Chemistry, the basic concepts of which we will consider, is a science that studies substances and their transformations that occur with a change in structure and composition, and therefore, properties. First of all, it is necessary to determine what the term “substance” means. Speaking about it in a broad sense, it is a form of matter that has a mass of rest. A substance is any elementary particle, for example, a neutron. In chemistry, this concept is used in a narrower sense.
To begin with, we briefly describe the basic terms and concepts of chemistry, atomic-molecular studies. After that, we will explain them, and also outline some important laws of this science.
The basic concepts of chemistry (substance, atom, molecule) are familiar to each of us since school. Below is a brief description of them, as well as other, not so obvious terms and phenomena.
Atoms
First of all, all substances studied in chemistry are composed of small particles called atoms. Neutrons are not the object of study of this science. It should also be said that atoms can combine with each other, as a result of which chemical bonds are formed. In order to break this connection, an expenditure of energy is required. Therefore, atoms under ordinary conditions do not exist individually (with the exception of "noble gases"). They are connected to each other at least in pairs.
Continuous heat movement
Continuous thermal motion characterizes all the particles that chemistry studies. The basic concepts of this science cannot be stated without talking about it. With continuous motion, the average kinetic energy of particles is proportional to temperature (however, it should be noted that the energies of individual particles are different). Ekin = kT / 2, where k is the Boltzmann constant. This formula is valid for any kind of movement. Since Ekin = mV 2/2, the motion of massive particles is slower. For example, if the temperature is the same, oxygen molecules on average move 4 times slower than carbon molecules. This is because their mass is 16 times greater. The movement is oscillatory, translational and rotational. Oscillatory is observed both in liquid, and in solid, and in gaseous substances. But translational and rotational is most easily carried out in gases. It is harder in liquids, and even harder in solids.
Molecules
We continue to describe the basic concepts and definitions of chemistry. If atoms combine with each other, forming small groups (they are called molecules), such groups take part in the thermal motion, acting as a whole. Up to 100 atoms are present in typical molecules, and their number in the so-called high molecular weight compounds can reach 105.
Non-molecular substances
However, atoms are often combined into huge collectives from 107 to 1027 in number. In this form, they practically no longer take part in thermal motion. These associations are already a little like molecules. They are more like solid pieces. These substances are called non-molecular. In this case, the thermal movement is carried out inside the piece, and he does not fly, like a molecule. There is also a transitional region of sizes, which includes associations consisting of atoms in an amount of 105 to 107. These particles are either very large molecules, or are small particles of powder.
Jonah
It should be noted that atoms and their groups can have an electric charge. In this case, they are called ions in a science such as chemistry, the basic concepts of which we are studying. Since the charges of the same name always repel each other, a substance where there is a significant excess of certain charges cannot be stable. Negative and positive charges in space always alternate. And the substance as a whole remains electrically neutral. Note that the charges considered to be large in electrostatics are insignificant from the point of view of chemistry (by 105-1015 atoms - 1e).
Objects of study in chemistry
It is necessary to clarify that the objects of study in chemistry are those phenomena in which atoms do not arise and do not collapse, but only rearrange, that is, reunite in a new way. Some bonds are broken, as a result of which others are formed. In other words, new substances appear from atoms that were part of the starting materials. If, however, both atoms and the bonds existing between them remain (for example, during the evaporation of molecular substances), then these processes belong to the field of study not of chemistry, but of molecular physics. In the case when atoms are formed or destroyed, we are talking about the subjects of nuclear or atomic physics. However, the boundary between chemical and physical phenomena is blurred. Indeed, the division into separate sciences is arbitrary, while nature is indivisible. Therefore, knowledge of physics is very useful for chemists.
The basic concepts of chemistry were briefly stated by us. Now we suggest you consider them in more detail.
More About Atoms
Atoms and molecules are what many associate chemistry with. These basic concepts must be clearly defined. The fact that atoms exist two thousand years ago was brilliantly guessed. Then, already in the 19th century, scientists appeared experimental data (still indirect). We are talking about multiple relationships Avogadro, the laws of constancy of composition (below we will consider these basic concepts of chemistry). The atom was continued to be investigated in the 20th century, when many direct experimental confirmations arose. They were based on spectroscopy data, on the scattering of x-rays, alpha particles, neutrons, electrons, etc. The size of these particles is about 1 E = 1o- 10 m. Their mass is about 10 -27 - 10 -25 kg. At the center of these particles is a positively charged nucleus, around which electrons with a negative charge move. The size of the nucleus is about 10 -15 m. It turns out that the electron shell determines the size of the atom, but at the same time its mass is almost completely concentrated in the nucleus. Another definition should be introduced, considering the basic concepts of chemistry. A chemical element is a type of atom whose nucleus charge is the same.
