Electrons occupying one orbital are called. Two-center molecular orbitals

Atomic orbital is the one-electron wave function obtained by solving the Schrödinger equation for a given atom; is given by: principal n, orbital l, and magnetic m - quantum numbers. A single electron of the hydrogen atom forms a spherical orbital around the nucleus - a spherical electron cloud, like a loose ball of fluffy wool or a cotton ball.

Scientists agreed to call a spherical atomic orbital s-orbital... It is the most stable and is located quite close to the core. The more the energy of the electron in the atom, the faster it rotates, the more the area of \u200b\u200bits residence is stretched and finally turns into a dumbbell p-orbital:

Orbital hybridization - a hypothetical process of mixing different (s, p, d, f) orbitals of the central atom of a polyatomic molecule with the appearance of identical orbitals, equivalent in their characteristics.

5.Tetrahedral model of the carbon atom. Butlerov's structure theory

The theory of the chemical structure of organic substances was formulated by A.M. Butlerov in 1861.

Basic Provisions structural theory boil down to the following:

1) in molecules, atoms are connected to each other in a certain sequence in accordance with their valence. The order in which atoms are bonded is called chemical structure;

2) the properties of a substance depend not only on which atoms and in what quantity are included in the composition of its molecule, but also on the order in which they are connected to each other, that is, on the chemical structure of the molecule;

3) the atoms or groups of atoms that form the molecule mutually influence each other.

Basic ideas about chemical structure, laid by Butlerov, were supplemented by Van't Hoff and Le-Bel (1874), who developed the idea of \u200b\u200bthe spatial arrangement of atoms in the organic molecule. and raised the question of the spatial configuration and conformation of molecules. The work of Van't Hoff laid the foundation for the direction of org. Chemistry - stereochemistry - the doctrine of spatial structure. Want-Hoff proposed a tetrahedral model of the carbon atom - the four valences of an atom in carbon in methane are directed to the four corners of the tetrahedron, in the center of which is a carbon atom, and at the vertices there are hydrogen atoms.

Unsaturated carboxylic acids

Chemical properties.
The chemical properties of unsaturated carboxylic acids are due to both the properties of the carboxyl group and the properties of the double bond. Acids with a double bond close to the carboxyl group - alpha, beta-unsaturated acids - have specific properties. In these acids, the addition of hydrogen halides and hydration go against the Markovnikov rule:

CH 2 \u003d CH-COOH + HBr -\u003e CH 2 Br-CH 2 -COOH

With careful oxidation, dioxy acids are formed:

CH 2 \u003d CH-COOH + [O] + H 2 0 -\u003e HO-CH 2 -CH (OH) -COOH

With vigorous oxidation, the double bond breaks and a mixture of different products is formed, by which the position of the double bond can be determined. Oleic acid C 17 H 33 COOH is one of the most important higher unsaturated acids. It is a colorless liquid that hardens in the cold. Its structural formula: CH 3 - (CH 2) 7 -CH \u003d CH- (CH 2) 7 -COOH.

Derivatives of carboxylic acids

Derivatives of carboxylic acids - These are compounds in which the hydroxyl group of the carboxylic acid is replaced by another functional group.

Simple ethers - organic matterhaving formula R-O-R", where R and R" are hydrocarbon radicals. However, it should be borne in mind that such a group can be a part of other functional groups of compounds that are not ethers

Esters (or esters) - derivatives of oxo acids (both carboxylic and inorganic) with the general formula R k E (\u003d O) l (OH) m, where l ≠ 0, which are formally products of the replacement of hydrogen atoms of hydroxyls -OH of the acid function by a hydrocarbon residue (aliphatic, alkenyl, aromatic or heteroaromatic); are also considered as acyl derivatives of alcohols. The IUPAC nomenclature also includes acyl derivatives of chalcogenide analogs of alcohols (thiols, selenols and tellurols) as esters.

Differ from ethers (ethers), in which two hydrocarbon radicals are connected by an oxygen atom (R 1 -O-R 2)

Amides - derivatives of oxo acids (both carboxylic and mineral) R k E (\u003d O) l (OH) m, (l ≠ 0), which are formally the products of substitution of hydroxyl groups -OH of the acid function for an amino group (unsubstituted and substituted); are also considered as acyl derivatives of amines. Compounds with one, two or three acyl substituents at the nitrogen atom are called primary, secondary and tertiary amides, secondary amides are also called imides.

Amides of carboxylic acids - carboxamides RCO-NR 1 R 2 (where R 1 and R 2 are hydrogen, acyl or an alkyl, aryl or other hydrocarbon radical) are usually referred to as amides; in the case of other acids, in accordance with the IUPAC recommendations, when naming an amide, the name of the acid residue is indicated as a prefix, for example, sulfonic acid amides RS (\u003d O 2 NH 2 are referred to as sulfamides.

