Conceptual integration of covalent bond models by Algerian students

2014 ◽  
Vol 15 (4) ◽  
pp. 675-688 ◽  
Author(s):  
Hazzi Salah ◽  
Alain Dumon
Keyword(s):  
Covalent Bond ◽  
Covalent Bonding ◽  
Quantum Model ◽  
Covalent Bonds ◽  
Conceptual Integration ◽  
Knowledge Framework ◽  
Chemistry Learning ◽  
Valence Electrons ◽  
Lewis Structures ◽  
Hybrid Orbitals

The concept of covalent bonding is characterized by an interconnected knowledge framework based on Lewis and quantum models of atoms and molecules. Several research studies have shown that students at all levels of chemistry learning find the quantum model to be one of the most difficult subjects to understand. We have tried in this paper to analyze the extent to which Algerian students, at the end of their training, have integrated the covalent bonding theories based on the quantum model of atom theory and are able to interpret Lewis structures using the quantum model. The analysis of the responses to a written questionnaire showed that this integration was not achieved by our students and that they are not able to correctly describe covalent bonds in a Lewis structure using the concepts of the quantum model. They have a “quantum box” conception of atomic or hybrid orbitals. This conception acts as a “pedagogical learning impediment” to the integration of the geometrical representations of atomic and hybrid orbitals, the conditions of their overlapping to give bonds and consequently the description of covalent bonds using the quantum model. So, the students use an alternative conceptual framework based on the use of Lewis model paired valence electrons to form covalent bonds that we have named the: “electrons pair framework”. Furthermore, the students restricted the denomination of a covalent bond to the sharing of one electron (either s or p but not spn) from each atom to give one “electron pair σ”, and thought that σ bonds are only formed in single bonds.

scholarly journals Identifikasi miskonsepsi materi ikatan kovalen pada mahasiswa kimia tahun pertama universitas negeri malang menggunakan tes diagnostik two-tier

2021 ◽  
Vol 1 (6) ◽  
Author(s):  
Wardatul Istiqomah ◽  
Sri Rahayu ◽  
M. Muchson
Keyword(s):  
Molecular Form ◽  
Covalent Bonding ◽  
Table Salt ◽  
Metallic Elements ◽  
Double Bonds ◽  
Covalent Bonds ◽  
Bonding Material ◽  
Formal Charge ◽  
Valence Electrons ◽  
Coordination Bonds

