The introduction of a quantitative research method and the establishment of the law of conservation of mass were of great importance for the further development of chemistry. But chemistry received a solid scientific foundation only after the establishment of atomic-molecular teaching.

The emergence of atomic-molecular science

The fundamentals of atomic-molecular science were first outlined M. V. Lomonosov in 1741 year in one of his first works - “Elements of Mathematical Chemistry”, in which he formulated the most important provisions of the corpuscular theory of structure.

According to Lomonosov’s ideas, everything consists of tiny “insensitive” particles, physically indivisible and capable of mutual cohesion. The properties of substances and, above all, their state of aggregation are determined by the properties of these particles; the difference in the properties of substances depends only on the difference in the particles themselves or the way they are interconnected.

He 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. According to his definition, “An element is a part of a body that does not consist of any other smaller or different bodies. A corpuscle is a collection of elements forming one small mass.”

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 the reason for the difference in substances was considered not only the difference in the composition of the corpuscles, but also the different arrangement of elements in the corpuscle.

Explaining his views on “insensitive” particles, he especially emphasized that each corpuscle has certain finite, albeit very small dimensions, as a result of which it cannot be seen, and has a certain mass. Like all physical bodies, corpuscles can move according to the laws of mechanics; Without motion, corpuscles cannot collide with each other, repel each other, or otherwise act on each other and change. The movement of corpuscles, in particular, explains phenomena such as heating and cooling of bodies.

Since all changes in substances are caused by the movement of corpuscles, chemical transformations must be studied not only by the methods of chemistry, but also by the methods of physics and mathematics.

Lomonosov's assumptions at that time could not be verified experimentally due to the lack of accurate data on the quantitative composition of various complex substances. Therefore, the main provisions of the corpuscular theory could be confirmed only after chemistry had gone through a long path of development, accumulated a large amount of experimental material and mastered new research methods.

Lecture topic: BASIC CONCEPTS AND LAWS OF CHEMISTRY.

Plan:

BASIC CONCEPTS OF CHEMISTRY. ATOMIC-MOLECULAR TEACHING

BASIC LAWS OF CHEMISTRY

BASIC GAS LAWS

CHEMICAL EQUIVALENT. LAW OF EQUIVALENT RELATIONS

CHEMICAL REACTIONS. CLASSIFICATION OF CHEMICAL REACTIONS

THE PLACE OF CHEMISTRY AMONG OTHER SCIENCES

Chemistry refers to the natural sciences that study the material world around us, its phenomena and laws.

The basic law of nature is the law of the eternity of matter and its motion. Separate forms of motion of matter are studied by separate sciences. The place of chemistry, which deals primarily with the molecular (and atomic) level of organization of matter, is between particle physics (subatomic level) and biology (supramolecular level).

Chemistry- the science of substances, their composition, structure, properties and transformations associated with changes in the composition, structure and properties of the particles that form them.

The great Russian scientist M.V. Lomonosov said: “Chemistry extends its hands widely into human affairs.” Indeed, there is practically no technical discipline that could do without knowledge of chemistry. Even such modern and seemingly distant sciences as electronics and computer science have today received a new impetus in their development by concluding an “alliance” with chemistry (recording information at the molecular level, developing biocomputers, etc.). What then can we say about the fundamental disciplines: physics, biology, etc., where independent sections bordering on chemistry have long existed (chemical physics, biochemistry, geochemistry, etc.).

BASIC CONCEPTS OF CHEMISTRY.

ATOMIC-MOLECULAR TEACHING

The idea of ​​atoms as structural elements of the material world originated in ancient Greece (Leucippus, Democritus, 1st-3rd centuries BC). But only at the end of the 18th - beginning of the 19th centuries. Atomic-molecular science was created. The most important contribution to the generalization of the accumulated material was made by M. V. Lomonosov.

Atomic-molecular teaching includes the following basic principles:

1. All substances are not solid, but consist of particles (molecules, atoms, ions).

2. Molecules are made up of atoms (elements).

3. Differences between substances are determined by the differences in the particles that form them, which differ from each other in composition, structure and properties.

4. All particles are in constant motion, the speed of which increases when heated.

Atom- the smallest particle of a chemical element that is the carrier of its properties. This is an electrically neutral microsystem, the behavior of which obeys the laws of quantum mechanics.

