Everything that surrounds us has its own physical and chemical nature. What is called a substance and what types of it exist? It is a physical substance with a specific chemical composition. In Latin, the word "substance" is denoted by the term Substantia, which is also often used by scientists. What does it represent?
To date, more than 20 million different substances are known. There are all kinds of gases in the air, in the ocean, seas and rivers - water with minerals and salts. The solid surface layer of our planet consists of numerous rocks. A huge number of different substances are present in any living organism.
General concepts
In modern chemistry, a substance whose definition is understood as having a rest mass. It consists of elementary particles or quasiparticles. An integral feature of any substance is its mass. As a rule, at relatively low densities and temperatures, elementary particles such as electrons, neutrons, and protons are most often found in its composition. The latter two make up atomic nuclei. All these elementary particles form such substances as molecules and crystals. In essence, their atomic substance (atoms) consists of electrons, protons and neutrons.
From the point of view of biology, "substance" is the concept of matter that forms the tissues of any organisms. It is part of the organelles that are found in cells. In a general sense, "substance" is a form of matter from which all physical bodies are formed.
Matter properties
The properties of a substance are called a set of objective characteristics that determine individuality. They allow you to distinguish one substance from another. The most characteristic physical and chemical properties of a substance:
Density;
Boiling and melting points;
Thermodynamic characteristics;
Chemical properties;
Crystal structure values.
All listed parameters are non-changing constants. Since all substances are different from each other, they have certain characteristics. What is meant by this concept? The properties of a substance are its features, determined by measurement or observation, without transforming it into another substance. The most important of them are:
State of aggregation;
Color and luster;
The presence of an odor;
Insolubility or solubility in water;
melting and boiling point;
Density;
electrical conductivity;
Thermal conductivity;
Hardness;
fragility;
Plastic.
It is also characterized by such a physical property as shape. Color, taste, smell are determined visually and with the help of the senses. Physical parameters such as density, melting and boiling points, electrical conductivity are calculated using various measurements. Information about the physical properties of most substances is presented in special reference books. They depend on the aggregate state of the substance. So, the density of water, ice and steam is completely different. Oxygen is colorless in the gaseous state, but blue in the liquid state. Due to the differences in physical properties, many substances can be distinguished. So, copper is the only metal that has a reddish tint. It just tastes salty. In most cases, in order to define a substance, it is necessary to take into account several of its known properties.
Relationship of concepts
Many people confuse the concepts of "chemical element", "atom", "simple substance". In fact, they differ from each other. So, an atom is a concrete concept, since it really exists. Chemical element - abstract (collective) definition. In nature, it exists only in the form of bound or free atoms. In other words, it is a simple or complex substance. Each chemical element has its own symbol - a sign (symbol). In some cases, it also expresses the composition of a simple substance (B, C, Zn). But often this symbol denotes only a chemical element. This is clearly demonstrated by the formula of oxygen. So O is just a chemical element, and the simple substance oxygen is denoted by the formula O 2.
There are other differences between these concepts. It is necessary to distinguish between the characteristics (properties) of simple substances, which are a collection of particles, and a chemical element, which is an atom of a certain type. There are some differences in the names as well. Most often, the designation of a chemical element and a simple substance is the same. However, there are exceptions to this rule.
Substance classification
What is called a substance from the point of view of science? The number of different substances is very large. A natural substance, the definition of which is related to its natural origin, can be organic or inorganic. Man has learned to synthesize many compounds artificially. The definition of "substance" implies the division into simple (individual) substances and mixtures. The attitude to classification depends on how many of them are included in it.
The definition of a simple substance understands an abstract concept, which means a set of atoms interconnected according to certain physical and chemical laws. Despite this, the boundary between it and the mixture is very vague, since some substances have a variable composition. For them even the exact formula is not offered yet. Due to the fact that for a simple substance only its final purity is achievable, this concept remains an abstraction. In other words, in any of them there is a mixture of chemical elements in which one predominates. Often the purity of a substance directly affects its properties. In a general sense, a simple substance is built from the atoms of one chemical element. For example, an oxygen gas molecule contains 2 identical atoms (O 2).
