The electron has a dual nature: in different experiments, it can exhibit the properties of a particle and a wave. Properties of an electron as a particle: mass, charge; wave properties- in the features of movement, interference and diffraction.

The motion of an electron obeys the laws quantum mechanics .

The main characteristics that determine the movement of an electron around the nucleus: energy and spatial features of the corresponding orbital.

When interacting (overlapping) atomic orbitals(AO ) belonging to two or more atoms are formed molecular orbitals(MO).

Molecular orbitals are filled with socialized electrons and carry out covalent bond.

Before the formation of molecular orbitals, hybridization of atomic orbitals of one atom.

Hybridization - changing the shape of some orbitals during the formation of a covalent bond for more effective overlap. The same hybrids are formed JSC who are involved in education MO, overlapping the atomic orbitals of other atoms. Hybridization is possible only for atoms that form chemical bonds, but not for free atoms.

hydrocarbons

Main questions:

Hydrocarbons. Classification. Nomenclature.
Structure. Properties.
The use of hydrocarbons.

hydrocarbons- Class organic compounds which are made up of two elements: carbon and hydrogen.

Choose isomers and homologues:

Name alkanes:

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Ä nitration reaction (Konovalov's reaction, 1889) is the reaction of substitution of hydrogen for a nitro group.

Conditions: 13% HNO 3, t \u003d 130 - 140 0 C, P \u003d 15 - 10 5 Pa. On an industrial scale, the nitration of alkanes is carried out in the gas phase at 150 - 170 0 C with nitric oxide (IV) or nitric acid vapor.

CH 4 + HO - NO 2 → CH 3 - NO 2 + H 2 O

nitromethane

@ Solve tasks:

1. The composition of alkanes reflects the general formula:

a) C n H 2 n +2; b) C n H 2 n -2; c) C n H 2 n; d) C n H 2 n -6.

2. What reagents can alkanes interact with:

A) Br 2 (solution); b) Br 2 , t 0 ; V) H 2 SO 4 ; G) HNO 3 (dilute), t 0 ; d) KMnO 4 ; e) CON?

Answers: 1) reagents a, b, d, e; 2) reagents b, c, e;

3) reagents b, d; 4) reagents b, d, e, f.

Establish a correspondence between the type of reaction and the scheme (equation) of the reaction:

Specify the substance that is formed during the complete chlorination of methane:

a) trichloromethane; b) carbon tetrachloride; c) dichloromethane; d) tetrachloroethane.

Specify the most probable product of monobromination of 2,2,3-trimethylbutane:

a) 2-bromo-2,3,3-trimethylbutane; b) 1-bromo-2,2,3-trimethylbutane;

c) 1-bromo-2,3,3-trimethylbutane; d) 2-bromo-2,2,3-trimethylbutane.

Write an equation for the reaction.

Wurtz reaction – the action of metallic sodium on halogen derivatives of hydrocarbons. When two different halogen derivatives react, a mixture of hydrocarbons is formed, which can be separated by distillation.

CH 3 I + 2 Na + CH 3 I → C 2 H 6 + 2 NaI

@ Solve tasks:

1. Specify the name of the hydrocarbon that is formed when bromoethane is heated with sodium metal:

a) propane; b) butane; c) pentane; d) hexane; e) heptane.

Write an equation for the reaction.

What hydrocarbons are formed by the action of metallic sodium on a mixture:

a) iodomethane and 1-bromo-2-methylpropane; b) 2-bromopropane and 2-bromobutane?

Cycloalkanes

1. For small cycles (C 3 - C 4) are characteristic addition reactions hydrogen, halogens and hydrogen halides. The reactions are accompanied by the opening of the cycle.

2. For other cycles (from 5 and above) are characteristic substitution reactions.

Unsaturated hydrocarbons(unsaturated):

Alkenes (olefins, double bond unsaturated hydrocarbons, ethylene hydrocarbons): Structure: sp 2 hybridization, planar placement of orbitals (flat square). Reactions: addition (hydrogenation, halogenation, hydrohalogenation, polymerization), substitution (not typical), oxidation (combustion, KMnO 4), decomposition (without oxygen access).

@ Solve tasks:

What is the hybridization of carbon atoms in an alkene molecule:

a) 1 and 4 - sp 2, 2 and 3 - sp 3; b) 1 and 4 - sp 3, 2 and 3 - sp 2;

c) 1 and 4 - sp 3, 2 and 3 - sp; d) 1 and 4 - not hybridized, 2 and 3 - sp2.

2. Name the alkene:

Write reaction equations using the example of butene-1, name the products obtained.

4. In the transformation scheme below, ethylene is formed in the reaction:

a) 1 and 2; b) 1 and 3; c) 2 and 3;

d) ethylene is not formed in any reaction.