The concept of chemistry must be well understood because the concept of chemistry is hierarchical and sequential. In addition, the concept of chemistry is abstract, which can provoke misconceptions. This study aims to identify misconceptions about the covalent bonding material and to determine the percentage of misconceptions about these materials. The results showed that a misconception was observed in 10 concepts of covalent bonding material with the following percentages: 1) 23 percent of the concepts forming elements of covalent compounds, the covalent compounds must be composed of non-metallic elements with non-metallic elements; 2) 69 percent on the Lewis structure concept, the total number of electrons based on the Lewis structure drawing is the number of valence electrons; 3) 54 percent in the concept of double bonds, the breaking energy of the double bonds is twice that of the energy of the single bonds; 4) 35 percent on the concept of covalent coordination bonds, the covalent coordination bonds are shorter than the covalent bonds; 5) 54 percent on the concept of polar covalent bonds and molecular polarity, the pair of binding electrons is located at the same distance between two bonding atoms; 6) 27 percent in the concept of formal charge, the value of the influences of electronegativity in the determination of the formal charge; 7) on the notion of byte rule and the stability of covalent compounds, 27 percent of the stable Lewis structure does not have a free electron pair (PEB) and respects the byte rule; 62 percent chlorine gas will form the Cl2 molecule because it follows the octet rule; and 54 percent of the covalent bonds store chemical energy; 8) 42 percent on the concept of molecular form, the molecular form of a compound is determined by the repulsion of binding electron pairs; 9) on the concept of intermolecular forces and the properties of covalent compounds, 38 percent of the energy required to boil the table salt is superior because the table salt is an ionic bond; and 81 percent of the strongest interactions are hydrogen bonds; and 10) in the concept of valence bond theory, 23 percent of the most important particles in the formation of covalent bonds are valence electrons; and 27 percent electron sharing means sharing one (1) electron with two atoms, as in the case of sharing an apple for two people. Konsep ilmu kimia perlu dipahami dengan baik, karena konsep ilmu kimia berjenjang dan berurutan. Selain itu, konsep ilmu kimia bersifat abstrak, sehingga dapat menyebabkan miskonsepsi. Penelitian ini bertujuan untuk mengidentifikasi miskonsepsi pada materi ikatan kovalen dan mengetahui persentase miskonsepsi pada materi tersebut. Hasil penelitian menunjukkan bahwa miskonsepsi terjadi pada 10 konsep materi ikatan kovalen dengan persentase sebagai berikut: 1) 23 persen pada konsep unsur-unsur pembentuk senyawa kovalen, senyawa kovalen harus tersusun atas unsur non logam dengan unsur non logam; 2) 69 persen pada konsep struktur Lewis, elektron total berdasarkan gambar struktur Lewis adalah jumlah elektron valensi; 3) 54 persen pada konsep ikatan rangkap, energi pemutusan ikatan rangkap dua kali lipat daripada energi pemutusan ikatan tunggal; 4) 35 persen pada konsep ikatan kovalen koordinasi, ikatan kovalen koordinasi lebih pendek daripada ikatan kovalen; 5) 54 persen pada konsep ikatan kovalen polar dan kepolaran molekul, pasangan elektron ikatan terletak pada jarak yang sama diantara dua atom yang berikatan; 6) 27 persen pada konsep muatan formal, nilai elektronegativitas berpengaruh dalam menentukan muatan formal; 7) pada konsep aturan oktet dan kestabilan senyawa kovalen, 27 persen struktur Lewis yang stabil tidak memiliki Pasangan Elektron Bebas (PEB) dan memenuhi aturan oktet; 62 persen gas klorin akan membentuk molekul Cl2 karena memenuhi aturan oktet; dan 54 persen ikatan kovalen menyimpan energi kimia; 8) 42 persen pada konsep bentuk molekul, bentuk molekul suatu senyawa ditentukan tolakan pasangan elektron ikatan; 9) pada konsep gaya antar molekul dan sifat-sifat senyawa kovalen, 38 persen energi yang dibutuhkan untuk mendidihkan garam dapur lebih besar karena garam dapur merupakan ikatan ionik; dan 81 persen interaksi tarik-menarik yang paling kuat adalah ikatan hidrogen; dan 10) pada konsep teori ikatan valensi, 23 persen partikel paling penting dalam pembentukan ikatan kovalen adalah elektron valensi; dan 27 persen sharing electron berarti pemakaian bersama 1 (satu) elektron oleh dua atom, seperti pada kasus berbagi sebuah apel untuk dua orang.

scholarly journals PENGEMBANGAN PERANGKAT PEMBELAJARAN KIMIA DENGAN MODEL PEMBELAJARAN KOOPERATIF TERPADU NUMBERD HEAD TOGETHER DAN TWO STAY TWO STRAY DALAM UPAYA MENGATASI KESULITAN BELAJAR SISWA KELAS X SMA MEMAHAMI KONSEP-KONSEP KIMIA

2014 ◽  
Vol 9 (1) ◽  
Author(s):  
Mukhtar Haris ◽  
Muntari Muntari ◽  
I Nyoman Loka Loka
Keyword(s):  
Learning Difficulties ◽  
Covalent Bond ◽  
Learning Tools ◽  
Chemistry Learning ◽  
Valence Electrons ◽  
Chemical Concepts ◽  
Chemical Equations ◽  
Ionic Bonds ◽  
Binary Compounds ◽  
Octet Rule

