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 simple substances may 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) - complex substances, their molecules are composed 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) a diamond carbon dioxide, ozone, 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 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 the compound, calculated based on the proposal of a purely ionic character 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
In the previous chapter, it was said that not only atoms of one chemical element, but also atoms of different elements can form bonds with each other. Substances formed by atoms of one chemical element are called simple substances, and substances formed by atoms of different chemical elements are called complex substances. Some simple substances have a molecular structure, i.e. are made up of molecules. For example, substances such as oxygen, nitrogen, hydrogen, fluorine, chlorine, bromine, and iodine have a molecular structure. Each of these substances is formed by diatomic molecules, so their formulas can be written as O 2, N 2, H 2, F 2, Cl 2, Br 2 and I 2, respectively. As you can see, simple substances can have the same name with the elements that form them. Therefore, it is important to distinguish clearly between situations where we are talking about a chemical element, and when about a simple substance.
Often, simple substances have not molecular, but atomic structure. In such substances, atoms can form various types of bonds with each other, which will be discussed in detail a little later. Substances of this structure are all metals, for example, iron, copper, nickel, as well as some non-metals - diamond, silicon, graphite, etc. These substances are usually characterized not only by the coincidence of the name of the chemical element with the name of it formed substance, but are also identical to the formula of a substance and the designation of a chemical element. For example, the chemical elements iron, copper and silicon, which have the designations Fe, Cu and Si, form simple substances, the formulas of which are Fe, Cu and Si, respectively. There is also a small group of simple substances, consisting of disparate atoms, not connected in any way. Such substances are gases, which are called, due to their extremely low chemical activity, noble. These include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn).
Since there are only about 500 known simple substances, it follows logically that many chemical elements are characterized by a phenomenon called allotropy.
Allotropy is the phenomenon when one chemical element can form several simple substances. Different chemical substances, formed by one chemical element, are called allotropic modifications or allotropes.
So, for example, the chemical element oxygen can form two simple substances, one of which has the name of the chemical element - oxygen. Oxygen as a substance consists of diatomic molecules, i.e. its formula is O 2 . It is this compound that is part of the vital air we need. Another allotropic modification of oxygen is the triatomic gas ozone, whose formula is O 3 . Despite the fact that both ozone and oxygen are formed by the same chemical element, their chemical behavior is very different: ozone is much more active than oxygen in reactions with the same substances. In addition, these substances differ from each other in physical properties, at least due to the fact that molecular mass Ozone is 1.5 times more than oxygen. This leads to the fact that its density in the gaseous state is also 1.5 times greater.
Many chemical elements tend to form allotropic modifications that differ from each other in the structural features of the crystal lattice. So, for example, in Figure 5, you can see schematic representations of fragments of the crystal lattices of diamond and graphite, which are allotropic modifications of carbon.
Figure 5. Fragments of crystal lattices of diamond (a) and graphite (b)
In addition, carbon can also have a molecular structure: such a structure is observed in such a type of substances as fullerenes. Substances of this type are formed by spherical carbon molecules. Figure 6 shows 3D models of the c60 fullerene molecule and a soccer ball for comparison. Note their interesting resemblance.
Figure 6. C60 fullerene molecule (a) and soccer ball (b)
Compounds are substances that are made up of atoms of different elements. They, like simple substances, can have a molecular and non-molecular structure. Non-molecular type The structure of complex substances can be more diverse than that of simple ones. Any complex chemical substances can be obtained either by direct interaction of simple substances, or by a sequence of their interactions with each other. It is important to be aware of one fact, which is that the properties of complex substances, both physical and chemical, are very different from the properties of the simple substances from which they are derived. For example, table salt, which has a NaCl forum and is colorless transparent crystals, can be obtained by reacting sodium, which is a metal with properties characteristic of metals (luster and electrical conductivity), with chlorine Cl 2, a yellow-green gas.
Sulfuric acid H 2 SO 4 can be formed by a series of successive transformations from simple substances - hydrogen H 2 , sulfur S and oxygen O 2 . Hydrogen is a gas lighter than air, forming explosive mixtures with air, sulfur is a solid yellow color, capable of burning, and oxygen, a gas slightly heavier than air, in which many substances can burn. Sulfuric acid, which can be obtained from these simple substances, is a heavy oily liquid with strong water-removing properties, due to which it chars many substances of organic origin.
Obviously, in addition to individual chemicals, there are also mixtures of them. It is mainly mixtures of various substances that form the world around us: metal alloys, food, drinks, various materials that make up the objects around us.
For example, the air we breathe consists mainly of nitrogen N 2 (78%), oxygen that is vital for us (21%), while the remaining 1% is impurities of other gases (carbon dioxide, noble gases, etc.).
Mixtures of substances are divided into homogeneous and heterogeneous. Homogeneous mixtures are those mixtures that do not have phase boundaries. Homogeneous mixtures are a mixture of alcohol and water, metal alloys, a solution of salt and sugar in water, mixtures of gases, etc. heterogeneous mixtures called such mixtures that have a phase boundary. Mixtures of this type include a mixture of sand and water, sugar and salt, a mixture of oil and water, etc.
The substances that make up mixtures are called components.
Mixtures of simple substances, unlike chemical compounds that can be obtained from these simple substances, retain the properties of each component.
