1. Definition of chemistry and its basic concepts: atom, molecule, relative atomic and molecular masses, chemical amount of a substance, chemical elements, isotopes. Simple and complex substances. The concept of structural and formulaic unit of matter. Pure substances and mixtures.

Chemistry- one of the most important and extensive areas of natural science, the science of substances, their composition and structure, their properties, their transformations leading to a change in composition - chemical reactions, as well as the laws and patterns that these transformations obey.

Atom - smallest particle chemical element, which has all of its properties. An atom consists of a nucleus and a "cloud" of electrons around it. The nucleus is made up of positively charged protons and neutral neutrons. The number of protons in the nucleus is always constant (coinciding with the number of electrons), while the number of neutrons can change (often the number of neutrons exceeds the number of protons). For this reason, there are atoms that have the same nuclear charge, but differ in mass. They got the name isotopes . Atoms (more precisely, atomic nuclei) are chemically indivisible. By interacting, atoms can form molecules.

Molecule- a particle consisting of two or more atoms, which can independently exist. It has a constant qualitative and quantitative composition. Its properties depend on the atoms that make up its composition, and on the nature of the bonds between them, on the molecular structure and on the spatial arrangement (isomers). It can have several different states and move from one state to another under the influence of external factors. The properties of a substance consisting of certain molecules depend on the state of the molecules and on the properties of the molecule.

Absolute masses of atoms and molecules are very small, but modern research methods allow them to be determined with great accuracy. So the mass of a hydrogen atom is 1.674 10 -27 kg, a carbon atom - 1.993 10 -26 kg, water molecules - 2.990 10 -26 kg. It is inconvenient to use such values ​​in calculations. Therefore, in chemistry, not absolute mass values ​​are used, but relative ones.

Relative atomic mass shows , how many times the mass of an atom of a given element is greater than the so-called atomic mass unit (a.m.u.) .

The atomic mass unit (a.m.u.) is 1/12 of the mass of the carbon-12 atom, i.e. carbon isotope 12 C.

1 amu = 1.66 10 -27 kg

In this way , the relative atomic mass (or simply atomic mass) of the element the mass of its atom is called, expressed in atomic mass units (dimensionless value), denoted by Ar, where the index r is the initial letter English word relative - relative; sometimes this index is omitted. For example, relative atomic mass of oxygen:

Ar(O) = m(O) / 1/12 m(C) = 15.999

This value of the relative atomic mass of oxygen is given in the Periodic Table of the Elements.

Since the mass of a molecule of any substance is composed of the masses of its constituent atoms, then relative molecular weight Mr of the substance is the mass of its molecule, expressed in atomic mass units. For example, the relative molecular weight of water is:

Mr(H 2 O) \u003d m (H 2 O) / 1/12 m (C) \u003d 2.990 10 -26 / 1.66 10 -27 \u003d 18.01

Mr(H 2 O) \u003d 2Ar (H) + 1Ar (O) \u003d 2 1 + 1 16 \u003d 18 (the relative molecular weight is equal to the sum of the products of the relative atomic masses of atoms by their number).

In other words, the relative atomic Ar and molecular Mr masses show how many times the masses of a given atom and a given molecule are greater than 1/12 of the mass of an atom of the carbon-12 isotope.

Along with units of mass and volume in chemistry, a unit of the amount of a substance is also used - mole. mole - this is the amount of a substance that contains as many structural units as there are in 12 g of the carbon isotope 12 C. Structural units include atoms, molecules, ions and other particles that make up the substance.

Since we already know the absolute mass of a carbon atom, we can calculate how many carbon atoms are contained in 12 g of carbon 12 C or in 1 mole of any substance.

N A \u003d 0.012 / 1.993 10 -26 \u003d 6.02 10 23

The number N A = 6.02 10 23 is called Avogadro's number. N A does not depend on the nature of the substance, nor on its state of aggregation.

