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. The natural environment is recreated in laboratory conditions with the help of special devices, installations, objects, i.e. models (from the Latin modulus - measure, sample). Models copy only the most important features and properties of an object.

For example, in order to study the natural phenomenon of lightning, scientists did not have to wait for a thunderstorm. 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 (Fig. 33).

Rice. 33.
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 used, for example, for welding and cutting metals. This is how the electric welding process, familiar to every student today, appeared (Fig. 34).

Rice. 34.
The natural phenomenon of lightning can be simulated in the laboratory

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.

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 (Fig. 35, a) - a miniature three-dimensional image of our planet, with 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 applied to a flat sheet of paper, then such a model is called a geographic map (Fig. 35, b).

Rice. 35.
The most famous geographical models: a - globe; b - map

Models are widely used in the study of biology. It is enough to mention, for example, models - dummies of human organs, etc. (Fig. 36).

Rice. 36.
Biological models: a - eye; b - brain

Modeling is no less important in chemistry. Conventionally, chemical models can be divided into two groups: objective and symbolic, or symbolic (Scheme 1).

Subject models of atoms, molecules, crystals, chemical industrial plants are used for greater clarity.

You've probably seen a picture of a model of an atom that resembles the structure of the solar system (Fig. 37).

Rice. 37.
Atomic structure model

Ball-and-stick or three-dimensional models are used to model chemical molecules. They are assembled from balls symbolizing individual atoms. The difference is that in ball-and-stick 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 three-dimensional models of water molecules are shown in Figure 38.

Rice. 38.
Models of a water molecule: a - ball-and-rod; b - volumetric

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. 39).

Rice. 39.
Copper crystal model

However, most often chemists use not object-based, but iconic, or symbolic, models. These are chemical symbols, chemical formulas, equations of chemical reactions.

You will begin learning the chemical language of signs and formulas in the next lesson.

Questions and tasks

1. What is a model? 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?

Many schoolchildren do not like chemistry and consider it a boring subject. Many people find this subject difficult. But studying it can be interesting and educational if you approach the process creatively and show everything clearly.

We offer you a detailed guide to sculpting molecules from plasticine.

Before making molecules, we need to decide in advance what chemical formulas we will use. In our case, these are ethane, ethylene, methylene. We will need: plasticine in contrasting colors (in our case, red and blue) and some green plasticine, matches (toothpicks).

1. Roll 4 balls with a diameter of about 2 cm (carbon atoms) from red plasticine. Then roll 8 smaller balls from blue plasticine, about a centimeter in diameter (hydrogen atoms).

2. Take 1 red ball and insert 4 matches (or toothpicks) into it as shown in the picture.

3. Take 4 blue balls and put them on the free ends of the matches inserted into the red ball. The result is a molecule of natural gas.

4. Repeat step No. 3 and get two molecules for the next chemical substance.

5. The molecules made must be connected to each other with a match in order to form an ethane molecule.

6. You can also create a molecule with a double bond - ethylene. To do this, from each molecule obtained in step No. 3, take out 1 match with a blue ball on it and connect the parts together with two matches.

7. Take a red ball and 2 blue ones and connect them together with two matches so that you get a chain: blue – 2 matches – red – 2 matches – blue. We have another molecule with a double bond - methylene.

8. Take the remaining balls: red and 2 blue and connect them with matches as shown in the figure. Then we roll 2 small balls from green plasticine and attach them to our molecule. We have a molecule with two negatively charged electrons.

Studying chemistry will become more interesting, and your child will develop an interest in the subject.

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Today we will conduct a lesson not only in modeling, but also in chemistry, and we will make models of molecules from plasticine. Plasticine balls can be imagined as atoms, and ordinary matches or toothpicks will help to show structural connections. This method can be used by teachers when explaining new material in chemistry, by parents when checking and studying homework, and by children themselves who are interested in the subject. There is probably no easier and more accessible way to create visual material for mental visualization of micro-objects.

Here are representatives from the world of organic and inorganic chemistry as examples. By analogy with them, other structures can be made, the main thing is to understand all this diversity.

Materials for work:

• plasticine of two or more colors;
• structural formulas of molecules from the textbook (if necessary);
• matches or toothpicks.

1. Prepare plasticine for modeling spherical atoms from which molecules will be formed, as well as matches to represent the bonds between them. Naturally, it is better to show atoms of different types in a different color, so that it is clearer to imagine a specific object in the microworld.

2. To make balls, pinch off the required number of portions of plasticine, knead in your hands and roll into shapes in your palms. To sculpt organic hydrocarbon molecules, you can use larger red balls - this will be carbon, and smaller blue balls - hydrogen.

3. To form a methane molecule, insert four matches into the red ball so that they point towards the vertices of the tetrahedron.

4. Place blue balls on the free ends of the matches. The natural gas molecule is ready.

5. Prepare two identical molecules to explain to your child how you can get the molecule of the next representative of hydrocarbons - ethane.

