Computer models in teaching chemistry. Chemical models of natural objects
O.S.GABRIELYAN,
I.G. OSTROUMOV,
A.K.AKHLEBININ
START IN CHEMISTRY
7th grade
Continuation. See the beginning in No. 1, 2/2006
Chapter 1.
Chemistry at the center of natural science
(continuation)
§ 3. Modeling
In addition to observation and experiment, modeling plays an important role in understanding the natural world and chemistry.
We have already said that one of the main goals of observation is to search for patterns in the results of experiments.
However, some observations are inconvenient or impossible to carry out directly in nature. Natural environment recreated in laboratory conditions using special devices, installations, objects, i.e. models. Only the most important ones are copied in the models important signs and properties of the object and those that are not essential for study are omitted. The word “model” has French-Italian roots and is translated into Russian as “sample”. Modeling is the study of a certain phenomenon using its models, i.e. substitutes, analogues.
For example, in order to study lightning ( a natural phenomenon), scientists did not have to wait for bad weather. Lightning can be simulated in physics class and in the school laboratory. Two metal balls need to be given opposite electrical charges - positive and negative. When the balls approach a certain distance, a spark jumps between them - this is lightning in miniature. The greater the charge on the balls, the earlier the spark jumps when approaching, the longer the artificial lightning. Such lightning is produced using a special device called an electrophore machine.
Studying the model allowed scientists to determine that natural lightning is a giant electrical discharge between two thunderclouds or between clouds and the ground. However, a real scientist strives to find practical application for each phenomenon studied. The more powerful the electric lightning, the higher its temperature. But the conversion of electrical energy into heat can be “tamed” and used, for example, for welding and cutting metals. This is how the electric welding process, familiar to everyone today, was born.
Each natural science uses its own models that help to visually imagine a real natural phenomenon or object.
The most famous geographical model is the globe. This is a miniature three-dimensional image of our planet, with the help of which you can study the location of continents and oceans, countries and continents, mountains and seas. If an image of the earth's surface is drawn on a sheet of paper, then such a model is called a map.
Modeling in physics is used especially widely. In lessons on this subject, you will become familiar with a variety of models that will help you study electrical and magnetic phenomena, patterns of movement of bodies, and optical phenomena.
Models are also widely used in the study of biology. It is enough to mention, for example, models - dummies of a flower, human organs, etc.
Modeling is no less important in chemistry. Conventionally, chemical models can be divided into two groups: material and symbolic (or symbolic).
Material models Chemists use atoms, molecules, crystals, chemical production for greater clarity.
You've probably seen a picture of a model of an atom that resembles the structure solar system(Fig. 30).
To model the molecules of chemical substances, ball-and-stick or three-dimensional models are used. They are assembled from balls symbolizing individual atoms. The difference is that in ball-and-rod models the ball-atoms are located at a certain distance from each other and are fastened to each other by rods. For example, ball-and-stick and volumetric models of water molecules are shown in Fig. 31.
Models of crystals resemble ball-and-stick models of molecules, however, they do not depict individual molecules of a substance, but show the relative arrangement of particles of a substance in a crystalline state (Fig. 32).
However, most often chemists use not material, but iconic models- these are chemical symbols, chemical formulas, equations of chemical reactions.
You will start speaking chemical language, the language of signs and formulas from the next lesson.
1. What is a model and what is modeling?
2. Give examples of: a) geographical models; b) physical models; c) biological models.
3. What models are used in chemistry?
4. Make ball-and-stick and three-dimensional models of water molecules from plasticine. What shape do these molecules have?
5. Write down the formula for the cruciferous flower if you studied this plant family in biology class. Can this formula be called a model?
6. Write down an equation to calculate the speed of a body if the path and time it takes the body to travel are known. Can this equation be called a model?
§ 4. Chemical signs and formulas
Symbolic models in chemistry include signs or symbols chemical elements, formulas of substances and equations of chemical reactions that form the basis of “chemical writing”. Its founder is the Swedish chemist Jens Jakob Berzelius. Berzelius's writing is based on the most important of chemical concepts - “chemical element”. A chemical element is a type of identical atoms.