The mass of one mole of a given substance is called its molar mass . The molar mass is expressed in g/mol or kg/mol. It is equal to the quotient of dividing the mass of a substance (in kg) by its amount (in moles)

M(X) = m(X) / ?(X)

It is important to remember (easy to show) that molar mass The M of a substance is numerically equal to its relative atomic or molecular weight.

It is necessary to distinguish between the molar mass M and the molecular mass Mr, expressed in a.m.u. If the molar mass is expressed in g / mol, then their numerical values ​​\u200b\u200bare equal. If the molar mass is expressed in kg / mol, then its numerical value is 1000 times less than Mr. For example, the molecular weight of sulfuric acid H 2 SO 4 is 98 amu, and its molar mass is 98 g / mol, or 98 10 -3 kg / mol.

Chemical element is a type of atom with a specific positive charge kernels. All chemical elements are listed in the Periodic system of elements of D. I. Mendeleev; each element has its own serial (atomic) number in the Periodic system. The value of the serial number of the element and the value of the charge of the nucleus of an atom of the same element are the same, that is, a chemical element is a collection of atoms with the same serial number.

In the free state, chemical elements are in the form of simple substances.

Simple Substances that are made up of atoms of one element are called. They are denoted by the chemical formula E n, where E is the symbol of the chemical element; n is the number of atoms in the molecule.

Among the simple substances are metals, constituting the majority known elements, and non-metals ( hydrogen H, boron B, carbon C, silicon Si, nitrogen N, phosphorus P, arsenic As, oxygen O, sulfur S, selenium Se, tellurium Te, fluorine F, chlorine Cl, bromine Br, iodine I, astatine At, helium He , neon Ne, argon Ar, krypton Kr, xenon Xe, radon Rn).

Complex Substances, or chemical compounds are made up of atoms of two or more elements.

Complex substances are often called chemical compounds.

For example, water is made up of oxygen and hydrogen atoms, iron sulfide is made up of iron and sulfur atoms.

Structural formula – chemical formula, composed of symbols of chemical elements and special signs reflecting the structure of a given chemical, excluding mutual arrangement atoms in space.

In the water molecule, the oxygen atom is connected by simple (single) bonds with two hydrogen atoms, and the hydrogen atoms are not connected to each other. This is clearly shown by the structural formula of water. H-------O------H

Another example: the sulfur molecule S 8 . In this molecule, 8 sulfur atoms form an eight-membered cycle in which each sulfur atom is connected to two other atoms by simple bonds.

The structural formula of phosphoric acid shows that in the molecule of this substance one of the four oxygen atoms is connected only with the phosphorus atom by a double bond, and the phosphorus atom, in turn, is connected with three more oxygen atoms by simple bonds. Each of these three oxygen atoms, in addition, is connected by a single bond with one of the three hydrogen atoms present in the molecule.

Nonmolecular substances do not contain molecules. For the convenience of carrying out chemical calculations in a nonmolecular substance, the so-called formula unit.

formula unit- a group of atoms that make up a non-molecular substance, corresponding to the simplest formula of this substance.

Examples of the composition of the formula units of some substances:

1) silicon dioxide (quartz sand, quartz) SiO 2 - formula unit consists of one silicon atom and two oxygen atoms;

2) sodium chloride (common salt) NaCl - the formula unit consists of one sodium atom and one chlorine atom;

3) iron Fe - the formula unit consists of one iron atom.

Like a molecule, a formula unit is the smallest portion of a substance that retains its chemical properties.

In nature, substances are found mainly in the form of mixtures. Homogeneous mixtures are such mixtures in which even with the help of a microscope it is impossible to detect particles of substances included in the mixture.

For example, solutions of sugar or sodium chloride in water.

Heterogeneous are such mixtures in which particles of the substances that make up the mixture can be seen with the naked eye or with a microscope.

For chemical laboratories and industry often require pure substances. Pure substances are substances that have constant physical properties e.g. distilled water. (Practically absolutely pure waters have not been obtained.)

The main methods of separation of mixtures (purification of substances):

1. heterogeneous

settling - settling clay particles in water. It is used in the purification of drinking water.

