The fundamentals of atomic-molecular science were first outlined by Lomonosov. In 1741, in one of his first works - “Elements of Mathematical Chemistry” - Lomonosov formulated the most important provisions of the so-called corpuscular theory of the structure of matter that he created.
According to Lomonosov’s ideas, all substances consist of tiny “insensitive” particles, physically indivisible and capable of mutual adhesion. The properties of substances are determined by the properties of these particles. Lomonosov distinguished two types of such particles: smaller ones - “elements”, corresponding to atoms in the modern understanding of this term, and larger ones - “corpuscles”, which we now call molecules.
Each corpuscle has the same composition as the whole substance. Chemically different substances also have corpuscles of different composition. “Corpuscules are homogeneous if they consist of the same number of the same elements, connected in the same way,” and “corpuscles are heterogeneous when their elements are different and connected in different ways or in different numbers.”
From the above definitions it is clear that Lomonosov believed that the reason for the differences in substances was not only the difference in the composition of the corpuscles, but also the different arrangement of elements in the corpuscle.
Lomonosov emphasized that corpuscles move according to the laws of mechanics; Without motion, the corpuscles cannot collide with each other or otherwise act on each other and change. Since all changes in substances are caused by the movement of corpuscles, chemical transformations should be studied not only by the methods of chemistry, but also by the methods of physics and mathematics.
Over the more than 200 years that have passed since Lomonosov lived and worked, his ideas about the structure of matter have undergone comprehensive testing, and their validity has been fully confirmed. Currently, all our ideas about the structure of matter, the properties of substances and the nature of physical and chemical phenomena are based on atomic-molecular science.
The basis of atomic-molecular teaching is the principle of discreteness (discontinuity of structure) of matter: every substance is not something continuous, but consists of individual very small particles. The difference between substances is due to the difference between their particles; Particles of one substance are the same, particles of different substances are different. Under all conditions, particles of matter are in motion; the higher the body temperature, the more intense this movement.
For most substances, the particles are molecules. A molecule is the smallest particle of a substance that has its chemical properties. Molecules, in turn, are made up of atoms. An atom is the smallest particle of an element that has its chemical properties. A molecule can contain a different number of atoms. Thus, the molecules of noble gases are monoatomic, the molecules of substances such as hydrogen, nitrogen are diatomic, water is triatomic, etc. The molecules of the most complex substances - higher proteins and nucleic acids - are built from a number of atoms that is measured in hundreds of thousands.
In this case, atoms can combine with each other not only in different ratios, but also in different ways. Therefore, with a relatively small number of chemical elements, the number of different substances is very large.
Students often wonder why the molecule of a given substance does not have its physical properties. In order to better understand the answer to this question, let's consider several physical properties of substances, for example, melting and boiling points, heat capacity, mechanical strength, hardness, density, electrical conductivity.
Properties such as melting and boiling points, mechanical strength and hardness are determined by the strength of the bonds between the molecules in a given substance at its given state of aggregation; therefore, applying such concepts to a single molecule does not make sense. Density is a property that an individual molecule has that can be calculated. However, the density of a molecule is always greater than the density of a substance (even in the solid state), because in any substance there is always some free space between the molecules. And such properties as electrical conductivity and heat capacity are determined not by the properties of molecules, but by the structure of the substance as a whole. In order to be convinced of this, it is enough to remember that these properties change greatly when the state of aggregation of a substance changes, while the molecules do not undergo profound changes. Thus, the concepts of some physical properties are not applicable to an individual molecule, while others are applicable, but these properties themselves are different in magnitude for the molecule and for the substance as a whole.
Not in all cases the particles that make up a substance are molecules. Many substances in solid and liquid states, for example most salts, have an ionic structure rather than a molecular one. Some substances have an atomic structure. The structure of solids and liquids will be discussed in more detail in Chapter V, but here we will only point out that in substances with an ionic or atomic structure, the bearer of chemical properties is not molecules, but those combinations of ions or atoms that form the given substance.