Berzelius proposed denoting chemical elements by the first letter of their Latin names. So the symbol of oxygen became the first letter of its Latin name: oxygen - O (read “o”, because the Latin name of this element oxygenium ). Accordingly, hydrogen received the symbol H (read “ash”, since the Latin name of this element is hydrogenium), carbon – C (read “ce”, because the Latin name of this element carboneum). However Latin names chromium ( chromium ), chlorine ( chlorum
) and copper (
cuprum
) just like carbon, begin with “C”. How to be? Berzelius proposed an ingenious solution: write such symbols with the first and one of the subsequent letters, most often the second. Thus, chromium is designated Cr (read “chrome”), chlorine is Cl (read “chlorine”), copper is Cu (read “cuprum”).
Russian and Latin names, signs of 20 chemical elements and their pronunciations are given in table. 2.
| Our table only fit 20 elements. | To see all 110 elements known today, you need to look at D.I. Mendeleev’s table of chemical elements. | table 2 | Names and symbols of some chemical elements |
|---|---|---|---|
| Russian name | Chemical sign | Pronunciation | Latin name |
| Nitrogen | N | Nitrogen | En |
| Nitrogenium | Aluminum | Al | Aluminum |
| Hydrogen | N | Ash | Hydrogenium |
| Iron | Fe | Ferrum | Ferrum |
| Gold | Au | Gold | Aurum |
| Aurum | Potassium | Aurum | K |
| Kalium | Calcium | Calcium | Ca |
| Calcium | Oxygen | Calcium | ABOUT |
| Oxigenium | Magnesium | Mg | Magnium |
| Copper | Cu | Copper | Kuprum |
| Cuprum | Sodium | Na | Natrium |
| Mercury | Hg | Hydrargyrum | Hydrargirum |
| Lead | Pb | Plumbum | Plumbum |
| Sulfur | S | Es | Sulfur |
| Silver | Ag | Argentum | Argentum |
| Carbon | WITH | Tse | Carboneum |
| Phosphorus | R | Phosphorus | Pe |
| Phosporus | Chlorine | Phosporus | Cl |
| Chlorum | Chromium | Chlorum | Cr |
Chromium Zinc Zn Zincum Most often, substances contain atoms of several chemical elements. You can depict the smallest particle of a substance, for example a molecule, using ball models as you did in the previous lesson. In Fig. 33 shows three-dimensional models of water molecules(A) , sulfur dioxide.
More often, chemists use symbolic rather than material models to designate substances. Formulas of substances are written using symbols of chemical elements and indices. The index shows how many atoms of a given element are included in the molecule of a substance. It is written at the bottom right of the chemical element symbol. For example, the formulas of the substances mentioned above are written as follows: H 2 O, SO 2, CH 4, CO 2.
The chemical formula is the main symbolic model in our science. It carries information that is very important for a chemist. The chemical formula shows: a specific substance; one particle of this substance, for example one molecule; high-quality composition substances, i.e. atoms of which elements are included in the composition of this substance; quantitative composition, i.e. how many atoms of each element are included in a molecule of a substance.
The formula of a substance can also determine whether it is simple or complex.
Simple substances are substances consisting of atoms of one element. Complex substances are formed by atoms of two or more different elements.
For example, hydrogen H2, iron Fe, oxygen O2 - simple substances, and water H 2 O, carbon dioxide CO 2 and sulfuric acid H 2 SO 4 – complex.
1. Which chemical elements have the capital letter C in their symbols? Write them down and say them.
2. From the table 2 Write down the signs of the metal and non-metal elements separately.
3. Say their names.
What is the chemical formula? Write down the formulas of the following substances:
a) sulfuric acid, if it is known that its molecule contains two hydrogen atoms, one sulfur atom and four oxygen atoms;
b) hydrogen sulfide, the molecule of which consists of two hydrogen atoms and one sulfur atom;
4. c) sulfur dioxide, a molecule of which contains one sulfur atom and two oxygen atoms.
What do all these substances have in common?
Make three-dimensional models of molecules of the following substances from plasticine:
a) ammonia, a molecule of which contains one nitrogen atom and three hydrogen atoms;
b) hydrogen chloride, the molecule of which consists of one hydrogen atom and one chlorine atom;
c) chlorine, the molecule of which consists of two chlorine atoms.
5. Write the formulas of these substances and read them.
6. Give examples of transformations when lime water is a determined substance, and when it is a reagent.
7. Conduct a home experiment to determine starch in food. What reagent did you use for this? In Fig. 33 shows models of four molecules. How many chemical elements do these substances form? Write down their symbols and say their names.
