§ 1 M.V. Lomonosov as the founder of the atomic and molecular theory

Since the 17th century, science has had a molecular theory that has been used to explain physical phenomena. The practical application of molecular theory in chemistry was limited by the fact that its provisions could not explain the essence of the course of chemical reactions, answer the question of how new substances are formed from some substances in the course of a chemical process.

The solution of this problem turned out to be possible on the basis of the atomic-molecular theory. In 1741, in the book "Elements of Mathematical Chemistry", Mikhail Vasilyevich Lomonosov actually formulated the foundations of the atomic and molecular theory. The Russian scientist-encyclopedist considered the structure of matter not as a certain combination of atoms, but as a combination of larger particles - corpuscles, which, in turn, consist of smaller particles - elements.

Lomonosov's terminology underwent changes over time: what he called corpuscles began to be called molecules, and the term element was replaced by the term atom. However, the essence of the ideas and definitions expressed by him brilliantly stood the test of time.

§ 2 History of the development of atomic and molecular science

The history of the development and establishment of atomic and molecular theory in science turned out to be very difficult. Working with objects of the microcosm caused great difficulties: it was impossible to see atoms and molecules and, thus, to be convinced of their existence, and attempts to measure atomic masses often ended in erroneous results. 67 years after the discovery of Lomonosov, in 1808, the famous English scientist John Dalton put forward the atomic hypothesis. According to it, atoms are the smallest particles of matter that cannot be divided into constituent parts or transformed into each other. According to Dalton, all atoms of one element have exactly the same weight and differ from the atoms of other elements. By combining the theory of atoms with the theory of chemical elements developed by Robert Boyle and Mikhail Vasilievich Lomonosov, Dalton provided a solid foundation for further theoretical research in chemistry. Unfortunately, Dalton denied the existence of molecules in simple substances. He believed that only complex substances are composed of molecules. This did not contribute to the further development and application of the atomic and molecular theory.

The conditions for the dissemination of the ideas of the atomic and molecular theory in natural science developed only in the second half of the 19th century. In 1860, at the International Congress of Naturalists in the German city of Karlsruhe, scientific definitions of the atom and molecule were adopted. There was no doctrine of the structure of substances at that time, therefore, the position was accepted that all substances consist of molecules. It was believed that simple substances, such as metals, consist of monatomic molecules. Subsequently, such a continuous extension of the principle of molecular structure to all substances turned out to be erroneous.

§ 3 Basic provisions of the atomic and molecular theory

1. Molecule - the smallest part of a substance that retains its composition and essential properties.

2. Molecules are made up of atoms. The atoms of one element are similar to each other, but differ from the atoms of other chemical elements.

M. V. Lomonosov, J. Dalton, A. Lavoisier, J. Proust, A. Avogadro, J. Berzelius, D. I. Mendeleev, A. M. Butlerov made a great contribution to the development of atomic and molecular theory. The first to define chemistry as a science was MV Lomonosov. Lomonosov created the doctrine of the structure of matter, laid the foundation for the atomic-molecular theory. It boils down to the following:

1. Each substance consists of the smallest, further physically indivisible particles (Lomonosov called them corpuscles, later they were called molecules).

2. Molecules are in constant, spontaneous motion.

3. Molecules consist of atoms (Lomonosov called them elements).

4. Atoms are characterized by a certain size and mass.

5. Molecules can consist of both identical and different atoms.

A molecule is the smallest particle of a substance that retains its composition and chemical properties. The molecule cannot be broken down further without changing the chemical properties of the substance. Between the molecules of a substance there is a mutual attraction, which is different for different substances. Molecules in gases are attracted to each other very weakly, while between the molecules of liquid and solid substances, the forces of attraction are relatively large. The molecules of any substance are in constant motion. This phenomenon explains, for example, the change in the volume of substances when heated.

Atoms are the smallest, chemically indivisible particles that make up molecules. An atom is the smallest particle of an element that retains its chemical properties. Atoms differ in nuclear charges, mass and size. In chemical reactions, atoms do not arise and do not disappear, but form molecules of new substances. An element should be considered as a kind of atoms with the same nuclear charge.

The chemical properties of atoms of the same chemical element are the same, such atoms can differ only in mass. Varieties of atoms of the same element with different masses are called isotopes. Therefore, there are more varieties of atoms than chemical elements.

It is necessary to distinguish between the concepts of "chemical element" and "simple substance".