The foundations of the atomic-molecular theory were created by the Russian scientist M.V. Lomonosov (1741) and the English scientist J. Dalton (1808).
Atomic-molecular theory is the doctrine of the structure of matter, the main provisions of which are:
1. All substances consist of molecules and atoms. A molecule is the smallest particle of a substance that is capable of existing independently and cannot be crushed further without losing the basic chemical properties of the substance. The chemical properties of a molecule are determined by its composition and chemical structure.
2. Molecules are in continuous motion. Molecules move randomly and continuously. The speed of movement of molecules depends on the state of aggregation of substances. As the temperature increases, the speed of movement of molecules increases.
3. Molecules of the same substance are the same, but molecules of different substances differ in mass, size, structure and chemical properties. Every substance exists as long as its molecules remain. As soon as the molecules are destroyed, the given substance ceases to exist: new molecules, new substances appear. During chemical reactions, molecules of some substances are destroyed and molecules of other substances are formed.
4. Molecules consist of smaller particles - atoms. An atom is the smallest particle of a chemical element that cannot be broken down chemically.
Therefore, the atom determines the properties of the element.
Atom– an electrically neutral particle consisting of a positively charged nucleus and negatively charged electrons.
Chemical element called a type of atoms characterized by a certain set of properties.
Currently, an element is defined as a species of atoms that have the same nuclear charge.
Substances whose molecules consist of atoms of one element are called simple substances(C, H 2, N 2, O 3, S 8, etc.).
Substances whose molecules consist of atoms of two or more elements are called complex substances ( H 2 O, H 2 SO 4, KHCO 3, etc.). The number and relative arrangement of atoms in a molecule are essential.
The ability of atoms of the same element to form several simple substances different in structure and properties is called allotropy, and the formed substances - allotropic modifications or modifications, for example, the element oxygen forms two allotropic modifications: O 2 - oxygen and O 3 - ozone; element carbon - three: diamond, graphite and carbine, etc.
The phenomenon of allotropy is caused by two reasons: a different number of atoms in the molecule (oxygen O 2 and ozone O 3), or the formation of different crystalline forms (diamond, graphite and carbyne).
Elements are usually designated by chemical symbols. Should always remember, that each symbol of a chemical element means:
1. element name;
2. one atom of it;
3. one mole of its atoms;
4. relative atomic mass of the element;
5. its position in the periodic table of chemical elements
DI. Mendeleev.
So, for example, the sign S shows what is before us:
1. chemical element sulfur;
2. one atom of it;
3. one mole of sulfur atoms;
4. The atomic mass of sulfur is 32 a. u.m. (atomic mass unit);
5. serial number in the periodic system of chemical elements D.I. Mendeleev 16.
The absolute masses of atoms and molecules are negligible, therefore, for convenience, the mass of atoms and molecules is expressed in relative units. Currently the unit of atomic mass is taken to be atomic mass unit(abbreviated A. eat.), representing 1/12 of the mass of the carbon isotope 12 C, 1 a. e.m. is 1.66 × 10 -27 kg.
Atomic mass of the element is called the mass of its atom, expressed in a. eat.
Relative atomic mass of the element is the ratio of the mass of an atom of a given element to 1/12 of the mass of the carbon isotope 12 C.
Relative atomic mass is a dimensionless quantity and is denoted Ar,
for example for hydrogen 
for oxygen 
.
Molecular mass of the substance is the mass of the molecule, expressed in a. e.m. It is equal to the sum of the atomic masses of the elements that make up the molecule of a given substance.
Relative molecular weight of the substance is the ratio of the mass of a molecule of a given substance to 1/12 of the mass of the carbon isotope 12 C. It is designated by the symbol Mr. Relative molecular mass is equal to the sum of the relative atomic masses of the elements included in the molecule, taking into account the number of atoms. For example, the relative molecular mass of orthophosphoric acid H 3 PO 4 is equal to the mass of the atoms of all elements included in the molecule:
Mr(H 3 PO 4) = 1.0079 × 3 + 30.974 × 1 + 15.9994 × 4 = 97.9953 or ≈ 98
Relative molecular weight shows how many times the mass of a molecule of a given substance is greater than 1 a. eat.