Which reaction goes against Markovnikov's rule:

a) CH 3 - CH \u003d CH 2 + HBr →; b) CH 3 - CH \u003d CH 2 + H 2 O →;;

c) CH 3 - CH \u003d CH - CH 2 + HCI →; d) CCI 3 - CH \u003d CH 2 + HCI →?

þ Dienes with conjugated bonds:hydration 1,3-butadiene - 2-butene is formed (1,4-addition):

þ hydrogenation 1,3-butadiene in the presence of a Ni-butane catalyst:

þ halogenation 1,3-butadiene - 1,4-addition (1,4 - dibromo-2-butene):

þ diene polymerization:

Polyena(unsaturated hydrocarbons with many double bonds) are hydrocarbons whose molecules contain at least three double bonds.

Obtaining dienes:

Ø action of an alcoholic solution of alkali:

Ø Lebedev method (divinyl synthesis):

Ø dehydration of glycols (alkanediols):

Alkynes (acetylenic hydrocarbons, hydrocarbons with one triple bond): Structure: sp hybridization, linear placement of orbitals. Reactions: addition (hydrogenation, halogenation, hydrohalogenation, polymerization), substitution (formation of salts), oxidation (combustion, KMnO 4), decomposition (without access to oxygen).	5-methylhexine-2 1-Pentyne 3-methylbutyne-1
	1. Which hydrocarbons correspond general formula C n H 2n-2: a) acetylene, diene; b) ethylene, diene; c) cycloalkanes, alkenes; d) acetylene, aromatic? 2. A triple bond is a combination of: a) three σ-bonds; b) one σ-bond and two π-bonds; c) two σ-bonds and one π-bond; d) three π-bonds. 3. Compose the formula of 3-methylpentine -3.
I. Addition reactions
v hydrogenation occurs through the stage of formation of alkenes:
v Addition of halogens happens worse than in alkenes: Alkynes decolorize bromine water ( qualitative reaction).
v Addition of hydrogen halides:
Addition products to unsymmetrical alkynes are determined Markovnikov's rule:
v Accession of water (hydration)- reaction of M.G. Kucherov, 1881.
For acetylene homologues, the product of water addition is a ketone:
III. Salt formation (acidic properties) - substitution reactions
ð Interaction with active metals: Acetylides are used for the synthesis of homologues.
ð Interaction of alkynes with ammonia solutions of silver oxide or copper(I) chloride:

Qualitative reaction to the final triple bond - the formation of a grayish-white precipitate of silver acetylenide or red-brown - copper (I) acetylenide:	HC ≡ CH + СuCI → СuC ≡ ССu ↓ + 2HCI Reaction does not occur
IV. Oxidation reactions
mild oxidation– discoloration of an aqueous solution of potassium permanganate ( a qualitative reaction to a multiple bond):	When acetylene interacts with a dilute solution of KMnO 4 (room temperature) - oxalic acid.

m quantum numbers.

The wave function is calculated according to the Schrödinger wave equation within the one-electron approximation (the Hartree-Fock method) as the wave function of an electron in a self-consistent field created by the atomic nucleus with all other electrons of the atom.

E. Schrodinger himself considered an electron in an atom as a negatively charged cloud, the density of which is proportional to the square of the value of the wave function at the corresponding point of the atom. In this form, the concept of an electron cloud was also perceived in theoretical chemistry.

However, most physicists did not share E. Schrödinger's beliefs - there was no evidence of the existence of an electron as a "negatively charged cloud". Max Born substantiated the probabilistic interpretation of the square of the wave function. In 1950, E. Schrödinger in the article “What is an elementary particle?” forced to agree with the arguments of M. Born, who in 1954 was awarded Nobel Prize in physics with the wording "For fundamental research in quantum mechanics, especially for the statistical interpretation of the wave function."

Quantum numbers and orbital nomenclature

Radial probability density distribution for atomic orbitals for various n And l.

Principal quantum number n can take any integer positive values, starting from one ( n= 1,2,3, … ∞) and determines the total energy of an electron in a given orbital (energy level):

Energy for n= ∞ corresponds to the single-electron ionization energy for the given energy level.

The orbital quantum number (also called the azimuthal or complementary quantum number) determines the angular momentum of an electron and can take integer values from 0 to n - 1 (l = 0,1, …, n- 1). The angular momentum in this case is given by the relation

Atomic orbitals are usually named according to the letter designation of their orbital number:

The letter designations of atomic orbitals originated from the description of spectral lines in atomic spectra: s (sharp) is a sharp series in atomic spectra, p (principal)- home, d (diffuse) - diffuse, f (Fundamental) is fundamental.

