generation dendrimers possessing sparse distributions of terminal groups while high-generation dendrimers having compact surface groups, which offer abundant base materials for further study of the HyBER theory. We have designed a potent amyloid inhibitor with generation 5 PAMAM. To provide new insights into the HyBER mechanism, we have herein proposed to synthesize phenyl-modified PAMAM dendrimers of generations 3 to 6 (G3-P to G6-P) and study the effect of the generation number on Aβ fibrillation. Results show that phenyl derivatives of low-generation dendrimers (G3-P and G4-P) do not show any interference with Aβ aggregation, whereas the phenyl derivatives of high-generation dendrimers (G5-P and G6-P) significantly inhibit Aβ42 aggregation and alter the ultrastructure of Aβ42 aggregates. The results indicate that the density and distribution of surface functional groups on a dendrimer is of great importance for the HyBER effect to happen. The new understanding on the HyBER mechanism would benefit in the development of potent amyloid inhibitors based on the theory.

Valence-Shell Electron-Pair Repulsion Theory Revisited: An Explanation for Core Polarization.

Valence-shell electron-pair repulsion (VSEPR) theory constitutes one of the pillars of theoretical predictive chemistry. It was proposed even before the advent of the concept of "spin", and it is still a very useful tool in chemistry. In this article we propose an extension of VSEPR theory to understand the core structure and predict core polarization in the main-group elements. We show from first principles (Electron Localization Function analysis) how the inner- and outer-core shells are organized. In particular, electrons in these regions are structured following the shape of the dual polyhedron of the valence shell (3rd period) or the equivalent polyhedron (4th and 5th periods). We interpret these results in terms of "hard" and "soft" core character. All the studied systems follow this trend, providing a framework for predicting electron distribution in the core. We also show that lone pairs behave as "standard ligands" in terms of core polarization. The predictive character of the model was tested by proposing the core polarization in different systems not included in the original set (such as XeF4 and [Fe(CN)6 ]3- ) and checking the hypothesis by means of a posteriori calculations. From the experimental point of view, the extension of VSEPR to the core region has consequences for current crystallography research. In particular, it explains the core polarization revealed by high resolution X-ray experiments.

Competitive effects of interfacial interactions on ion-tuned wettability by atomic simulations

The dependence of wettability on brine ionic composition in organic-brine-mineral systems, which is denoted as ion-tuned wettability in this paper, has important industrious applications but is still not well understood. The dominant mechanisms and their relative importance are still under debate. This paper uses molecular dynamics to study three possible mechanisms of ion-tuned wettability in an oil-brine-quartz system, including electrical double layer (EDL) repulsion, cation bridging, and hydration repulsion. We compare the contact angle and COO− distribution of the molecular system under different interface charging conditions and the contact angle predicted by EDL repulsion theory. The results indicate the existence of Ca2+ bridging and K+ bridging, and that medium ionic strength favors the form of K+ bridging most. The three mechanisms are all proved to have impact on wettability, of which Ca2+ bridging is the strongest, EDL repulsion and hydration repulsion the weaker, K+ bridging the weakest. Based on the results, we suggest that all the three mechanisms should be evaluated to predict the ion-tuned wettability, and conclude several possible brine-modifying strategies to make sandstone reservoir more water-wet.

A VSEPR-inspired force field for determining molecular properties of PF5

ABSTRACTValence Shell Electron Pair Repulsion (VSEPR) theory, commonly taught in introductory chemistry courses, provides a basis for understanding the molecular structures of molecules of the type XY, where X is a central atom surrounded by m Y ligands. While VSEPR is generally thought of only as a qualitative theory, Bartell and coworkers constructed a semi-quantitative model potential to address the physical underpinnings of VSEPR by introducing a points-on-a-sphere (POS) potential such that all X-Y bonds are of fixed length and all atoms Y repel each other. More than forty years ago, this simple model was shown to be effective in reproducing relative quadratic and cubic bending force constants for a variety of binary XY compounds when compared to values computed with semi-empirical and fairly primitive methods. The work presented here endeavours to go beyond the model used in the early investigations by Bartell and coworkers. Specifically, stretching force constants are clearly omitted from any POS model with a fixed radius, and are (primitively) included here by treating all X-Y bonds as simple (and equivalent) Morse oscillators. With the additional degrees of freedom in the parametrization that come from the Morse potential, the resulting model was investigated. The degree to which this simple mechanical model can reproduce quadratic and cubic force fields for PF is studied here, as well as how it works for a more difficult problem – the energetics and transition state properties for the intermediate in the (Berry) pseudorotation process that interchanges axial and equatorial fluorines in this prototype molecule. The five parameter Morse-POS model is shown to be do quite well in describing the quadratic and cubic force fields, as well as the pseudorotation process, a fairly impressive feat given the naivete of the model.