Filtration - used in the purification of drinking water.

magnet action - separation of iron from other substances.

2. homogeneous

Evaporation - the release of table salt from the water of salt lakes.

crystallization - production of sugar, etc.

distillation - obtaining distilled water.

Chromatography - separation and purification of various medicinal substances, etc.

THEME 1

Chemical element- set of atoms with the same charge nucleus, the number of protons, coinciding with the ordinal, or atomic, number in the periodic table. Each chemical element has its own name and symbol, which are given in the Periodic Table of the Elements of Dmitry Ivanovich Mendeleev.

The form of existence of chemical elements in a free form are simple substances

(single element

Atom (from other Greekἄτομος - indivisible) - the smallest chemically indivisible part chemical element, which is the carrier of its properties . An atom is made up of atomic nucleus and the surrounding electron cloud. The nucleus of an atom is made up of positive charged protons and uncharged neutrons, and the surrounding cloud consists of negatively charged electrons. If the number of protons in the nucleus coincides with the number of electrons, then the atom as a whole is electrically neutral. Otherwise, it has some positive or negative charge and called ion. Atoms are classified according to the number of protons and neutrons in the nucleus: the number of protons determines whether the atom belongs to some chemical element, and the number of neutrons - isotope this element.

atoms different kind in different quantities, connected by interatomic bonds, form molecules.

Atomic mass, relative atomic mass(old name - atomic weight) is the value of the mass of an atom, expressed in atomic mass units. Currently, the atomic mass unit is assumed to be 1/12 of the mass of the neutral atom of the most common isotope of carbon 12 C, so the atomic mass of this isotope is, by definition, exactly 12. The difference between the atomic mass of an isotope and its mass number is called the mass excess (usually expressed in MeV). It can be both positive and negative; the reason for its occurrence is the nonlinear dependence of the binding energy of nuclei on the number of protons and neutrons, as well as the difference in the masses of the proton and neutron.

Avogadro's number, Avogadro's constant - physical constant, numerically equal to the number of specified structural units ( atoms, molecules, ions, electrons or any other particles) in 1 mole substances. Defined as the number of atoms in 12 grams(exactly) pure isotope carbon-12. Usually denoted as N A, less often like L .

N A \u003d 6.022 141 79 (30) × 10 23 mol −1.

Nucleus (of an atom) in nuclear physics - part atom, which has a positive electrical charge, in which almost all of its weight.

The electron shell of an atom is a region of space of the probable location of electrons characterized by the same value of the main quantum number n and, as a result, located on close energy levels . Each electron shell can have a specific maximum number electrons. Proton (from other Greekπρῶτος - first, main) - elementary particle. Refers to baryons, It has spin 1/2,electric charge+1. In elementary particle physics, it is considered as nucleon with projection isospin+1/2 (in nuclear physics, the opposite sign of the isospin projection is accepted). Consists of three quarks(one d -quark and two u -quark). Stable (lower limit on lifetime- 2.9×10 29 years regardless of the decay channel, 1.6×10 33 years for decay in positron and neutral peony).

The proton mass, expressed in different units, is (recommended values CODATA 2006, indicated in brackets error values ​​in units of the last significant digit, one standard deviation):

§ 938.272 013(23) MeV;

§ 1.007 276 466 77(10) a. eat.;

§ 1.672 621 637(83) × 10 −27 kg;

§ 1836,152 672 47(80) masses electron.

A neutron is an elementary particle that does not have electric charge. The neutron is a fermion and belongs to the class of baryons. Atomic nuclei are made up of neutrons and protons. The neutron is the only elementary particle with a rest mass for which gravitational interaction has been directly observed - a curvature in the terrestrial gravitational field of the trajectory of a well-collimated beam of cold Neutrons. The measured gravitational acceleration of neutrons, within the accuracy of the experiment, coincides with the gravitational acceleration of macroscopic bodies. Those. is the only particle that is subject to the law gravity" formulated by Newton Isaac.