Carboxylic acid chloride (acyl chloride) is a carboxylic acid derivative in which the hydroxyl group -OH in the carboxyl group -COOH is replaced by a chlorine atom. General formula R-COCl. The first representative with R \u003d H (formyl chloride) does not exist, although the mixture of CO and HCl in the Guttermann - Koch reaction behaves like the acid chloride.

Receiving

R-COOH + SOCl 2 → R-COCl + SO 2 + HCl

Nitriles - organic compounds general formula R-C≡N, which are formally C-substituted hydrocyanic acid derivatives HC≡N

Capron (poly-ε-caproamide, nylon-6, polyamide 6) - synthetic polyamide fiber obtained from oil, a product of caprolactam polycondensation

[-HN (CH 2) 5 CO-] n

In industry, it is obtained by polymerizing a derivative

Nylon (eng. nylon) is a family of synthetic polyamides used primarily in the production of fibers.

The two most common types of nylon are polyhexamethylene adipinamide ( anid (USSR / Russia), nylon 66 (USA)), often called nylon proper and poly-ε-caproamide ( nylon (USSR / Russia), nylon 6 (USA)). Other species are also known, for example, poly-ω-enantoamide ( enant (USSR / Russia), nylon 7 (USA)) and poly-ω-undecanamide ( undecane (USSR / Russia), nylon 11 (USA), Rilsan (France, Italy)

Anide fiber formula: [-HN (CH 2) 6 NHOC (CH 2) 4 CO-] n. Anide is synthesized by polycondensation of adipic acid and hexamethylenediamine. To ensure the stoichiometric ratio of reagents 1: 1, required to obtain a polymer with a maximum molecular weight, a salt of adipic acid and hexamethylenediamine ( AG-salt):

R \u003d (CH 2) 4, R "\u003d (CH 2) 6

Formula of nylon (nylon-6) fiber: [-HN (CH 2) 5 CO-] n. Synthesis of capron from caprolactam is carried out by hydrolytic polymerization of caprolactam according to the "ring opening - addition" mechanism:

Plastic products can be made of rigid nylon - ecolon, by injecting liquid nylon into a mold under high pressure, which achieves a higher density of the material.

Classification

KETO ACIDS - organic substances, the molecules of which include carboxyl (COOH-) and carbonyl (-CO-) groups; serve as precursors of many compounds that perform important biological functions in the body. Significant metabolic disorders that occur in a number of pathological conditions are accompanied by an increase in the concentration in the human body of certain keto acids

keto enol tautomerism

Methods for producing alpha and beta keto acids

α-Keto acids are produced by oxidation of α-hydroxy acids.

β-Keto acids, due to their instability, are obtained from esters by Claisen condensation.

IN organic chemistry the term "oxidation reaction" means that it is organic compound, while the oxidizing agent in most cases is an inorganic reagent.

Alkenes

KMnO 4 and H 2 O (neutral medium)

3СH2 \u003d CH2 + 2KMnO 4 + 4H 2 O \u003d 3C 2 H 4 (OH) 2 + 2MnO 2 + 2KOH - complete equation

(acidic environment)

there is a break in the double bond:

R-CH 2 \u003d CH 2 -R + [O] → 2R-COOH - schematic equation

Alkylarenes

Eithlbenzene-alkylarene

Ketones

Ketones are very stable to the action of oxidants and are oxidized only by strong oxidants when heated. During the oxidation process, a rupture occurs links C-C on both sides of the carbonyl group, and in general a mixture of four carboxylic acids is obtained:

The oxidation of the ketone is preceded by its enolization, which can take place in both alkaline and acidic media:

Wine acid (dioxysuccinic acid, tartaric acid, 2, 3-dihydroxybutanedioic acid) HOOC-CH (OH) -CH (OH) -COOH is a dibasic hydroxy acid. The salts and anions of tartaric acid are called tartrates.

Three stereoisomeric forms of tartaric acid are known: D - (-) - enantiomer (upper left), L - (+) - enantiomer (upper right) and meso-form (meso-tartaric acid):

Diastereomers - stereoisomers that are not mirror images of each other. Diastereomerism occurs when a compound has multiple stereocenters. If two stereoisomers have opposite configurations of all corresponding stereocenters, then they are enantiomers.

Orbitals exist regardless of whether there is an electron on them (occupied orbitals) or absent (vacant orbitals). The atom of every element, from hydrogen to the last element received so far, has a complete set of all orbitals at all electronic levels. Their filling with electrons occurs as the ordinal number, that is, the charge of the nucleus, increases.

s-Orbitals, as shown above, have a spherical shape and, therefore, the same electron density in the direction of each axis of three-dimensional coordinates:

At the first electronic level of each atom there is only one s-orbital. From the second electronic level in addition to s-orbitals also appear three r-orbital. They have the shape of volumetric eights, this is how the area of \u200b\u200bthe most likely location looks like r-electron in the area atomic nucleus... Each r-orbital is located along one of three mutually perpendicular axes, in accordance with this in the name r-orbitals indicate, using the appropriate index, the axis along which its maximum electron density is located:

In modern chemistry, the orbital is a defining concept that allows us to consider the processes of the formation of chemical bonds and analyze their properties, while focusing on the orbitals of those electrons that participate in the formation of chemical bonds, that is, valence electrons, usually electrons of the last level.