Magnetic quantum number m l determines the projection of the orbital angular momentum on the direction magnetic field and can take integer values ranging from - l before l, including 0 ( m l = -l … 0 … l):

In the literature, orbitals are denoted by a combination of quantum numbers, with the principal quantum number denoted by a number, the orbital quantum number by the corresponding letter (see table below) and the magnetic quantum number by a subscript expression showing the projection of the orbital onto the Cartesian axes x, y, z, For example 2p x, 3d xy, 4f z(x²-y²). For orbitals of the outer electron shell, that is, in the case of describing valence electrons, the main quantum number in the record of the orbital, as a rule, is omitted.

Geometric representation

The geometric representation of an atomic orbital is a region of space bounded by a surface of equal density (equidensity surface) of probability or charge. The probability density on the boundary surface is chosen based on the problem being solved, but usually in such a way that the probability of finding an electron in a limited area lies in the range of 0.9-0.99.

Since the energy of an electron is determined by the Coulomb interaction and, consequently, by the distance from the nucleus, the main quantum number n sets the size of the orbital.

The shape and symmetry of the orbital are given by the orbital quantum numbers l And m: s-orbitals are spherically symmetrical, p, d And f-orbitals have more complex shape determined by the angular parts of the wave function - the angular functions. Angular functions Y lm (φ , θ) - eigenfunctions of the squared angular momentum operator L², depending on quantum numbers l And m(see Spherical functions), are complex and describe in spherical coordinates (φ, θ) the angular dependence of the probability of finding an electron in the central field of an atom. The linear combination of these functions determines the position of the orbitals relative to the Cartesian coordinate axes.

For linear combinations Y lm the following notation is accepted:

The value of the orbital quantum number	0	1	2
The value of the magnetic quantum number	0	0	0
Linear Combination
Designation

An additional factor, sometimes taken into account in the geometric representation, is the sign of the wave function (phase). This factor is essential for orbitals with an orbital quantum number l, different from zero, that is, not having spherical symmetry: the sign of the wave function of their "petals" lying on opposite sides of the nodal plane is opposite. The sign of the wave function is taken into account in the MO LCAO molecular orbital method (molecular orbitals as a linear combination of atomic orbitals). Today, science knows the mathematical equations that describe geometric figures, representing orbitals (depending on the electron coordinates on time). These are the equations harmonic vibrations reflecting the rotation of particles in all available degrees of freedom - orbital rotation, spin, ... Hybridization of orbitals is represented as the interference of oscillations.

The filling of orbitals with electrons and the electronic configuration of the atom

Each orbital can have no more than two electrons, differing in the value of the spin quantum number s(back). This prohibition is determined by the Pauli principle. The order in which electrons fill orbitals of the same level (orbitals with the same value of the principal quantum number n) is determined by the Klechkovsky rule, the order in which electrons fill orbitals within the same sublevel (orbitals with the same values principal quantum number n and orbital quantum number l) is determined by Hund's Rule.

Brief entry distribution of electrons in an atom over various electron shells of the atom, taking into account their principal and orbital quantum numbers n And l called

Orbitals

A careful examination of the atomic spectra shows that the "thick" lines due to transitions between energy levels are in fact split into thinner lines. This means that the electron shells are actually split into subshells. Electronic subshells are designated according to the types of lines corresponding to them in atomic spectra:

s- subshell named after "sharp" s-lines - sharp;
p- subshell named after "main" p-lines - principal;
d- subshell named for "diffuse" d-lines - diffuse;
f- subshell named after "fundamental" f-lines - Fundamental.

The lines due to transitions between these subshells experience further splitting if the atoms of the elements are placed in an external magnetic field. This splitting is called the Zeeman effect. It was experimentally found that s- the line does not split, R- the line splits into 3, d-line - by 5, f-line - by 7.
According to the Heisenberg uncertainty principle, the position and momentum of an electron cannot be determined simultaneously with absolute accuracy. However, despite the impossibility exact definition the position of an electron, you can specify the probability of finding an electron in a certain position at any time. There are two important consequences of Heisenberg's uncertainty principle.
1. The movement of an electron in an atom is a movement without a trajectory. Instead of a trajectory in quantum mechanics, another concept is introduced - probability the stay of an electron in a certain part of the volume of an atom, which correlates with the electron density when considering an electron as an electron cloud.
2. An electron cannot fall on a nucleus. Bohr's theory did not explain this phenomenon. Quantum mechanics provided an explanation for this phenomenon. An increase in the degree of certainty of the coordinates of an electron when it falls on the nucleus would cause a sharp increase in the energy of the electron up to 10 11 kJ/mol and more. An electron with such an energy, instead of falling onto the nucleus, will have to leave the atom. It follows that force is needed not to keep the electron from falling onto the nucleus, but to "force" the electron to be within the atom.
A function that depends on the coordinates of an electron, through which the probability of its being at a particular point in space is determined, is called orbital. The concept of "orbital" should not be identified with the concept of "orbit", which is used in Bohr's theory. Under the orbit in Bohr's theory is understood the trajectory (path) of the electron around the nucleus.
It is often customary to consider an electron as a negatively charged cloud diffused in space with a total charge equal to that of the electron. Then the density of such an electron cloud at any point in space is proportional to the probability of finding an electron in it. The electron cloud model is very convenient for a visual description of the electron density distribution in space. Wherein s the orbital is spherical R-orbital - the shape of a dumbbell, d-orbital - a four-petal flower or a double dumbbell (Fig. 1.10).