8. Take plasticine of four colors. Roll the smallest balls white - these are models of hydrogen atoms, larger blue balls are models of oxygen atoms, black balls are models of carbon atoms and, finally, the largest balls yellow color
– models of sulfur atoms. (Of course, we chose the color of the atoms arbitrarily, for clarity.) Using ball-atoms, make three-dimensional models of the molecules shown in Fig. 33.
Physico-chemical model of processes in an anodic microdischarge V.F. Borbat, O.A. Golovanova, A.M. Sizikov, Omsk State University
, Department of Inorganic Chemistry Oxide layers formed on anodes made of aluminum, titanium, tantalum and some other metals during the passage electric current between electrodes immersed in an electrolyte, in some cases they have high protective and dielectric properties. Currently, laboratories in various countries are conducting a significant amount of research aimed at establishing the possibilities of improving the protective and electrical properties of anodic coatings, searching for optimal electrolyte compositions, increasing the manufacturability of the process, and so on. Accumulated in Lately practical experience in using plasma-electrolytic anodic treatment to create protective coatings has significantly outstripped those available in specified area
theoretical ideas.
Based on the literature and our experimental data, we can accept the physical model of the anodic microdischarge, the main idea of which is that the anodic microdischarge is a combination of spark breakdown of the barrier part of the oxide film and a gas discharge in the gas-plasma bubble that appears after the breakdown. Let us consider the correspondence of the proposed model to experimental results, taking into account the sequence of processes.
When studying the phase and elemental composition of coatings obtained by plasma-electrolytic treatment, it was found that with this method of producing coatings, sulfate ions are introduced into the film. Moreover, the appearance of the recording patterns gives reason to assume that the “earning” of the electrolyte components occurs in places where anodic microdischarges occur at the time of their “healing”, therefore the distribution of the electrolyte components throughout the film is not uniform and differs from the distribution in films obtained by conventional anodization.
Breakdown is a complex probabilistic process that can occur at a given point of a dielectric in a fairly wide range of voltages and time. The most important processes for the onset of breakdown are a change in the space charge near the cathode (electrolyte solution) and an increase in the volumetric injection of electrons into the conduction zone of the dielectric film. These processes contribute to the development of a breakdown. The onset of breakdown is associated with the development of electron avalanches. It is likely that the source of primary ions may be impurity levels in the oxide. This mechanism assumes a special role for the electrolyte components embedded in the oxide, primarily anions. That is why the possibility of obtaining anodic-spark coatings is largely determined by the composition of the solution. Electrons entering the conduction band and accelerated by the field acquire energy sufficient to cause impact ionization of atoms in the oxide. The latter leads to the occurrence of avalanches, which, upon reaching the metal surface, form breakdown channels. The existence of a linear dependence of the breakdown voltage on the thickness indicates the uniformity of the field during breakdown and the electrical nature of the breakdown.
Destruction of the oxide film - when exposed to anodic microdischarges on sulfuric acid solutions, water and sulfuric acid molecules will be exposed to electrons accelerated in the electric field. Data on the ionization of these solutions are available in the literature. Based on them, the most probable ions in microdischarge plasma will most likely be ions with the lowest potentials of appearance, i.e. for water molecules one would expect H2O+, for sulfuric acid H2SO4+ and less likely HSO4+.
So, the processes of ionization and dissociative attachment of electrons produce the following ions when exposed to microdischarges on sulfuric acid solutions (reactions 1-5). e + H2O H2O+ + 2e (1), e + H2SO4 H2SO4+ + 2e (2), or HSO4 + H+ + 2e (3), e + H2O OH + H- (4), e + H2SO4 H + HSO4- (5).
The positive and negative ions formed in these reactions have two different ways their transformations: 1) neutralization of charges; 2) ion-molecular reactions. The radicals formed as a result of the dissociation of excited particles and ion-molecular reactions enter into reactions of abstraction of the H atom from the molecules located in the gas bubble and in recombination reactions.
After the formation of radicals, there are reactions of abstraction of the H atom: H(OH, HSO4) + H2SO4 → H2(H2O, H2SO4) + HSO4 (6), H(HSO3) + H2O → H2(H2SO3) + OH (7) and recombination reactions of radicals : HSO4 + OH H2SO4 (8), HSO4 + HSO4 H2S2O8 (9), OH + OH H2O2 (10), H + HSO4 H2SO4 (11).