The carbon atom in the initial state at the second (last) electronic level has two electrons on s-orbitals (marked in blue) and one electron per two r-orbital (marked in red and yellow), the third orbital - p z-vacant:

Hybridization.

In the case when a carbon atom participates in the formation of saturated compounds (not containing multiple bonds), one s-orbital and three r-orbitals combine to form new orbitals, which are hybrids of the original orbitals (a process called hybridization). The number of hybrid orbitals is always equal to the number of original ones, in this case, four. The resulting orbital-hybrids are the same in shape and outwardly resemble asymmetric volumetric eights:

The whole structure appears to be inscribed in regular tetrahedron - a prism assembled from regular triangles. In this case, hybrid orbitals are located along the axes of such a tetrahedron, the angle between any two axes is 109 °. The four valence electrons of carbon are located in these hybrid orbitals:

Participation of orbitals in the formation of simple chemical bonds.

The properties of electrons located in four identical orbitals are equivalent, respectively, the chemical bonds formed with the participation of these electrons when interacting with atoms of the same type will be equivalent.

The interaction of a carbon atom with four hydrogen atoms is accompanied by overlapping of elongated hybrid carbon orbitals with spherical hydrogen orbitals. There is one electron on each orbital; as a result of overlapping, each pair of electrons begins to move along the united - molecular orbital.

Hybridization leads only to a change in the shape of the orbitals inside one atom, and the overlap of the orbitals of two atoms (hybrid or conventional) leads to the formation chemical bond between them. In this case ( cm... figure below) the maximum electron density is located along the line connecting two atoms. This link is called an s-link.

The traditional spelling of the structure of the methane formed uses the valence bar symbol instead of overlapping orbitals. For a three-dimensional image of the structure, the valence directed from the plane of the drawing to the viewer is shown in the form of a solid wedge-shaped line, and the valence extending beyond the plane of the drawing is shown as a dashed wedge-shaped line:

Thus, the structure of a methane molecule is determined by the geometry of hybrid carbon orbitals:

The formation of an ethane molecule is similar to the process shown above, the difference is that when the hybrid orbitals of two carbon atoms overlap, education C-C - communications:

The geometry of the ethane molecule resembles methane, bond angles are 109 °, which is determined by the spatial arrangement of the hybrid carbon orbitals:

Participation of orbitals in the formation of multiple chemical bonds.

The ethylene molecule is also formed with the participation of hybrid orbitals, however, one s-orbital and only two r-orbitals ( p x and rU), the third orbital is p zdirected along the axis z, does not participate in the formation of hybrids. From the original three orbitals, three hybrid orbitals arise, which are located in the same plane, forming a three-beam star, the angles between the axes are 120 °:

Two carbon atoms attach four hydrogen atoms, and also connect to each other, forming a C-C s-bond:

Two orbitals p zthat did not participate in hybridization, overlap, their geometry is such that the overlap does not occur along the line communication C-C, but above and below it. As a result, two regions with increased electron density are formed, where two electrons (marked in blue and red) are located, participating in the formation of this bond. Thus, one molecular orbital is formed, consisting of two regions separated in space. The bond in which the maximum electron density is located outside the line connecting two atoms is called the p-bond:

The second valence feature in the designation of a double bond, which has been widely used to depict unsaturated compounds for more than one century, in the modern sense implies the presence of two regions with increased electron density located on opposite sides of the C-C bond line.

The structure of the ethylene molecule is given by the geometry of hybrid orbitals, the valence angle H-C-H - 120 °:

In the formation of acetylene, one one is involved in hybridization. s-orbital and one p x-orbital (orbitals p yand p z, do not participate in the formation of hybrids). The two formed hybrid orbitals are located on the same line along the axis x:

The overlapping of hybrid orbitals with each other and with the orbitals of hydrogen atoms leads to the formation of s-bonds C-C and C-H, depicted using a simple valence line:

Two pairs of remaining orbitals p yand p z overlap. In the figure below, colored arrows show that, for purely spatial reasons, overlapping of orbitals with the same indices is most likely x-x and ooh... As a result, two p-bonds are formed, surrounding a simple s-bond С-С:

As a result, the acetylene molecule has a rod-like shape:

In benzene, the backbone of the molecule is assembled from carbon atoms having hybrid orbitals composed of one s- and two r-orbitals arranged in the form of a three-pointed star (like ethylene), r-orbitals not participating in hybridization are shown as translucent:

In the formation of chemical bonds, vacant ones, that is, orbitals that do not contain electrons (), can also participate.

