Bodies are objects that surround us.
Bodies are made up of substances.
Physical bodies vary in shape, size, mass, and volume.
Substance is what the physical body is made of. An integral feature of a substance is its mass.
Material is the substance from which bodies are made.
Define “substance”, “material”, “body”.
What is the difference between the concepts “substance” and “body”? Give examples. Why are there more bodies than substances?
Figures and facts
One ton of waste paper can produce 750 kg of paper or 25,000 school notebooks.
20 tons of waste paper save a hectare of forest from deforestation.
For the curious
In the aviation and space industries, in gas turbines, in installations for the chemical processing of coal, where the temperature is high, composite materials are used. These are materials consisting of a plastic base (matrix) and filler. Composites include ceramic-metallic materials (cermets), norplasts (filled organic polymers). Metals and alloys, polymers, and ceramics are used as a matrix. Composites are much stronger than traditional materials.
Home experiment
Paper chromatography
Mix a drop of blue and red ink (maybe a mixture of water-soluble inks that do not interact with each other). Take a piece of filter paper, place a small drop of the mixture in the center of the paper, then water drips into the center of this drop. A color chromatogram will begin to form on the filter paper.
Familiarization with laboratory glassware and chemical equipment
In the process of studying chemistry, you have to conduct a lot of experiments, for which you use special equipment and utensils.
In chemistry, special glassware made of thin-walled and thick-walled glass is used. Products made from thin-walled glass are resistant to temperature changes; chemical operations that require heating are carried out in them. Chemical containers made of thick glass cannot be heated. According to their intended purpose, glassware can be general purpose, special purpose and measured. General purpose utensils are used to perform most jobs.
Thin-walled glassware for general purposes
Test tubes are used when performing experiments with small amounts of solutions or solids, for demonstration experiments. Let's use the dishes to perform the experiments.
Pour 1-2 ml into two small test tubes. hydrochloric acid solution. Add 1-2 drops of litmus to one, and the second - so much methyl orange. We observe a change in the color of the indicators. Litmus turns red and methyl orange turns pink.
Pour 1-2 ml of sodium hydroxide solution into three small test tubes. Add 1-2 drops of litmus to one, the color turns blue. The second time - the same amount of methyl orange - the color turns yellow. In the third - phenolphthalein, the color becomes crimson. So, using indicators you can determine the solution environment.
Place some sodium hydrogen carbonate soda in a large test tube and add 1-2 ml of acetic acid solution. We immediately observe a kind of “boiling” of the mixture of these substances. This impression is created due to the rapid release of carbon dioxide bubbles. If a lit match is inserted into the upper particle of a test tube when gas is released, it goes out without burning out.
Substances are dissolved in flasks, and the solutions are titrated by filtration. Beakers are used to carry out precipitation reactions, dissolving solids when heated. The special purpose group includes utensils used for a specific purpose. Experiments that do not require heating are performed in thick-walled containers. Most often, reagents are stored in it. Droppers, funnels, gasometers, Kipp apparatus, and glass rods are also made from thick glass.
Dip one glass rod in concentrated hydrochloric acid, and the second in concentrated ammonia. Let's bring the sticks closer to each other and observe the formation of “smoke without fire.”
Measuring glassware includes pipettes, burettes, flasks, cylinders, beakers, and beakers. Using measuring cups, the volume of liquids is accurately determined and solutions of various concentrations are prepared.
In addition to glassware, porcelain dishes are used in the laboratory: cups, crucibles, mortars. Porcelain cups are used to evaporate solutions, and porcelain crucibles are used to calcinate substances in muffle furnaces. Solids are ground in mortars.
Laboratory equipment
To heat substances in chemical laboratories, alcohol lamps, electric stoves with a closed spiral, water baths, and, if gas is available, gas burners are used. You can also use dry fuel, burning it on special stands.
When performing chemical experiments, auxiliary accessories are of great importance: a metal stand, a stand for test tubes, crucible tongs, an asbestos mesh.
Scales are used to weigh substances.
“How the world works” - Inanimate nature RAIN CLAY CLOUD GOLD. How the world works. What is nature? The sky is light blue. The golden sun is shining, the wind is playing with the leaves, a cloud is floating in the sky. Live nature. Types of nature. Living and inanimate nature are connected to each other. The science of biology studies living nature. Can a person do without nature?
“Multi-colored rainbow” - The sun shines and laughs, And rain pours on the Earth. The work of primary school teacher Kucherova I.V. And the Seven-Colored Arc emerges into the meadows. Know, Sits. Where. Colors of rainbow. Pheasant. Why is the rainbow multicolored? Hunter. Wishes. The sun's rays, falling on raindrops in the sky, break up into multi-colored rays.