The formation of sulfur dioxide is possible as a result of the interaction of plasma-excited microdischarges of sulfuric acid molecules with neighboring molecules: H2SO4* + H2SO4 H2SO3 + H2SO5 (12), or the mechanism is also possible: H2SO4* H2SO3 + O (13). Due to the high temperature in the microdischarge zone, the resulting H2SO3 and H2SO5 thermally dissociate according to the equations:
H2SO3 H2O + SO2 (14), 2H2SO5 2H2SO4 + 0.5 O2 (15).
Some radicals go beyond the gas bubble of the microdischarge into the surrounding liquid, where they enter into recombination reactions with each other and react with the components of the electrolyte. The yield of products as a result of processes occurring in the near-bubble layer of the electrolyte will depend on the concentration of sulfuric acid (i.e., on the proportion of ions present in solutions of sulfuric acid of different concentrations).
According to the proposed mechanism of chemical transformations of sulfuric acid, with an increase in its concentration in the solution, otherwise, with an increase in its concentration in the gas bubble of a microdischarge, there will be an increase in the number of directly ionized and excited by electron impact sulfuric acid molecules. Since, due to low ionization at electron energies typical for a gas discharge, chemical transformations of substances are carried out mainly through excited states, then in the case of exposure to microdischarges with an increase in the concentration of sulfuric acid, one should expect an increase in the yield of products for which excited particles are the precursor.
With an increase in the concentration of sulfuric acid (more than 14 M), the proportion of sulfuric acid molecules in the gas-plasma bubble increases, and accordingly, the decomposition of the dissolved substance occurs due to direct action microdischarge plasma. For solutions of sulfuric acid less than 14 M, the transformation of the solute mainly occurs due to the action of plasma on the solvent - indirect action. Due to this, the likelihood of reactions 9,10,11,13 occurring, leading to the formation of stable molecular products: sulfur dioxide and peroxide compounds, increases.
“Healing” the pore - further expansion of the plasma formation quickly leads to significant reduction temperature of the latter and, as a consequence, to a decrease in the concentration of discharge carriers, current interruption and rapid cooling of the channel. The disappearance of the gas-plasma bubble will occur after the gas discharge in it is extinguished. The extinction of a gas discharge, as is known, will occur when the current density in it decreases below the minimum permissible for self-sustaining discharge. In the case of microdischarges, the reasons for the decrease in gas discharge current density may be: 1) depletion of the near-bubble electrolyte layer with current carriers over time, due to which the electrolyte becomes unable to provide the minimum current density permissible for self-sustaining of the discharge, and the gas discharge goes out; 2) an increase in the size of the microdischarge bubble due to the evaporation of the surrounding liquid into it; 3) melting or “healing” (by anodizing in a gas plasma) of the breakdown channel in the barrier part of the oxide film. The crater formed during the first breakdown usually reaches the metal surface. At this point, the current density becomes maximum due to the relatively low resistance of the electrolyte in the crater, which ensures the rapid appearance of an oxide film (a product of the plasma-chemical reaction MexOy). The breakdown site is “healed,” and the thickness of the oxide film increases, mainly deep into the substrate material.
Thus, based on the experimental results and literature data, the work proposes a mechanism for the effect of an anodic microdischarge on sulfuric acid solutions, including the following stages:
The formation of excited and ionized molecules in a microdischarge bubble due to the flow of a gas discharge in it;
The occurrence of reactions with the formation of radicals and molecular products, the reactions of which with each other and the starting substances give the bulk of the final products;
Diffusion removal of the resulting radicals and other particles outside the gas bubble, the reactions of which lead to final molecular products in the near-bubble electrolyte layer.
Bibliography
Bakovets V.V., Polyakov O.V., Dolgovesova I.P. Plasma-electrolytic anodic processing of metals // Novosibirsk: Science, 1991. P.63-68.
Nagatant T.,Yashinara S.T. Studies on the fragment ion distribution and their reaction by the of a charge spectrometer // J. Bull. chem. Soc. Jap., 1973. V.46. N 5. P.1450-1454.
Mann M., Hastrulid A., Tate J. Ionization and dissociation of water vapor and ammonia by electron impact // J. Phys. Rev. 1980. V.58. P.340-347.
Ivanov Yu.A., Polak L.S. Energy distribution of electrons in low-temperature plasma // Plasma Chemistry M.: Atomizdat, 1975. Vol. 2. P.161-198.