Chemical element- a type of atoms that have the same positive nuclear charge and are characterized by a certain set of properties.

Isotopes- atoms of the same element that differ in mass (the number of neutrons in the nucleus).

Any chemical element in nature is represented by a certain isotopic composition, therefore its mass is calculated as a certain average value from the masses of isotopes, taking into account their content in nature.

Molecule- the smallest particle of a substance that is the bearer of its properties and is capable of independent existence.

Simple substance- a substance whose molecules consist only of atoms of one element.

Allotropy- the ability of an element to form simple substances having different composition, structure and properties.

Varieties of allotropic modifications are defined:

A different number of atoms of an element in the molecule of a simple substance, for example, oxygen (O 2) and ozone (O 3).

Differences in the structure of the crystal lattice of a simple substance, for example, a carbon compound: graphite (flat, or two-dimensional, lattice) and diamond (volumetric, or three-dimensional lattice).

Complex substance- a substance whose molecules consist of atoms of different elements.

Complex substances consisting of only two elements are called binary, for example:

Ø oxides: CO, CO 2, CaO, Na 2 O, FeO, Fe 2 O 3;

Ø sulfides: ZnS, Na 2 S, CS 2;

Ø hydrides: CaH 2, LiH, NaH;

Ø nitrides: Li 3 N, Ca 3 N 2, AlN;

Ø phosphides: Li 3 P, Mg 3 P 2, AlP;

Ø carbides: Be 2 C, Al 4 C 3, Ag 2 C 2;

Ø silicides: Ca 2 Si, Na 4 Si.

Complex compounds consisting of more than two elements belong to the main classes of inorganic compounds. These are hydroxides (acids and bases) and salts, including complex compounds.

Atoms and molecules have absolute mass, for example, the mass of a C 12 atom is 2·10 -26 kg.

It is inconvenient to use such quantities in practice, which is why the relative mass scale is adopted in chemistry.

Atomic mass unit(a.u.m.) is equal to 1/12 of the mass of the C 12 isotope.

Relative atomic mass (A r- dimensionless quantity) is equal to the ratio of the average mass of an atom to a. eat.

Relative molecular weight (M r- dimensionless quantity) is equal to the ratio of the average mass of a molecule to a. eat.

Mole(ν - “nude” or n) - the amount of a substance containing the same number of structural units (atoms, molecules or ions) as there are atoms in 12 g of the C 12 isotope.

Avogadro's number- the number of particles (atoms, molecules, ions, etc.) contained in 1 mole of any substance.

N A = 6.02·10 23 .

More precise values ​​of some fundamental constants are given in the tables in the appendix.

Molar mass of the substance (M) is the mass of 1 mole of a substance. It is calculated as the ratio of the mass of a substance to its quantity:

The molar mass is numerically equal A r(for atoms) or M r(for molecules).

From equation 1, you can determine the amount of a substance if its mass and molar mass are known:

(2)

Molar volume (V m for gases) is the volume of one mole of a substance. It is calculated as the ratio of the volume of gas to its quantity:

(3)

Volume of 1 mole of any gas under normal conditions (P = 1 atm = 760 mm. rt. Art. = 101.3 kPa; T = 273TS = 0°C) is equal to 22.4 l.

(4)

The density of a substance is equal to the ratio of its mass to volume.

(5)

1.Chemistry as a subject of natural science Chemistry studies that form of movement of matter in which the interaction of atoms occurs with the formation of new specific substances. Chemistry-the science of the composition, structure and properties of substances, their transformations or the phenomena that accompany these transformations. Modern chemistry includes: general, organic, colloidal, analytical, physical, geological, biochemistry, chemistry of building materials. Chemistry subject- chemical elements and their compounds, as well as the laws that govern various chemical reactions.