Often there is a definition of an atom as the smallest particle of a substance, chemically indivisible. How to understand "chemically"? As we have already noted, the division of phenomena into physical and chemical is arbitrary. But the existence of atoms is unconditional. Therefore, chemistry is better defined through them, and not vice versa, atoms through chemistry.
Chemical bond
This is why atoms are held together. It does not allow them to fly apart under the influence of thermal motion. Note the main characteristics of the bonds - this is the internuclear distance and energy. These are also the basic concepts of chemistry. The bond length is determined experimentally with fairly high accuracy. Energy is also, but not always. For example, it is impossible to objectively determine what it is in relation to an individual bond in a complex molecule. However, the atomization energy of a substance, necessary for breaking all existing bonds, is always determined. Knowing the bond length, it is possible to determine which atoms are bound (they have a short distance) and which are not (long distance).
Coordination number and coordination
The basic concepts of analytical chemistry include these two terms. What do they mean? Let's figure it out.
The coordination number is the number of nearest neighbors of a given atom. In other words, this is the number of those with whom he is chemically bonded. Coordination is the relative position, type and number of neighbors. In other words, this concept is more meaningful. For example, the coordination number of nitrogen, which is characteristic of ammonia and nitric acid molecules, is the same - 3. However, their coordination is different - non-planar and flat. It is determined independently of the understanding of the nature of the bond, while the degree of oxidation and valency are conditional concepts that are created in order to predict coordination and composition in advance.
Molecule Definition
We have already touched on this concept, considering the basic concepts and laws of chemistry briefly. Now dwell on it in more detail. In textbooks, the definition of a molecule as the smallest neutral particle of a substance that has its chemical properties and is also able to exist independently is often found. It should be noted that this definition is now outdated. Firstly, what all physicists and chemists call a molecule does not preserve the properties of matter. Water dissociates, but this requires at least 2 molecules. The degree of dissociation of water is 10 -7 . In other words, only one molecule out of 10 million can undergo this process. If you have one molecule, or even one hundred, you will not be able to get an idea about its dissociation. The fact is that the thermal effects of reactions in chemistry usually include the energy of interaction between molecules. Therefore, they cannot be found by one of them. Both the chemical and physical properties of a molecular substance can only be determined by a large group of molecules. In addition, there are substances in which the "smallest" particle capable of existing on its own is indefinitely large and very different from the usual molecules. The molecule is actually a group of atoms, not electrically charged. In the particular case, it can be one atom, for example, Ne. This group should be able to participate in diffusion, as well as in other types of thermal motion, acting as a whole.
As you can see, the basic concepts of chemistry are not so simple. A molecule is something that needs to be carefully studied. It has its own properties, as well as molecular weight. We’ll talk about the latter now.
Molecular mass
How to determine the molecular weight in the experiment? One way is based on the Avogadro law, relative steam density. The most accurate method is mass spectrometric. The electron is knocked out of the molecule. The resulting ion is first accelerated in an electric field, then magnetically deflected. The ratio of charge to mass is determined precisely by the magnitude of the deviation. There are also methods based on the properties that solutions have. However, the molecules in all these cases must certainly be in motion - in solution, in vacuum, in gas. If they do not move, it is impossible to objectively calculate their mass. And their very existence in this case is difficult to detect.
Features of non-molecular substances
Speaking of them, they note that they are composed of atoms, and not of molecules. However, the same is true for noble gases. These atoms move freely, therefore, it is better to consider them as monatomic molecules. However, this is not the main thing. More importantly, in non-molecular substances there are a lot of atoms that are connected together. It should be noted that the division of all substances into non-molecular and molecular is insufficient. Connectivity division is more substantial. Consider, for example, the difference in the properties of graphite and diamond. Both are carbon, but the first is soft and the second is hard. How do they differ from each other? The difference lies precisely in their connectivity. If we consider the structure of graphite, we will see that strong bonds are present in only two dimensions. But in the third, the interatomic distances are very significant, therefore, there is no strong bond. Graphite glides and splits easily along these layers.
Structure connectivity
Otherwise, it is called spatial dimension. It represents the number of dimensions of space, characterized by the fact that in them a continuous (almost infinite) system of skeletons (strong bonds). The values that it can take are 0, 1, 2, and 3. Therefore, it is necessary to distinguish between three-dimensionally connected, layered, chain, and island (molecular) structures.