What is a compound substance? Such a chemical compound includes various atoms that make up the molecule. It is sometimes referred to as a mixed chemical substance. Complex substances are mixtures whose molecules are formed from atoms of two or more elements. So, for example, in a water molecule there is one oxygen atom and 2 hydrogen (H 2 O). The concept of a complex substance corresponds to a molecule containing various chemical elements. There are many more such substances than simple ones. They can be natural and artificial.
Simple and the concept of which is to some extent conditional, differ in their properties. So, for example, titanium becomes strong only when it is freed from oxygen atoms to less than a hundredth of a percent. A complex and simple substance, the chemical definition of which is a bit difficult to understand, can be of two types: inorganic and organic.
inorganic substances
Inorganic are all chemical compounds that do not contain carbon. This group also includes some substances that contain this element (cyanides, carbonates, carbides, carbon oxides and several other substances). They do not have a skeleton characteristic of organic substances. Everyone can name a substance according to the formula thanks to the periodic system of Mendeleev and the school chemistry course. All of them are indicated by Latin letters. What is called the substance in this case? All inorganic substances are divided into the following groups:
Simple substances: metals (Mg, Na, Ca); non-metals (P, S); noble gases (He, Ar, Xe); amphoteric substances (Al, Zn, Fe);
Complex: salts, oxides, acids, hydroxides.
organic matter
The definition of organic matter is quite simple. These substances include chemical compounds that contain carbon. This class of substances is the most extensive. True, there are exceptions to this rule. So, organic substances do not include: carbon oxides, carbides, carbonates, carbonic acid, cyanides and thiocyanates.
The answer to the question "name includes a number of complex compounds. These include: amines, amides, ketones, anhydrides, aldehydes, nitriles, carboxylic acids, organosulfur compounds, hydrocarbons, alcohols, ethers and esters, amino acids.
The main classes of biological organic substances include lipids, proteins, nucleic acids, carbohydrates. They, in addition to carbon, have in their composition hydrogen, oxygen, phosphorus, sulfur, nitrogen. What are the characteristics of organic matter? Their diversity and diversity of structure is explained by the peculiarities of carbon atoms, which are able to form strong bonds when connected in chains. This results in very stable molecules. Carbon atoms form a zigzag chain, which is a characteristic feature of organic substances. In this case, the structure of molecules directly affects the chemical properties. Carbon in organic substances can be combined into open and cyclic (closed) chains.
Aggregate states
The definition of "substance" in chemistry does not give a detailed concept of its state of aggregation. They differ in the role that the interaction of molecules plays in their existence. There are 3 states of matter:
A solid in which the molecules are tightly connected. There is a strong attraction between them. In the solid state, the molecules of a substance are not able to move freely. They can only make oscillatory movements. Thanks to this, solids perfectly retain their shape and volume.
Liquid, in which the molecules are freer and can move from one place to another. Thanks to these properties, any liquid can take the form of a vessel and flow.
Gaseous, in which the elementary particles of matter move freely and randomly. Molecular bonds in this state are so weak that they can be far apart. In the gaseous state, the substance is able to fill large volumes.
Using water as an example, it is very easy to understand the difference between ice, liquid and vapor. All these states of aggregation do not belong to the individual characteristics of a chemical substance. They correspond only to the states of existence of a substance that depend on external physical conditions. That is why it is impossible to unambiguously attribute the attribute of liquid to water. When external conditions change, many chemicals pass from one state of aggregation to another. During this process, intermediate (boundary) types are discovered. The best known of these is the amorphous state, called glassy. Such a definition of "substance" in chemistry is associated with its structure (translated from Greek amorphos - shapeless).
