The concept of matter is studied by several sciences at once. We will analyze the question of what substances are from two points of view - from the position of chemical science and from the position of physics.

Substance in chemistry and physics

Chemists understand matter as a physical substance with a certain set of chemical elements. In modern physics, matter is considered as a kind of matter that consists of fermions or a kind of matter that contains fermions, bosons, and has a rest mass. As usual, matter should be composed of particles, mostly electrons, protons and neutrons. Protons and neutrons form atomic nuclei, and together these elements form atoms (atomic matter).

Matter properties

Almost every substance has its own unique set of properties. Properties are understood as characteristics that indicate the individuality of a substance, which in turn demonstrates its differences from all other substances. Characteristic physical and chemical properties are constants - density, various types of temperatures, thermodynamics, indicators of the crystal structure.

Chemical classification of substances

In chemistry, substances are divided into compounds and their mixtures. In addition, organic substances should be said. A compound is a set of atoms that are connected to each other, taking into account certain patterns. It should be noted that the boundary between a compound and a mixture of substances is quite difficult to clearly define. This is due to the fact that science knows substances of variable composition. For them, it is impossible to make an exact formula. In addition, the compound is by and large an abstraction, since in a practical sense only the final purity of the substance under study can be achieved. Any sample that exists in real life is a mixture of substances, but with a predominance of one substance from the entire group. In addition, it should be said what organic substances are. This group of complex substances contains carbon (proteins, carbohydrates).

Simple and complex substances

Simple substances (O2, O3, H2, Cl2) are those substances that consist of only atoms of one chemical element. These substances are a form of the existence of elements in a free form. In other words, these chemical elements, which are not associated with other elements, form simple substances. More than 400 varieties of such substances are known to science. Simple substances are classified according to the type of bond between atoms. So, simple substances are divided into metals (Na, Mg, Al, Bi, etc.) and non-metals (H 2, N 2, Br 2, Si, etc.).

Compounds are chemical compounds that are made up of two or more elements bonded together. Simple substances also have the right to be called chemical compounds if their molecules will consist of atoms connected by a covalent bond (nitrogen, oxygen, bromine, fluorine,). But it would be a mistake to call inert (noble) gases and atomic hydrogen chemical compounds.

Physical classification of substances

From the point of view of physics, substances exist in several states of aggregation - body, liquid and gas. About what solids, for example, can be seen with the naked eye. The same can be said about the other state of aggregation. What liquid substances are in nature, we know from school. It is noteworthy that such a substance as water can exist in three states at once - like ice, liquid water and steam. Three aggregate states of a substance are not considered individual characteristics of substances, but correspond to different ones, depending on the external conditions for the existence of substances. In the transition from states of aggregate states to real states of a chemical substance, a number of intermediate types can be identified, which in science are called amorphous or glassy states, as well as liquid crystal states and polymer states. In this regard, scientists often use the concept of "phase".

In addition to others, physics also considers the fourth state of aggregation of a chemical substance. This is a plasma, that is, a state that is fully or partially ionized, and the density of positive and negative charges in this state is the same, in other words, the plasma is electrically neutral. In general, there are many substances in nature, but now you know what substances are, and this is much more important.

Chemical element, simple and complex substance, allotropy. Relative atomic and molecular masses, mol, molar mass. Valency, oxidation state, chemical bond, structural formula.

Workshop: Calculations by chemical formulas, chemical equations. Solving problems for finding the chemical formula of a substance. Solving problems using the concept of "molar mass". Calculations by chemical equations, if one of the substances is taken in excess, if one of the substances contains impurities. Solving problems to determine the yield of the reaction product.

Chemistry is the science of substances, their properties and transformations that occur as a result of chemical reactions, as well as the fundamental laws that these transformations obey. Since all substances are composed of atoms, which, due to chemical bonds, are able to form molecules, chemistry is mainly concerned with the study of interactions between atoms and molecules resulting from such interactions.

Chemical element - a certain type of atom that has a name, serial number, and position in the periodic table is called a chemical element. Currently, 118 chemical elements are known, ending with Uuo (Ununoctium - Ununoctium). Each element is labeled with a symbol that represents one or two letters from its Latin name (hydrogen is denoted by the letter H, the first letter of its Latin name Hydrogenium).