Along with units of mass, in chemistry they also use a unit of quantity of a substance, called pray(abbreviation "moth").
Mole of substance- the amount of a substance containing as many molecules, atoms, ions, electrons or other structural units as is contained in 12 g (0.012 kg) of the 12 C carbon isotope.
Knowing the mass of one carbon atom 12 C (1.993 × 10 -27 kg), we can calculate the number of atoms in 0.012 kg of carbon:
The number of particles in a mole of any substance is the same. It is equal to 6.02 × 10 23 and is called Avogadro's constant or Avogadro's number (N A).
For example, three moles of carbon atoms will contain
3 × 6.02 × 10 23 = 18.06 × 10 23 atoms
When using the concept of “mole”, it is necessary in each specific case to indicate exactly which structural units are meant. For example, one should distinguish between a mole of hydrogen atoms H, a mole of hydrogen molecules H2, a mole of hydrogen ions, or One mole of particles has a certain mass.
Molar mass is the mass of one mole of a substance. Denoted by the letter M.
Molar mass is numerically equal to relative molecular mass and has units of g/mol or kg/mol.
Mass and quantity of a substance are different concepts. Mass is expressed in kg (g), and the amount of substance is expressed in moles. There are relationships between the mass of a substance (m, g), the amount of substance (n, mol) and the molar mass (M, g/mol):
n = , g/mol; M = , g/mol; m = n × M, g.
Using these formulas it is easy to calculate the mass of a certain amount of a substance, the molar mass of a substance or amount of a substance.
Example 1 . What is the mass of 2 moles of iron atoms?
Solution: The atomic mass of iron is 56 amu. (rounded), therefore, 1 mole of iron atoms weighs 56 g, and 2 moles of iron atoms have a mass of 56 × 2 = 112 g
Example 2 . How many moles of potassium hydroxide are contained in 560 g of KOH?
Solution: The molecular weight of KOH is 56 amu. Molar = 56 g/mol. 560 g of potassium hydroxide contains: 10 mol KOH. For gaseous substances there is the concept of molar volume V m. According to Avogadro's law, a mole of any gas under normal conditions (pressure 101.325 kPa and temperature 273 K) occupies a volume of 22.4 liters. This quantity is called molar volume(it is occupied by 2 g of hydrogen (H 2), 32 g of oxygen (O 2), etc.
Example 3 . Determine the mass of 1 liter of carbon monoxide (ΙV) under normal conditions (no.).
Solution: The molecular mass of CO 2 is M = 44 amu, therefore, the molar mass is 44 g/mol. According to Avogadro's law, one mole of CO 2 at no. occupies a volume of 22.4 liters. Hence the mass of 1 liter of CO 2 (n.s.) is equal to g.
Example 4. Determine the volume occupied by 3.4 g of hydrogen sulfide (H 2 S) under normal conditions (n.s.).
Solution: The molar mass of hydrogen sulfide is 34 g/mol. Based on this, we can write: 34 g H 2 S at standard conditions. occupies a volume of 22.4 liters.
3.4 g ________________________ X l,
hence X = 
l.
Example 5. How many molecules of ammonia are there?
a) in 1 liter b) in 1 g?
Solution: Avogadro's number 6.02 × 10 23 indicates the number of molecules in 1 mole (17 g/mol) or 22.4 liters at standard conditions, therefore, 1 liter contains
6.02 × 10 23 × 1= 2.7 × 10 22 molecules.
The number of ammonia molecules in 1 g is found from the proportion:
hence X = 6.02 × 10 23 × 1= 3.5 × 10 22 molecules.
Example 6. What is the mass of 1 mole of water?
Solution: The molecular mass of water H 2 O is 18 amu. (atomic mass of hydrogen – 1, oxygen – 16, total 1 + 1 + 16 = 18). This means that one mole of water is equal in mass to 18 grams, and this mass of water contains 6.02 × 10 23 water molecules.