Abstrak: Telah dilakukan penelitian dengan tujuan untuk menganalisis kesulitan belajar siswa dalam memahami konsep-konsep kimia dan mengembangkan perangkat pembelajaran kimia dengan model  pembelajaran kooperatif terpadu Numberd Head Together dan Two Stay Two Stray.  Kegiatan ini dilakukan pada siswa kelas X di SMAN 3 Mataram dan SMAN 7 Mataram semester gasal tahun 2013. Hasil penelitian tentang kesulitan belajar yang diperoleh adalah terdapat beberapa kesulitan belajar siswa dalam memahami konsep-konsep kimia terutama lebih dari 50% siswa mengalami kesulitan belajar. Pada materi struktur atom & sistem periodik unsur berupa kesulitan belajar dalam hal memahami tabel periodik unsur, menentukan elektron valensi, menentukan jumlah netron dan elektron dari ion, dan kesulitan menentukan golongan dan periode unsur. Pada materi ikatan kimia, kesulitan dalam hal menentukan senyawa yang memiliki ikatan ion, menentukan rumus senyawa yang terbentuk dan jenis ikatannya, menentukan senyawa yang tidak memenuhi kaidah oktet, menentukan senyawa kovalen polar, menentukan kemampuan suatu unsur yang diketahui nomor atomnya, menentukan pasangan unsur yang dapat membentuk ikatan ion dan pasangan golongan unsur yang dapat membentuk ikatan kovalen. Sedangkan pada materi tata nama senyawa dan persamaan reaksi, siswa kesulitan pada semua konsep tentang tata nama senyawa biner dan penyetaraan persamaan reaksi.Kata Kunci: kesulitan belajar, konsep kimia  Abstract: This research was conducted with the objective to analysis of students' learning difficulties in understanding the concepts of chemistry and to develop chemistry learning tools with an integrated model of cooperative learning Numberd Head Together and Two Stay Two Stray. This activity is done in class X in SMAN 3 Mataram and SMAN 7 Mataram odd semester of 2013. The results of the acquired learning difficulties are there some students' learning difficulties in understanding the concepts of chemistry, especially that more than 50% of students experiencing learning difficulties. In the matter of atomic structure and the periodic system of elements in the form of learning difficulties in terms of understanding the periodic table of elements, determining the valence electrons, determining the number of neutrons and electrons from ions, and the difficulty of determining the group and period of elements. In the chemical bond, the difficulty was in determining a compound having an ionic bond, determine the formula compound formed and the type of bond, determining a compound that does not meet the octet rule, determine polar covalent compounds, determining the ability of a known element atomic number, determines the pairs of elements that can form ionic bonds and pairs group elements that can form a covalent bond. While in the material of compounds nomenclature and chemical equations, students difficulties were on the concepts of nomenclature of binary compounds and equalization of reaction.Keywords: learning difficulties, chemical concepts

scholarly journals Covalent Inhibition of SARS-CoV-2 RBD-ACE2 Interaction by Aptamers with Multiple Sulfur(VI) Fluoride Exchange Modifications

2021 ◽  
Author(s):  
Zichen Qin ◽  
Yiying Zhu ◽  
Yu Xiang
Keyword(s):  
Human Serum ◽  
Covalent Bond ◽  
Covalent Bonding ◽  
Peptide Fragmentation ◽  
Host Cells ◽  
Great Promise ◽  
Enzyme Linked Immunosorbent Assay ◽  
Covalent Bonds ◽  
Target Proteins ◽  
Covalent Inhibitors