Substance is a type of matter with certain chemical and physical properties. A set of atoms, atomic particles or molecules that is in a certain state of aggregation. Physical bodies consist of substances (copper is a substance, and a copper coin is a physical body).

A simple substance is a substance consisting of atoms of one chemical element: hydrogen, oxygen, etc.

A complex substance is a substance consisting of atoms of different chemical elements: acids, water, etc.

Allotropy is the ability of some chemical elements to exist in the form of two or more simple substances, different in structure and properties. For example: diamond and coal are composed of the same element - carbon.

Relative atomic mass. The relative atomic mass of an element is the ratio of the absolute mass of an atom to 1/12 of the absolute mass of an atom of the carbon isotope 12C. The relative atomic mass of an element is denoted by the symbol Ar, where r is the initial letter of the English word relative (relative).

Relative molecular weight. The relative molecular mass Mr is the ratio of the absolute mass of a molecule to 1/12 of the mass of an atom of the carbon isotope 12C.

Note that relative masses are, by definition, dimensionless quantities.

Thus, 1/12 of the mass of an atom of the 12C carbon isotope, which is called the atomic mass unit (a.m.u.), is chosen as a measure of relative atomic and molecular masses:

Moth. In chemistry, a special value is of extreme importance - the amount of a substance.

The amount of a substance is determined by the number of structural units (atoms, molecules, ions or other particles) of this substance, it is usually denoted n and is expressed in moles (mol).

A mole is a unit of the amount of a substance containing as many structural units of a given substance as there are atoms in 12 g of carbon, consisting only of the 12C isotope.

Avogadro's number. The definition of a mole is based on the number of structural units contained in 12 g of carbon. It is established that this mass of carbon contains 6.02 × 1023 carbon atoms. Therefore, any substance of 1 mol contains 6.02 × 1023 structural units (atoms, molecules, ions).

The number of particles 6.02 × 1023 is called Avogadro's number or Avogadro's constant and is denoted NA:

N A \u003d 6.02 × 10 23 mol -1

Molar mass. For the convenience of calculations based on chemical reactions and taking into account the amounts of initial reagents and interaction products in moles, the concept of the molar mass of a substance is introduced.

The molar mass M of a substance is the ratio of its mass to the amount of the substance:
where g is the mass in grams, n is the amount of substance in moles, M is the molar mass in g / mol - a constant value for each given substance.
The value of the molar mass numerically coincides with the relative molecular mass of a substance or the relative atomic mass of an element.

Valence - the ability of atoms of chemical elements to form a certain number of chemical bonds with atoms of other elements or the number of bonds that a substance can form.

The oxidation state (oxidation number, formal charge) is an auxiliary conditional value for recording the processes of oxidation, reduction and redox reactions, the numerical value of the electric charge attributed to an atom in a molecule on the assumption that the electron pairs that carry out the connection are completely shifted towards more electronegative atoms.
Ideas about the degree of oxidation form the basis for the classification and nomenclature of inorganic compounds.

The oxidation state corresponds to the charge of an ion or the formal charge of an atom in a molecule or in a formula unit, for example:

Na + Cl - , Mg 2+ Cl 2 - , N -3 H 3 - , C +2 O -2 , C +4 O 2 -2 , Cl + F - , H + N +5 O -2 3 , C -4 H 4 + , K +1 Mn +7 O -2 4 .

The oxidation state is indicated above the element symbol. In contrast to indicating the charge of an ion, when indicating the degree of oxidation, the sign is put first, and then the numerical value, and not vice versa.

H + N +3 O -2 2 - oxidation state, H + N 3+ O 2- 2 - charges.

The oxidation state of an atom in a simple substance is zero, for example:

O 0 3 , Br 0 2 , C 0 .

The algebraic sum of the oxidation states of atoms in a molecule is always zero:

H + 2 S +6 O -2 4 , (+1 2) + (+6 1) + (-2 4) = +2 +6 -8 = 0

Chemical bond, the mutual attraction of atoms, leading to the formation of molecules and crystals. It is customary to say that in a molecule or in a crystal there are chemical bonds between neighboring atoms. A chemical bond is determined by the interaction between charged particles (nuclei and electrons). The main characteristics of a chemical bond are strength, length, polarity.