6. Connect the two models by removing one match and two blue balls. Ethan is ready.

7. Next, continue the exciting activity and explain how a multiple bond is formed. Remove the two blue balls and make the bond between the carbons double. In a similar way, you can mold all the hydrocarbon molecules necessary for the lesson.

8. The same method is suitable for sculpting molecules of the inorganic world. The same plasticine balls will help you realize your plans.

9. Take the central carbon atom - the red ball. Insert two matches into it, defining the linear shape of the molecule; attach two blue balls, which in this case represent oxygen atoms, to the free ends of the matches. Thus, we have a carbon dioxide molecule of linear structure.

10. Water is a polar liquid, and its molecules are angular formations. They consist of one oxygen atom and two hydrogen atoms. The angular structure is determined by the lone pair of electrons on the central atom. It can also be depicted as two green dots.

These are the kind of exciting creative lessons you should definitely practice with your children. Students of any age will become interested in chemistry and will understand the subject better if, during the learning process, they are provided with a visual aid made by themselves.

This work is carried out with students who came to receive vocational education. Very often their knowledge of chemistry is weak, so they have no interest in the subject. But every student has a desire to learn. Even a poorly performing student shows interest in a subject when he manages to do something on his own.

The assignments in the work are designed taking into account gaps in knowledge. Strong theoretical material allows you to quickly recall the necessary concepts, which helps students complete the work. Having built models of molecules, it is easier for children to write structural formulas. For stronger students who complete the practical part of the work faster, calculation tasks are given. Each student achieves a result when doing work: some manage to build models of molecules, which they do with pleasure, others complete most of the work, others complete all the tasks, and each student receives a grade.

Lesson objectives:

• developing independent work skills;
• generalize and systematize students’ knowledge about the theory of the structure of organic compounds;
• consolidate the ability to compose structural formulas of hydrocarbons;
• practice the skills of naming according to international nomenclature;
• repeat solving problems to determine the mass fraction of an element in a substance;
• develop attention and creative activity;
• develop logical thinking;
• cultivate a sense of responsibility.

Practical work

“Making models of molecules of organic substances.
Drawing up structural formulas of hydrocarbons.”

Goal of the work:

1. Learn to make models of molecules of organic substances.
2. Learn to write down the structural formulas of hydrocarbons and name them according to the international nomenclature.

Theoretical material. Hydrocarbons are organic substances consisting of carbon and hydrogen atoms. The carbon atom in all organic compounds is tetravalent. Carbon atoms can form straight, branched, and closed chains. The properties of substances depend not only on the qualitative and quantitative composition, but also on the order in which the atoms are connected to each other. Substances that have the same molecular formula but different structures are called isomers. Prefixes indicate quantity di- two, three- three, tetra- four; cyclo- means closed.

Suffixes in the names of hydrocarbons indicate the presence of a multiple bond:

en single bond between carbon atoms (C C);
en double bond between carbon atoms (C = C);
in triple bond between carbon atoms (C C);
diene two double bonds between carbon atoms (C = C C = C);

Radicals: methyl -CH 3 ; ethyl -C 2 H 5 ;

chlorine -Cl; bromine -Br.

Example. Make a model of a propane molecule. Propane molecule C 3 H 8 contains three carbon atoms and eight hydrogen atoms. The carbon atoms are connected to each other. Suffix– en

indicates the presence of a single bond between carbon atoms. The carbon atoms are located at an angle of 10928 minutes.

The molecule has the shape of a pyramid. Draw carbon atoms as black circles, hydrogen atoms as white circles, and chlorine atoms as green circles.

When drawing models, observe the ratio of atomic sizes.

Find the molar mass using the periodic table

M (C 3 H 8) = 12 3 + 1 8 = 44 g/mol.

1. To name a hydrocarbon you need to:
2. Choose the longest chain.
3. Number starting from the edge to which the radical or multiple bond is closest.
4. Indicate the radical if several radicals are indicated each. (Number before the name).
5. Name the radical, starting with the smallest radical.
6. Name the longest chain.

Indicate the position of the multiple bond. (Number after name). When composing formulas by name

1. necessary:
2. Determine the number of carbon atoms in the chain.
3. Determine the position of the multiple bond. (Number after name).
4. Determine the position of radicals. (Number before the name).
5. Write down the formulas of radicals.

Lastly, determine the number and arrangement of hydrogen atoms.

The mass fraction of an element is determined by the formula:

Where

– mass fraction of the chemical element;

n – number of atoms of a chemical element;

Ar is the relative atomic mass of a chemical element;

Mr – relative molecular weight. When solving a problem, use

calculation formulas: Relative gas density Dg shows how many times the density of one gas is greater than the density of another gas.(H 2) - relative density of hydrogen. D(air) - relative density in air.