In physics, one more state of aggregation, called plasma, is considered. It is fully or partially ionized and is characterized by the same density of negative and positive charges. In other words: plasma is electrically neutral. This state of matter occurs only at extremely high temperatures. Sometimes they reach thousands of kelvins. In some of its properties, plasma is the opposite of gas. The latter has low electrical conductivity. A gas is made up of particles that are similar to each other. However, they rarely meet. Plasma has a high electrical conductivity. It consists of elementary particles that differ in electric charge. They constantly interact with each other.
There are also such intermediate states of matter as a polymer (highly elastic). In connection with the presence of these transitional forms, specialists often use the concept of "phase" more broadly. Under certain conditions, quite different from the usual ones, some substances pass into special states, for example, superconducting and superfluid.
crystals
Crystals are solids that have the natural shape of regular polyhedra. It is based on their internal structure and depends on the arrangement of its constituent atoms, molecules and ions. In chemistry, it is called a crystal lattice. Such a structure is individual for each substance, therefore it is one of the main physicochemical parameters.
The distances between the particles that make up the crystals are called lattice parameters. They are determined using physical methods of structural analysis. It is not uncommon for solids to have more than one form of crystal lattice. Such structures are called polymorphic modifications. Among simple substances, rhombic and monoclinic forms are common. Such substances include graphite, diamond, sulfur, which are hexagonal and cubic modifications of carbon. This form is also noted in complex substances, such as quartz, cristobalite, tridymite, which are modifications of silicon dioxide.
Substance as a form of matter
Despite the fact that the concepts of "substance" and "matter" are very close in their meaning, they are not completely equivalent. This is claimed by many scientists. So, when mentioning the term "matter" most often they mean a rough, inert and dead reality, subject to the domination of mechanical laws. The definition of "substance" is more understood as a material that, due to its shape, evokes the idea of life suitability and form.
Today, scientists consider matter to be an objective reality that exists in space and changes in time. It can be presented in two forms:
The first has a wave nature. It includes weightlessness, permeability, continuity. It can travel at the speed of light.
The second is corpuscular, having a rest mass. It consists of elementary particles that differ in their localization. It is hardly permeable or impenetrable and cannot propagate at the speed of light.
The first form of the existence of matter is called a field, and the second - substance. They have a lot in common, because even electrons have the properties of a particle and a wave. They appear at the level of the microcosm. That is why the division into field and substance is very convenient.
Unity of matter and field
Scientists have long established that the more massive and larger the elementary particle of matter, the sharper its individuality and delimitation is expressed. At the same time, the contrast between matter and the field, which is characterized by continuity, is more clearly visible. The smaller the elementary particles of a substance, the smaller its mass. In this case, contrasting it with the field becomes more difficult. In various microwaves, it generally loses its meaning, since different elementary particles are quanta excited by the states of different fields (electromagnetic - photons, nuclear - mesons).
The unity of matter and field and the absence of a clear boundary between them is expressed in the fact that under certain conditions particles arise due to the field, and in other cases - vice versa. An illustrative example of this is such a phenomenon as annihilation (the phenomenon of transformation of elementary particles). Any material body is a stable whole, possible due to the connection of its elements through fields.
About atoms and chemical elements
There is nothing else in nature
neither here nor there, in the depths of space:
everything - from small grains of sand to planets -
of the elements consists of a single.
S. P. Shchipachev, "Reading Mendeleev."
In chemistry, apart from terms "atom" and "molecule" concept is often used "element". What is common and how do these concepts differ?
Chemical element – they are atoms of the same type . So, for example, all hydrogen atoms are the element hydrogen; all oxygen and mercury atoms are the elements oxygen and mercury, respectively.
Currently, more than 107 types of atoms, that is, more than 107 chemical elements, are known. It is necessary to distinguish between the concepts of “chemical element”, “atom” and “simple substance”
Simple and complex substances
According to the elemental composition, they are distinguished simple substances, consisting of atoms of one element (H 2, O 2, Cl 2, P 4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H 2 O, NH 3, OF 2, H 2 SO 4, MgCl 2, K 2 SO 4).
Currently, 115 chemical elements are known, which form about 500 simple substances.