The SARS-CoV-2 spike protein uses its receptor-binding domain (RBD) to interact with the angiotensin-converting enzyme 2 (ACE2) receptor on host cells, establishing the first step of SARS-CoV-2 infection. Inhibitors of RBD-ACE2 interaction, therefore, have shown great promise in preventing SARS-CoV-2 infection. Currently known RBD-ACE2 inhibitors are all based on reversible binding and must compete with ACE2 or RBD at the equilibrium. On the other hand, covalent inhibitors, such as those based on sulfur(VI) fluoride exchange (SuFEx) chemistry, can form irreversible chemical bonds with target proteins and offer advantages including higher potency and longer duration of inhibition. Here, we report covalent aptamer inhibitors that can block RBD-ACE2 by forming covalent bonds with RBD. These covalent aptamer inhibitors were developed by equipping known RBD aptamers with multiple SuFEx (mSuFEx) modifications. The mSuFEx-aptamer 6C3-7SF underwent strong covalent bonding with RBD and some of its variants at fast rates (t1/2 = 20 ~ 29 min−1) and induced more efficient RBD-ACE2 inhibition (IC50 = 26 ~ 37 nM) than the original aptamer (IC50 > 200 nM) according to an in vitro enzyme-linked immunosorbent assay (ELISA). The covalent bond formation was highly selective to RBD over human serum albumin (HSA) and ACE2, and could occur efficiently in diluted human serum. Peptide fragmentation analyses of the RBD-6C3-7SF adducts revealed multiple sites of covalent bonding on RBD, including K378, R408, Y422, Y424, Y453, and K458. The surprising R408 suggests that context-specific non-N-terminal arginine could be a new type of targetable residue by SuFEx-based covalent inhibitors, which were never reported as reactive with any non-N-terminal arginine in target proteins. In addition, RBD R408 is responsible for binding with ACE2 N90 glycan, and this arginine is conserved in SARS-CoV-2 variants of concern or interest, suggesting that R408 could be the potential site of interest for developing SuFEx-based covalent inhibitors against threatening SARS-CoV-2 variants. Although the compatibility of mSuFEx-based covalent aptamers in cellular and in vivo systems should be further investigated, our study demonstrated the promise of mSuFEx chemistry in constructing potent covalent aptamers to inhibit important protein-protein interactions (PPIs).

MANY-ATOM VAN DER WAALS INTERACTIONS LEAD TO DIRECTION-SENSITIVE INTERACTIONS OF COVALENT BONDS

2008 ◽  
Vol 06 (04) ◽  
pp. 693-707 ◽  
Author(s):  
ALEXEI V. FINKELSTEIN ◽  
MICHAEL Y. LOBANOV ◽  
NIKITA V. DOVIDCHENKO ◽  
NATALIA S. BOGATYREVA
Keyword(s):  
Physical Theory ◽  
Van Der Waals ◽  
Protein Structures ◽  
Covalent Bond ◽  
Covalent Bonding ◽  
Van Der Waals Interactions ◽  
Binding Affinities ◽  
Dispersion Interactions ◽  
Energy Effect ◽  
Covalent Bonds

Strict physical theory and numerical calculations show that a specific coupling of many-atom van der Waals interactions with covalent bonding can significantly (half as much) increase the strength of attractive dispersion interactions when the direction of interaction coincides with the direction of the covalent bond, and decrease this strength when the direction of interaction is perpendicular to the direction of the covalent bond. The energy effect is comparable to that caused by the replacement of atoms (e.g. N by C or O ) in conventional pairwise van der Waals interactions. Analysis of protein structures shows that they bear an imprint of this effect. This means that many-atom van der Waals interactions cannot be ignored in refinement of protein structures, in simulations of their folding, and in prediction of their binding affinities.

EFEKTIVITAS MODEL PEMBELAJARAN KOOPERATIF TIPE TEAMS GAMES TOURNAMENT (TGT) BERBANTUAN MEDIA KARTU SOAL PADA SUB MATERI IKATAN KOVALEN KELAS X MIA DI SMA ISLAM HARUNIYAH PONTIANAK

2018 ◽  
Vol 6 (2) ◽  
Author(s):  
Zulfadhli Abdillah
Keyword(s):  
Student Learning ◽  
Learning Outcomes ◽  
Covalent Bond ◽  
Student Learning Outcomes ◽  
Learning Model ◽  
Covalent Bonds ◽  
Team Games ◽  
Bonding Material ◽  
Before And After ◽  
Tenth Grade

 This  study  is  motivated  by  the  low  learning  outcomes  in  the  Sub-covalent  Bond class of tenth-grade students, SMA Islam Haruniyah Pontianak. This problem is due to the  lack  of  students'  understanding  of  the  concept  of  Covalent  Bonds.  Therefore,  a proper learning model is required to improve students’ understanding of Covalent Bond concepts  based  on  the  characteristics  of  both  learning  materials    and  students.  This study  aimed  to  investigate  the  differences  in  the  student  learning  outcomes  and  the effectiveness of the question card-based on TGT learning in the Sub-covalent Bonding material. Using the pre-experimental method of one-group pretest-posttest design, the tenth-grade  students  of  Math  and  Science  Class  of  SMS  Islam  Haruniyah  Pontianak participated in this study. The data collection tools used were learning outcomes tests, observation sheets, and interview sheets. The results of data analysis revealed that the average  pretest  score  was  36  and  the  posttest  was  62.94.  In  addition,  the  t-test statistical  analysis  indicated  a  significance  value  of  0.00  (0.00  <0.05)  which  meanth that there were differences in student learning outcomes between before and after the question  card-based  TGT  learning  model  implemented.  The  gain  value  was  0.42.  In other words, the  question card-based on TGT learning model is effective in improving the student  learning outcomes with good category. Keywords: Covalent Bond, Question Card, Team Games Tournament (TGT)