Elementary electric charge - the minimum portion ( quantum) electric charge. Closely associated with fine structure constant describing electromagnetic interaction

The charge number of the atomic nucleus (synonyms: atomic number, atomic number, the serial number of a chemical element) - the number of protons in the atomic nucleus. The charge number is equal to the charge of the nucleus in units elementary charge and at the same time it is equal to the serial number of the chemical element corresponding to the nucleus in the periodic table.

The charge number is usually denoted by the letter Z. Nuclei with the same charge number but different mass number A(which is equal to the sum of the number of protons Z and number of neutrons N) are different isotopes of the same chemical element, since it is the charge of the nucleus that determines the structure electron shell an atom and hence its chemical properties.

Periodic system of chemical elements ( periodic table) - classification of chemical elements, establishing the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphical expression of the periodic law established by the Russian chemist D. I. Mendeleev in 1869. Its original version was developed by D. I. Mendeleev in 1869-1871 and established the dependence of the properties of elements on their atomic weight (in modern terms, on atomic mass). In total, several hundred variants of the representation of the periodic system (analytical curves, tables, geometric figures, etc.) have been proposed. In the modern version of the system, it is supposed to reduce the elements into a two-dimensional table, in which each column (group) determines the main physical and chemical properties, and the rows represent periods similar to each other to a certain extent.

And he ( other Greekἰόν - going) - monatomic or polyatomic electrically charged particle resulting from the loss or addition of one or more electronovate or molecule. Ionization(the process of formation of ions) can occur when high temperatures, under the influence of an electric field.

In the form of independent particles, ions are found in all aggregate states of matter - in gases(particularly in atmosphere), in liquids(in melts and solutions), in crystals and in plasma(particularly in interstellar space).

Isotopes (from Greek ισος - "equal", "same", and τόπος - "place") - varieties of atoms (and nuclei) of the same chemical element with a different number of neutrons in the nucleus. The name is due to the fact that the isotopes are located in the same place (in the same cell) of the periodic table. The chemical properties of an atom depend practically only on the structure of the electron shell, which, in turn, is determined mainly by the charge of the nucleus Z(that is, the number of protons in it) and almost does not depend on its mass number A(that is, the total number of protons Z and neutrons N). All isotopes of the same element have the same nuclear charge, differing only in the number of neutrons. Usually an isotope is denoted by the symbol of the chemical element to which it belongs, with the addition of an upper left index indicating the mass number (for example, 12 C, 222 Rn). You can also write the name of the element with a hyphenated mass number (for example, carbon-12, radon-222). Some isotopes have traditional names of their own (for example, deuterium, actinon).

Molecule ( Novolat. molecule, diminutive of lat. moles- mass) - the smallest particle chemical, which has all chemical properties .

The molecule is made up of two or more atoms, characterized by the number of constituents atomic nuclei and electrons, as well as a certain structure.

The binding energy (for a given state of the system) is the difference between the total energy the bound state of a system of bodies or particles and the energy of the state in which these bodies or particles are infinitely distant from each other and are at rest.

The binding energy of a system consisting of particles at rest at infinity is considered to be equal to zero.

For a system of i components (particles), the binding energy is defined as

where is the energy of the i-th component (of an infinitely distant resting particle) and is the energy of the system.

So, for example, the binding energy of a diatomic molecule corresponds to the thermal energy dissociation, binding energies atomic nucleus - mass defect.

The specific binding energy, that is, the change in the energy of the system when one particle is added, is called chemical potential ; for a system consisting of several particles, there are several chemical potentials.

Na - Avogadro's number the number of structural elements contained in one mole of matter

1/mol=const

N(number of particles)=\/*Na

\/ - number of items

N = m/M*Na M-molar mass- constant for a given thing

The proposed summary provides definitions of basic chemical concepts, many of which will be discussed in more detail when studying the relevant topics of the course.

All around us physical bodies are made up of substances.