Thus, s- subshell consists of one s-orbitals, p- subshell - of three p-orbitals, d- subshell - out of five d-orbitals, f- subshell - of seven f-orbitals.

Ticket№1

Chemistry- one of the most important and extensive areas of natural science, the science of substances, their properties, structure and transformations occurring 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. The subject of chemistry is the chemical elements and their compounds, as well as the patterns that various chemical reactions. Chemistry has much in common with physics and biology, in fact the boundary between them is conditional. Modern chemistry is one of the most extensive disciplines among all natural sciences. Chemistry as an independent discipline was determined in the XVI-XVII centuries, after a series of scientific discoveries who substantiated the mechanistic picture of the world, the development of industry, the creation of factories, the emergence of bourgeois society. However, due to the fact that chemistry, unlike physics, could not be expressed quantitatively, there were disputes whether chemistry is a quantitatively reproducible science or is it some other kind of knowledge. In 1661, Robert Boyle created the work "The Skeptic Chemist", in which he explained the difference in the properties of various substances by the fact that they are built from different particles (corpuscles), which are responsible for the properties of the substance. Van Helmont, studying combustion, introduced the concept gas for the substance that is formed during it, he discovered carbon dioxide. In 1672, Boyle discovered that when metals are fired, their mass increases, and explained this by the capture of "weighty particles of the flame." subject of chemistry. One of the main objects of chemistry is the substances that make up all the bodies around us. A body is anything that has mass and volume. Raindrops, frost on branches, fog - bodies consisting of one substance - water. Phenomena in which new substances are formed from one substance are called chemical. Chemistry is the study of such phenomena. Chemistry is the science of the transformation of substances. This definition has become a classic. Chemistry studies the composition and structure of substances, the conditions and ways of transformation of some substances into others, the dependence of the properties of substances on their composition and structure.

The main task of chemistry- identification and description of such properties of substances, due to which it is possible to transform some substances into others as a result of chemical phenomena, or chemical reactions. Theoretical basis inorganic chemistry- the periodic law and the periodic system of elements of Mendeleev. Modern inorganic chemistry studies the structure and properties inorganic substances using not only chemical, but also physical methods (for example, spectroscopy).

Ticket number 2

According to Heisenberg's uncertainty principle, the position and momentum of an electron cannot be determined simultaneously with absolute accuracy. However, despite the impossibility of accurately determining the position of an electron, it is possible to specify the probability of finding an electron in a certain position at any given time. The region of space in which the probability of finding an electron is high is called an orbital. The concept of "orbital" should not be identified with the concept of orbit, which is used in Bohr's theory. The orbit in Bohr's theory is understood as the trajectory (path) of an electron around the nucleus. Electrons can occupy four different types of orbitals, which are called S-, p-, d- and f-orbitals. These orbitals can be represented by 3D bounding surfaces. The regions of space bounded by these surfaces are usually chosen so that there is a 95% probability of finding one electron inside them. On fig. 1.18 schematically shows the shape of the s- and p-orbitals. The s-orbital is spherical, while the p-orbitals are dumbbell-shaped. Since an electron has a negative charge, its orbital can be thought of as some kind of charge distribution. This distribution is called the electron cloud.

Schrödinger equation- an equation describing the change in space and time of a pure state, given by the wave function, in Hamiltonian quantum systems. Plays in quantum mechanics the same important role, as the equation of Newton's second law in classical mechanics. It can be called the equation of motion of a quantum particle. Established by Erwin Schrödinger in 1926. The Schrödinger equation is intended for spinless particles moving at speeds much less than the speed of light. In the case of fast particles and particles with spin, its generalizations are used.

wave function, or psi function is a complex-valued function used in quantum mechanics to describe the pure state of a system. It is the expansion coefficient of the state vector in terms of the basis (usually the coordinate one):

where is the coordinate basis vector, and is the wave function in the coordinate representation. |ψ| 2 - the probability of finding a particle in a given region of space

Let the wave function be given in N-dimensional space, then at each point with coordinates , at a certain point in time t it will look like . In this case, the Schrödinger equation will be written as:

where , - Planck's constant; is the mass of the particle, is the potential energy external to the particle at the point , is the Laplace operator (or Laplacian), is equivalent to the square of the operator nabla

Ticket number 3

atomic orbital- one-electron wave function in spherically symmetrical electric field atomic nucleus, given main n,orbital l And magnetic m quantum numbers.