Properties - a set of features by which some substances differ from others, they are chemical and physical.

Physical properties - signs of a substance, in the course of which the substance does not change its chemical composition. (Density, state of aggregation, melting and boiling points, etc.)

Chemical properties - the ability of substances to interact with other substances or change under the influence of certain conditions. The result is the transformation of one substance or substances into other substances.

Physical phenomena - new matter is not formed.
Chemical phenomena - new substance is formed.

SUBSTANCE

SUBSTANCE

kind of matter, which, in contrast to the physical. fields, has a rest mass. Ultimately, the wave is composed of elementary particles whose rest is not equal to zero (mostly from electrons, protons, neutrons). In the classic V. physics and physical. fields were absolutely opposed to each other as two types of matter, the first of which is discrete, and the second is continuous. Quantum, which introduced the idea of ​​duals. corpuscular-wave nature of any micro-object, led to the leveling of this opposition. The revelation of the close interrelationship between water and the field led to a deepening of ideas about the structure of matter. On this basis, V. and matter were strictly delimited, throughout pl. centuries, identified both with philosophy and science, and philosophy significance remained with the category of matter, and V. retained the scientific one in physics and chemistry. Vacuum occurs under terrestrial conditions in four states: gases, liquids, solids, and plasma. It is stated that V. can also exist in a special, superdense (e.g. in neutron) condition.

Vavilov S. I., Development of the idea of ​​matter, Sobr. op., t. 3, M., 1956, With.-41-62; Structure and forms of matter. [Sat. Art.], M., 1967.

I. S. Alekseev.

Philosophical encyclopedic dictionary. - M.: Soviet Encyclopedia. Ch. editors: L. F. Ilyichev, P. N. Fedoseev, S. M. Kovalev, V. G. Panov. 1983 .

SUBSTANCE

close in meaning to the concept matter, but not completely equivalent. While the word "" is mainly associated with ideas about rough, inert, dead reality, in which exclusively mechanical laws dominate, the substance is a "material", which, due to the receipt of a form, evokes form, life suitability, ennoblement. Cm. Gestalt weaving.

Philosophical Encyclopedic Dictionary. 2010 .

SUBSTANCE

one of the basic forms of matter. V. include macroscopic. bodies in all states of aggregation (gases, liquids, crystals, etc.) and the particles that form them and have their own mass ("rest mass"). A large number of types of particles are known in V.: "elementary" particles (electrons, protons, neutrons, mesons, positrons, etc.), atomic nuclei, atoms, molecules, ions, free radicals, colloidal particles, macromolecules, etc. (see Elementary particles of matter).

Lit.: Engels F., Dialectics of Nature, Moscow, 1955; his own, Anti-Dühring, M., 1957; V. I. Lenin, Materialism and empirio-criticism, Soch., 4th ed., vol. 14; Vavilov S. I., Development of the idea of ​​matter, Sobr. soch., vol. 3, M., 1956; his, Lenin and modern, ibid; his own, Lenin and the philosophical problems of modern physics, ibid.; Goldansky V., Leikin E., Transformations of atomic nuclei, M., 1958; Kondratyev VN, Structure and chemical properties of molecules, M., 1953; "Advances in Physical Sciences", 1952, vol. 48, no. 2 (dedicated to the problem of mass and energy); Ovchinnikov N. F., Concepts of mass and energy ..., M., 1957; Kedrov B. M., Evolution of the concept of an element in chemistry, M., 1956; Novozhilov Yu. V., Elementary particles, Moscow, 1959.

Philosophical Encyclopedia. In 5 volumes - M .: Soviet Encyclopedia. Edited by F. V. Konstantinov. 1960-1970 .

Synonyms:

What is a substance - one of those questions, the answer to which seems to be clear, but on the other hand - try to answer! At first glance, everything is simple: the substance is what the bodies are made of ... somehow it turned out indefinitely. Let's try to figure it out.