Substance is a type of matter that has a rest mass and is characterized by constant physical and chemical properties that make it possible to distinguish it from other substances. For comparison: another kind of matter - the field - has no rest mass.

Physical properties of matter - a set of information about the properties of a substance that can be measured by physical methods. These include state of aggregation, density, solubility, melting point, boiling point, color, taste, smell, etc.

Chemical properties of a substance - a set of information about what other substances and under what conditions a given substance reacts.

Aggregate state of matter is the physical state in which a substance is at a certain pressure and temperature. Currently, there are four main states of aggregation - solid, liquid, gaseous and plasma. The gas is characterized by the chaotic movement of weakly interacting molecules, does not have a constant structure, its own shape and volume. A liquid usually consists of molecules in constant thermal motion, has volume but no shape. Solid differs in elasticity, has a certain volume and shape, can have both an ordered and disordered structure, mono- or polycrystalline. Plasma is a completely or almost completely ionized gas.

physical phenomena - phenomena in which the shape or aggregate state of a substance changes or new atoms are formed (for example, during nuclear reactions).

chemical phenomena - phenomena in which some substances are transformed into others with a new composition and properties; the composition of the nuclei does not change. Characteristic signs by which one can judge that a chemical phenomenon (reaction) is taking place are a change in color and smell, the formation of a precipitate, the release of gas, heat or light.

To express the composition of a substance in chemistry, chemical formulas. Distinguish empirical formulas(or gross formulas), they show the qualitative and quantitative composition of a substance, and structural formulas , they show the composition and structure of the structural units of matter.

For reflection chemical phenomena(reactions) use a specific notation - chemical equations. Any chemical equation must be correctly drawn up in accordance with the law of conservation of mass of substances. On the left side chemical equation write down the initial reagents, in the right - the products of the reaction.

Reagent is the starting material involved in chemical reaction(can be in the form of molecules, atoms or ions).

reaction product A substance that is formed as a result of a chemical reaction.

Atom (from Greek. atomos- indivisible) - an electrically neutral system of interacting elementary particles, consisting of a nucleus and electrons. The atom is preserved in all chemical transformations and is the carrier of the properties of a chemical element.

To the main elementary particles include protons, neutrons, electrons (there also exist and are sufficiently studied the positron, neutrino, etc.). Protons and neutrons make up the nucleus of an atom and have common name- nucleons. Electrons move around the nucleus.

The main characteristic of any atom is the nuclear charge ( Z) equal to the number of protons. A type of atom with the same nuclear charge and identical chemical properties is called chemical element. Currently, more than 110 chemical elements are known, 89 of which are found in nature, the rest are obtained artificially.

Molecule is the electrically neutral smallest set of atoms that form a certain structure through chemical bonds. A molecule retains all the properties of a given substance. If a molecule is made up of atoms of one element, then matter is simple. AT complex substance Molecules are made up of different kinds of atoms.

Each element forms at least one simple substance. Some chemical elements exhibit the ability to allotropy.

Allotropy - the ability of chemical elements to form several simple substances that differ in structure and properties. There are two types of allotropy: the first arises from a difference in the composition of molecules (for example, oxygen and ozone), the second is a consequence of a different structure of molecules (for example, diamond, graphite and carbine). Different simple substances formed by the same chemical element are called allotropic modifications. Due to allotropy, the number of known simple substances (~400) is much more number chemical elements.

In nature, as a rule, not pure substances are found, but mixtures- systems resulting from the mixing of two or more components that retain their properties. The composition of the mixture is not constant. Using physical methods, the mixture can be separated into the original substances. There are homogeneous (homogeneous) and heterogeneous (heterogeneous) mixtures.

homogeneous called a mixture in which there is no interface between the components (air, true solutions).

heterogeneous is called a mixture in which there is an interface between the components (sand and salt, water and oil, water and chalk).