Native gold is a simple substance.
The ability of one element to exist in the form of various simple substances that differ in properties is called allotropy.For example, the element oxygen O has two allotropic forms - dioxygen O 2 and ozone O 3 with a different number of atoms in molecules.
The allotropic forms of the element carbon C - diamond and graphite - differ in the structure of their crystals. There are other reasons for allotropy.
chemical compounds, for example, mercury (II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O 2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br 2).
So let's summarize the above. Molecules of matter are of two types:
1. Simple Molecules of such substances consist of atoms of the same type. In chemical reactions, they cannot decompose with the formation of several simpler substances.
2. Complex- Molecules of such substances consist of atoms of different types. In chemical reactions, they can decompose to form simpler substances.
The difference between the concepts of "chemical element" and "simple substance"
Distinguish concepts "chemical element" and "simple substance" when comparing the properties of simple and complex substances. For example, a simple substance oxygen- a colorless gas necessary for breathing, supporting combustion. The smallest particle of a simple substance oxygen is a molecule that consists of two atoms. Oxygen is also included in the composition of carbon monoxide (carbon monoxide) and water. However, the composition of water and carbon monoxide includes chemically bound oxygen, which does not have the properties of a simple substance, in particular, it cannot be used for breathing. Fish, for example, do not breathe chemically bound oxygen, which is part of the water molecule, but free, dissolved in it. Therefore, when it comes to the composition of any chemical compounds, it should be understood that these compounds do not include simple substances, but atoms of a certain type, that is, the corresponding elements.
When complex substances are decomposed, atoms can be released in a free state and combined to form simple substances. Simple substances are made up of atoms of one element. The difference between the concepts of "chemical element" and "simple substance" is also confirmed by the fact that one and the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic oxygen molecules and triatomic ozone molecules. Oxygen and ozone are completely different simple substances. This explains the fact that much more simple substances are known than chemical elements.
Using the concept of "chemical element", we can give the following definition of simple and complex substances:
Simple substances are substances that consist of atoms of one chemical element.
Substances that are composed of atoms of different chemical elements are called complex.
The difference between the concepts of "mixture" and "chemical compound"
Compounds are often called chemical compounds.
Try to answer the questions:
1. What is the difference in the composition of the mixture from chemical compounds?
2. Compare the properties of mixtures and chemical compounds?
3. In what ways can a mixture and a chemical compound be divided into constituent components?
4. Is it possible to judge by external signs the formation of a mixture and a chemical compound?
Comparative characteristics of mixtures and chemical
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Questions for comparing mixtures with chemical compounds |
Mapping |
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Mixes |
Chemical compounds |
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How do mixtures differ from chemical compounds in composition? |
Substances can be mixed in any ratio, i.e. the composition of mixtures is variable |
The composition of chemical compounds is constant. |
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Compare the properties of mixtures and chemical compounds? |
Substances in mixtures retain their properties |
Substances that form compounds do not retain their properties, since chemical compounds with different properties are formed. |
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How can a mixture and a chemical compound be separated into its constituent components? |
Substances can be separated by physical means |
Chemical compounds can only be decomposed by chemical reactions |
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Is it possible to judge by external signs the formation of a mixture and a chemical compound? |
Mechanical mixing is not accompanied by heat release or other signs of chemical reactions |
The formation of a chemical compound can be judged by signs of chemical reactions |
Tasks for fixing
I. Work with the machines
II. Solve the task
NaCl, H 2 SO 4 , K, S 8 , CO 2 , O 3 , H 3 PO 4 , N 2 , Fe.
Explain your choice, in each case.
III. Answer the questions
№1
How many simple substances are written in a series of formulas:
H 2 O, N 2, O 3, HNO 3, P 2 O 5, S, Fe, CO 2, KOH.
№2
Both substances are complex:
A) C (coal) and S (sulfur);
B) CO 2 (carbon dioxide) and H 2 O (water);
B) Fe (iron) and CH 4 (methane);
D) H 2 SO 4 (sulfuric acid) and H 2 (hydrogen).