connects physical-mathematical and biological-social sciences. 2.Class of inorganic compounds. Basic chemical properties of acids, bases, salts. According to the properties of inorganic compounds are divided into traces. Classes: oxides, bases, acids, salts. Oxides:- a combination of elements with oxygen, in which the latter is a more electronegative element, namely, it exhibits an oxidation state of -2. and only the element O2 is connected. The general formula is CxOy. There are acidic e-capable of salt formation with basic oxides and bases (SO3+Na2O=Na2SO4; So3+2NaOH=Na2SO4=H2O), main- capable of forming salts with acidic oxides and acids (CaO+CO2=CaCO3; CaO+2HCl=CaCl2+H2O), amphoteric (to you and basics) and with this and with that (ZnO, BeO, Cr2O3, SnO, PbO, MnO2). and non-salt-forming (CO,NO,N2O): Grounds -substances, during the electrolytic dissociation of which the anion may only hydroxyl group OH. The acidity of a base is the number of OH ions formed during the dissociation of hydroxide.Hydroxides, substances containing the OH group, are obtained by combining oxides with water. There are3 typesbasic(bases) acidic (oxygen-containing acids) and amphoteric (ampholytes - exhibit basic and acidic properties Cr(OH)3,Zn(OH)2,Be(OH)2,Al(OH)3) Acids-substances during electrolytic dissociation cat. Cation m.b. only + charged ion H. There are: oxygen-free, oxygen-containing The H number is the basicity of the acid. meta and ortho forms of water molecules. Salts-substances, during the electrolytic dissociation of which the cation can be an ammonium ion (NH4) or a metal ion, and the anion can be any acidic residue There are: medium(complete substitution. consist of an acid residue and a metal ion), sour e (incomplete substitution. presence of unsubstituted H in the composition), basic (incomplete substitution. presence of unsubstituted OH) Based on composition, inorganic substances are divided into

3. Basic provisions of atomic-molecular teaching

1. All substances consist of molecules (corpuscles); during physical phenomena, the molecules are preserved, but during chemical phenomena they are destroyed.

2. Molecules consist of atoms (elements); during chemical reactions, atoms are preserved.

3. Atoms of each type (element) are identical to each other, but differ from atoms of any other type.

4. When atoms interact, molecules are formed: homonuclear (when atoms of one element interact) or heteronuclear (when atoms of different elements interact).

5. Chemical reactions involve the formation of new substances from the same atoms that make up the original substances. + 6. molecules.

. Atom and the atoms are in continuous motion, and heat consists in the internal movement of these particles - the smallest particle of an element that retains its chemical properties.

Atoms differ in nuclear charges, mass and size Chemical element - type of atoms with the same position. Core charge. Physical properties characteristic of a simple substance cannot be attributed to a chemical element. Simple substances - these are substances consisting of atoms of the same chemical element. 4.Basic laws of chemistry (law of conservation, constancy of composition, multiple ratios, Avagadro’s law) Conservation Law: The mass of substances that react is equal to the mass of substances formed as a result of the reaction. : Law of Constancy of Composition

(any chemical compound has the same quantitative composition, regardless of the method of its preparation) The ratios between the masses of the elements included in the composition of a given compound are constant and do not depend on the method of obtaining this compound. : Law of Multiples

If two elements form several chemical compounds with each other, then the masses of one of the elements in these compounds per the same mass of the other are related to each other as small integers. Avogadro's law.

Equal volumes of any gases taken at the same temperature and the same pressure contain the same number of molecules. . 5. Law of Equivalents Substance equivalent The ratio of equivalent masses, volumes, reacting or forming substances is directly proportional to the ratio of their masses (volumes) or E (simple) = A (atomic mass) / B (valency of the element) E (acids) = M (molar mass) / basic (acid base ) E(Hydroxide)=M/Acid)Acidity of hydroxide) E(salt oxides) = M/a (number of atoms of an element in the sample. Oxide (salts) * in (valence of this element or metal)