High level orbitals.

Starting from the fourth electronic level, atoms have five d-orbitals, their filling with electrons occurs in transition elements, starting with scandium. Four d-orbital have the form of voluminous quatrefoils, sometimes called "clover leaf", they differ only in orientation in space, the fifth d-orbital is a three-dimensional figure threaded into a ring:

d-Orbitals can form hybrids with s-and p-orbitals. Parameters d-orbitals are usually used in the analysis of the structure and spectral properties of transition metal complexes.

Starting from the sixth electronic level, atoms have seven f-orbitals, their filling with electrons occurs in the atoms of lanthanides and actinides. f-Orbitals have a rather complex configuration, the figure below shows the shape of three of seven such orbitals, which have the same shape and are oriented in space in different ways:

f-Orbitals are rarely used when discussing the properties of various compounds, since the electrons located on them practically do not participate in chemical transformations ..

Perspectives.

The eighth electronic level contains nine g-orbitals. Elements containing electrons in these orbitals should appear in the eighth period, while they are unavailable (in the near future, it is expected to receive element number 118, the last element of the seventh period of the Periodic system, its synthesis is carried out at the Joint Institute nuclear research in Dubna).

The form g-orbitals, calculated by quantum chemistry methods, is even more complex than that of f-orbitals, the area of \u200b\u200bthe most probable location of the electron in this case looks very bizarre. Below is the appearance of one of nine such orbitals:

In modern chemistry, the concept of atomic and molecular orbitals is widely used in the description of the structure and reaction properties of compounds, also in the analysis of the spectra of various molecules, in some cases - to predict the possibility of reactions.

Mikhail Levitsky

An atomic orbital with spherical symmetry (Fig. 3) is usually denoted as s -orbital (s-AO), and the electrons in it - ass-electrons.

The radius of the atomic s-orbital increases with increasing energy level number; The 1s-AO is located inside the 2s-AO, the latter is inside the 3s-AO, etc. with the center corresponding to the atomic nucleus. On the whole, the structure of the electron shell of an atom in the orbital model appears to be layered. Each energy level containing electrons is geometrically considered as electronic layer.

For the abbreviated designation of an electron occupying an atomic s-orbital, the designation of the s-AO itself is used with a superscript indicating the number of electrons. For example, 1s is the designation of a single electron in a hydrogen atom.

The energy level number answers the principal quantum number, and the type of orbital - orbital quantum number.

2s Li \u003d 1s 2s ,Be \u003d 1s 2s

1s H \u003d 1s , He

Electronic formula combined with energy diagramthe electron shell of the atom (Fig. 3) reflect its electronic configuration.

An atomic orbital with rotational (axial) symmetry is usually denoted as p-orbital (p -AO) (fig. 3); the electrons in it are p-electrons.

Each atomic p-orbital can accept (at maximum filling) two electrons, like any other AO. These electrons collectively occupy both halves p-orbital. Each atomic energy level (except for the first) has three atomic orbitals, which correspond to the maximum population of six electrons.

All three p- AOs of the same energy level differ from each other in spatial arrangement; their own axes, passing through both halves of the orbital and perpendicular to its nodal plane, form a Cartesian coordinate system (notation for the proper axes x, y, z). Therefore, at each energy level there is a set of three atomic p-orbitals: p x -, p y - and p z -AO. The letters x, y, z correspond to magnetic quantum number, which makes it possible to judge the effect of an external magnetic field on the electron shell of an atom.

Atomic s-orbitals are available at all energy levels, atomic p-orbital - at all levels except the first. At the third and subsequent energy levels to one s-AO and three p-AO joins five atomic orbitals, named d -orbitals(Fig. 4), and at the fourth and subsequent levels there are seven more atomic orbitals, called f -orbitals.

2.3. Energy sublevels

multielectron atom. principles

building an electronic shell

Quantum-mechanical calculations show that in many-electron atoms the energy of electrons of the same level is not the same; electrons fill atomic orbitals different types and have different energies.

The energy level is characterized by principal quantum numbern. For all known elements, the values \u200b\u200bof n vary from 1 to 7. Electrons in a multielectron atom located in mostly (unexcited) state, occupy energy levels from the first to the seventh.

The energy sublevel is characterized by orbital quantum numberl. For each level (n \u003d const) the quantum number l takes everything integer values from 0 to (n-1), for example, with n \u003d 3 values l will be 0, 1 and 2. The orbital quantum number determines the geometric shape (symmetry) of the orbitals s-, p-, d-, f-sublevel. Obviously, in all cases n\u003e l; for n \u003d 3 the maximum value l is equal to 2.

The existing sublevels for the first four energy levels, the number of atomic orbitals and electrons in them are given in Table 1.