The name "orbital" (and not orbit) reflects the geometric representation of stationary states electron V atom; such a special name reflects the fact that the state of an electron in an atom is described by the laws quantum mechanics and different from classical movement along trajectories. The set of atomic orbitals with the same value of the principal quantum number n constitute one electron shell.

quantum numbers and nomenclature of orbitals

Radial probability density distribution for atomic orbitals for various n And l.

Principal quantum number n can take any positive integer values, starting from one ( n= 1,2,3, … ∞) and determines the total energy of an electron in a given orbital (energy level):

Energy for n= ∞ corresponds to single electron ionization energy for a given energy level.

The orbital quantum number (also called the azimuthal or complementary quantum number) determines angular momentum electron and can take integer values from 0 to n - 1 (l = 0,1, …, n - 1). angular momentum is given by the relation

Atomic orbitals are usually named according to the letter designation of their orbital number:

Magnetic quantum number m l defines the projection of the orbital angular momentum on the direction of the magnetic field and can take integer values in the range from - l before l, including 0 ( m l = -l … 0 … l):

Ticket number 4

Each orbital can have no more than two electrons, differing in the value of the spin quantum number s(back). This prohibition is determined by the Pauli principle. The order in which electrons fill orbitals of the same level (orbitals with the same value of the principal quantum number n) is determined by the Klechkovsky rule, the order in which electrons fill orbitals within the same sublevel (orbitals with the same values of the principal quantum number n and orbital quantum number l) is determined by Hund's Rule.

A brief record of the distribution of electrons in an atom over various electron shells of the atom, taking into account their principal and orbital quantum numbers n And l called the electronic configuration of an atom.

Pauli principle(exclusion principle) - one of the fundamental principles of quantum mechanics, according to which two or more identical fermions cannot simultaneously be in the same quantum state.

The Pauli principle can be formulated as follows: within one quantum system, only one particle can be in a given quantum state, the state of another must differ by at least one quantum number.

Formulation of Klechkovsky's rule

the orbital energy consistently increases as the sum increases, and at the same value of this sum, the atomic orbital with a lower value of the principal quantum number has a relatively lower energy. For example, at , the orbital energies follow a sequence, since here the principal quantum number for the orbital is the smallest, for the orbital; the largest, -orbital occupies an intermediate position.

When filling the orbital shells of the atom, it is more preferable (more energetically favorable), and, therefore, those states for which the sum of the main quantum number and the side (orbital) quantum number, i.e., is of lesser value, are filled earlier.

rulehunda(Gunda) determines the order of filling the orbitals of a certain sublayer and is formulated as follows: the total value of the spin quantum number of electrons of a given sublayer should be maximum.

This means that in each of the orbitals of the sublayer, one electron is first filled, and only after the unfilled orbitals are exhausted, a second electron is added to this orbital. In this case, there are two electrons with half-integer spins of the opposite sign in one orbital, which pair (form a two-electron cloud) and, as a result, the total spin of the orbital becomes equal to zero.

Ticket number 5

Ionization energy- a kind of binding energy or, as it is sometimes called, the first ionization potential (I 1), represents the smallest energy required to remove an electron from a free atom in its lowest energy (ground) state to infinity.

The ionization energy is one of the main characteristics of the atom, on which the nature and strength of the chemical bonds formed by the atom largely depend. The ionization energy of the atom also substantially depends on the reducing properties of the corresponding simple substance.

For a multielectron atom, there are also concepts of second, third, etc. ionization potentials, which are the energy of removal of an electron from its free unexcited cations with charges +1, +2, etc. These ionization potentials, as a rule, are less important for characterizing chemical element.

The ionization energy always has an endoenergy value (this is understandable, since in order to tear off an electron from an atom, it is required to apply energy, this cannot happen spontaneously).

The ionization energy of an atom is most significantly affected by the following factors:

the effective charge of the nucleus, which is a function of the number of electrons in the atom that screen the nucleus and are located in deeper inner orbitals;

the radial distance from the nucleus to the maximum charge density of the outer, most weakly bound to the atom and leaving it during ionization, electron;

a measure of the penetrating power of that electron;

interelectronic repulsion among outer (valence) electrons.

The ionization energy is also influenced by less significant factors, such as quantum mechanical exchange interaction, spin and charge correlation, etc.

The ionization energy of elements is measured in electron volts per atom, or in joules per mole.

The affinity energy of an atom to an electron, or just him electron affinity, called the energy released in the process of attaching an electron to a free atom in its ground state with its transformation into a negative ion (the affinity of an atom for an electron is numerically equal, but opposite in sign, to the ionization energy of the corresponding isolated singly charged anion).