6. Structure of atoms. Core. Nuclear reactions. Types of radiation. Rutherford model: 1.almost all the mass is concentrated in the nucleus 2.+ are compensated – 3.charge is equal to the group number. The simplest is H hydrogen The modern concept of chemistry. An element is a type of atom with the same position. According to the nuclear charge, an atom consists of a positively charged nucleus and an electron shell. The electron shell is formed by electrons. The number of electrons is equal to the number of protons, therefore the charge of the atom as a whole is 0. The number of protons, the charge of the nucleus and the number of electrons are numerically equal to the atomic number of the chemical element. Almost all the mass of an atom is concentrated in the nucleus. Electrons move around the nucleus of an atom, not randomly, but depending on the energy they have, forming the so-called electron layer. Each electronic layer can contain a certain number of electrons: on the first - no more than 2, on the second - no more than 8, on the third - no more than 18. The number of electronic layers is determined by the period number. The number of electrons on the last (outer) layer is determined by the group number. during the period there is a gradual weakening of metallic properties and an increase in the properties of non-metals A nuclear reaction is the process of formation of new nuclei or particles during collisions of nuclei or particles. Atoms with the same nuclear charge, but different mass numbers, are called isotopes (for example, 35/17 Cl and 37/17Cl) Atoms with the same mass numbers, but a different number of protons in the nucleus, are called isobars (for example, 40/19K and 40/20Ca) Half-life (T ½) is the time during which half of the original amount of a radioactive isotope decays.

1. All substances are made up of molecules. Molecule - the smallest particle of a substance that has its chemical properties.

2. Molecules are made up of atoms. Atom - the smallest particle of a chemical element that retains all its chemical properties. Different elements correspond to different atoms.

3. Molecules and atoms are in continuous motion; there are forces of attraction and repulsion between them.

Chemical element - this is a type of atoms characterized by certain nuclear charges and the structure of electronic shells. Currently, 117 elements are known: 89 of them are found in nature (on Earth), the rest are obtained artificially. Atoms exist in a free state, in compounds with atoms of the same or other elements, forming molecules. The ability of atoms to interact with other atoms and form chemical compounds is determined by its structure. Atoms consist of a positively charged nucleus and negatively charged electrons moving around it, forming an electrically neutral system that obeys the laws characteristic of microsystems.

Atomic nucleus - the central part of the atom, consisting of Z protons and N neutrons, in which the bulk of the atoms is concentrated.

Core charge - positive, equal in value to the number of protons in the nucleus or electrons in a neutral atom and coincides with the atomic number of the element in the periodic table. The sum of protons and neutrons of an atomic nucleus is called the mass number A = Z + N.

Isotopes - chemical elements with identical nuclear charges, but different mass numbers due to different numbers of neutrons in the nucleus.

Allotropy - the phenomenon of the formation by a chemical element of several simple substances that differ in structure and properties.

Chemical formulas

Any substance can be characterized by its qualitative and quantitative composition. The qualitative composition is understood as a set of chemical elements that form a substance, and the quantitative, in general case, is the relationship between the number of atoms of these elements. The atoms that form a molecule are connected to each other in a certain sequence, this sequence is called the chemical structure of the substance (molecule).

The composition and structure of a molecule can be depicted using chemical formulas. The qualitative composition is written in the form of symbols of chemical elements, the quantitative composition is written in the form of subscripts for the symbol of each element. For example: C 6 H 12 O 6.

Chemical formula - this is a conventional notation of the composition of a substance using chemical symbols (proposed in 1814 by J. Berzelius) and indices (index is the number at the bottom right of the symbol. Indicates the number of atoms in the molecule). The chemical formula shows which atoms of which elements and in what ratio are connected to each other in a molecule.

Chemical formulas are of the following types:

a) molecular - show how many atoms of elements are included in the molecule of a substance, for example H 2 O - one water molecule contains two hydrogen atoms and one oxygen atom.

b) graphical - show in what order the atoms in the molecule are connected, each bond is represented by a dash; for the previous example, the graphical formula will look like this: H-O-H

c) structural - show the relative positions in space and the distances between the atoms that make up the molecule.

It must be borne in mind that only structural formulas allow a substance to be uniquely identified; molecular or graphic formulas can correspond to several or even many substances (especially in organic chemistry).

International Atomic Mass Unit equal to 1/12 of the mass of the 12C isotope - the main isotope of natural carbon.

1 amu = 1/12 m (12C) = 1.66057 10 -24 g

Relative atomic mass (Ar)- a dimensionless quantity equal to the ratio of the average mass of an atom of an element (taking into account the percentage of isotopes in nature) to 1/12 of the mass of a 12C atom.