The regularity of filling the electronic shells of atoms is determined by the exclusion principle established in 1925 by the Swiss physicist Pauli.

Pauli principle: an atom cannot contain two electrons in identical states.

The difference between electrons occupying different atomic orbitals of one sublevel ( n, l = const), apart from the s-sublevel, is characterized by magnetic quantum numberm. This number is called magnetic because it characterizes the behavior of electrons in an external magnetic field. If the value l determines the geometric shape of the atomic orbitals of the sublevel, then the value of the quantum number m establishes the relative spatial position of these orbitals.

Table 1

Energy levels, sublevels and orbitals

multielectron atom

Energy level n	Energy sublevel		Orbital designation	Orbi number n	Number of electrons 2n
		orbital view

Magnetic quantum number m l within this sublevel ( n, l = const) takes all integer values \u200b\u200bfrom + l before - l, including zero. For the s-sublevel ( n = const, l = 0 ) only one value is possible m l = 0, whence it follows that the s-sublevel of any (from the first to the seventh) energy level contains one s-AO.

For the p-sublevel ( n> 1, l = 1) m l can take three values \u200b\u200b+1, 0, -1, therefore, the p-sublevel of any (from the second to the seventh) energy level contains three p-AOs.

For the d-sublevel ( n> 2, l = 2) m l has five values \u200b\u200b+2, +1, 0, -1, -2 and, as a result, d- sublevel of any (from the third to the seventh) energy level necessarily contains five d- JSC.

Similarly, for each f- sublevel ( n> 3, l = 3) m has seven values \u200b\u200b+3, +2, +1, 0, -1, -2, -3 and therefore any f- sublevel contains seven f- JSC.

Thus, each atomic orbital is uniquely determined by three quantum numbers - the mainn , orbital l and magnetic m l .

When n = const all values \u200b\u200brelated to a given energy level are strictly defined land at l = const – all values \u200b\u200brelated to this energy sublevel m l .

Due to the fact that each orbital can be filled with two electrons as much as possible, the number of electrons that can be located at each energy level and sublevel is twice the number of orbitals at a given level or sublevel. Since electrons in the same atomic orbital have the same quantum numbers n, l and m l , then for two electrons in one orbital, the fourth is used, spin quantum numbers, which is determined by the electron spin.

According to Pauli's principle, it can be argued that every electron in an atom is uniquely characterized by its own set of four quantum numbers - the mainn , orbitall , magneticm and spins.

The population of energy levels, sublevels and atomic orbitals with electrons obeys the following rule (the principle of minimum energy): in an unexcited state, all electrons have the lowest energy.

This means that each of the electrons filling the atomic shell occupies such an orbital so that the atom as a whole has a minimum energy. A sequential quantum increase in the energy of the sublevels occurs in the following order:

1s – 2s – 2p – 3s – 3p – 4s – 3d – 4p – 5s - …..

The filling of atomic orbitals within one energy sublevel occurs in accordance with the rule formulated by the German physicist F. Hund (1927).

Hund's rule: atomic orbitals belonging to the same sublevel are filled each first with one electron, and then they are filled with the second electrons.

Hund's rule is also called the principle of maximum multiplicity, i.e. maximum possible parallel direction of the electron spins of one energy sublevel.

At the highest energy level of a free atom, there can be no more than eight electrons.

Electrons that are at the highest energy level of the atom (in the outer electron layer) are called external; the number of outer electrons in an atom of any element is never more than eight. For many elements, it is the number of external electrons (with filled internal sublevels) that largely determines their chemical properties. For other electrons, whose atoms have an unfilled internal sublevel, for example 3 d- sublevel at atoms of elements such as Sc, Ti, Cr, Mn, etc., chemical properties depend on the number of both internal and external electrons. All of these electrons are called valence; in the abbreviated electronic formulas of atoms, they are written after the symbol of the atomic core, that is, after the expression in square brackets.

The physical and chemical properties of atoms, and hence of matter as a whole, are largely determined by the characteristics of the electron cloud around the atomic nucleus. A positively charged nucleus attracts negatively charged electrons. Electrons revolve around the nucleus so fast that it is impossible to pinpoint their exact location. The electrons moving around the nucleus can be compared to a cloud or fog, in some places more or less dense, in others - completely rarefied. The shape of the electron cloud, as well as the probability of finding an electron at any point, can be determined by solving the corresponding equationsquantum mechanics... The regions where electrons are most likely to be found are called orbitals. Each orbital is characterized by a certain energy, and there can be no more than two electrons on it. Usually, the lowest-energy orbitals closest to the core are filled first, then the higher-energy orbitals, etc.

A collection of electron orbitals with similar energies forms a layer (i.e., a shell, or energy level). Energy levels are numbered starting from the atomic nucleus: 1, 2, 3,... ... The farther from the nucleus, the more spacious the layers are and the more orbitals and electrons they can accommodate. So, onn -th level n 2 orbitals, and they can accommodate up to 2n 2 electrons. For known elements, electrons are found only at the first seven levels, and only the first four of them are filled.