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 that has 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. Great amount various substances 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 last two are 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 Chemical properties substances:
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 physical properties ah most substances are 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. Complex and simple matter chemical definition which is a bit difficult to perceive, can be of two types: inorganic and organic.
inorganic substances
All are inorganic chemical compounds containing no 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, simple 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 kind character traits in 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 matter can be combined into open and cyclic (closed) circuits.
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 do oscillatory movements. Thereby 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 thing is considered state of aggregation called plasma. 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 is made up of elementary particles 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 defined using physical methods 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 rough, inert and dead reality, subject to domination 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 objective reality, which 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. good example this can be served by 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.
Substances can be composed of atoms of the same or different chemical elements. On this basis, all substances are divided into simple and complex.
Substances consisting of atoms of one chemical element are called simple. Simple substances are divided into metals (formed by metal atoms: Na, K, Ca, Mg) and non-metals (formed by non-metal atoms H2, N2, O2, Cl2, F2, S, P, Si) according to their physical and chemical properties.
Substances consisting of atoms of different chemical elements are called complex substances. To the main classes of complex inorganic substances include oxides, bases, acids and salts.
Oxides are binary compounds (compounds consisting of two chemical elements), which include the element oxygen in the oxidation state -2.
Oxides are divided into basic, amphoteric, acidic and non-salt-forming:
1. Basic oxides are formed by atoms typical metals and oxygen atoms. For example, Na2O, CaO, LiO. They correspond to hydroxides - bases.
2. Amphoteric oxides are formed by atoms transition metals and oxygen atoms. For example, BeO, ZnO, Al2O3. They correspond to amphoteric hydroxides.
3. Acid oxides are formed by non-metal atoms and oxygen atoms. For example, CO2, SiO2, N2O3, NO2, N2O5, P2O3, P2O5, SO2, SO3, Cl2O7, etc. They correspond to hydroxides - acids.
4. Non-salt-forming oxides are formed by non-metal atoms and oxygen. Non-salt-forming oxides include 4 oxides: CO, SiO, N2O, NO.
Bases are compounds that contain a metal (or ammonium) cation and one or more hydroxyl groups. For example, NaOH, Ca(OH)2, KOH, NH4OH.
Soluble bases, which are called alkalis, are especially distinguished. These include hydroxides of alkali and alkaline earth metals.
According to the number of hydroxyl groups, bases are divided into one-, two- and three-acid ones.
Amphoteric hydroxides are formed by beryllium, zinc or aluminum cations and hydroxide anions: Be(OH)2, Zn(OH)2, Al(OH)3.
Acids are compounds that contain hydrogen cations and anions of an acidic residue. According to the number of hydrogen cations, acids are divided into one-, two- and three-basic. According to the presence of oxygen in the acid residue, acids are divided into anoxic and oxygen-containing.
HF - hydrofluoric (or hydrofluoric) acid
HCl - hydrochloric (or hydrochloric) acid
HBr - hydrobromic acid
HI - hydroiodic acid
H2S - hydrosulphuric acid
HNO3 - nitric acid (corresponds acid oxide N2O5)
HNO2 - nitrous acid (corresponds to the acid oxide N2O3)
H2SO4 - sulphuric acid(corresponds to acid oxide SO3)
H2SO3 - sulfurous acid (corresponds to acid oxide SO2)
H2CO3 - carbonic acid (corresponds to the acidic oxide CO2)
H2SiO3 - silicic acid (corresponds to the acid oxide SiO2)
H3PO4 - phosphoric acid (corresponds to the acid oxide P2O5).
Salts are compounds that include a metal (or ammonium) cation and an anion of an acid residue.
According to the composition of the acid are divided into:
1. Medium - consist of a metal cation and an acid residue - this is the product of the complete replacement of acid hydrogen atoms with metal (or ammonium) cations. For example, Na2SO4, K3PO4.
Salts of hydrofluoric acid - fluorides,
salts of hydrochloric acid - chlorides,
salts of hydrobromic acid - bromides,
salts of hydroiodic acid - iodides,
salts of hydrosulphuric acid - sulfides,
salts of nitric acid - nitrates,
salts of nitrous acid - nitrites,
salts of sulfuric acid - sulfates,
salts of sulfurous acid - sulfites,
salts of carbonic acid - carbonates,
silicic acid salts - silicates,
salts of phosphoric acid - phosphates.
2. Acid salts - consist of a metal (or ammonium) cation, a hydrogen cation (s) and an anion of an acid residue - this is the product of incomplete replacement of acid hydrogen atoms by metal cations. Acidic salts can only form dibasic and tribasic acids. The prefix hydro- (or digdro) is added to the name of the salt. For example, NaHSO4 (sodium hydrogen sulfate), KH2PO4 (potassium dihydrogen phosphate).
3. Basic salts - consist of a metal (or ammonium) cation, hydroxydanion and an anion of an acid residue - this is the product of incomplete replacement of the hydroxyl groups of the base with acid residues. Basic salts can form only two- and three-acid bases. The prefix hydroxo- is added to the name of the salt. For example, (CuOH)2CO3 is copper (II) hydroxocarbonate.
All the substances that we are talking about in school course Chemistry is 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. In group 8 Periodic system inert gases are located. 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.