Average absolute atomic mass (m) equal to the relative atomic mass times the amu.

m (Mg) = 24.312 1.66057 10 -24 = 4.037 10 -23 g

Relative molecular weight (Mr)- a dimensionless quantity showing how many times the mass of a molecule of a given substance is greater than 1/12 the mass of a 12C carbon atom.

Mr = mg / (1/12 mа(12C))

m r is the mass of a molecule of a given substance;

m a (12C) is the mass of the 12C carbon atom.

Mr = S Ar(e). The relative molecular mass of a substance is equal to the sum of the relative atomic masses of all elements, taking into account the indices.

Mr(B 2 O 3) = 2 Ar(B) + 3 Ar(O) = 2 11 + 3 16 = 70

Mr (KAl(SO 4) 2) = 1 Ar(K) + 1 Ar(Al) + 1 2 Ar(S) + 2 4 Ar(O) == 1 39 + 1 27 + 1 2 32 + 2 4 16 = 258

Absolute molecular mass equal to the relative molecular mass times the amu. The number of atoms and molecules in ordinary samples of substances is very large, therefore, when characterizing the amount of a substance, a special unit of measurement is used - the mole.

Amount of substance, mol . Means a certain number of structural elements (molecules, atoms, ions). Denoted n and measured in moles. A mole is the amount of a substance containing as many particles as there are atoms in 12 g of carbon.

Avogadro's number (N A ). The number of particles in 1 mole of any substance is the same and equals 6.02 · 10 23. (Avogadro's constant has the dimension - mol -1).

How many molecules are there in 6.4 g of sulfur?

The molecular weight of sulfur is 32 g/mol. We determine the amount of g/mol of substance in 6.4 g of sulfur:

n(s) = m(s) / M(s) = 6.4 g / 32 g/mol = 0.2 mol

Let's determine the number of structural units (molecules) using Avogadro's constant NA

N(s) = n(s) NA = 0.2 6.02 1023 = 1.2 1023

Molar mass shows the mass of 1 mole of a substance (denoted M).

The molar mass of a substance is equal to the ratio of the mass of the substance to the corresponding amount of the substance.

The molar mass of a substance is numerically equal to its relative molecular mass, however, the first quantity has the dimension g/mol, and the second is dimensionless.

M = N A m(1 molecule) = N A Mg 1 amu = (N A · 1 amu) Mr = Mr

This means that if the mass of a certain molecule is, for example, 80 amu. (SO 3), then the mass of one mole of molecules is equal to 80 g. Avogadro’s constant is a proportionality coefficient that ensures the transition from molecular relationships to molar ones. All statements regarding molecules remain valid for moles (with replacement, if necessary, of amu by g). For example, the reaction equation: 2Na + Cl 2 2NaCl, means that two sodium atoms react with one chlorine molecule or that the same thing, two moles of sodium react with one mole of chlorine.

Law of conservation of mass of substances

The mass of all substances that entered into a chemical reaction is equal to the mass of all products

*Atomic-molecular teaching explains this law as follows: as a result of chemical reactions, atoms do not disappear or appear, but their rearrangement occurs (i.e., a chemical transformation is the process of breaking some bonds between atoms and forming

others, as a result of which molecules of the reaction products are obtained from the molecules of the starting substances). Since the number of atoms before and after the reaction remains unchanged, their total mass should also not change. Mass was understood as a quantity characterizing the quantity

Based on the law of conservation of mass, it is possible to draw up equations for chemical reactions and perform calculations using them. It is the basis of quantitative chemical analysis.

Law of Constancy of Composition

All individual chemicals are of constant quality and

quantitative composition and specific chemical structure, regardless of the method of preparation.

From the law of constancy of composition it follows that when a complex substance is formed, the elements

combine with each other in certain mass ratios.

Law of Avogadro di Quaregna (1811)

Equal volumes of different gases under the same conditions (temperature, pressure, etc.) contain the same number of molecules. (The law is valid only for gaseous substances.)

Consequences.

1. The same number of molecules of different gases under the same conditions occupies

the same volumes.

2. Under normal conditions (0°C = 273°K, 1 atm = 101.3 kPa) 1 mole of any gas occupies

volume 22.4 l.__

Law of mass action

aA + bB + . . . = . . .

V = k [A]a [B]b . . .