Quantitatively, the mass of 1 mole of a substance is the mass of the substance in grams, numerically equal to its atomic or molecular mass.
For example, the mass of 1 mole of sulfuric acid H 2 SO 4 is 98 g
(1 +1 + 32 + 16 + 16 + 16 + 16 = 98),
and the mass of one molecule of H 2 SO 4 is equal to 98 g= 16.28 × 10 -23 g
Thus, any chemical compound is characterized by the mass of one mole or molar (molar) mass M, expressed in g/mol (M(H 2 O) = 18 g/mol, and M(H 2 SO 4) = 98 g/mol).
Atomic-molecular science was developed and first applied in chemistry by the great Russian scientist M.V. Lomonosov. The main provisions of this doctrine are set out in the work “Elements of Mathematical Chemistry” (1741) and a number of others. The essence of Lomonosov's teachings can be reduced to the following provisions.
1. All substances consist of “corpuscles” (as Lomonosov called molecules).
2. Molecules consist of “elements” (as Lomonosov called atoms).
3. Particles - molecules and atoms - are in continuous motion. The thermal state of bodies is the result of the movement of their particles.
4. Molecules of simple substances consist of identical atoms, molecules of complex substances - of different atoms.
67 years after Lomonosov, the English scientist John Dalton applied atomistic teaching to chemistry. He outlined the basic principles of atomism in the book “A New System of Chemical Philosophy” (1808). At its core, Dalton's teaching repeats Lomonosov's teaching. However, Dalton denied the existence of molecules in simple substances, which is a step backward in comparison with Lomonosov’s teaching. According to Dalton, simple substances consist only of atoms, and only complex substances consist of “complex atoms” (in the modern sense, molecules). The atomic-molecular theory in chemistry was finally established only in the middle of the 19th century. At the international congress of chemists in Karlsruhe in 1860, definitions of the concepts of molecule and atom were adopted.
A molecule is the smallest particle of a given substance that has its chemical properties. The chemical properties of a molecule are determined by its composition and chemical structure.
An atom is the smallest particle of a chemical element that is part of the molecules of simple and complex substances. The chemical properties of an element are determined by the structure of its atom. This leads to a definition of an atom that corresponds to modern concepts:
An atom is an electrically neutral particle consisting of a positively charged atomic nucleus and negatively charged electrons.
According to modern concepts, substances in gaseous and vaporous states are made up of molecules. In the solid state, only substances whose crystal lattice has a molecular structure consist of molecules. Most solid inorganic substances do not have a molecular structure: their lattice does not consist of molecules, but of other particles (ions, atoms); they exist in the form of macrobodies (crystal of sodium chloride, piece of copper, etc.). Salts, metal oxides, diamond, silicon, and metals do not have a molecular structure.
Chemical elements
Atomic-molecular science made it possible to explain the basic concepts and laws of chemistry. From the point of view of atomic-molecular theory, a chemical element is each individual type of atom. The most important characteristic of an atom is the positive charge of its nucleus, which is numerically equal to the atomic number of the element. The value of the nuclear charge serves as a distinctive feature for different types of atoms, which allows us to give a more complete definition of the concept of an element:
Chemical element- This is a certain type of atom with the same positive charge on the nucleus.
There are 107 known elements. Currently, work continues on the artificial production of chemical elements with higher atomic numbers.
All elements are usually divided into metals and non-metals. However, this division is conditional. An important characteristic of elements is their abundance in the earth’s crust, i.e. in the upper solid shell of the Earth, the thickness of which is assumed to be approximately 16 km. The distribution of elements in the earth's crust is studied by geochemistry - the science of the chemistry of the Earth. Geochemist A.P. Vinogradov compiled a table of the average chemical composition of the earth's crust. According to these data, the most common element is oxygen - 47.2% of the mass of the earth's crust, followed by silicon - 27.6, aluminum - 8.80, iron -5.10, calcium - 3.6, sodium - 2.64, potassium - 2.6, magnesium - 2.10, hydrogen - 0.15%.