№3
Choose the correct statement:
Simple substances are made up of atoms of the same kind.
A) right
B) False
№4
Mixtures are characterized by
A) they have a constant composition;
B) Substances in the "mixture" do not retain their individual properties;
C) Substances in "mixtures" can be separated by physical properties;
D) Substances in "mixtures" can be separated by a chemical reaction.
№5
For "chemical compounds" the following is typical:
A) Variable composition;
B) Substances in the composition of a "chemical compound" can be separated by physical means;
C) The formation of a chemical compound can be judged by the signs of chemical reactions;
D) permanent composition.
№6
In what case is it about gland how about chemical element?
A) Iron is a metal that is attracted by a magnet;
B) Iron is part of the composition of rust;
C) Iron has a metallic luster;
D) Iron sulfide contains one iron atom.
№7
In what case is it about oxygen as a simple substance?
A) Oxygen is a gas that supports respiration and combustion;
B) Fish breathe oxygen dissolved in water;
C) The oxygen atom is part of the water molecule;
D) Oxygen is present in the air.
All substances can be divided into simple and complex. Simple Substances are called substances whose molecules are composed of atoms of the same element. Molecules of simple substances can consist of one (for example, He, Mg, Kr), two (for example, Cl 2, H 2, N 2) and more atoms (for example, O 3, S 8) of one element. Simple substances can be metals (eg iron, copper) and non-metals (eg sulfur, nitrogen).
complex substances or chemical compounds substances are called substances whose molecules consist of atoms of two or more elements. For example NO 2 , AgCL, NaOH.
EXERCISE 1 Indicate which of the substances, the composition of which is expressed by the formulas: Na, H 2 S, O 2 , H 2 O, are simple, which are complex? Express the composition of the last compound as a percentage (by mass).
ANSWER Simple substances are sodium (Na), oxygen (O 2), consisting of atoms of one element, hydrogen sulfide (H 2 S) and water (H 2 O) are complex substances, their molecules consist of atoms of various elements.
According to the formulas of chemical compounds, one can determine the molar mass of a substance, its quantitative composition, i.e. the content (in mass ratios or percentages) of each element in a given substance.
The molar mass of H 2 O is 18 g/mol, which is 100%. Hydrogen in the compound is 2 moles of atoms, and oxygen is 1 mole of atoms, which is as a percentage (by mass):% H 2 \u003d 2 100 / 18 \u003d 11.1
% O 2 \u003d 16 100 / 18 \u003d 88.9
EXERCISE 1(for self-control)
1. In the given examples, indicate simple and complex substances:
a) diamond, carbon dioxide, ozone, table salt:
b) graphite, phosphorite, hydrogen sulfide, sulfur;
c) oxygen, sulfur dioxide, slaked lime, magnesium.
Indicate the atoms of which elements each substance consists of.
2. Express the composition as a percentage (by mass) of the following compounds: a) H 2 S, FeO; b) CuS, CaO; c) Fe 2 O 3, H 2 SO 4; d) FeCL 3 , SO 3 ; e) CO 2 , Cu 2 S.
3. Indicate which of the substances whose composition is expressed by the following formulas are complex: S 8, Cu 2 S, SO 3, Na, NH 4 OH? Indicate the atoms of which elements they are composed of.
4. Which of the oxides is richer in iron content; FeO, Fe 2 O 3, Fe 3 O 4?
5. Which of the connections: Cu 2 S, CuS, CuSO 4 contains more sulfur?
OXIDATION STATE AND VALENCE OF ATOMS
Oxidation State (S.O.) is the conditional charge of an atom in a compound, calculated on the basis of the proposal of a purely ionic nature of the chemical bond. The oxidation state can have a negative, positive and zero value, which is indicated by Arabic numerals with the sign ""+"" or ""-"" and placed above the element symbol, for example: Cl 2 0, K + 2 O -2, H + N +5 O -2
Simple and complex substances. Chemical element
About atoms and chemical elements
In chemistry, in addition to the terms "atom" and "molecule" the concept of " element" is often used. What is common and how do these concepts differ?