“Inhabitants of the soil” - And people said: “Earth to live!” The shoes said: "Earth to walk on." Medvedka. The soil. Toad. Earthworm. A bucket of potatoes in a wonderful pantry turns into twenty buckets. Inhabitants of the soil. A. Teterin. Ground beetle. Scolopendra. The shovel said: “Earth to dig.” Ticks. May beetle larva.
“Protection of Nature” - We ourselves are part of Nature, And the little fish... I want to be transported here... We all live on the same planet. And to our green forest. And a man without nature?... LET'S SAVE NATURE Completed by: Ilya Kochetygov, 5 “B”. Nature can exist without man, Man! Let's protect and preserve our nature! Insects also need protection
“Soil composition” - Contents. There is water in the soil. Sand settles to the bottom, and clay settles on top of the sand. The soil. Water. Experience No. 2. There is humus in the soil. Experience No. 3. The soil contains salts. Experiment No. 1. There is air in the soil. Experience No. 5. Soil composition. Humus. Fertility is the main property of the soil. Experience No. 4. Sand. Air.
"Game about nature" - The Cloak Bearer. Bullfrog. Raspberries. The sound of which amphibian can be heard at 2-3 km? Cherry. Primary school teacher, MAOU Secondary School No. 24 Rodina Victoria Evgenievna. Chamomile. Hedgehog. Turtle. Celandine. Porcupine. A game. Medicinal plants. Clover. Lily of the valley. Cicada. But I have respected Heart Remedy since childhood. Leafy sea dragon.
There are a total of 36 presentations in the topic
1.1. Bodies and environments. Introduction to systems
While studying physics last year, you learned that the world we live in is a world physical bodies And Wednesday. How is the physical body different from the environment? Any physical body has shape and volume.
For example, physical bodies are a wide variety of objects: an aluminum spoon, a nail, a diamond, a glass, a plastic bag, an iceberg, a grain of table salt, a lump of sugar, a raindrop. What about the air? It is constantly around us, but we do not see its form. For us, air is a medium. Another example: for a person, the sea is, although very large, but still a physical body - it has shape and volume. And for the fish that swim in it, the sea is most likely an environment.
From your life experience, you know that everything that surrounds us consists of something. The textbook that lies in front of you consists of thin sheets of text and a more durable cover; the alarm clock that wakes you up in the morning is made of many different parts. That is, we can argue that a textbook and an alarm clock represent system.
It is very important that the components of the system are connected, since in the absence of connections between them, any system would turn into a “heap”.
The most important feature of each system is its compound And structure. All other features of the system depend on the composition and structure.
We need an idea of systems in order to understand what physical bodies and environments consist of, because they are all systems. (Gaseous media (gases) form a system only together with what keeps them from expanding.)
BODY, ENVIRONMENT, SYSTEM, COMPOSITION OF THE SYSTEM, STRUCTURE OF THE SYSTEM.
1. Give several examples of physical bodies that are missing from the textbook (no more than five).
2.What physical environments does a frog encounter in everyday life?
3. How, in your opinion, differs the physical body from the environment?
1.2. Atoms, molecules, substances
If you look into a sugar bowl or salt shaker, you will see that sugar and salt consist of fairly small grains. And if you look at these grains through a magnifying glass, you can see that each of them is a polyhedron with flat edges (crystalline). Without special equipment, we will not be able to discern what these crystals are made of, but modern science is well aware of methods that allow this to be done. These methods and the instruments that use them were developed by physicists. They use very complex phenomena that we will not consider here. Let's just say that these methods can be likened to a very powerful microscope. If we examine a crystal of salt or sugar through such a “microscope” with greater and greater magnification, then, in the end, we will discover that this crystal contains very small spherical particles. They are usually called atoms(although this is not entirely true, their more accurate name is nuclides). Atoms are part of all bodies and environments around us.
Atoms are very small particles, their size ranges from one to five angstroms (denoted by A o.). One angstrom is 10–10 meters. The size of a sugar crystal is approximately 1 mm; such a crystal is approximately 10 million times larger than any of its constituent atoms. To better understand how small particles atoms are, consider this example: if an apple is enlarged to the size of the globe, then an atom enlarged by the same amount will become the size of an average apple.
Despite such small sizes, atoms are quite complex particles. You will become familiar with the structure of atoms this year, but for now let’s just say that any atom consists of atomic nucleus and related electron shell, that is, it also represents a system.
Currently, just over a hundred types of atoms are known. Of these, about eighty are stable. And from these eighty types of atoms all the objects around us are built in all their infinite diversity.
One of the most important characteristics of atoms is their tendency to combine with each other. Most often this results in the formation of molecules.
A molecule can contain from two to several hundred thousand atoms. Moreover, small molecules (diatomic, triatomic...) can consist of identical atoms, while large ones, as a rule, consist of different atoms. Since a molecule consists of several atoms and these atoms are connected, a molecule is a system. In solids and liquids, molecules are connected to each other, but in gases they are not.
The bonds between atoms are called chemical bonds, and the bonds between molecules are intermolecular bonds.
