What is the electronic structure of an atom. Structure of atoms of chemical elements

Electrons

The concept of atom arose in ancient world to designate particles of matter. Translated from Greek atom means "indivisible".

Irish physicist Stoney, based on experiments, came to the conclusion that electricity is transferred tiny particles, existing in the atoms of all chemical elements. In 1891, Stoney proposed to call these particles electrons, which means “amber” in Greek. A few years after the electron got its name, English physicist Joseph Thomson and French physicist Jean Perrin proved that electrons carry a negative charge. This is the smallest negative charge, which in chemistry is taken as one (-1). Thomson even managed to determine the speed of the electron (the speed of the electron in the orbit is inversely proportional to the orbit number n. The radii of the orbits increase in proportion to the square of the orbit number. In the first orbit of the hydrogen atom (n=1; Z=1) the speed is ≈ 2.2·106 m/ s, that is, about a hundred times less than the speed of light c = 3·108 m/s) and the mass of the electron (it is almost 2000 times less than the mass of the hydrogen atom).

State of electrons in an atom

The state of an electron in an atom is understood as a set of information about the energy of a particular electron and the space in which it is located. An electron in an atom does not have a trajectory of motion, i.e. we can only talk about the probability of finding it in the space around the nucleus.

It can be located in any part of this space surrounding the nucleus, and the totality of its various positions is considered as an electron cloud with a certain negative charge density. Figuratively, this can be imagined this way: if it were possible to photograph the position of an electron in an atom after hundredths or millionths of a second, as in a photo finish, then the electron in such photographs would be represented as dots. If countless such photographs were superimposed, the picture would be of an electron cloud with the greatest density where there would be the most of these points.

Space around atomic nucleus, in which the electron is most likely to be found is called an orbital. It contains approximately 90% electronic cloud, and this means that about 90% of the time the electron is in this part of space. They are distinguished by shape 4 currently known types of orbitals, which are designated by Latin letters s, p, d and f. Graphic image some forms electron orbitals shown in the figure.

The most important characteristic of the motion of an electron in a certain orbital is energy of its connection with the nucleus. Electrons with similar energy values ​​form a single electron layer, or energy level. Energy levels are numbered starting from the nucleus - 1, 2, 3, 4, 5, 6 and 7.

The integer n, indicating the number of the energy level, is called the principal quantum number. It characterizes the energy of electrons occupying a given energy level. Electrons of the first energy level, closest to the nucleus, have the lowest energy. Compared to electrons of the first level, electrons of subsequent levels will be characterized by a large supply of energy. Consequently, the electrons of the outer level are least tightly bound to the atomic nucleus.

The largest number of electrons at an energy level is determined by the formula:

N = 2n 2 ,

where N - maximum number electrons; n is the level number, or the main quantum number. Consequently, at the first energy level closest to the nucleus there can be no more than two electrons; on the second - no more than 8; on the third - no more than 18; on the fourth - no more than 32.

Starting from the second energy level (n = 2), each of the levels is divided into sublevels (sublayers), slightly different from each other in the binding energy with the nucleus. The number of sublevels is equal to the value of the main quantum number: the first energy level has one sublevel; the second - two; third - three; fourth - four sublevels. The sublevels, in turn, are formed by orbitals. Each valuen corresponds to the number of orbitals equal to n.

Sublevels are usually designated with Latin letters, as well as the shape of the orbitals of which they are composed: s, p, d, f.

Protons and Neutrons

An atom of any chemical element is comparable to a tiny solar system. Therefore, this model of the atom, proposed by E. Rutherford, is called planetary.

The atomic nucleus, in which the entire mass of the atom is concentrated, consists of particles of two types - protons and neutrons.

Protons have a charge equal to charge electrons, but opposite in sign (+1), and mass, equal to mass hydrogen atom (it is taken as a unit in chemistry). Neutrons carry no charge, they are neutral and have a mass equal to the mass of a proton.

Protons and neutrons together are called nucleons (from the Latin nucleus - nucleus). The sum of the number of protons and neutrons in an atom is called the mass number. For example, the mass number of an aluminum atom is:

13 + 14 = 27

number of protons 13, number of neutrons 14, mass number 27

Since the mass of the electron, which is negligibly small, can be neglected, it is obvious that the entire mass of the atom is concentrated in the nucleus. Electrons are designated e - .

Since the atom electrically neutral, then it is also obvious that the number of protons and electrons in an atom is the same. It is equal to the serial number of the chemical element assigned to it in the Periodic Table. The mass of an atom consists of the mass of protons and neutrons. Knowing the atomic number of the element (Z), i.e. the number of protons, and the mass number (A), equal to the sum numbers of protons and neutrons, you can find the number of neutrons (N) using the formula:

N = A - Z

For example, the number of neutrons in an iron atom is:

56 — 26 = 30

Isotopes

Varieties of atoms of the same element that have same charge nuclei but different mass numbers are called isotopes. Chemical elements found in nature are a mixture of isotopes. Thus, carbon has three isotopes with masses 12, 13, 14; oxygen - three isotopes with masses 16, 17, 18, etc. The relative atomic mass of a chemical element usually given in the Periodic Table is the average value of the atomic masses of a natural mixture of isotopes of a given element, taking into account their relative abundance in nature. Chemical properties The isotopes of most chemical elements are exactly the same. However, hydrogen isotopes vary greatly in properties due to the dramatic multiple increase in their relative atomic mass; they are even given individual names and chemical symbols.