There are four types of orbitals, they are designateds , p , d and f ... Each level (layer) has ones -orbital, which contains the electrons most strongly bound to the nucleus. It is followed by threep -orbital, five d -orbitals and finally sevenf -orbitals.

Shell n	Orbitals n 2	Orbital type	Number of electrons 2n 2
		s, p
		s, p, d
		s, p, d, f

s - Orbitals are spherical,p – the shape of a dumbbell or two touching spheres, atd -orbitals - 4 "petals", while f -orbitals - 8. In section, these orbitals look something like the one shown in the figure.

Three r-orbitals are oriented in space along the axes of a rectangular coordinate system and are designated accordinglyp x, p y and p z; d- and f -orbitals are also located at certain angles to each other; sphericals -orbitals have no spatial orientation.

Every next item in the period has an atomic number one higher than the number of the previous element, and contains one more electron. This extra electron occupies the next orbital in ascending order. It should be borne in mind that the electronic layers are diffuse and the energy of some orbitals of the outer layers is lower than that of the inner ones. Therefore, for example, it is first filled withs -orbital of the fourth level (4s -orbital), and only after it is filling 3d -orbital. Orbitals are usually filled in the following order: 1s , 2 s , 2 p , 3 s , 3 p , 4 s , 3 d , 4 p , 5 s , 4 d , 5 p , 6 s , 4 f , 5 d , 6 p , 7 s . In the notation used to represent the electronic configuration of an element, the superscript next to the letter denoting an orbital indicates the number of electrons in that orbital. For example, the entry1 s 2 2 s 2 2 p 5 means that 1s -orbital of an atom there are two electrons, 2s -orbitals - two, for 2r - five electrons. Neutral atoms with 8 electrons on the outer electron shell (i.e., filleds - and r -orbital), so stable that they practically do not enter into any chemical reactions... These are the atoms of inert gases. Electronic configuration of helium1 s 2, neon - 2 s 2 2 p 6, argon - 3 s 2 3 p 6, krypton - 4 s 2 3 d 10 4 p 6, xenon - 5 s 2 4 d 10 5 p 6 and finally radon -6 s 2 4 f 14 5 d 10 6 p 6 .

Ticket№1

Chemistry - one of the most important and extensive areas of natural science, the science of substances, their properties, structure and transformations that occur as a result of chemical reactions, as well as the fundamental laws that govern these transformations. Since all substances are composed of atoms that, thanks 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 chemical elements and their compounds, as well as the laws governing various chemical reactions. Chemistry has much in common with physics and biology, in fact, the border between them is conditional. Modern chemistry is one of the most extensive disciplines of all natural sciences. Chemistry as an independent discipline was defined in the XVI-XVII centuries, after a number of scientific discoveries that substantiated the mechanistic picture of the world, the development of industry, the creation of factories, the emergence of a bourgeois society. However, due to the fact that chemistry, unlike physics, could not be expressed quantitatively, there was controversy over whether chemistry is a quantitatively reproducible science or is it some other kind of cognition. 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 with him, he discovered carbon dioxide. In 1672, Boyle discovered that when metals are burned, their mass increases, and he explained this by the capture of "weighty particles of flame". Chemistry subject... One of the main objects of chemistry is the substances that make up all the bodies around us. Anything that has mass and volume is called a body. Raindrops, frost on branches, fog - bodies consisting of one substance - water. The phenomena in which new substances are formed from some substances are called chemical. Chemistry deals with the study of such phenomena. Chemistry is the science of transforming substances. This definition has become classic. Chemistry studies the composition and structure of substances, the conditions and ways of converting 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, thanks to which it is possible to transform some substances into others as a result of chemical phenomena, or chemical reactions. Theoretical basis inorganic chemistry - periodic law and periodic system of elements of Mendeleev. Modern inorganic chemistry studies the structure and properties of inorganic substances using not only chemical, but also physical methods (eg spectroscopy).

Ticket number 2

According to the Heisenberg uncertainty principle, the position and moment of an electron cannot be simultaneously determined with absolute precision. However, despite the impossibility of accurately determining the position of the electron, you can indicate the probability of finding the electron in a certain position at any 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 equated with the concept of orbit, which is used in Bohr's theory. An orbit in Bohr's theory means 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 three-dimensional bounding surfaces. The areas of space bounded by these surfaces are usually chosen so that the probability of finding one electron inside them is 95%. In fig. 1.18 schematically depicts the shape of the s and p orbitals. The s-orbital is spherical and 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. Such a distribution is usually called an electron cloud.