Molecules connected to each other form substances.
Substances made up of molecules are called molecular substances. Thus, water consists of water molecules, sugar - from sucrose molecules, and polyethylene - from polyethylene molecules.
In addition, many substances consist directly of atoms or other particles and do not contain molecules. For example, aluminum, iron, diamond, glass, and table salt do not contain molecules. Such substances are called non-molecular.
In non-molecular substances, atoms and other chemical particles, as in molecules, are interconnected by chemical bonds. The division of substances into molecular and non-molecular is a classification of substances by type of structure.
Assuming that interconnected atoms retain a spherical shape, it is possible to construct three-dimensional models of molecules and non-molecular crystals. Examples of such models are shown in Fig. 1.1.
Most substances are usually found in one of three states of aggregation: solid, liquid or gaseous. When heated or cooled, molecular substances can change from one state of aggregation to another. Such transitions are shown schematically in Fig. 1.2.
The transition of a non-molecular substance from one state of aggregation to another may be accompanied by a change in the type of structure. Most often, this phenomenon occurs during the evaporation of non-molecular substances.
At melting, boiling, condensation and similar phenomena that occur with molecular substances, the molecules of the substances are not destroyed or formed. Only intermolecular bonds are broken or formed. For example, ice turns into water when melting, and water when boiling turns into water vapor. In this case, water molecules are not destroyed, and, therefore, as a substance, water remains unchanged. Thus, in all three states of aggregation this is the same substance - water.
But not all molecular substances can exist in all three states of aggregation. Many of them when heated decompose, that is, they are transformed into other substances, while their molecules are destroyed. For example, cellulose (the main component of wood and paper) does not melt when heated, but decomposes. Its molecules are destroyed, and completely different molecules are formed from the “fragments”.
So, a molecular substance remains itself, that is, chemically unchanged, as long as its molecules remain unchanged.
But you know that molecules are in constant motion. And the atoms that make up molecules also move (oscillate). As the temperature increases, the vibrations of atoms in molecules increase. Can we say that the molecules remain completely unchanged? Of course not! What then remains unchanged? The answer to this question is in one of the following paragraphs.
Water. Water is the most famous and very widespread substance on our planet: the surface of the Earth is 3/4 covered with water, a person is 65% water, life is impossible without water, since all cellular processes of the body take place in an aqueous solution. Water is a molecular substance. It is one of the few substances that naturally occurs in solid, liquid and gaseous states, and the only substance for which each of these states has its own name. |
| Iron- silvery-white, shiny, malleable metal. This is a non-molecular substance. Among metals, iron ranks second after aluminum in terms of abundance in nature and first place in importance for humanity. Together with another metal - nickel - it forms the core of our planet. Pure iron does not have wide practical applications. The famous Qutub Column, located in the vicinity of Delhi, is about seven meters high and weighs 6.5 tons, almost 2800 years old (it was erected in the 9th century BC) - one of the few examples of the use of pure iron (99.72 %); it is possible that it is the purity of the material that explains the durability and corrosion resistance of this structure. In the form of cast iron, steel and other alloys, iron is used in literally all branches of technology. Its valuable magnetic properties are used in electric current generators and electric motors. Iron is a vital element for humans and animals, as it is part of blood hemoglobin. With its deficiency, tissue cells do not receive enough oxygen, which leads to very serious consequences. |
ATOM (NUCLIDE), MOLECULE, CHEMICAL BONDS, INTERMOLECULAR BONDS, MOLECULAR SUBSTANCE, NON-MOLECULAR SUBSTANCE, TYPE OF STRUCTURE, STATE OF AGGREGATE.
1.Which bonds are stronger: chemical or intermolecular?
2.What is the difference between solid, liquid and gaseous states? How do molecules move in gases, liquids and solids?
3.Have you ever observed the melting processes of any substances (except ice)? What about boiling (except for water)?
4.What are the features of these processes? Give examples of sublimation of solids known to you.
5. Give examples of substances known to you that can be found a) in all three states of aggregation; b) only in solid or liquid state; c) only in the solid state.
1.3. Chemical elements
As you already know, atoms can be the same and different. How different atoms differ from each other in structure, you will soon find out, but for now let’s just say that different atoms are different chemical behavior, that is, their ability to connect with each other, forming molecules (or non-molecular substances).
In other words, chemical elements are the same types of atoms that were mentioned in the previous paragraph.
Each chemical element has its own name, for example: hydrogen, carbon, iron, and so on. In addition, each element is also assigned its own symbol. You see these symbols, for example, in the “Table of Chemical Elements” in the school chemistry classroom.
A chemical element is an abstract aggregate. This is the name for any number of atoms of a given type, and these atoms can be located anywhere, for example: one on Earth, and the other on Venus. The chemical element cannot be seen or touched with your hands. The atoms that make up a chemical element may or may not be bonded to each other. Consequently, a chemical element is neither a substance nor a material system.