Equipment: A set of ball-and-stick models of molecules, plasticine of different colors, matches, table “Saturated hydrocarbons”, periodic table. Individual tasks.

Progress. Completing tasks according to options.

Option #1.

Task No. 1 . Make models of molecules: a) butane, b) cyclopropane. Draw molecular models in your notebook. Write the structural formulas of these substances. Find their molecular weights.

Task No. 3. Compose structural formulas of substances:

a) butene-2, write its isomer;
b) 3,3 - dimethylpentine-1.

Task No. 4. Solve problems:

Task 1 Determine the mass fraction of carbon and hydrogen in methane.

Task 2. Carbon black is used to produce rubber. Determine how many g of soot (C) can be obtained from the decomposition of 22 g of propane?

Option #2.

Task No. 1 . Make models of molecules: a) 2-methylpropane, b) cyclobutane. Draw molecular models in your notebook. Write the structural formulas of these substances. Find their molecular weights.

Task No. 2. Name the substances:

Task No. 3 Compose structural formulas of substances:

a) 2-methylbutene-1, write its isomer;
b) propin.

Task No. 4. Solve problems:

Task 1. Determine the mass fraction of carbon and hydrogen in ethylene.

Task 2. Carbon black is used to produce rubber. Determine the mass of soot (C) that can be obtained from the decomposition of 36 g of pentane?

Option #3.

Task No. 1 . Make models of molecules: a) 1,2-dichloroethane, b) methylcyclopropane

Draw molecular models in your notebook. Write the structural formulas of these substances. How many times is dichloroethane heavier than air?

Task No. 2. Name the substances:

Task No. 3. Compose structural formulas of substances:

a) 2-methylbutene-2, write its isomer;
b) 3,4-dimethylpentine-1.

Task No. 4. Solve problems:

Task 1. Find the molecular formula of a substance containing 92.3% carbon and 7.7% hydrogen. The relative density for hydrogen is 13.

Problem 2. What volume of hydrogen will be released during the decomposition of 29 g of butane (n.o.)?

Option number 4.

Task No. 1 . Make models of molecules: a) 2,3-dimethylbutane, b) chlorocyclopropane. Draw molecular models in your notebook. Write the structural formulas of these substances. Find their molecular weights.

Task No. 2. Name the substances

Task No. 3. Compose structural formulas of substances:

a) 2-methylbutadientene-1,3; write the isomer.
b) 4-methylpentine-2.

Task No. 4. Solve problems:

Task 1. Find the molecular formula of a substance containing 92.3% carbon and 7.7% hydrogen. The relative density for hydrogen is 39.

Problem 2. What volume of carbon dioxide will be released during the complete combustion of 72 g of automobile fuel consisting of propane?

Choose a type of candy. To make side strands of sugar and phosphate groups, use hollow strips of black and red licorice. For nitrogenous bases, use gummy bears in four different colors.

• Whatever candy you use, it should be soft enough to be pierced with a toothpick.
• If you have colored marshmallows on hand, they are a great alternative to gummy bears.

Prepare the remaining materials. Take the string and toothpicks that you use to create the model. The rope will need to be cut into pieces about 30 centimeters long, but you can make them longer or shorter - depending on the length of the DNA model you choose.

• To create a double helix, use two pieces of string that are the same length.
• Make sure you have at least 10-12 toothpicks, although you may need a little more or less - again depending on the size of your model.

Chop the licorice. You will hang the licorice, alternating its color, the length of the pieces should be 2.5 centimeters.

Sort the gummy bears into pairs. In the DNA strand, cytosine and guanine (C and G), as well as thymine and adenine (T and A), are located in pairs. Choose four different colored gummy bears to represent different nitrogenous bases.

• It doesn’t matter in what sequence the pair C-G or G-C is located, the main thing is that the pair contains exactly these bases.
• Don't pair with mismatched colors. For example, you cannot combine T-G or A-C.
• The choice of colors can be completely arbitrary, it completely depends on personal preferences.

Hang the licorice. Take two pieces of string and tie each at the bottom to prevent the licorice from slipping off. Then string pieces of licorice of alternating colors onto the string through the central voids.

• The two colors of licorice symbolize sugar and phosphate, which form the strands of the double helix.
• Choose one color to be sugar, your gummy bears will attach to that color of licorice.
• Make sure the licorice pieces are in the same order on both strands. If you put them side by side, the colors on both threads should match.
• Tie another knot at both ends of the rope immediately after you finish stringing the licorice.

Attach the gummy bears using toothpicks. Once you have paired all the bears, creating groups C-G and T-A, use a toothpick and attach one bear from each group to both ends of the toothpicks.

• Push the gummy bears onto the toothpick so that at least half an inch of the pointy part of the toothpick sticks out.
• You may end up with more of some pairs than others. The number of pairs in actual DNA determines the differences and changes in the genes they form.