Chemical element are atoms of the same type. So, for example, all hydrogen atoms are the element hydrogen; all oxygen and mercury atoms are the elements oxygen and mercury, respectively.
Currently, more than 107 types of atoms, that is, more than 107 chemical elements, are known. It is necessary to distinguish between the concepts of "chemical element", "atom" and "simple substance"
Simple and complex substances
By elemental composition, simple substances are distinguished, consisting of atoms of one element (H2, O2, Cl2, P4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H2O, NH3, OF2, H2SO4, MgCl2, K2SO4) .
Currently, 115 chemical elements are known, which form about 500 simple substances.
Native gold is a simple substance.
The ability of one element to exist in the form of various simple substances that differ in properties is called allotropy. For example, the element oxygen O has two allotropic forms - dioxygen O2 and ozone O3 with a different number of atoms in the molecules.
The allotropic forms of the element carbon C - diamond and graphite - differ in the structure of their crystals. There are other reasons for allotropy.
Allotropic forms of carbon:
graphite:
diamond:
Complex substances are often called chemical compounds, for example, mercury (II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br2).
So let's summarize the above. Molecules of matter are of two types:
1. Simple Molecules of such substances consist of atoms of the same type. In chemical reactions, they cannot decompose with the formation of several simpler substances.
2.Complex- Molecules of such substances consist of atoms of different types. In chemical reactions, they can decompose to form simpler substances.
The difference between the concepts of "chemical element" and "simple substance"
The concepts of "chemical element" and "simple substance" can be distinguished by comparing the properties of simple and complex substances. For example, a simple substance - oxygen - a colorless gas necessary for breathing, supporting combustion. The smallest particle of a simple substance oxygen is a molecule that consists of two atoms. Oxygen is also included in the composition of carbon monoxide (carbon monoxide) and water. However, the composition of water and carbon monoxide includes chemically bound oxygen, which does not have the properties of a simple substance, in particular, it cannot be used for breathing. Fish, for example, do not breathe chemically bound oxygen, which is part of the water molecule, but free, dissolved in it. Therefore, when it comes to the composition of any chemical compounds, it should be understood that these compounds do not include simple substances, but atoms of a certain type, that is, the corresponding elements.
When complex substances are decomposed, atoms can be released in a free state and combined to form simple substances. Simple substances are made up of atoms of one element. The difference between the concepts of "chemical element" and "simple substance" is also confirmed by the fact that one and the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic oxygen molecules and triatomic ozone molecules. Oxygen and ozone are completely different simple substances. This explains the fact that much more simple substances are known than chemical elements.
Using the concept of "chemical element", we can give the following definition of simple and complex substances:
Simple Substances that are made up of atoms of a single chemical element are called.
complex Substances that are made up of atoms of different chemical elements are called.
The difference between the concepts of "mixture" and "chemical compound"
Complex substances are often called chemical compounds.
Follow the link and view the experience of the interaction of simple substances of iron and sulfur.
Try to answer the questions:
1. What is the difference in the composition of the mixture from chemical compounds?
2. Compare the properties of mixtures and chemical compounds?
3. In what ways can a mixture and a chemical compound be divided into constituent components?
4. Is it possible to judge by external signs the formation of a mixture and a chemical compound?
Comparative characteristics of mixtures and chemical
connections
|
Questions for comparing mixtures with chemical compounds | Mapping |
|
Mixes | Chemical compounds |
|
How do mixtures differ from chemical compounds in composition? | Substances can be mixed in any ratio, i.e. the composition of mixtures is variable | The composition of chemical compounds is constant. |
Compare the properties of mixtures and chemical compounds? | Substances in mixtures retain their properties | Substances that form compounds do not retain their properties, since chemical compounds with different properties are formed. |
How can a mixture and a chemical compound be separated into its constituent components? | Substances can be separated by physical means | Chemical compounds can only be decomposed by chemical reactions |
Is it possible to judge by external signs the formation of a mixture and a chemical compound? | Mechanical mixing is not accompanied by the release of heat or other signs of chemical reactions | The formation of a chemical compound can be judged by signs of chemical reactions |
Tasks for fixing
I. Work with the machines
Trainer #1
Trainer №2
Trainer №3
II. Solve the task
From the proposed list of substances, write out separately simple and complex substances:
NaCl, H2SO4, K, S8, CO2, O3, H3PO4, N2, Fe.