Law of Consistency
We have already studied the basic concepts of chemistry. The substance was briefly reviewed by us. Now let's talk about the law that applies to it. Usually it is formulated as follows: any individual substance (that is, pure), regardless of how it was obtained, has the same quantitative and qualitative composition. But what does the concept of "pure substance" mean ? Let's figure it out.
Two thousand years ago, when the structure of substances could not yet be studied by direct methods, when the basic chemical concepts and laws of chemistry, familiar to us, did not even exist, it was described descriptively. For example, water is the liquid that forms the basis of seas and rivers. She has no smell, color, or taste. It has such freezing and melting points; copper sulfate turns blue from it . Salty sea water is because it is not clean. However, salts can be separated by distillation. Something like this, a descriptive method, determined the basic chemical concepts and laws of chemistry.
For scientists of that time, it was not obvious that a liquid that was isolated in various ways (by burning hydrogen, dehydrating vitriol, distilling sea water) had the same composition. A major discovery in science was the proof of this fact. It became clear that the ratio of oxygen and hydrogen cannot smoothly change. This means that the elements are composed of atoms - indivisible portions. Thus, formulas of substances were obtained, as well as the idea of scientists about molecules was justified.
Nowadays, any substance is explicitly or implicitly determined primarily by the formula, and not by the melting point, taste or color. Water is H 2 O. If other molecules are present, it will no longer be pure. Therefore, a pure molecular substance is one that is composed of molecules of only one kind.
However, what about electrolytes in this case? After all, their composition contains ions, and not just molecules. A stricter definition is needed. A pure molecular substance is one that is composed of molecules of the same species, as well as, possibly, products of their reversible rapid transformation (isomerization, association, dissociation). The word “fast” in this context means that we cannot get rid of these products, they immediately reappear. The word "reversible" indicates that the transformation is not carried through to the end. If it is brought up, then it is better to say that it is unstable. In this case, it is not a pure substance.
The law of conservation of mass of matter
Since ancient times, this law has been known in metaphorical form. He said that the substance is indissoluble and indestructible. Then came his quantitative formulation. According to it, weight (and from the end of the 17th century - mass) is a measure of the amount of substance.
This law in its usual form was discovered in 1748 by Lomonosov. In 1789, it was supplemented by A. Lavoisier, a French scientist. Its modern formulation is as follows: the mass of substances entering into a chemical reaction is equal to the mass of substances that result from it.
Avogadro law, the law of volumetric gas relations
The last of them was formulated in 1808 by J. L. Gay-Lussac, a French scientist. This law is currently referred to as the Gay-Lussac Act. According to him, the volumes of reacting gases relate to each other, as well as to the volumes of the obtained gaseous products as whole small numbers.
The pattern that Gay-Lussac discovered explains the law, which was discovered a little later, in 1811, by Amedeo Avogadro, an Italian scientist. It states that under equal conditions (pressure and temperature) in gases having the same volumes, the same number of molecules is present.
Two important consequences follow from the law of Avogadro. The first is that under the same conditions, one mole of any gas occupies an equal volume. The volume of any of them under normal conditions (which are a temperature of 0 ° C, as well as a pressure of 101.325 kPa) is 22.4 liters. The second consequence of this law is the following: under equal conditions, the ratio of the masses of gases having the same volume is equal to the ratio of their molar masses.
There is another law that must be mentioned. Let's talk about it briefly.
Periodic law and table
D. I. Mendeleev, based on the chemical properties of elements and atomic-molecular theory, discovered this law. This event occurred on March 1, 1869. The periodic law is one of the most important in nature. It can be formulated as follows: the properties of elements and the complex and simple substances formed by them have a periodic dependence on the charges of the nuclei of their atoms.
The periodic table that Mendeleev created consists of seven periods and eight groups. Groups are its vertical columns. . , , ( ).
. , , , – , . . . . 18. . 18 , . – 32 . . (Fr). , 32 , . 24.
According to the rule of repetition, all elements strive to acquire an electron or lose it in order to have an 8-electron configuration of the noble gas closest to them. Ionization energy is the amount of energy needed to separate an electron from an atom. The rule of repetition states that when moving from left to right on the periodic table, more energy is needed to detach the electron. Therefore, elements located on the left side tend to lose an electron. On the contrary, those located on the right side are eager to acquire it.
The laws and basic concepts of chemistry are briefly outlined. Of course, this is just general information. In the framework of one article, it is impossible to talk in detail about such a serious science. The basic concepts and laws of chemistry, summarized in our article, are just a starting point for further study. Indeed, in this science there are many sections. There is, for example, organic and inorganic chemistry. The basic concepts of each of the sections of this science can be studied for a very long time. But those presented above are related to general issues. Therefore, we can say that these are the basic concepts of organic chemistry, as well as inorganic.