CHEMICAL ELEMENT, ELEMENT SYMBOL.
1. Define the concept of “chemical element” using the words “type of atoms”.
2. How many meanings does the word “iron” have in chemistry? What are these meanings?
1.4. Classification of substances
Before you begin classifying any objects, you must select the characteristic by which you will carry out this classification ( classification sign). For example, when arranging a pile of pencils into boxes, you can be guided by their color, shape, length, hardness, or something else. The selected characteristic will be the classification criterion. Substances are much more complex and diverse objects than pencils, therefore there are much more classification features here.
All substances (and you already know that matter is a system) consist of particles. The first classification feature is the presence (or absence) of atomic nuclei in these particles. On this basis, all substances are divided into chemical substances And physical substances.
| Chemical substance– a substance consisting of particles containing atomic nuclei. |
Such particles (and they are called chemical particles) can be atoms (particles with one nucleus), molecules (particles with several nuclei), non-molecular crystals (particles with many nuclei) and some others. Any chemical particle, in addition to nuclei or nuclei, also contains electrons.
In addition to chemicals, there are other substances in nature. For example: the matter of neutron stars, consisting of particles called neutrons; flows of electrons, neutrons and other particles. Such substances are called physical.
| Physical substance– a substance consisting of particles that do not contain atomic nuclei. |
On Earth you almost never encounter physical substances.
According to the type of chemical particles or type of structure, all chemical substances are divided into molecular And non-molecular, you already know that.
A substance may consist of chemical particles identical in composition and structure - in this case it is called clean, or individual, substance. If the particles are different, then - mixture.
This applies to both molecular and non-molecular substances. For example, the molecular substance “water” consists of water molecules that are identical in composition and structure, and the non-molecular substance “table salt” consists of crystals of table salt that are identical in composition and structure.
Most natural substances are mixtures. For example, air is a mixture of molecular substances “nitrogen” and “oxygen” with impurities of other gases, and the rock “granite” is a mixture of non-molecular substances “quartz”, “feldspar” and “mica” also with various impurities.
Individual chemicals are often referred to simply as substances.
Chemical substances may contain atoms of only one chemical element or atoms of different elements. Based on this criterion, substances are divided into simple And complex.
For example, the simple substance “oxygen” consists of diatomic oxygen molecules, and the substance “oxygen” contains only atoms of the element oxygen. Another example: the simple substance “iron” consists of iron crystals, and the substance “iron” contains only atoms of the element iron. Historically, a simple substance usually has the same name as the element whose atoms make up that substance.
However, some elements form not one, but several simple substances. For example, the element oxygen forms two simple substances: "oxygen", consisting of diatomic molecules, and "ozone", consisting of triatomic molecules. The element carbon forms two well-known non-molecular simple substances: diamond and graphite. This phenomenon is called allotropy.
These simple substances are called allotropic modifications. They are identical in qualitative composition, but differ from each other in structure.
Thus, the complex substance “water” consists of water molecules, which, in turn, consist of hydrogen and oxygen atoms. Therefore, hydrogen atoms and oxygen atoms are part of water. The complex substance "quartz" consists of quartz crystals, quartz crystals consist of silicon atoms and oxygen atoms, that is, silicon atoms and oxygen atoms are part of quartz. Of course, a complex substance may contain atoms of more than two elements.
Complex substances are also called connections.
Examples of simple and complex substances, as well as their type of structure, are given in Table 1.
Table I. Simple and complex substances molecular (m) and non-molecular (n/m) type of structure
Simple substances |
Complex substances |
||
Name |
Type of building |
Name |
Type of building |
| Oxygen | Water | ||
| Hydrogen | Salt | ||
| Diamond | Sucrose | ||
| Iron | Copper sulfate | ||
| Sulfur | Butane | ||
| Aluminum | Phosphoric acid | ||
| White phosphorus | Soda | ||
| Nitrogen | Baking soda | ||
In Fig. Figure 1.3 shows a scheme for classifying substances according to the characteristics we have studied: by the presence of nuclei in the particles forming the substance, by the chemical identity of substances, by the content of atoms of one or more elements and by type of structure. The scheme is supplemented by dividing mixtures into mechanical mixtures And solutions, here the classification feature is the structural level at which the particles are mixed.