For simplicity, let's start with a concept that is even more complex and abstract - matter. Today it is believed that matter is an objective reality that exists in space and changes in time.

This reality exists in two forms. One of these forms has a wave nature: weightlessness, continuity, permeability, the ability to propagate at the speed of light. The nature of another form is corpuscular: it has a rest mass, consists of localized particles (atomic nuclei and electrons), is poorly permeable (and in some cases impenetrable at all), and is far from the speed of light. The first form of the existence of matter is called a field, the second a substance.

Here it is necessary to make a reservation: such a clear division was carried out in the 19th century, later - with the discovery of corpuscular-wave dualism - it had to be called into question. It turned out that the field and matter have much more in common than one might have expected, because even an electron exhibits the properties of both particles and waves! However, this manifests itself in the microcosm, at the level of elementary particles, in the macrocosm - at the level of bodies - this is not obvious, so the division into matter and field is quite suitable.

But back to our substance. As we all remember from school, it can exist in three states. One of them is solid: the molecules are practically motionless, strongly attracted to each other, so the body retains its shape. The other is liquid: molecules can move from place to place, the body takes the form of the vessel in which it is located, without having its own form. And finally - gaseous: the chaotic movement of molecules, a weak connection between them, as a result - the absence of not only a form, but also a volume: the gas will fill a container of any volume, being distributed over it. Any substance can be in such states, the only question is what conditions are needed for this - for example, metallic hydrogen, which is available on Jupiter, cannot yet be obtained on Earth even in the laboratory.

But there is also a fourth state of matter - plasma. This is an ionized gas - i.e. a gas in which, along with neutral atoms, there are positively and negatively charged particles - ions (atoms that have lost part of the electrons) and electrons, while the number of positively and negatively charged particles balances each other - this is called quasi-neutrality. Such a state of matter is possible at a very high temperature - the count goes to thousands of kelvins. This begs the question: if plasma is an ionized gas, why should it be considered the fourth state of matter, why cannot it be considered as a kind of gas?

It turns out you can't! In some properties, a plasma is opposite to a gas. Gases have extremely low electrical conductivity, while plasmas have high electrical conductivity. Gases are made up of particles that are similar to each other, which rarely collide, and plasmas are made up of particles that differ in electric charge, constantly interacting with each other.

If it’s hard for you to imagine what plasma is, don’t be discouraged: you see it every day, and if you’re lucky, then every night, because stars, including our Sun, are made of it! A person has also learned to use it: it is neon or argon plasma that “works” in luminous signs!

Thus, one can speak with confidence not about three, but about four states of matter ... wasn’t this what the philosophers of antiquity guessed about when speaking about the four elements of being: “earth” (solid), “water” (liquid), “air” (gaseous ), "fire" (plasma)? And we, unreasonable descendants, are still looking for some kind of mysticism in this!

Relative molecular mass - mass (amu) 6.02 × 10 23 molecules of a complex substance. Numerically equal to the molar mass, but differs in dimension.

1. Atoms in molecules are connected to each other in a certain sequence. Changing this sequence leads to the formation of a new substance with new properties.
2. The connection of atoms occurs in accordance with their valency.
3. The properties of substances depend not only on their composition, but also on the "chemical structure", that is, on the order of connection of atoms in molecules and the nature of their mutual influence. Atoms that are directly bonded to each other have the strongest influence on each other.

Thermal effect of the reaction- is the heat that is released or absorbed by the system during the course of a chemical reaction in it. Depending on whether the reaction occurs with the release of heat or is accompanied by the absorption of heat, exothermic and endothermic reactions are distinguished. The first, as a rule, includes all reactions of the connection, and the second - decomposition reactions.

The rate of a chemical reaction- change in the amount of one of the reacting substances per unit of time in a unit of reaction space.

Internal energy of the system- the total energy of the internal system, including the energy of interaction and movement of molecules, atoms, nuclei, electrons in atoms, intranuclear and other types of energy, except for the kinetic and potential energy of the system as a whole.

Standard enthalpy (heat) of formation of a complex substance- thermal effect of the reaction of formation of 1 mol of this substance from simple substances that are in a stable state of aggregation under standard conditions (= 298 K and a pressure of 101 kPa).