Electron affinity is expressed in kilojoules per mole (kJ/mol) or electron volts per atom (eV/atom).

Unlike the ionization potential of an atom, which always has an endoenergetic value, the affinity of an atom for an electron is described by both exoenergetic and endoenergetic values

atomic radii. Atomic radii are taken as values found on the basis of certain assumptions. Theoretically, the so-called orbital radii are calculated, or the distance from the center of the nucleus to the maximum electron density farthest from it.

The periodicity of the change in atomic radii is especially pronounced for s- and p-elements: in periods from left to right, the radii decrease, and in groups from top to bottom increase. The patterns of change in atomic radii for d- and f-elements are more complex

Ticket number 6

Chemical element- a set of atoms with the same nuclear charge and the number of protons, coinciding with the ordinal (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)

At present, the Periodic Law of D. I. Mendeleev has the following formulation: "the properties of chemical elements, as well as the forms and properties of the simple substances and compounds they form, are in a periodic dependence on the magnitude of the charges of the nuclei of their atoms".

The most common are 3 forms of the periodic table: "short" (short period), "long" (long period) and "extra long". In the "extra-long" version, each period occupies exactly one line. In the "long" version, the lanthanides and actinides are removed from the general table, making it more compact. In the "short" form of entry, in addition to this, the fourth and subsequent periods occupy 2 lines; the symbols of the elements of the main and secondary subgroups are aligned relative to different edges of the cells.

The short form of the table, containing eight groups of elements, was officially abolished by IUPAC in 1989. Despite the recommendation to use the long form, the short form continues to be given in a large number of Russian reference books and manuals after this time. From modern foreign literature, the short form is completely excluded; instead, the long form is used.

Ticket number 10

Molecular Orbital Method Critical Method quantum chemistry. The method is based on the idea that each electron of a molecule is described by its own wave function - a molecular orbital (MO). In the general case, the MO method considers the formation of chemical bonds as a result of the movement of all electrons in the total field created by all electrons and all nuclei of the initial atoms. However, since the electrons of the outer (valence) shells make the main contribution to the formation of bonds, it is usually limited to considering only these electrons. In chemistry, the MO method (especially in the form of MO LCAO) is important because it makes it possible to obtain data on the structure and properties of molecules based on the corresponding characteristics of atoms. Therefore, almost all modern concepts chemical bond and chemical reactivity are based on the concepts of the MO method. Theory of molecular orbitals(MO) gives an idea of the distribution of electron density and explains the properties of molecules. In this theory, quantum mechanical dependences for an atom are extended to a more complex system - a molecule. The molecule is considered as a whole, and not as a collection of atoms that have retained their individuality. In a molecule (as in an atom) there are discrete energy states of individual electrons (molecular orbitals) with their self-consistent motion in the field of each other and all nuclei of the molecule. Each orbital is characterized by its own set of quantum numbers that reflect the properties of electrons in a given energy state. In contrast to the single-center orbitals of atoms, the orbitals of molecules are multicenter, that is, molecules have common orbitals for two or more atomic nuclei. Each molecular orbital has a certain energy, which is approximately characterized by the corresponding ionization potential.

Two-center molecular orbitals

The molecular orbital method uses the idea of a molecular orbital to describe the distribution of electron density in a molecule (similar to the atomic orbital for an atom). Molecular orbitals are the wave functions of an electron in a molecule or other polyatomic chemical particle. Each molecular orbital (MO), like the atomic orbital (AO), can be occupied by one or two electrons. The state of an electron in the binding region is described by the bonding molecular orbital, in the loosening region - by the loosening molecular orbital. The distribution of electrons in molecular orbitals follows the same rules as the distribution of electrons in atomic orbitals in an isolated atom. Molecular orbitals are formed by certain combinations of atomic orbitals. Their number, energy and shape can be derived from the number, energy and shape of the orbitals of the atoms that make up the molecule. ???????????????????????????????????????????????????? ???

Ticket number 11: Ionic bond. Metal connection. Hydrogen bond. Van der Waals forces.

Ionic bond- a strong chemical bond formed between atoms with a large difference (> 1.7 on the Pauling scale) of electronegativity, at which the common electron para is completely transferred to an atom with a higher electronegativity. This is the attraction of ions as oppositely charged bodies. An example is the compound CsF, in which the “degree of ionicity” is 97%. Let us consider the method of formation using sodium chloride NaCl as an example. The electronic configuration of sodium and chlorine atoms can be represented as: 11 Na 1s2 2s2 2p 6 3s1; 17 Cl 1s2 2s2 2p6 3s2 3p5 As these are atoms with incomplete energy levels. Obviously, to complete them, it is easier for a sodium atom to give up one electron than to add seven, and it is easier for a chlorine atom to add one electron than to give up seven. In a chemical interaction, the sodium atom completely gives up one electron, and the chlorine atom accepts it. Schematically, this can be written as: Na. - l e -> Na + sodium ion, stable eight-electron 1s2 2s2 2p6 shell due to the second energy level. :Cl + 1e --> .Cl - chlorine ion, stable eight-electron shell. Electrostatic attraction forces arise between the Na+ and Cl- ions, as a result of which a compound is formed. An ionic bond is an extreme case of the polarization of a covalent polar bond. Formed between typical metal and non-metal. In this case, the electrons from the metal completely pass to the non-metal. Ions are formed.