Like individual substances, solutions can be solid, liquid (usually called simply "solutions"), or gaseous (called mixtures of gases). Examples of solid solutions: jewelry alloy of gold and silver, ruby gemstone. Examples of liquid solutions are well known to you: for example, a solution of table salt in water, table vinegar (a solution of acetic acid in water). Examples of gaseous solutions: air, oxygen-helium mixtures for breathing scuba divers, etc.
| Diamond– allotropic modification of carbon. It is a colorless gem valued for its play of colors and brilliance. The word "diamond" translated from the ancient Indian language means "one that does not break." Among all minerals, diamond has the greatest hardness. But, despite its name, it is quite fragile. Cut diamonds are called brilliants. Natural diamonds, too small or of poor quality, which cannot be used in jewelry, are used as cutting and abrasive materials (abrasive material is a material for grinding and polishing). According to its chemical properties, diamond is a low-active substance. |
| Graphite– the second allotropic modification of carbon. This is also a non-molecular substance. Unlike diamond, it is black-gray, greasy to the touch and quite soft, in addition, it conducts electricity quite well. Due to its properties, graphite is used in a wide variety of areas of human activity. For example: you all use “simple” pencils, but the writing rod - the lead - is made of the same graphite. Graphite is very heat-resistant, so it is used to make refractory crucibles in which metals are melted. In addition, heat-resistant lubricant is made from graphite, as well as movable electrical contacts, in particular those installed on trolleybus bars in places where they slide along electrical wires. There are other, equally important areas of its use. Compared to diamond, graphite is more reactive. |
CHEMICAL SUBSTANCE, INDIVIDUAL SUBSTANCE, MIXTURE, SIMPLE SUBSTANCE, COMPLEX SUBSTANCE, ALLOTROPY, SOLUTION.
1. Give at least three examples of individual substances and the same number of examples of mixtures.
2.What simple substances do you constantly encounter in life?
3.Which of the individual substances you gave as an example are simple substances and which are complex?
4. Which of the following sentences are talking about a chemical element, and which ones are talking about a simple substance?
a) An oxygen atom collides with a carbon atom.
b) Water contains hydrogen and oxygen.
c) A mixture of hydrogen and oxygen is explosive.
d) The most refractory metal is tungsten.
e) The pan is made of aluminum.
f) Quartz is a compound of silicon with oxygen.
g) An oxygen molecule consists of two oxygen atoms.
h) Copper, silver and gold have been known to people since ancient times.
5.Give five examples of solutions known to you.
6.What, in your opinion, is the external difference between a mechanical mixture and a solution?
1.5. Characteristics and properties of substances. Separation of mixtures
Each of the objects of the material system (except for elementary particles) is itself a system, that is, it consists of other, smaller objects interconnected. So, any system itself is a complex object, and almost all objects are systems. For example, a system important for chemistry - a molecule - consists of atoms connected to each other by chemical bonds (you will learn about the nature of these bonds by studying Chapter 7). Another example: atom. It is also a material system consisting of an atomic nucleus and electrons bound to it (you will learn about the nature of these bonds in Chapter 3).
Each object can be described or characterized in more or less detail, that is, it can be listed characteristics.
In chemistry, objects are primarily substances. Chemical substances come in a wide variety of forms: liquid and solid, colorless and colored, light and heavy, active and inert, and so on. One substance differs from another in a number of ways, which, as you know, are called characteristics.
| Characteristics of the substance- a feature inherent in a given substance. |
There are a wide variety of characteristics of substances: state of aggregation, color, smell, density, ability to melt, melting point, ability to decompose when heated, decomposition temperature, hygroscopicity (ability to absorb moisture), viscosity, ability to interact with other substances and many others. The most important of these characteristics are compound And structure. It is on the composition and structure of a substance that all its other characteristics, including properties, depend.
Distinguish high-quality composition And quantitative composition substances.
To describe the qualitative composition of a substance, they list the atoms of which elements are included in the composition of this substance.
When describing the quantitative composition of a molecular substance, the atoms of which elements and in what quantity form the molecule of this substance are indicated.
When describing the quantitative composition of a non-molecular substance, indicate the ratio of the number of atoms of each of the elements that make up this substance.
The structure of a substance is understood as a) the sequence of connections between the atoms that form the substance; b) the nature of the connections between them and c) the relative arrangement of atoms in space.
Now let's return to the question with which we ended paragraph 1.2: what remains unchanged in molecules if the molecular substance remains itself? Now we can already answer this question: the composition and structure of molecules remains unchanged. And if so, then we can clarify the conclusion we made in paragraph 1.2:
A substance remains itself, that is, chemically unchanged, as long as the composition and structure of its molecules remain unchanged (for non-molecular substances - as long as its composition and the nature of the bonds between atoms are preserved ).
As for other systems, among the characteristics of substances, a special group is allocated properties of substances, that is, their ability to change as a result of interaction with other bodies or substances, as well as as a result of the interaction of the constituent parts of a given substance.
The second case is quite rare, therefore the properties of a substance can be defined as the ability of this substance to change in a certain way under any external influence. And since external influences can be very diverse (heating, compression, immersion in water, mixing with another substance, etc.), they can also cause different changes. When heated, a solid may melt, or it may decompose without melting, turning into other substances. If a substance melts when heated, then we say that it has the ability to melt. This is a property of a given substance (it appears, for example, in silver and is absent in cellulose). Also, when heated, a liquid may boil, or it may not boil, but also decompose. This is the ability to boil (it manifests itself, for example, in water and is absent in molten polyethylene). A substance immersed in water may or may not dissolve in it; this property is the ability to dissolve in water. Paper brought to the fire ignites in air, but gold wire does not, that is, paper (or rather, cellulose) exhibits the ability to burn in air, but gold wire does not have this property. Substances have many different properties.