To prepare this work, materials were used from the site http://www.omsu.omskreg.ru/
1.4.1 Chemical models
In addition to observation and experiment, modeling plays an important role in understanding the natural world and chemistry. One of the main goals of observation is to search for patterns in the results of experiments. However, some observations are inconvenient or impossible to carry out directly in nature. The natural environment is recreated in laboratory conditions with the help of special devices, installations, objects, i.e., models. Models copy only the most important features and properties of an object and omit those that are not essential for study. Thus, in chemistry, models can be divided into two groups: material and iconic.
Models of chemical and industrial apparatus
Chemists use material models of atoms, molecules, crystals, and chemical industries for greater clarity.
The most common representation of an atom is a model that resembles the structure of the solar system.
To model the molecules of substances they often use ball-and-rod models. Models of this type are assembled from colored balls that represent the atoms that make up the molecule. The balls are connected by rods, symbolizing chemical bonds. Using ball-and-stick models, bond angles in a molecule are reproduced quite accurately, but internuclear distances are reflected only approximately, since the lengths of the rods connecting the balls are not proportional to the lengths of the bonds.
Dreading Models quite accurately convey bond angles and the ratio of bond lengths in molecules. The nuclei of atoms in them, unlike ball-and-rod models, are designated not by balls, but by points of connection between the rods.
Hemispherical models, also called Stewart-Brigleb models, they are assembled from balls with cut segments. Atom models are connected to each other by slice planes using buttons. Hemispherical models accurately convey both the ratio of bond lengths and bond angles, as well as the occupancy of the internuclear space in molecules. However, this fullness does not always allow one to obtain a visual representation of the relative position of the nuclei.
Models of crystals resemble ball-and-stick models of molecules, however, they do not depict individual molecules of a substance, but show the relative arrangement of particles of a substance in a crystalline state.
However, more often chemists use not material, but iconic models – These are chemical symbols, chemical formulas, equations of chemical reactions. Formulas of substances are written using symbols of chemical elements and indices. The index shows how many atoms of a given element are included in the molecule of a substance. It is written to the right of the chemical element symbol.
A chemical formula is the main symbolic model in chemistry. It shows: a specific substance; one particle of this substance; qualitative composition of a substance, i.e., atoms of which elements are included in the composition of this substance; quantitative composition, i.e., how many atoms of each element are included in the molecule of a substance.
All of the above models are widely used in creating interactive computer models.
1.4.2 Classification of computer models
Among the various types of pedagogical software, those that use computer models are especially distinguished. The use of computer models allows not only to increase the visibility of the learning process and intensify it, but also to radically change this process. IN last years The improvement of computers is proceeding at a rapid pace, and their possibilities for modeling have become almost limitless, so the importance of computer models in the study of school disciplines can increase significantly. E.E. Nifantiev, A.K. Akhlebinin, V.N. Likhachev note that the main advantage of computer models is the ability to simulate almost any processes and phenomena, interactive user interaction with the model, as well as the implementation of problem-based, research approaches in the learning process.
V. N. Likhachev proposes to classify educational computer models according to a number of criteria, the main ones being the presence of animation when displaying the model, the control method, and the method of visual display of the model. Based on the presence of animation, RCMs can be dynamic or static. Dynamic ones contain animation fragments to display simulated objects and processes; static ones do not have them. According to the method of control, CCMs can be controlled, which allow you to change the parameters of the model, and uncontrolled, which do not provide such an opportunity.
Among the demonstration (uncontrolled) models, two more groups can be distinguished according to the possibility of interaction with the user: interactive and non-interactive. Interactive ones allow you to change the type of display of the model or the observation point on the model without changing its parameters. Non-interactive ones do not provide such opportunities.
E.E. Nifantiev, A.K. Akhlebinin and V.N. Likhachev is considered the most useful from a methodological point of view classification according to the modeling object. Based on the level of represented objects, models used in teaching chemistry can be divided into two groups : models of the macroworld, which reflect the external properties of the simulated objects and their changes And microworld models, which reflect the structure of objects and the changes occurring in them at the level of their atomic-molecular representation. And models of such objects as chemical substances, chemical reactions and physical and chemical processes can be created both at the level of the microworld and at the level of the macrocosm.
The classification of UCM can be presented in the form of a diagram for greater clarity.