Schrödinger's equation - an equation describing the change in space and time of a pure state given by a wave function in Hamiltonian quantum systems. Plays the same important role in quantum mechanics as the equation of Newton's second law in classical mechanics. It can be called the equation of motion of a quantum particle. Installed by Erwin Schrödinger in 1926. Schrödinger's 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 coefficient of expansion of the state vector in the basis (usually coordinate):

where is the coordinate basis vector, and is the wave function in coordinate representation. | ψ | 2 - the probability of finding a particle in a given area of \u200b\u200bspace

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

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

Ticket number 3

Atomic orbital - one-electron wave function in a spherical symmetrical electric field atomic nucleusasking the main n,orbital l and magnetic m quantum numbers.

The name "orbital" (not orbit) reflects the geometric concept of stationary states electron in atom; this special name reflects the fact that the states of an electron in an atom are described by the laws quantum mechanics and differs from classic movement along trajectories... The set of atomic orbitals with the same principal quantum number n is one electronic shell.

Quantum numbers and nomenclature of orbitals

Radial probability density distribution for atomic orbitals at different n and l.

Principal Quantum Number n can take any positive integer values, starting from one ( n \u003d 1,2,3, ... ∞) and determines the total energy of an electron in a given orbital (energy level):

Energy for n \u003d ∞ corresponds to one-electron ionization energy for a given energy level.

The orbital quantum number (also called the azimuthal or complementary quantum number) defines angular momentum electron and can take integer values \u200b\u200bfrom 0 to n - 1 (l = 0,1, …, n - 1). Moment of impulse in this case is given by the relation

Atomic orbitals are usually called by the letter designation of their orbital number:

Magnetic quantum number m l determines the projection of the orbital angular momentum on the direction of the magnetic field and can take integer values \u200b\u200bin 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 that differ in the value of the spin quantum number s (back). This prohibition is determined by the Pauli principle. The order of filling the orbitals of the same level with electrons (orbitals with the same principal quantum number n) is determined by the Klechkovsky rule, the order of filling of orbitals with electrons within one sublevel (orbitals with the same values \u200b\u200bof the principal quantum number n and the orbital quantum number l) is determined by the Hund Rule.

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

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

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

Formulation of the Klechkovsky rule

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

When filling the orbital shells of the atom, they are more preferable (more energetically favorable), and, therefore, those states are filled earlier for which the sum of the principal quantum number and the secondary (orbital) quantum number, i.e., has a smaller value.

The 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 must be maximum.

This means that in each of the sublayer orbitals, first one electron is filled, and only after the empty orbitals are exhausted, a second electron is added to this orbital. In this case, on the same orbital there are two electrons with half-integer spins of the opposite sign, 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), is 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 reducing properties of the corresponding simple substance also substantially depend on the ionization energy of the atom.

For a multielectron atom, there are also concepts of the second, third, etc. ionization potentials, which represent 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 endoenergetic value (this is understandable, since in order to detach an electron from an atom, one needs to apply energy, this cannot happen spontaneously).

The following factors have the most significant influence on the ionization energy of an atom:

the effective charge of the nucleus, which is a function of the number of electrons in the atom, shielding the nucleus and located in deeper internal orbitals;

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

a measure of the penetrating power of this electron;

interelectronic repulsion among the outer (valence) electrons.

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

Ionization energies of elements are measured in Electron volts per atom or Joule per mole.

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

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

In contrast to 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. Values \u200b\u200bfound on the basis of certain assumptions are taken as atomic radii. Theoretically, the so-called orbital radii, or the distance from the center of the nucleus to the most distant maximum of the electron density, are calculated.

The periodicity of changes 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 they 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, which coincides 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.

Form of existence chemical elements in free form are simple substances (singleton)

Currently, D.I.Mendeleev's Periodic Law 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 periodically dependent 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 "super-long". In the "extra-long" version, each period occupies exactly one line. In the "long" version, lanthanides and actinides are removed from the general table, making it more compact. In the "short" notation, in addition to this, the fourth and subsequent periods occupy 2 lines; symbols of 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 canceled by IUPAC in 1989. Despite the recommendation to use the long form, the short form continues to be cited in a large number of Russian reference books and manuals after this time. The short form is completely excluded from modern foreign literature; instead, the long form is used.

Ticket number 10

Molecular Orbital Method Most Important 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 main contribution to the formation of bonds comes from the electrons of the outer (valence) shells, they are usually limited to considering only these electrons. In chemistry, the MO method (especially in the form of MO LCAO) is important in that it allows obtaining data on the structure and properties of molecules based on the corresponding characteristics of atoms. Therefore, almost all modern concepts of chemical bonding and chemical reactivity are based on the concepts of the MO method. Molecular orbital theory (MO) gives an idea of \u200b\u200bthe distribution of electron density and explains the properties of molecules. In this theory, the quantum mechanical dependences for the atom are extended to more complex system - a molecule. The molecule is viewed 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. Unlike single-center orbitals of atoms, orbitals of molecules are multicenter, that is, molecules have common orbitals for two or more atomic nuclei. Each molecular orbital has a certain energy, approximately characterized by the corresponding ionization potential.