Law of energy conservation: the energy of an isolated system (not exchanging either matter or energy with the environment) remains constant, only its transitions from one type to another are possible.

Law of conservation of electric charge: The algebraic sum of electric charges in an isolated system is conserved.

2. Basic Law of Chemistry as a special case of the general law of the material world. Concepts: matter, substance, field, movement - and their quantitative characteristics and interrelation. Mathematical expressions of the laws of conservation of mass and energy.

Law of mass action

The rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants.

aA + bB + . . . = . . .

V = k [A]a [B]b . . .

Matter exists in the form of matter and field. Chemistry studies the world around us under the unified concept of matter existing outside and independently of human consciousness.

a substance is any collection of atoms and molecules

Law of conservation of mass: The mass of substances that reacted is equal to the mass of substances formed as a result of the reaction.

* Another formulation is completely equivalent to this: in a chemical reaction, the number of atoms of a chemical element is conserved. The latter formulation is the basis for writing stoichiometric reaction equations.

Law of energy conservation: the energy of an isolated system (not exchanging either matter or energy with the environment) remains constant; only its transitions from one type to another are possible.

3. Atomic-molecular science: modern provisions, brief history (founders).

ATOMIC-MOLECULAR THEORY

Atomic-molecular science is the doctrine of the structure of substances from atoms and molecules, created by the works of Lomonosov and Dalton.

*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-molecular science.

The composition and properties of a chemical compound do not depend on the method and conditions of its preparation.

All molecules are made up of atoms. A collection or set of atoms of the same type is called a chemical element.

Atomic-molecular theory basic principles:

All substances are made up of atoms

Atoms of one chemical substance (chemical element) have the same properties, but differ from atoms of another substance

When atoms interact, molecules are formed (homonuclear - simple substances, heteronuclear - complex substances)

During physical phenomena, molecules do not change; during chemical phenomena, their composition changes.

Chemical reactions involve the formation of new substances from the same atoms that made up the original substances

4. Basic concepts of chemistry : atom, molecule, chemical element, substance (simple and complex). Quantitative characteristics of an atom and molecule: dimensions, absolute and relative atomic and molecular masses, atomic mass unit (a.u.m.).

An atom is an electrically neutral particle consisting of a positively charged nucleus and one or more electrons.

A molecule is the smallest particle of a substance that has all the chemical properties of that substance. For some substances, the concepts of atom and molecule are the same.

A simple substance is a substance whose molecules consist of atoms of one element.

Compounds or complex substances are substances whose molecules consist of atoms of different elements.

Molecules of different substances differ from each other in mass, size and chemical properties. All molecules of one substance are the same.

Molecules are made up of smaller particles called atoms. Molecules of simple substances consist of identical atoms, molecules of complex substances consist of different atoms.

Atoms of one element differ from atoms of other elements in the charge of the atomic nucleus, size and chemical properties. Chemical reactions change the composition of the molecule. Atoms are not destroyed during chemical reactions.

International Atomic Mass Unit equal to 1/12 of the mass of the 12C isotope - the main isotope of natural carbon.

Relative molecular weight (Mr)- a dimensionless quantity showing how many times the mass of a molecule of a given substance is greater than 1/12 the mass of a 12C carbon atom.

Absolute molecular mass equal to the relative molecular mass times the amu.

5. Calculation of quantity, molar mass and molar volume of a substance. Avogadro's number.

The molar mass of a substance M is equal to the ratio of the mass of the substance to its quantity

and has the dimension g/mol accepted in chemistry. The molar mass of a substance, expressed in g/mol, is numerically equal to its relative molecular mass. Numerical equality means the coincidence of the numerical values ​​of quantities, but not their dimensions.

Molar volume is defined similarly as the ratio of the volume of a substance to its quantity:

Molar volume can have dimensions m3/mol, l/mol, cm3/mol. Molar volume is defined for any state of aggregation of a substance and is related to its molar mass through density:

Avogardo's law: equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules.

NA = 6.022 141 29(27) 10 23 mol−1

6. Chemical element, symbols of elements. Chemical formula of a substance, type of formula: empirical, molecular, graphic. Concepts: valency (stoichiometric, bond, coordination) and oxidation state of a chemical element. Examples.

A chemical element is a type of atom characterized by a certain nuclear charge.