Since it is inconvenient to use absolute values ​​of atomic masses in calculations (for example, the mass of a hydrogen atom is 1.67 10 -27 kg), atomic mass units (a.m.u.) are used in chemistry.

atomic unit masses(a.m.u., carbon unit) - 1/12 of the mass of a carbon-12 atom, 1 a.m.u. is approximately 1.66 10 -27 kg.

Relative atomic mass (BUT r ) - the ratio of the mass of an atom to 1/12 of the mass of a carbon-12 atom. Value BUT r- dimensionless.

Relative molecular weight (M r ) - the ratio of the mass of a molecule of a substance to 1/12 of the mass of a carbon-12 atom. Value M r is dimensionless, it is calculated as the sum of all BUT r elements that make up this molecule.

The unit of quantity of a substance in chemistry is the mole.

mole - this is the amount of a substance containing as many structural units (molecules, atoms, ions, electrons, etc.) as they are contained in 12 g of carbon-12 (approximately 6.02 10 23 - Avogadro number, N A).

Molar mass M r substances - the mass of 1 mol of a substance, the ratio of the absolute mass of a substance to the amount of a substance, is numerically equal to M r, but measured in g/mol.

Valence element - the ability of an atom of a given chemical element to form a certain number of chemical bonds with atoms of other elements. Typically, valence is equal to the number of unpaired electrons in the outer level of an atom, but exceptions are possible. So, if the element forms covalent bonds both by the exchange and by the donor-acceptor mechanism, its valence is determined by total number orbitals at the outer level (NH 4 +, HNO 3, N 2 O 5). Some elements exhibit a constant valence, others - a variable. The reason for the variable valency is the possibility of depairing of electrons in the atoms of many elements during the transition to an excited state.

Oxidation state - a characteristic of the ability of atoms of a chemical element to give and receive electrons. This value is conditional, it is calculated on the assumption that there are only ionic bonds in the molecule of the substance. The oxidation state can take both positive and negative values, be integer, fractional, equal to zero.

Hybridization – alignment of electron orbitals in shape and energy. Separate s, p, d and other electronic orbitals of any atom are capable of "mixing" when forming bonds with other atoms, forming new, so-called "hybrid" orbitals.

Topic quiz
"Basic Chemical Concepts"

(Multiple correct answers possible)

1. The volume fractions of nitrogen and ethylene (C 2 H 4) in the mixture are the same. Mass fractions of gases in the same mixture:

A) are the same b) more in nitrogen;

C) more in ethylene; d) depend on pressure.

2. Mass of 10 m 3 air at n.o. is equal to (in kg):

A) 20.15; b) 16.25; c) 14.50; d) 12.95.

3. 465 mg of calcium phosphate contains the following number of cations and anions, respectively:

A) 2.7 10 21 and 1.8 10 21; b) 4.5 10 20 and 3.0 10 20;

C) 2.7 10 25 and 1.8 10 25; d) 1.2 10 25 and 1.1 10 25 .

4. The number of moles of water molecules contained in 18.06 10 22 water molecules is:

A) 0.667; b) 0.5; c) 0.3; d) 12.

5. Of the following substances, simple ones include:

BUT) sulphuric acid; b) sulfur;

B) hydrogen; d) bromine.

6. An atom having a mass of 2.66 10 -26 kg corresponds to the element:

A) sulfur; b) magnesium;

B) oxygen; d) zinc.

7. A particle that is chemically divisible is:

A) a proton b) a molecule;

B) a positron d) an atom.

8. About carbon as about simple matter the statement says:

A) carbon is common in nature in the form of an isotope with a mass number of 12;

B) during combustion, depending on the conditions, carbon can form two oxides;

C) carbon is a part of carbonates;

D) carbon has several allotropic modifications.

9. The valency of an atom is:

A) the number of chemical bonds formed by a given atom in the compound;

B) the oxidation state of the atom;

C) the number of given or received electrons;

D) the number of electrons missing before obtaining the electron configuration of the nearest inert gas.

10. Which of the following is a chemical phenomenon?

A) melting ice b) water electrolysis;

C) sublimation of iodine; d) photosynthesis.