Explain your choice, in each case.
III. Answer the questions
№1
How many simple substances are written in a series of formulas:
H2O, N2, O3, HNO3, P2O5, S, Fe, CO2, KOH.
№2
Both substances are complex:
A) C (coal) and S (sulfur);
B) CO2 (carbon dioxide) and H2O (water);
C) Fe (iron) and CH4 (methane);
D) H2SO4 (sulfuric acid) and H2 (hydrogen).
№3
Choose the correct statement:
Simple substances are made up of atoms of the same kind.
A) right
B) False
№4
Mixtures are characterized by
A) they have a constant composition;
B) Substances in the "mixture" do not retain their individual properties;
C) Substances in "mixtures" can be separated by physical properties;
D) Substances in "mixtures" can be separated by a chemical reaction.
№5
For "chemical compounds" the following is typical:
A) Variable composition;
B) Substances in the composition of a "chemical compound" can be separated by physical means;
C) The formation of a chemical compound can be judged by the signs of chemical reactions;
D) permanent composition.
№6
In what case is it about iron as a chemical element?
A) Iron is a metal that is attracted by a magnet;
B) Iron is part of the composition of rust;
C) Iron has a metallic luster;
D) Iron sulfide contains one iron atom.
№7
In what case is it about oxygen as a simple substance?
A) Oxygen is a gas that supports respiration and combustion;
B) Fish breathe oxygen dissolved in water;
C) The oxygen atom is part of the water molecule;
D) Oxygen is present in the air.
All substances that we talk about in the school chemistry course are usually divided into simple and complex. Simple substances are those substances whose molecules contain atoms of the same element. Atomic oxygen (O), molecular oxygen (O2) or simply oxygen, ozone (O3), graphite, diamond are examples of simple substances that form the chemical elements oxygen and carbon. Compounds are divided into organic and inorganic. Among inorganic substances, the following four classes are primarily distinguished: oxides (or oxides), acids (oxygenous and oxygen-free), bases (water-soluble bases are called alkalis) and salts. Compounds of non-metals (excluding oxygen and hydrogen) are not included in these four classes, we will call them conditionally "and other complex substances."
Simple substances are usually divided into metals, non-metals and inert gases. Metals include all chemical elements whose d- and f-sublevels are being filled, these are elements in the 4th period: Sc - Zn, in the 5th period: Y - Cd, in the 6th period: La - Hg, Ce - Lu, in the 7th period Ac - Th - Lr. If we now draw a line from Be to At among the remaining elements, then metals will be located to the left and below it, and non-metals to the right and top. Group 8 of the Periodic Table contains inert gases. Elements located on the diagonal: Al, Ge, Sb, Po (and some others. For example, Zn) in the free state have the properties of metals, and hydroxides have the properties of both bases and acids, i.e. are amphoteric hydroxides. Therefore, these elements can be considered metal-non-metals, occupying an intermediate position between metals and non-metals. Thus, the classification of chemical elements depends on what properties their hydroxides will have: basic - it means metal, acidic - non-metal, and both (depending on conditions) - metal-non-metal. The same chemical element in compounds with the lowest positive oxidation state (Mn + 2, Cr + 2) exhibits pronounced "metallic" properties, and in compounds with the maximum positive oxidation state (Mn + 7, Cr + 6) it exhibits the properties of a typical non-metal. To see the relationship of simple substances, oxides, hydroxides and salts, we present a summary table.