Molecular (gross) formula showing the number of atoms in a molecule - C6H14,

Graphic

The empirical formula gives only the ratio of elements C:H = 3:7 - C3H7

Valence is the property of atoms of a given element to attach or replace a certain number of atoms of other elements in a molecule. The unit of valency is the valency of hydrogen.

The oxidation state of an atom is the magnitude of the electrostatic charge of an atom in a simple substance, in a molecule of a chemical compound, in an ion

7. Concepts and quantitative determination of the mass, mole and volume fraction of an element in a molecule of a substance and a substance in a mixture. Algorithm for establishing empirical and molecular formulas.

Mass fraction is the ratio of the mass of the solute to the mass of the solution. Mass fraction is measured in fractions of a unit or as a percentage:

m is the total mass of the solution, g.

Volume fraction is the ratio of the volume of a solute to the volume of a solution. The volume fraction is measured in fractions of a unit or as a percentage.

V1 - volume of dissolved substance, l;

V - total volume of solution, l.

Mole fraction is the ratio of the number of moles of a given component to the total number of moles of all components. The mole fraction is expressed in fractions of a unit.

νi is the amount of the i-th component, mol;

n - number of components;

The titer of a solution is the mass of the dissolved substance in 1 ml of solution.

m1 - mass of dissolved substance, g;

V - total volume of solution, ml;

The empirical formula of a chemical compound is a recording of the simplest expression of the relative number of each type of atom in it; is a linear notation of symbols of chemical elements, accompanied by subscripts indicating the ratio of elements in the compound

Molar mass equivalents are usually denoted as or. The ratio of the equivalent molar mass of a substance to its actual molar mass is called the equivalence factor (usually denoted as).

Molar mass of equivalents of a substance is the mass of one mole of equivalents, equal to the product of the equivalence factor by the molar mass of this substance.

Meq = feq×M

Equivalence factor [edit]

The ratio of the equivalent molar mass to its own molar mass is called the equivalence factor (usually denoted as).

Equivalence number [edit]

The equivalence number z is a small positive integer equal to the number of equivalents of a substance contained in 1 mole of that substance. The equivalence factor is related to the equivalence number z by the following relationship: =1/z.

For example, in react:

Zn(OH)2 + 2HCl = ZnCl2 + 2H2O

The equivalent is the ½Zn(OH)2 particle. The number ½ is the equivalence factor, z in this case is equal to 2

9. Chemical reaction: definition, signs, difference from physical phenomena, classification.

A chemical reaction is the transformation of one or more initial substances (reagents) into substances (reaction products) that differ from them in chemical composition or structure. Unlike nuclear reactions, during chemical reactions the nuclei of atoms do not change, in particular, their total number and the isotopic composition of chemical elements do not change, while a redistribution of electrons and nuclei occurs and new chemical substances are formed.

Classification

By changing the oxidation states of reactants[edit]

In this case, there is a distinction

Redox reactions in which the atoms of one element (oxidizing agent) are reduced, that is, they lower their oxidation state, and the atoms of another element (the reducing agent) are oxidized, that is, they increase their oxidation state. A special case of redox reactions are disproportionation reactions, in which the oxidizing and reducing agents are atoms of the same element in different oxidation states.

An example of a redox reaction is the combustion of hydrogen (reducing agent) in oxygen (oxidizing agent) to form water:

An example of a disproportionation reaction is the decomposition reaction of ammonium nitrate when heated. In this case, the oxidizing agent is nitrogen (+5) of the nitro group, and the reducing agent is nitrogen (-3) of the ammonium cation:

NH4NO3 = N2O + 2H2O (up to 250 °C)

Non-redox reactions - respectively, reactions in which there is no change in the oxidation states of atoms, for example, the above neutralization reaction.

According to the thermal effect of the reaction[edit]

All reactions are accompanied by thermal effects. When chemical bonds in reagents are broken, energy is released, which is mainly used to form new chemical bonds. In some reactions the energies of these processes are close, and in this case the overall thermal effect of the reaction approaches zero. In other cases we can distinguish:

exothermic reactions that release heat (positive thermal effect), for example, the above-mentioned combustion of hydrogen

endothermic reactions during which heat is absorbed (negative thermal effect) from the environment.