Structure study of the chalcogens and chalcogenides by X-ray absorption fine structure

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Hiroyuki Ikemoto ◽  
Takafumi Miyanaga
Keyword(s):  
Fine Structure ◽  
Covalent Bond ◽  
Narrow Channel ◽  
Structure Study ◽  
Chain Structure ◽  
Covalent Bonds ◽  
X Ray ◽  
Absorption Fine ◽  
Amorphous States ◽  
X Ray Absorption

AbstractIn this review, we make a survey of the structure studies for the chalcogen elements and several chalcogenides in liquid, amorphous and nanosized state by using X-ray absorption fine structure (XAFS). The chalcogen elements have hierarchic structures; the chain structure constructed with the strong covalent bond as a primary structure, and the weaker interaction between chains as a secondary one. Existence of these two kinds of interactions induces exotic behaviors in the liquid, amorphous and nanosized state of the chalcogen and chalcogenides. XAFS is a powerful structure analysis technique for multi-element systems and the disordered materials, so it is suitable for the study of such as liquid, amorphous and nanosized mixtures. In section 2, the structures for the liquid state are discussed, which show the interesting semiconductor-metal transition depending on their temperatures and components. In section 3, the structure for the amorphous states are discussed. Especially, some of chalcogens and chalcogenides present the photostructural change, which is important industrial application. In section 4, the structures of nanosized state, nanoparticles and isolated chain confined into the narrow channel, are discussed. The studies of the nanoparticle and the isolated chain reveal the alternative role between the intrachain covalent bonds and the interchain interaction.

Influence factors and adjusting method of refractive indices of solid media

2018 ◽  
Vol 32 (32) ◽  
pp. 1850391 ◽  
Author(s):  
Tao Zhang
Keyword(s):  
Refractive Index ◽  
Solid Medium ◽  
Influence Factors ◽  
Covalent Bond ◽  
High Refractive Index ◽  
Covalent Bonds ◽  
Molecular Density ◽  
Nephelauxetic Effect ◽  
Solid Media ◽  
Bond Property

It is of great significance to explore changing behavior and adjustment method of the refractive index. Expression of the refractive index, which was derived from the electron-cloud conductor model, contains the equivalent volume V of the electron clouds and the molecular density [Formula: see text]. The expression shows that the refractive index increases with V and [Formula: see text]. Based on this expression, main factors influencing the refractive index of solid medium are analyzed and summarized: the Nephelauxetic Effect, number of bonding electrons in the molecule, chemical bond property, number of nonbonding electrons in outermost layer of the molecule, and molecular density of the medium (electromagnetic wave factor is not considered). The relationship between the refractive index and the Nephelauxetic Effect is established. The calculations show that the Nephelauxetic Effect helps to increase the refractive index. Some viewpoints related to the Nephelauxetic Effect are supplemented. Characteristics of the solid medium that has a high refractive index are proposed: (1) Covalent bond component is high, and number of covalent bonds in one molecule is large. (2) Periodic number is as large as possible without increasing the ionic bond component. (3) Molecular density is high. According to these characteristics, method of adjusting the refractive index is discussed, and the results are consistent with the real situations.