If a chemical bond is formed between atoms that have a very large electronegativity difference (EO > 1.7 according to Pauling), then the shared electron pair is completely transferred to the atom with a larger EO. The result of this is the formation of a compound of oppositely charged ions:

Between the formed ions there is an electrostatic attraction, which is called ionic bonding. Rather, such a view is convenient. In fact, the ionic bond between atoms in its pure form is not realized anywhere or almost nowhere; usually, in fact, the bond is partly ionic and partly covalent. At the same time, the bonding of complex molecular ions can often be considered purely ionic. The most important differences between ionic bonds and other types of chemical bonds are non-directionality and unsaturation. That is why crystals formed due to ionic bonding gravitate towards various close packings of the corresponding ions.

characteristic of such compounds is good solubility in polar solvents (water, acids, etc.). This is due to the charged parts of the molecule. In this case, the dipoles of the solvent are attracted to the charged ends of the molecule, and, as a result of Brownian motion, they “pull” the molecule of the substance into parts and surround them, preventing them from reuniting. The result is ions surrounded by dipoles of the solvent.

When such compounds are dissolved, as a rule, energy is released, since the total energy of the formed solvent-ion bonds is greater than the anion-cation bond energy. Exceptions are many salts of nitric acid (nitrates), which, when dissolved, absorb heat (solutions cool). The latter fact is explained on the basis of the laws that are considered in physical chemistry.

A metallic bond is a chemical bond due to the presence of relatively free electrons. It is typical for both pure metals and their alloys and intermetallic compounds.

Metal bond mechanism

Positive metal ions are located in all nodes of the crystal lattice. Between them randomly, like gas molecules, valence electrons move, unhooked from atoms during the formation of ions. These electrons play the role of cement, holding the positive ions together; otherwise, the lattice would disintegrate under the action of repulsive forces between the ions. At the same time, electrons are also held by ions within the crystal lattice and cannot leave it. Communication forces are not localized and not directed. Therefore, in most cases, high coordination numbers appear (for example, 12 or 8).

[edit] Characteristic crystal lattices

Most metals form one of the following highly symmetric close-packed lattices: body-centered cubic, face-centered cubic, and hexagonal.

In a body-centered cubic lattice (bcc), the atoms are located at the vertices of the cube and one atom is located at the center of the volume of the cube. Metals have a cubic body-centered lattice: Pb, K, Na, Li, β-Ti, β-Zr, Ta, W, V, α-Fe, Cr, Nb, Ba, etc.

In a face-centered cubic lattice (fcc), atoms are located at the vertices of the cube and at the center of each face. Metals of this type have a lattice: α-Ca, Ce, α-Sr, Pb, Ni, Ag, Au, Pd, Pt, Rh, γ-Fe, Cu, α-Co, etc.

In a hexagonal lattice, atoms are located at the vertices and the center of the hexagonal bases of the prism, and three atoms are located in the middle plane of the prism. Metals have such a packing of atoms: Mg, α-Ti, Cd, Re, Os, Ru, Zn, β-Co, Be, β-Ca, etc.

[edit] Other properties

Freely moving electrons cause high electrical and thermal conductivity. Substances with a metallic bond often combine strength with ductility, since when atoms are displaced relative to each other, bonds do not break.

Van der Waals forces- forces of intermolecular interaction with an energy of 0.8 - 8.16 kJ / mol. This term originally denoted all such forces, in modern science it is usually applied to forces arising from the polarization of molecules and the formation of dipoles. Discovered by J. D. van der Waals in 1869.

Van der Waals forces include interactions between dipoles (permanent and induced). The name comes from the fact that these forces are the cause of the correction for internal pressure in the van der Waals equation of state for a real gas. These interactions mainly determine the forces responsible for the formation of the spatial structure of biological macromolecules.

Van der Waals forces also arise between a particle (macroscopic particle or nanoparticle) and a molecule and between two particles.

Classification of van der Waals forces

The van der Waals interaction consists of three types of weak interactions:

Orientation forces, dipole-dipole attraction. It is carried out between molecules that are permanent dipoles. An example is HCl in liquid and solid state. The energy of such an interaction is inversely proportional to the cube of the distance between the dipoles.