Material from Uncyclopedia
The leading idea of atomic-molecular science, which forms the foundation of modern physics, chemistry and natural science, is the idea of discreteness (discontinuity of structure) of matter.
The first ideas that matter consists of individual indivisible particles appeared in ancient times and were initially developed in line with general philosophical ideas about the world. For example, some philosophical schools of Ancient India (1st millennium BC) recognized not only the existence of primary indivisible particles of matter (anu), but also their ability to combine with each other, forming new particles. Similar teachings existed in other countries of the ancient world. The greatest fame and influence on the subsequent development of science was exerted by ancient Greek atomism, the creators of which were Leucippus (5th century BC) and Democritus (b. c. 460 BC - d. c. 370 BC. ). “The causes of all things,” wrote the ancient Greek philosopher and scientist Aristotle (384–322 BC), expounding the Democritus’ doctrine, “are certain differences in atoms. And there are three differences: form, order and position.” In the works of Aristotle himself there is an important concept of mixis - a homogeneous compound formed from various substances. Later, the ancient Greek materialist philosopher Epicurus (342–341 BC - 271–270 BC) introduced the concept of the mass of atoms and their ability to spontaneously deflect during movement.
It is important to note that, according to many ancient Greek scientists, a complex body is not a simple mixture of atoms, but a qualitatively new integral formation, endowed with new properties. However, the Greeks had not yet developed the concept of special “polyatomic” particles - molecules, intermediate between atoms and complex bodies, which would be the smallest carriers of the properties of bodies.
The Middle Ages saw a sharp decline in interest in ancient atomism. The Church accused ancient Greek philosophies of asserting that the world arose from random combinations of atoms, and not by the will of God, as required by Christian dogma.
In the XVI–XVII centuries. In an atmosphere of general cultural and scientific upsurge, the revival of atomism begins. During this period, leading scientists from different countries: G. Galileo (1564–1642) in Italy, P. Gassendi (1592–1655) in France, R. Boyle (1627–1691) in England and others - proclaimed the principle: do not look for truth in Holy Scripture, and “directly” read the book of nature
P. Gassendi and R. Boyle owe the main credit for the further development of ancient atomism. Gassendi introduced the concept of a molecule, by which he understood a qualitatively new formation, composed by combining several atoms. A broad program for the creation of a corpuscular philosophy of nature was proposed by R. Boyle. The world of corpuscles, their movement and “plexus”, according to the English scientist, is very complex. The world as a whole and its smallest particles are purposefully arranged mechanisms. Boyle's corpuscles are no longer the primary, unbreakable atoms of ancient philosophers, but a complex whole capable of changing its structure through movement.
“Ever since I read Boyle,” wrote M.V. Lomonosov, “I have been possessed by a passionate desire to explore the smallest particles.” The great Russian scientist M.V. Lomonosov (1711–1765) developed and substantiated the doctrine of material atoms and corpuscles. He attributed to atoms not only indivisibility, but also an active principle - the ability to move and interact. “Insensitive particles must differ in mass, shape, motion, inertial force or location.” Corpuscles of homogeneous bodies, according to Lomonosov, “consist of the same number of the same elements, connected in the same way... Corpuscles are heterogeneous when their elements are different or connected in different ways or in different numbers.” Only because the study of mass relations at the beginning of the 18th century. just beginning, Lomonosov was unable to create a quantitative atomic-molecular theory.
This was done by the English scientist D. Dalton (1766–1844). He considered an atom as the smallest particle of a chemical element, differing from atoms of other elements primarily in mass. A chemical compound, according to his teaching, is a collection of “complex” (or “composite”) atoms containing certain numbers of atoms of each element, characteristic only for a given complex substance. The English scientist compiled the first table of atomic masses, but due to the fact that his ideas about the composition of molecules were often based on arbitrary assumptions based on the principle of “greatest simplicity” (for example, for water he accepted the formula OH), this table turned out to be inaccurate.