The ability to melt, the ability to boil, the ability to deform and similar properties refer to physical properties substances.
The ability to react with other substances, the ability to decompose, and sometimes the ability to dissolve belong to chemical properties substances.
Another group of characteristics of substances is quantitative characteristics. Of the characteristics given at the beginning of the paragraph, the quantitative ones are density, melting point, decomposition temperature, and viscosity. They all represent physical quantities. In a physics course, you were introduced to physical quantities in seventh grade and continue to study them. You will study the most important physical quantities used in chemistry in detail this year.
Among the characteristics of a substance there are those that are neither properties nor quantitative characteristics, but are very important in describing the substance. These include composition, structure, state of aggregation and other characteristics.
Each individual substance has its own set of characteristics, and the quantitative characteristics of such a substance are constant. For example, pure water at normal pressure boils at exactly 100 o C, ethyl alcohol under the same conditions boils at 78 o C. Both water and ethyl alcohol are individual substances. And gasoline, for example, being a mixture of several substances, does not have a specific boiling point (it boils in a certain temperature range).
Differences in the physical properties and other characteristics of substances make it possible to separate mixtures consisting of them.
To separate mixtures into their constituent substances, a variety of physical separation methods are used, for example: upholding With by decanting(by draining the liquid from the sediment), filtration(straining), evaporation,magnetic separation(magnetic separation) and many other methods. You will become familiar with some of these methods practically.
| Gold– one of the precious metals known to man since ancient times. People found gold in the form of nuggets or panned gold sand. In the Middle Ages, alchemists considered the Sun to be the patron of gold. Gold is a non-molecular substance. This is a rather soft, beautiful yellow metal, malleable, heavy, with a high melting point. Due to these properties, as well as the ability not to change over time and immunity to various influences (low reactivity), gold has been very highly valued since ancient times. Previously, gold was used mainly for minting coins, for making jewelry and in some other areas, such as for making precious tableware. To this day, part of the gold is used for jewelry purposes. Pure gold is a very soft metal, so jewelers use not gold itself, but its alloys with other metals - the mechanical strength of such alloys is significantly higher. However, now most of the gold mined is used in electronic equipment. However, gold is still a currency metal. |
| Silver- also one of the precious metals known to man since ancient times. Native silver occurs in nature, but much less frequently than gold. In the Middle Ages, alchemists considered the Moon to be the patron saint of silver. Like all metals, silver is a non-molecular substance. Silver is a fairly soft, ductile metal, but less ductile than gold. People have long noticed the disinfecting and antimicrobial properties of silver itself and its compounds. In Orthodox churches, the font and church utensils were often made of silver, and therefore the water brought home from church remained clear and clean for a long time. Silver with a particle size of about 0.001 mm is included in the drug "collargol" - drops in the eyes and nose. It has been shown that silver is selectively accumulated by various plants, such as cabbage and cucumbers. Previously, silver was used to make coins and in jewelry. Silver jewelry is still valued to this day, but, like gold, it is increasingly finding technical applications, in particular in the production of film and photographic materials, electronic products, and batteries. In addition, silver, like gold, is a currency metal. |
CHARACTERISTICS OF THE SUBSTANCE, QUALITATIVE COMPOSITION, QUANTITATIVE COMPOSITION, STRUCTURE OF THE SUBSTANCE, PROPERTIES OF THE SUBSTANCE, PHYSICAL PROPERTIES, CHEMICAL PROPERTIES.
1.Describe how the system
a) any object well known to you,
b) Solar system. Indicate the components of these systems and the nature of the connections between the components.
2. Give examples of systems consisting of the same components, but having different structures
3. List as many characteristics as possible of some household item, for example, a pencil (as a system!). Which of these characteristics are properties?
4.What is the characteristic of a substance? Give examples.
5.What is a property of a substance? Give examples.
6.The following are sets of characteristics of three substances. All these substances are well known to you. Determine what substances we are talking about
a) A colorless solid with a density of 2.16 g/cm 3 forms transparent cubic crystals, odorless, soluble in water, the aqueous solution has a salty taste, melts when heated to 801 o C, and boils at 1465 o C, in moderate doses are not toxic to humans.
b) An orange-red solid with a density of 8.9 g/cm 3, the crystals are indistinguishable to the eye, the surface is shiny, does not dissolve in water, conducts electricity very well, is plastic (easily drawn into a wire), melts at 1084 o C , and at 2540 o C it boils, in air it gradually becomes covered with a loose pale blue-green coating.
c) Transparent colorless liquid with a pungent odor, density 1.05 g/cm 3, miscible with water in all respects, aqueous solutions have a sour taste, in dilute aqueous solutions it is not toxic to humans, used as a seasoning for food, when cooled to - 17 o C hardens, and when heated to 118 o C it boils and corrodes many metals. 7.Which of the characteristics given in the three previous examples represent a) physical properties, b) chemical properties, c) values of physical quantities.