1.4.3 Computer models of the microworld
Objects for modeling at the microworld level are atoms, ions, molecules, crystal lattices, and structural elements of atoms. At the level of the microcosm, the structural features of matter and the interactions of the particles that make up the matter are modeled. For modeling chemical reactions at the microcosm level, the mechanisms of chemical processes are of great interest. And in models of physical and chemical processes, processes occurring at the electronic or atomic-molecular level are considered.
It is clear that CCMs that simulate models of the microworld become excellent assistants in studying the structure of atoms, types of chemical bonds, structure of matter, etc.
Models of atoms of periods 1–3 of the periodic table are implemented in the program “ 1C: Tutor. Chemistry» in the form of models of the Bohr atom. More modern ideas about the structure of the atom are implemented in the program Chemland, where the distribution of electrons among the energy sublevels of atoms of elements and the type of individual orbitals at various energy levels are considered.
Of particular interest is the program HyperChem. It is one of the main professional programs for the theoretical calculation of various thermodynamic and electronic parameters of molecules. With its help, it is possible to build spatial models of various compounds, study the features of their geometric structure, determine the shape and energy of molecular orbitals, the nature of the electron density distribution, dipole moment, etc. All output data is provided in the form of color drawings, which can then be printed on printer, obtaining high-quality images of chemical compounds in the required angles and projections. The advantage of the program is the ability to examine a molecule from different angles and become familiar with the features of its spatial structure. This seems extremely important, since, as teaching practice shows, students usually do not develop ideas about molecules as spatial structures. The traditional depiction of chemicals in one plane leads to the loss of an entire dimension and does not stimulate the development of spatial imagination.
In the multimedia course " Chemistry for everyone» a program is used - a stereo demonstrator of molecules. It allows you to provide three-dimensional images of molecules consisting of hydrogen, oxygen, carbon and nitrogen atoms. Wireframe models of molecules are used for demonstration. Models can be moved, rotated, and images of several different molecules can be shown simultaneously. The program allows you to create new models of molecules yourself. In total, models of 25 organic molecules are given, however, the didactic value of these models is small, since the models provided are fairly simple compounds that every student can assemble using plasticine and matches.
Demonstration orbital-blade three-dimensional models of some molecules are implemented in the program " Valence bond method: hybridization of atomic orbitals." And in the program “ Nature of the chemical bond"explains the reasons for the formation of a chemical bond using the example of the formation of a hydrogen molecule from atoms. Both of these programs are included in the set of training programs " Chemistry for everyone – 2000».
Interactive demo wireframes used in programs ChemLand– 115 molecules of predominantly organic compounds, and “ Chemistry for everyone" These two programs have their pros and cons: in the “Chemistry for Everyone” program, models can be shown on the full screen of the monitor, but in the ChemLand program there is no such function, however, the program presents a large number of molecules. In the ChemLand program dynamic models are used that demonstrate the spatial structure of molecules with the ability to measure bond angles and bond lengths, which makes it possible to trace the change in polarity of a triangular molecule depending on the type of atoms.
When studying the structure of molecules and crystals, programs more intended for research purposes can be useful. For example, this is the program CS Chem3D Pro, which allows you to create, modify and display the three-dimensional structure of various molecules. The program is also useful Crystal Designer, which is designed to visualize the three-dimensional structure of the crystal lattice. These programs can be useful in creating three-dimensional images of molecules and crystals and for demonstrating them in class using a computer.
Program " Assemble the molecule", although inferior in its capabilities to the above-mentioned programs, can be effectively used for individual work of schoolchildren.
Models of physical and chemical processes and mechanisms are implemented in the program " Chemistry for everyone" Non-interactive models on the topic “Electrolytic dissociation” are demonstrated here: dissociation of salts, acids, alkalis, hydrolysis of salts. The same program implements some models of organic reaction mechanisms: bromination of alkanes, esterification, general mechanism of polymerization reactions, etc. All models of reaction mechanisms are non-interactive, shown in full screen, have sound, but there is no text description of the phenomena occurring, which significantly limits the use of the program.
In the online version of the interactive textbook for secondary school in organic chemistry for grades X – XI, edited by G. I. Deryabina, A. V. Solovov the exchange and donor-acceptor mechanisms of covalent bond formation, homolytic and heterolytic mechanisms of covalent bond cleavage using the example of the abstraction of a hydrogen atom from a methane molecule, and the process of sp - hybridization are presented. Of great interest interactive 3D demonstration models of organic molecules and mechanisms of chemical reactions: methane chlorination and the general mechanism of nucleophilic substitution. It is very important that when working with models, you can change their position in space, and for the reaction mechanism, you can change the position of the observation point.