In addition, in the first half of the 19th century. many chemists did not believe in the possibility of determining true atomic masses and preferred to use equivalents that could be found experimentally. Therefore, different formulas were assigned to the same compound, and this led to the establishment of incorrect atomic and molecular masses.
One of the first who began the struggle for the reform of theoretical chemistry were the French scientists C. Gerard (1816–1856) and O. Laurent (1807–1853), who created the correct system of atomic masses and chemical formulas. In 1856, the Russian scientist D. I. Mendeleev (1834–1907), and then, independently of him, the Italian chemist S. Cannizzaro (1826 - 1910) proposed a method for calculating the molecular weight of compounds from the double density of their vapors relative to hydrogen. By 1860, this method was established in chemistry, which was crucial for the establishment of the atomic-molecular theory. In his speech at the International Congress of Chemists in Karlsruhe (1860), Cannizzaro convincingly proved the correctness of the ideas of Avogadro, Gerard and Laurent, the need for their adoption for the correct determination of atomic and molecular masses and the composition of chemical compounds. Thanks to the work of Laurent and Cannizzaro, chemists realized the difference between the form in which an element exists and reacts (for example, for hydrogen, it is H 2), and the form in which it is present in a compound (HCl, H 2 O, NH 3 and etc.). As a result, Congress adopted the following definitions of an atom and a molecule: molecule - “a quantity of a body that enters into reactions and determines chemical properties”; atom - “the smallest amount of an element included in particles (molecules) of compounds.” It was also accepted that the concept of “equivalent” should be considered empirical, not coinciding with the concepts of “atom” and “molecule”.
The atomic masses established by S. Cannizzaro served as the basis for D. I. Mendeleev in the discovery of the periodic law of chemical elements. The decisions of the congress had a beneficial effect on the development of organic chemistry, because the establishment of formulas of compounds opened the way for the creation of structural chemistry.
Thus, by the beginning of the 1860s. The atomic-molecular doctrine was formed in the form of the following provisions.
1. Substances consist of molecules. A molecule is the smallest particle of a substance that has its chemical properties. Many physical properties of a substance - boiling and melting points, mechanical strength, hardness, etc. - are determined by the behavior of a large number of molecules and the action of intermolecular forces.
2. Molecules consist of atoms that are connected to each other in certain relationships (see Molecule; Chemical bond; Stoichiometry).
3. Atoms and molecules are in constant spontaneous motion.
4. Molecules of simple substances consist of identical atoms (O 2, O 3, P 4, N 2, etc.); molecules of complex substances - from different atoms (H 2 O, HCl).
6. The properties of molecules depend not only on their composition, but also on the way in which the atoms are connected to each other (see Theory of chemical structure; Isomerism).
Modern science has developed the classical atomic-molecular theory, and some of its provisions have been revised.
It was established that the atom is not an indivisible structureless formation. However, many scientists in the last century also guessed about this.
It turned out that not in all cases the particles that form a substance are molecules. Many chemical compounds, especially in solid and liquid states, have ionic structures, such as salts. Some substances, such as noble gases, consist of individual atoms that weakly interact with each other even in liquid and solid states. In addition, a substance may consist of particles formed by the combination (association) of several molecules. Thus, chemically pure water is formed not only by individual H 2 O molecules, but also by polymer molecules (H 2 O)n, where n = 2–16; At the same time, it contains hydrated H + and OH − ions. A special group of compounds consists of colloidal solutions. And finally, when heated to temperatures of the order of thousands and millions of degrees, the substance passes into a special state - plasma, which is a mixture of atoms, positive ions, electrons and atomic nuclei.
It turned out that the quantitative composition of molecules with the same qualitative composition can sometimes vary within wide limits (for example, nitrogen oxide can have the formula N 2 O, NO, N 2 O 3, NO 2, N 2 O 4, N 2 O 5, NO 3 ), while if we consider not only neutral molecules, but also molecular ions, the boundaries of possible compositions expand. Thus, the NO 4 molecule is unknown, but the NO 3− 4 ion was recently discovered; there is no CH 5 molecule, but the CH + 5 cation is known, etc.