Two-center molecular orbitals

The molecular orbital method uses the concept of a molecular orbital (similar to an atomic orbital for an atom) to describe the distribution of electron density in a molecule. 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 bonding region is described by the bonding molecular orbital, in the loosening region - by the loosening molecular orbital. The distribution of electrons over molecular orbitals follows the same rules as the distribution of electrons over atomic orbitals in an isolated atom. Molecular orbitals are formed by specific combinations of atomic orbitals. Their number, energy and shape can be deduced from the number, energy and shape of the orbiters of the atoms that make up the molecule. ????????????????????????????? ??????????????????????????????????????????????????? ???

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

Ionic bond - a strong chemical bond formed between atoms with a large difference (\u003e 1.7 on the Pauling scale) of electronegativities, in which the total electron paraplenosity goes to an atom with a greater electronegativity. This is the attraction of ions as oppositely charged bodies. An example is the CsF compound, in which the "degree of ionicity" is 97%. Let us consider the method of formation by the example of sodium chloride NaCl. The electronic configuration of sodium and chlorine atoms can be represented: 11 Na 1s2 2s2 2p 6 3s1; 17 Cl 1s2 2s2 2p6 Зs2 3p5 How are atoms with incomplete energy levels. Obviously, for their completion, it is easier for a sodium atom to donate one electron than to attach seven, and it is easier for a chlorine atom to attach one electron than to donate seven. In chemical interaction, the sodium atom completely donates one electron, and the chlorine atom accepts it. It can be schematically written as: Na. - l е -\u003e Na + sodium ion, stable eight-electron 1s2 2s2 2p6 shell due to the second energy level. : Cl + 1e -\u003e .Cl - chlorine ion, stable eight-electron shell. The forces of electrostatic attraction arise between the Na + and Cl- ions, as a result of which a compound is formed. Ionic bond is an extreme case of polarization of a covalent polar bond. Formed between typical metal and non-metal. In this case, the electrons of the metal are completely transferred to the non-metal. Ions are formed.

If a chemical bond is formed between atoms that have a very large difference in electronegativity (EO\u003e 1.7 according to Pauling), then the total electron pair is completely transferred to the atom with a higher EO. This results in the formation of a compound of oppositely charged ions:

An electrostatic attraction occurs between the formed ions, which is called ionic bond. Rather, this look is convenient. In fact, the pure ionic bond between atoms is not realized anywhere or almost nowhere; usually, in fact, the bond is partially ionic and partially covalent. At the same time, the bond 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 tend to different densest packing of the corresponding ions.

Characteristic such compounds are good solubility in polar solvents (water, acids, etc.). This is due to the charging of the parts of the molecule. In this case, the solvent dipoles are attracted to the charged ends of the molecule, and, as a result of Brownian motion, "pull" the substance molecule apart and surround them, preventing them from being combined again. The result is ions surrounded by solvent dipoles.

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

A metal bond is a chemical bond caused by the presence of relatively free electrons. It is typical for both pure metals and their alloys and intermetallic compounds.

Metal link mechanism

Positive metal ions are located at all nodes of the crystal lattice. Between them, valence electrons, detached from atoms during the formation of ions, move randomly, like gas molecules. These electrons act as cement to hold the positive ions together; otherwise, the lattice would disintegrate under the action of repulsive forces between the ions. At the same time, electrons are held by ions within the crystal lattice and cannot leave it. Communication forces are not localized and 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 lattices with close packing of atoms: cubic body-centered, cubic face-centered, and hexagonal.

In a cubic body-centered lattice (BCC), atoms are located at the vertices of the cube and one atom in 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 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 provide 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 are not broken.

Van der Waals forces - the 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 the 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 (constant and induced). The name comes from the fact that these forces are the cause of the internal pressure correction in the equation of state for a real van der Waals 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

Van der Waals interactions consist of three types of weak interactions:

Orientation forces, dipole-dipole attraction. Carried out between molecules that are permanent dipoles. An example is HCl in liquid and solid state. The energy of this 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 this interaction is inversely proportional to the sixth power of the distance between the dipoles.

Induction attraction. Interaction between permanent dipole and induced (induced). The energy of this 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 the experimental data: the scale of the Debye temperature anisotropy and, accordingly, the scale of the anisotropy of lattice reflection. 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 (internal) 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) (Peyron's salt) Pt (NH 3) 2 Cl 2, the central platinum atom is bonded to four ligands.

The concept of the coordination number is also used to characterize the central atom in molecules, mainly for those cases when the number of chemically bound 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 when 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 the nearest neighbors of an atom. It can 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 nonmetal, for example, silicon and phosphorus in the 2– and - anions, respectively. CA forms chemical bonds with ligands, coordinates them around itself. As a result, a coordination compound is formed.

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