Another program demonstrating the mechanisms of chemical reactions, program Organic Reaction Animations. It contains 34 organic reaction mechanisms. Moreover, each mechanism is presented in the form of four variants of molecular models: ball-and-rod, volumetric and two variants of orbital-blade models. One of the variants of orbital-blade models demonstrates a change in the outer orbitals of the substrate during the reaction, and the other - the reagent. This makes it easier to observe the change in the outer orbitals of the reactants during the reaction. If necessary, you can use the theoretical material of the interactive multichannel cognition tool. Development students of their own...
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1.4.1 Chemical models
In addition to observation and experiment, modeling plays an important role in understanding the natural world and chemistry. One of the main goals of observation is to search for patterns in the results of experiments. However, some observations are inconvenient or impossible to carry out directly in nature. The natural environment is recreated in laboratory conditions with the help of special devices, installations, objects, i.e., models. Models copy only the most important features and properties of an object and omit those that are not essential for study. Thus, in chemistry, models can be divided into two groups: material and symbolic.
Chemists use material models of atoms, molecules, crystals, and chemical industries for greater clarity.
The most common representation of an atom is a model that resembles the structure of the solar system.
Ball-and-stick models are often used to model the molecules of substances. Models of this type are assembled from colored balls that represent the atoms that make up the molecule. The balls are connected by rods, symbolizing chemical bonds. Using ball-and-stick models, bond angles in a molecule are reproduced quite accurately, but internuclear distances are reflected only approximately, since the lengths of the rods connecting the balls are not proportional to the lengths of the bonds.
Dreding's models quite accurately convey bond angles and bond length ratios in molecules. The nuclei of atoms in them, unlike ball-and-rod models, are designated not by balls, but by points of connection between the rods.
Hemispherical models, also called Stewart-Brigleb models, are assembled from balls with cut segments. Atom models are connected to each other by slice planes using buttons. Hemispherical models accurately convey both the ratio of bond lengths and bond angles, as well as the occupancy of the internuclear space in molecules. However, this fullness does not always allow one to obtain a visual representation of the relative position of the nuclei.
Models of crystals resemble ball-and-stick models of molecules, however, they do not depict individual molecules of a substance, but show the relative arrangement of particles of a substance in a crystalline state.
However, more often chemists use symbolic rather than material models - these are chemical symbols, chemical formulas, equations of chemical reactions. Formulas of substances are written using symbols of chemical elements and indices. The index shows how many atoms of a given element are included in the molecule of a substance. It is written to the right of the chemical element symbol.
A chemical formula is the main symbolic model in chemistry. It shows: a specific substance; one particle of this substance; qualitative composition of a substance, i.e., atoms of which elements are included in the composition of this substance; quantitative composition, i.e., how many atoms of each element are included in the molecule of a substance.
All of the above models are widely used in creating interactive computer models.
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Study of the kinetics of the alkylation reaction of isobutane with isobutylene to isooctane by the method mathematical modeling
Study of the kinetics of benzene chlorination reaction
R = k*C1*Ck? For the best processing of the resulting model, we will transform the form of the function, since the dependence of the reaction rate on time is constant and for the first 3 experiments is equal to 0.0056...
Modeling method in chemistry
Currently, you can find many different definitions of the concepts “model” and “simulation”. Let's look at some of them. “A model is understood as a representation of facts, things and relationships of a certain field of knowledge in the form of a simpler...
Scientific foundations of rheology
The stress-strain state of a body is generally three-dimensional and it is unrealistic to describe its properties using simple models. However, in those in rare cases when uniaxial bodies are deformed...
Synthesis and analysis of chemical substances in gasoline production
The chemical model of the catalytic cracking process has a very complex look. Let's consider the simplest of the reactions occurring during the cracking process: CnH2n+2 > CmH2m+2 + CpH2p...
Synthesis of chemical technological system (CTS)
Production processes varied in their characteristics and degree of complexity. If the process is complex and deciphering its mechanism requires a lot of effort and time, an empirical approach is used. Mathematical models...
Comparison of plug-flow and full-mix reactors in isothermal operating mode