8.Make your own lists of characteristics of two more substances known to you.
Separation of substances by filtration.
1.6. Physical and chemical phenomena. Chemical reactions
Everything that happens with the participation of physical objects is called natural phenomena. These include transitions of substances from one state of aggregation to another, and the decomposition of substances when heated, and their interactions with each other.
During melting, boiling, sublimation, liquid flow, bending of a solid body and other similar phenomena, the molecules of substances do not change.
What happens, for example, when sulfur burns?
When sulfur burns, sulfur molecules and oxygen molecules change: they turn into sulfur dioxide molecules (see Fig. 1.4). Please note that both the total number of atoms and the number of atoms of each element remain unchanged.
Therefore, there are two types of natural phenomena:
1) phenomena in which the molecules of substances do not change – physical phenomena;
2) phenomena in which the molecules of substances change – chemical phenomena.
What happens to substances during these phenomena?
In the first case, the molecules collide and fly apart unchanged; in the second, when molecules collide, they react with each other, while some molecules (old) are destroyed, while others (new) are formed.
What changes in molecules during chemical phenomena?
In molecules, atoms are connected by strong chemical bonds into a single particle (in non-molecular substances - into a single crystal). The nature of atoms in chemical phenomena does not change, that is, atoms do not transform into each other. The number of atoms of each element also does not change (atoms do not disappear or appear). What is changing? Bonds between atoms! In the same way, in non-molecular substances, chemical phenomena change the bonds between atoms. Changing connections usually comes down to their breaking and the subsequent formation of new connections. For example, when sulfur burns in air, the bonds between sulfur atoms in sulfur molecules and between oxygen atoms in oxygen molecules are broken, and bonds are formed between sulfur and oxygen atoms in sulfur dioxide molecules.
The appearance of new substances is detected by the disappearance of the characteristics of the reacting substances and the appearance of new characteristics inherent in the reaction products. Thus, when sulfur burns, yellow sulfur powder turns into a gas with a sharp, unpleasant odor, and when phosphorus burns, clouds of white smoke are formed, consisting of tiny particles of phosphorus oxide.
So, chemical phenomena are accompanied by the breaking and formation of chemical bonds, therefore, chemistry as a science studies natural phenomena in which the breaking and formation of chemical bonds (chemical reactions) occurs, the accompanying physical phenomena and, naturally, the chemical substances involved in these reactions.
To study chemical phenomena (that is, chemistry), you must first study the connections between atoms (what they are, what they are, what their features are). But bonds are formed between atoms. Therefore, it is necessary first of all to study the atoms themselves, or more precisely, the structure of atoms of different elements.
Thus, in 8th and 9th grades you will study
1) structure of atoms;
2) chemical bonds and structure of substances;
3) chemical reactions and processes accompanying them;
4) properties of the most important simple substances and compounds.
In addition, during this time you will become familiar with the most important physical quantities used in chemistry and the relationships between them, as well as learn how to carry out basic chemical calculations.
| Oxygen. Without this gaseous substance our life would be impossible. After all, this colorless gas, tasteless and odorless, is necessary for breathing. About one-fifth of the Earth's atmosphere consists of oxygen. Oxygen is a molecular substance; each molecule is formed by two atoms. In the liquid state it is light blue, in the solid state it is blue. Oxygen is very reactive and reacts with most other chemicals. The combustion of gasoline and wood, the rusting of iron, rotting and respiration are all chemical processes involving oxygen. In industry, most oxygen is obtained from atmospheric air. Oxygen is used in the production of iron and steel by raising the temperature of the flames in furnaces and thus speeding up the smelting process. Oxygen-enriched air is used in non-ferrous metallurgy, for welding and cutting metals. It is also used in medicine to ease the breathing of patients. Oxygen reserves on Earth are continuously replenished - green plants produce about 300 billion tons of oxygen annually. The components of chemical substances, a kind of “bricks” from which they are built, are chemical particles, and these are primarily atoms and molecules. Their sizes lie in the length range of the order of 10 -10 – 10 -6 meters (see Fig. 1.5).