scholarly journals Protein-Based Nanohydrogels for Bioactive Delivery

2021 ◽  
Vol 9 ◽  
Author(s):  
Subhash Chander ◽  
Giriraj T. Kulkarni ◽  
Neerupma Dhiman ◽  
Harsha Kharkwal
Keyword(s):  
Drug Delivery ◽  
Electrostatic Interactions ◽  
Hydrophobic Interactions ◽  
Biological Fluids ◽  
Three Dimensional ◽  
Covalent Bond ◽  
Ionic Concentration ◽  
Covalent Bonds ◽  
Encapsulation Process ◽  
Insightful Analysis

Hydrogels possess a unique three-dimensional, cross-linked network of polymers capable of absorbing large amounts of water and biological fluids without dissolving. Nanohydrogels (NGs) or nanogels are composed of diverse types of polymers of synthetic or natural origin. Their combination is bound by a chemical covalent bond or is physically cross-linked with non-covalent bonds like electrostatic interactions, hydrophobic interactions, and hydrogen bonding. Its remarkable ability to absorb water or other fluids is mainly attributed to hydrophilic groups like hydroxyl, amide, and sulphate, etc. Natural biomolecules such as protein- or peptide-based nanohydrogels are an important category of hydrogels which possess high biocompatibility and metabolic degradability. The preparation of protein nanohydrogels and the subsequent encapsulation process generally involve use of environment friendly solvents and can be fabricated using different proteins, such as fibroins, albumin, collagen, elastin, gelatin, and lipoprotein, etc. involving emulsion, electrospray, and desolvation methods to name a few. Nanohydrogels are excellent biomaterials with broad applications in the areas of regenerative medicine, tissue engineering, and drug delivery due to certain advantages like biodegradability, biocompatibility, tunable mechanical strength, molecular binding abilities, and customizable responses to certain stimuli like ionic concentration, pH, and temperature. The present review aims to provide an insightful analysis of protein/peptide nanohydrogels including their preparation, biophysiochemical aspects, and applications in diverse disciplines like in drug delivery, immunotherapy, intracellular delivery, nutraceutical delivery, cell adhesion, and wound dressing. Naturally occurring structural proteins that are being explored in protein nanohydrogels, along with their unique properties, are also discussed briefly. Further, the review also covers the advantages, limitations, overview of clinical potential, toxicity aspects, stability issues, and future perspectives of protein nanohydrogels.

2. The fundamentals

2017 ◽  
pp. 6-24
Author(s):  
Graham Patrick
Keyword(s):  
Functional Groups ◽  
Atomic Number ◽  
Outer Shell ◽  
Intramolecular Interactions ◽  
Covalent Bonds ◽  
Linear Chains ◽  
Element Carbon ◽  
Carbon Carbon Bonds ◽  
Valence Electrons ◽  
Branched Chains

‘The fundamentals’ investigates why the element carbon is so suited for the generation of so many compounds. Carbon has atomic number six, meaning it has six protons in its nucleus and six electrons around the nucleus, four of which are valence electrons held in the outer shell. Carbon achieves a stable, full outer shell of electrons by sharing electrons with other elements and other carbon atoms to form covalent bonds. The carbon–carbon bonds are one of the principle reasons why so many organic molecules are possible, including linear chains, branched chains, and rings. The naming of compounds and identification of structures is also explained along with stereochemistry, functional groups, and intermolecular and intramolecular interactions.

Characterization of Si–C Covalent Bonding Fabricated between Single Carbon Nanotube and Si Substrate

2014 ◽  
Vol 543-547 ◽  
pp. 3711-3715
Author(s):  
Xia Liu ◽  
Lian Zhen Cao
Keyword(s):  
Carbon Nanotube ◽  
Vapor Deposition ◽  
Covalent Bonding ◽  
Si Substrate ◽  
Covalent Bonds ◽  
Thermal Vapor Deposition ◽  
Individual Cnts ◽  
Imaging And Spectroscopy ◽  
Gas Blowing

The SiC covalent bonding between Carbon nanotube and Si substrate was fabricated by thermal vapor deposition using photolithography and gas blowing technology. Scanning electron microscopy, micro-Raman imaging and spectroscopy were used to investigate the interaction of individual CNTs and Si substrate. The characterization results showed that covalent bonds were formed between certain CNTs and Si substrate. Moreover, the reasons for the fabrication of SiC covalent bonding between CNTs and Si substrate were also proposed.

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