So-called compounds of variable composition were discovered, in which per unit mass of a given element there is a different mass of another element, for example: Fe 0.89–0.95 O, TiO 0.7–1.3, etc.
The position that molecules consist of atoms was clarified. According to modern quantum mechanical concepts (see Quantum chemistry), only the core of atoms in a molecule remains more or less unchanged, i.e., the core and internal electron shells, while the nature of the movement of external (valence) electrons radically changes so that a new, molecular electron shell is formed, covering the entire molecule (see Chemical bond). In this sense, there are no unchanging atoms in molecules.
Taking into account these clarifications and additions, it should be borne in mind that modern science has preserved the rational grain of the classical atomic-molecular teaching: ideas about the discrete structure of matter, the ability of atoms to produce, by combining with each other in a certain order, qualitatively new and more complex formations and about the continuous movement of particles that make up matter.
Atomic-molecular science- a set of provisions, axioms and laws that describe all substances as a set of molecules consisting of atoms.
Ancient Greek philosophers Long before the beginning of our era, they already put forward the theory of the existence of atoms in their works. Rejecting the existence of gods and otherworldly forces, they tried to explain all incomprehensible and mysterious natural phenomena by natural causes - the connection and separation, interaction and mixing of particles invisible to the human eye - atoms. But for many centuries, church ministers persecuted adherents and followers of the doctrine of atoms and subjected them to persecution. But due to the lack of necessary technical devices, ancient philosophers could not scrupulously study natural phenomena, and under the concept of “atom” they hid the modern concept of “molecule”.
Only in the middle of the 18th century the great Russian scientist M.V. Lomonosov substantiated atomic-molecular concepts in chemistry. The main provisions of his teaching are set out in the work “Elements of Mathematical Chemistry” (1741) and a number of others. Lomonosov named the theory corpuscular-kinetic theory.
M.V. Lomonosov clearly distinguished between two stages in the structure of matter: elements (in the modern sense - atoms) and corpuscles (molecules). The basis of his corpuscular-kinetic theory (modern atomic-molecular teaching) is the principle of discontinuity of the structure (discreteness) of matter: any substance consists of individual particles.
In 1745 M.V. Lomonosov wrote:“An element is a part of a body that does not consist of any smaller and different bodies... Corpuscles are a collection of elements into one small mass. They are homogeneous if they consist of the same number of the same elements connected in the same way. Corpuscles are heterogeneous when their elements are different and connected in different ways or in different numbers; the infinite variety of bodies depends on this.
Molecule is the smallest particle of a substance that has all its chemical properties. Substances having molecular structure, consist of molecules (most non-metals, organic substances). A significant part of inorganic substances consists of atoms(atomic crystal lattice) or ions (ionic structure). Such substances include oxides, sulfides, various salts, diamond, metals, graphite, etc. The carrier of chemical properties in these substances is a combination of elementary particles (ions or atoms), that is, a crystal is a giant molecule.
Molecules are made up of atoms. Atom- the smallest, further chemically indivisible component of the molecule.
It turns out that molecular theory explains the physical phenomena that occur with substances. The study of atoms comes to the aid of molecular theory in explaining chemical phenomena. Both of these theories - molecular and atomic - are combined into the atomic-molecular theory. The essence of this doctrine can be formulated in the form of several laws and regulations:
- substances are made up of atoms;
- when atoms interact, simple and complex molecules are formed;
- during physical phenomena, molecules are preserved, their composition does not change; with chemicals - they are destroyed, their composition changes;
- molecules of substances consist of atoms; in chemical reactions, atoms, unlike molecules, are preserved;
- the atoms of one element are similar to each other, but different from the atoms of any other element;
- chemical reactions involve the formation of new substances from the same atoms that made up the original substances.
Thanks to its atomic-molecular theory M.V. Lomonosov is rightfully considered the founder of scientific chemistry.
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