Dispersive attraction (London forces). Interaction between instantaneous and induced dipole. The energy of such an interaction is inversely proportional to the sixth power of the distance between the dipoles.

inductive attraction. Interaction between a permanent dipole and an induced (induced) one. The energy of such an interaction is inversely proportional to the sixth power of the distance between the dipoles.

Until now, many authors proceed from the assumption that van der Waals forces determine the interlayer interaction in layered crystals, which contradicts experimental data: the Debye temperature anisotropy scale and, accordingly, the lattice reflection anisotropy scale. Based on this erroneous assumption, many two-dimensional models have been built that “describe” the properties, in particular, of graphite and boron nitride.

Ticket number 12

Coordination number in chemistry

In chemistry, the concept of coordination number appeared with the development of the chemistry of complex compounds. It means the number of ligands (atoms, molecules, ions) that form the first coordination (inner) sphere of the complexing agent.

For example, in the complex salt of potassium hexacyanoferrate (III) K 3, the coordination number of the Fe 3+ ion is 6, and in cis-dichlorodiammineplatinum (II) (Peyronet's salt) Pt (NH 3) 2 Cl 2, the central platinum atom is associated with four ligands.

The concept of coordination number is also used to characterize the central atom in molecules, mainly for those cases where the number of chemically bonded nearest atoms is not equal to the numerical value of the valence. For example, in a nitric acid molecule, the formal valence of the central nitrogen atom is 4, the oxidation state is +5, and the coordination number is 3.

The concept of coordination number is also used in describing the structure of liquids and amorphous bodies. In this case, the coordination number is a measure of short-range order, the average number of nearest neighbors of an atom. It may be fractional.

central atom(CA) or a complexing agent is usually a metal ion or atom, although in some cases it can also be a non-metal, for example, silicon and phosphorus in anions 2– and –, respectively. CA forms chemical bonds with ligands and coordinates them around itself. As a result, a coordination compound is formed.

Ligand(from lat. ligare - to bind) - an atom, ion or molecule associated with a certain center (acceptor). The concept is used in biochemistry to designate agents that combine with biological acceptors (receptors, immunoglobulins), as well as in the chemistry of complex compounds, denoting particles attached to one or more central (complexing) metal atoms.

ORBITAL - the region of the most probable location of an electron in an atom (atomic orbital) or in a molecule (molecular orbital).

So far, five types of orbitals have been described: s, p, d, f, and g.
The names of the first three were formed historically, then the alphabetical principle was chosen. Orbital shapes are calculated by quantum chemistry methods.

s-Orbitals - have a spherical shape and the same electron density in the direction of each axis of three-dimensional coordinates
s-orbital - orbital sphere

Each p-orbital is located along one of three mutually perpendicular axes, in accordance with this, in the name of the p-orbital, the axis along which its maximum electron density is located is indicated using the corresponding index:
p-orbital - dumbbell orbital

d-orbital - complex shape orbital

Energy of electronic levels

Quantum numbers of electrons

The state of each electron in an atom is usually described using four quantum numbers:

n - energy level of the electron (remoteness of the level from the nucleus)
l - what type of orbital it moves in (s,p,d...)
m- magnetic (on which of p (out of three possible), d (out of 5 possible), etc.
s - spin (electron movement around its own axis).

Orbital Filling Principles

1. There cannot be two electrons in an atom, for which the values of all quantum numbers (n, l, m, s) would be the same, i.e. Each orbital can contain no more than two electrons (with opposite spins) (Pauli principle).

2. In the ground state, each electron is located so that its energy is minimal.
The energy of the orbitals increases in the series:
1S< 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 5d » 4f < 6p < 7s.
There is no need to memorize this sequence. It can be extracted from the Periodic table of D.I. Mendeleev

3. Electrons prefer to settle in orbitals of the same energy (for example, in three p-orbitals), first one by one, and only when there is already one electron in each such orbital, the filling of these orbitals with second electrons begins. When an orbital is populated by two electrons, these electrons are called paired .(Hund's rule)

Complete electronic formula element

A record that reflects the distribution of electrons in an atom of a chemical element over energy levels and sublevels is called the electronic configuration of this atom. In the ground (unexcited) state of an atom, all electrons satisfy the principle of minimum energy. This means that the sublevels are filled first, for which:

1. The number n is minimal
2. Inside the level, the s-sublevel is first filled, then p- and only then d- (l is minimal)
3. One sublevel contains the largest number of unpaired electrons.
4. When filling electronic atomic orbitals, the Pauli principle is fulfilled. Its consequence is that energy level number n can have at most 2n2 electrons located on n2 sublevels.

The electronic formula of the element with the serial number 7 (this is the element nitrogen, which has the symbol “N”) looks like this.