The heat of a reaction (enthalpy of reaction, ΔrH), which is often very important, can be calculated using Hess's law if the enthalpies of formation of the reactants and products are known. When the sum of the enthalpies of the products is less than the sum of the enthalpies of the reactants (ΔrH< 0) наблюдается выделение тепла, в противном случае (ΔrH >0) - absorption.

By type of transformation of reacting particles[edit]

connections:

decompositions:

substitutions:

exchange (type of reaction-neutralization):

exchange (type of reaction-exchange):

Chemical reactions are always accompanied by physical effects: the absorption and release of energy, for example in the form of heat transfer, a change in the state of aggregation of the reagents, a change in the color of the reaction mixture, etc. It is by these physical effects that the progress of chemical reactions is often judged.

Chemical processes occurring in matter differ from both physical processes and nuclear transformations. In physical processes, each of the substances involved retains its composition unchanged (although substances can form mixtures), but can change their external form or state of aggregation.

In chemical processes (chemical reactions), new substances are obtained with properties different from the reagents, but atoms of new elements are never formed. In the atoms of the elements participating in the reaction, modifications of the electron shell necessarily occur.

10.Scheme and equation of a chemical reaction (algorithm for writing the equation). Physical meaning of stoichiometric coefficients. Types of equation: complete, incomplete, molecular, ionic, thermochemical. Give examples.

In chemical reactions, some substances are transformed into others. Let us recall the well-known reaction of sulfur with oxygen. And in it, from some substances (starting substances or reagents) others are formed (final substances or reaction products).

Reaction diagrams and equations are used to record and transmit information about chemical reactions.

Chemical reaction diagram– a conditional notation that provides qualitative information about a chemical reaction.

A reaction diagram shows which substances react and which are formed as a result of the reaction. In both diagrams and reaction equations, substances are designated by their formulas.

The sulfur combustion scheme is written as follows: S8 + O2 SO2.

This means that when sulfur reacts with oxygen, a chemical reaction occurs, resulting in the formation of sulfur dioxide (sulfur dioxide). All substances here are molecular, therefore, when writing the diagram, the molecular formulas of these substances were used. The same applies to the scheme of another reaction - the combustion reaction of white phosphorus:

When calcium carbonate (chalk, limestone) is heated to 900 oC, a chemical reaction occurs: calcium carbonate is converted into calcium oxide (quicklime) and carbon dioxide (carbon dioxide) according to the following scheme:

CaCO3 CaO + CO2.

To indicate that the process occurs when heated, the diagram (and equation) is usually supplemented with the sign “t”, and the fact that carbon dioxide evaporates is indicated by an arrow pointing up:

CaCO3 CaO + CO2.

Calcium carbonate and calcium oxide are non-molecular substances, so the diagram uses their simplest formulas, reflecting the composition of their formula units. For a molecular substance - carbon dioxide - a molecular formula is used.

Let's consider the reaction scheme that occurs when phosphorus pentachloride interacts with water: PCl5 + H2O H3PO4 + HCl.

The diagram shows that phosphoric acid and hydrogen chloride are formed.

Sometimes a brief diagram of the reaction is sufficient to convey information about a chemical reaction, for example:

S8 SO2; P4 P4O10; CaCO3 CaO.

Naturally, several different reactions can correspond to a short scheme.

The equation of a chemical reaction is a conditional notation that provides qualitative and quantitative information about a chemical reaction.

For any chemical reaction, one of the most important laws of chemistry is true:

When chemical reactions occur, atoms do not appear, disappear, or transform into each other.

When writing equations of chemical reactions, in addition to formulas of substances, coefficients are used. As in algebra, the coefficient “1” in the equation of a chemical reaction is not put, but is implied. The reactions we have considered are described by the following equations:

1S8 + 8O2 = 8SO2, or S8 + 8O2 = 8SO2;

1P4 + 5O2 = 1P4O10, or P4 + 5O2 = P4O10;

1CaCO3 = 1CaO + 1CO2, or CaCO3 = CaO + CO2;

1PCl5 + 4H2O = 1H3PO4 + 5HCl, or PCI5 + 4H2O = H3PO4 + 5HCI.