Physics studies smaller particles and their interactions; these particles are called microphysical particles. Processes in which large particles and bodies take part are again studied by physics. Physical geography studies the natural objects that form the Earth's surface. The sizes of such objects range from several meters (for example, the width of a river) to 40 thousand kilometers (the length of the earth’s equator). Planets, stars, galaxies and the phenomena that occur with them are studied by astronomy and astrophysics. Geology studies the structure of the Earth. Another natural science, biology, studies the living organisms that inhabit the Earth. In terms of the complexity of their structure (but not in terms of the complexity of understanding the nature of interactions), microphysical objects are the simplest. Next come chemical particles and substances formed from them. Biological objects (cells, their “parts”, living organisms themselves) are formed from chemical substances, and, therefore, their structure is even more complex. The same applies to geological objects, for example, rocks consisting of minerals (chemicals). All natural sciences, when studying nature, rely on physical laws. Physical laws are the most general laws of nature to which all material objects, including chemical particles, are subject. Consequently, chemistry, studying atoms, molecules, chemical substances and their interactions, must make full use of the laws of physics. In turn, biology and geology, when studying “their” objects, are required to use not only the laws of physics, but also chemical laws. Thus, it becomes clear what place chemistry occupies among the related natural sciences. This location is shown schematically in Figure 1.6. Back in the 18th century, the close connection between these two natural sciences was noticed and used in his work by the famous Russian scientist Mikhail Vasilyevich Lomonosov (1711 – 1765), who wrote: “A chemist without knowledge of physics is like a person who must search for everything by touch. And these two sciences are like that connected to each other, that one cannot exist perfectly without the other.” Now let’s clarify what chemistry gives us as consumers? On the other hand, the human body contains a huge number of different chemicals. Knowledge of chemistry helps biologists understand their interactions and understand the reasons for the occurrence of certain biological processes. And this, in turn, allows medicine to more effectively preserve people’s health, treat diseases and, ultimately, prolong human life. |
Substances and bodies belong to the material component of reality. Both of them have their own signs. Let's consider how a substance differs from a body.
Definition
Substance call matter that has mass (as opposed to, for example, an electromagnetic field) and has a structure of many particles. There are substances consisting of independent atoms, such as aluminum. More often, atoms combine into more or less complex molecules. Such a molecular substance is polyethylene.
Body- a separate material object with its own boundaries, occupying part of the surrounding space. The permanent characteristics of such an object are considered to be mass and volume. Bodies also have specific sizes and shapes, from which a certain visual image of objects is formed. Bodies may already exist in nature or be the result of human creativity. Examples of bodies: book, apple, vase.
Comparison
In general, the difference between matter and body is as follows: matter is what existing objects are made of (the internal aspect of matter), and these objects themselves are bodies (the external aspect of matter). So, paraffin is a substance, and a candle made from it is a body. It must be said that the body is not the only state in which substances can exist.
Any substance has a set of specific properties, thanks to which it can be distinguished from a number of other substances. Such properties include, for example, features of the crystal structure or the degree of heating at which melting occurs.
By mixing existing components, you can obtain completely different substances that have their own unique set of properties. There are many substances created by people based on those found in nature. Such artificial products are, for example, nylon and soda. Substances from which something is made by people are called materials.
What is the difference between matter and body? A substance is always homogeneous in its composition, that is, all the molecules or other individual particles in it are the same. At the same time, the body is not always characterized by homogeneity. For example, a jar made of glass is a homogeneous body, but a digging shovel is a heterogeneous body, since its upper and lower parts are made of different materials.
From certain substances many different bodies can be made. For example, rubber is used to make balls, car tires, and rugs. At the same time, bodies that perform the same function can be made of different substances, like, say, an aluminum and a wooden spoon.
In life we are surrounded by various bodies and objects. For example, indoors this is a window, door, table, light bulb, cup, outdoors - a car, traffic light, asphalt. Any body or object consists of matter. This article will discuss what a substance is.
What is chemistry?
Water is an essential solvent and stabilizer. It has strong heat capacity and thermal conductivity. The aqueous environment is favorable for the occurrence of basic chemical reactions. It is characterized by transparency and is practically resistant to compression.
What is the difference between inorganic and organic substances?
There are no particularly strong external differences between these two groups of substances. The main difference lies in the structure, where inorganic substances have a non-molecular structure, and organic substances have a molecular structure.
Inorganic substances have a non-molecular structure, so they are characterized by high melting and boiling points. They do not contain carbon. These include noble gases (neon, argon), metals (calcium, calcium, sodium), amphoteric substances (iron, aluminum) and nonmetals (silicon), hydroxides, binary compounds, salts.
Organic substances of molecular structure. They have fairly low melting points and decompose quickly when heated. Mainly composed of carbon. Exceptions: carbides, carbonates, carbon oxides and cyanides. Carbon allows the formation of a huge number of complex compounds (more than 10 million of them are known in nature).
Most of their classes belong to biological origin (carbohydrates, proteins, lipids, nucleic acids). These compounds include nitrogen, hydrogen, oxygen, phosphorus and sulfur.
To understand what a substance is, it is necessary to imagine what role it plays in our lives. By interacting with other substances, it forms new ones. Without them, the life of the surrounding world is inseparable and unthinkable. All objects consist of certain substances, so they play an important role in our lives.