A substance is a certain set of atomic and molecular particles in any of the three states of aggregation.

Aggregate states of matter - a state of matter characterized by certain properties (the ability to maintain shape, volume).

There are three main states of aggregation: solid, liquid and gas. Sometimes it is not entirely correct to classify plasma as a state of aggregation. There are other states of aggregation, for example, liquid crystals or Bose-Einstein condensate.

A chemical element is a general concept of atoms with the same nuclear charge and chemical properties.

The physical properties characteristic of a simple substance cannot be attributed to a chemical element.

Simple substances are substances consisting of atoms of the same chemical element. The same element can form several simple substances.

Modern presentation of the main provisions of the atomic and molecular theory:

1. All substances are made up of atoms.
2. The atoms of each type (element) are the same among themselves, but differ from the atoms of any other type (element).
3. When atoms interact, molecules are formed: homonuclear (during the interaction of atoms of one element) or heteronuclear (during the interaction of atoms of different elements).
4. In physical phenomena, molecules are preserved, in chemical phenomena they are destroyed; In chemical reactions, atoms, unlike molecules, are preserved.
5. Chemical reactions consist in the formation of new substances from the same atoms that make up the original substances.

Of exceptional importance for the development of chemistry was the atomic and molecular theory, the cradle of which is Ancient Greece. The atomistics of the ancient Greek materialists is separated from us by a 25-century period, however, the logic of the Greeks is so striking that the philosophical doctrine of the discrete structure of matter, developed by them, involuntarily merges in consciousness with our current ideas. How did atomism originate? The main scientific method of ancient Greek philosophers was discussion, dispute. To search for “root causes” in disputes, many logical problems were discussed, one of which was the problem of a stone: what happens if you start crushing it?

Most philosophers believed that this process could be continued indefinitely. And only Leucippus (500-440 BC) and his school claimed that this process is not endless: when crushed, in the end, such a particle will be obtained, the further division of which will be simply impossible. Based on this concept, Leucippus argued: the material world is discrete, it consists of the smallest particles and emptiness. The student of Leucippus Democritus (460-370 BC) called the smallest particles “indivisible”, which in Greek means “atom”. We still use this name today. Democritus, developed a new doctrine - "atomism", attributed to the atoms such "modern" properties as size and shape, the ability to move.

Epicurus (342-270 BC), a follower of Democritus, completed the ancient Greek atomistics by assuming that atoms have an internal source of motion, and they themselves are able to interact with each other. All the provisions of ancient Greek atomism look amazingly modern, and they are naturally understandable to us. After all, any of us, referring to the experience of science, can describe many interesting experiments that confirm the validity of any of the proposed concepts. But they were completely incomprehensible 20-25 centuries ago, since the ancient Greek atomists could not provide any experimental evidence confirming the validity of their ideas. So, although the atomism of the ancient Greeks looks surprisingly modern, none of its provisions were proved at that time. Consequently, “atomistics, developed by Leucippus, Democritus and Epicurus, was and remains just a guess, a bold assumption, a philosophical concept, but supported by practice. This led to the fact that one of the brilliant conjectures of the human mind was gradually forgotten.

There were other reasons why the teachings of the atomists were forgotten for a long time. Unfortunately, the atomists did not leave behind systematic works, and the individual records of the disputes and discussions that were made only with difficulty made it possible to form a correct idea of ​​the doctrine as a whole. The main thing is that many concepts of atomism were heretical and the official church could not support them.

The teachings of the atomists were not remembered for almost 20 centuries. And only in the XVII century. The ideas of the ancient Greek atomists were revived thanks to the work of the French philosopher Pierre Gassendi (1592-1655). Almost 20 years he spent; to restore and collect together the forgotten concepts of the ancient Greek philosophers, which he detailed in his writings “C) the life, manners and teachings of Epicurus” and “Code of Philosophy of Epicurus”. These two books, in which the views of the ancient Greek materialists were presented systematically for the first time, became a "textbook" for European scientists and philosophers. Prior to this, the only source that provided information about the views of Democritus - Epicurus, was the poem of the Roman poet Lucretius "On the nature of things." The history of science knows many amazing coincidences. Here is one of them: the revival of ancient Greek atomistics coincides in time with the establishment by R. Boyle (1627-1691) of a fundamental regularity describing changes in the volume of a gas from its pressure. A qualitative explanation of the facts observed by Boyle can only be given by atomistics: if a gas has a discrete structure, i.e., consists of atoms and emptiness, then the ease of its compression is due to the approach of atoms as a result of a decrease in the free space between them. The first tentative attempt to apply atomism to explain quantitatively observable natural phenomena leads to two very important conclusions:

• 1. Having turned from a philosophical hypothesis into a scientific concept, atomistics can become a powerful tool that allows one to give the only correct interpretation of the most diverse natural phenomena.
• 2. For the speedy transformation of atomism from a philosophical hypothesis into a scientific concept, the proof of the existence of atoms must, first of all, be sought in the study of gases, and not liquid and solid substances, which were previously dealt with by chemists. However, it will take about 100 years before chemists come to grips with the study of gases. Then a cascade of discoveries of simple substances will follow: hydrogen, oxygen, nitrogen, chlorine. And a little later, gases will help to establish those laws that are commonly called the basic laws of chemistry. They will make it possible to formulate the main provisions of the atomic and molecular theory.

1. There are substances of molecular and non-molecular structure.

2. For substances of molecular structure in the solid state, there are molecules in the nodes of crystal lattices.

3. For substances of non-molecular structure, ions or atoms are located in the nodes of crystal lattices.

4. Between the molecules there are gaps, the dimensions of which depend on the state of aggregation of the substance and its temperature. The greatest distances exist between gas molecules, so gases are easily compressed. In solids, the gaps between particles are the smallest, and, accordingly, these substances are almost not subject to compression.

5. Molecules are in constant motion. Their speed depends on the temperature. As the temperature rises, the speed of movement increases.

6. In physical phenomena, molecules are preserved, in chemical phenomena they are destroyed.

7. Molecules are made up of atoms, which, like molecules, are in constant motion. One form of atomic movement is a chemical reaction.

8. The atoms of one element differ from the atoms of another element in size, mass and properties.

9. Atoms are preserved in chemical reactions.

10. A chemical reaction is the formation of new substances from the same atoms that made up the original substances.

We already know that many substances are made up of molecules, and molecules are made up of atoms. Information about atoms and molecules is combined into an atomic-molecular doctrine. You know that the main provisions of this doctrine were developed by the great Russian scientist M. V. Lomonosov. More than two hundred years have passed since then, and the theory of atoms and molecules has been further developed. For example, it is now known that not all substances are composed of molecules. Most of the solids we encounter in inorganic chemistry are non-molecular.

However, relative molecular masses are calculated both for substances with a molecular and for substances with a non-molecular structure. For the latter, the concepts of "molecule" and "relative molecular weight" are used conditionally.

The main provisions of the atomic-molecular theory can be formulated as follows:

1. There are substances with a molecular and non-molecular structure.

2. There are gaps between the molecules, the dimensions of which depend on the state of aggregation of the substance and temperature. The greatest distances exist between gas molecules. This explains their easy compressibility. It is more difficult to compress liquids where the gaps between molecules are much smaller. In solids, the gaps between molecules are even smaller, so they hardly compress.

3. Molecules are in continuous motion. Molecular speed depends on temperature. As the temperature rises, the speed of the molecules increases.

4. Between molecules there are forces of mutual attraction and repulsion. To the greatest extent, these forces are expressed in solids, to the least - in gases.

5. Molecules are made up of atoms, which, like molecules, are in continuous motion.

6. Atoms of one kind differ from atoms of another kind in mass and properties.

7. In physical phenomena, molecules are preserved; in chemical phenomena, as a rule, they are destroyed.

8. For substances with a molecular structure in the solid state, there are molecules in the nodes of the crystal lattices. Bonds between molecules located at the nodes of the crystal lattice, weak when heated, are broken. Therefore, substances with a molecular structure, as a rule, have low melting points.

9. Substances with a non-molecular structure have atoms or other particles in the nodes of crystal lattices. There are strong chemical bonds between these particles, which require a lot of energy to break.

Exercise

1. Select a slide with one of the provisions of the Atomic and Molecular Teachings. Pick up illustrations and examples from life that prove this position.

Deadlines: 25.01- 30.01.16
2. Rate the next slide after yours according to the following criteria:

1. The presence of an illustration corresponding to this provision. 0-1b

2. The selected facts prove this position. 0-1b

3. The material is presented in accessible language. 0-1b

4. Aesthetic design (good quality illustration, readable text). 0-1b