Elements of the first period

Diagram of the electronic structure of the hydrogen atom:

Diagrams of the electronic structure of atoms show the distribution of electrons across electronic layers (energy levels).

Graphic electronic formula of the hydrogen atom (shows the distribution of electrons by energy levels and sublevels):

Graphic electronic formulas of atoms show the distribution of electrons not only among levels and sublevels, but also among orbitals.

In a helium atom, the first electron layer is complete - it has 2 electrons. Hydrogen and helium are s-elements; The s-orbital of these atoms is filled with electrons.

For all elements of the second period the first electronic layer is filled, and electrons fill the s- and p-orbitals of the second electron layer in accordance with the principle of least energy (first s and then p) and the Pauli and Hund rules.

In the neon atom, the second electron layer is complete - it has 8 electrons.

For atoms of elements of the third period, the first and second electronic layers are completed, so the third electronic layer is filled, in which electrons can occupy the 3s-, 3p- and 3d-sublevels.

The magnesium atom completes its 3s electron orbital. Na and Mg are s-elements.

In aluminum and subsequent elements, the 3p sublevel is filled with electrons.

Elements of the third period have unfilled 3d orbitals.

All elements from Al to Ar are p-elements. The s- and p-elements form the main subgroups in the Periodic Table.

Elements of the fourth - seventh periods

A fourth electron layer appears in potassium and calcium atoms, and the 4s sublevel is filled, since it has lower energy than the 3d sublevel.

K, Ca - s-elements included in the main subgroups. For atoms from Sc to Zn, the 3d sublevel is filled with electrons. These are 3d elements. They are included in secondary subgroups, their outermost electronic layer is filled, and they are classified as transition elements.

Pay attention to the structure electron shells chromium and copper atoms. In them, one electron “fails” from the 4s to the 3d sublevel, which is explained by the greater energy stability of the resulting electronic configurations 3d 5 and 3d 10:

In the zinc atom, the third electron layer is complete - all sublevels 3s, 3p and 3d are filled in it, with a total of 18 electrons. In the elements following zinc, the fourth electron layer, the 4p sublevel, continues to be filled.

Elements from Ga to Kr are p-elements.

The krypton atom has an outer layer (fourth) that is complete and has 8 electrons. But there can be a total of 32 electrons in the fourth electron layer; the krypton atom still has unfilled 4d and 4f sublevels. For elements of the fifth period, sublevels are being filled in the following order: 5s - 4d - 5p. And there are also exceptions related to “ failure» electrons, y 41 Nb, 42 Mo, 44 ​​Ru, 45 Rh, 46 Pd, 47 Ag.

In the sixth and seventh periods, f-elements appear, i.e., elements in which the 4f- and 5f-sublevels of the third outside electronic layer are being filled, respectively.

4f elements are called lanthanides.

5f elements are called actinides.

The order of filling electronic sublevels in the atoms of elements of the sixth period: 55 Cs and 56 Ba - 6s elements; 57 La … 6s 2 5d x - 5d element; 58 Ce - 71 Lu - 4f elements; 72 Hf - 80 Hg - 5d elements; 81 T1 - 86 Rn - 6d elements. But here, too, there are elements in which the order of filling the electronic orbitals is “violated,” which, for example, is associated with the greater energy stability of half and fully filled f-sublevels, i.e. nf 7 and nf 14. Depending on which sublevel of the atom is filled with electrons last, all elements are divided into four electron families, or blocks:

• s-elements. The s-sublevel of the outer level of the atom is filled with electrons; s-elements include hydrogen, helium and elements of the main subgroups of groups I and II.

• p-elements. The p-sublevel of the outer level of the atom is filled with electrons; p-elements include elements of the main subgroups of groups III-VIII.

• d-elements. The d-sublevel of the pre-external level of the atom is filled with electrons; d-elements include elements of side subgroups Groups I-VIII, i.e. elements of inserted decades of large periods located between the s- and p-elements. They are also called transition elements.

• f-elements. The f-sublevel of the third outer level of the atom is filled with electrons; these include lanthanides and antinoids.

The Swiss physicist W. Pauli in 1925 established that in an atom in one orbital there can be no more than two electrons having opposite (antiparallel) spins (translated from English as “spindle”), i.e., having such properties that conditionally can be imagined as the rotation of an electron around its imaginary axis: clockwise or counterclockwise.

This principle is called Pauli principle. If there is one electron in the orbital, then it is called unpaired; if there are two, then these are paired electrons, i.e. electrons with opposite spins. The figure shows a diagram of the division of energy levels into sublevels and the order in which they are filled.

Very often, the structure of the electronic shells of atoms is depicted using energy or quantum cells - so-called graphical electronic formulas are written. For this notation, the following notation is used: each quantum cell is designated by a cell that corresponds to one orbital; Each electron is indicated by an arrow corresponding to the spin direction. When writing a graphical electronic formula, you should remember two rules: Pauli's principle and F. Hund's rule, according to which electrons occupy free cells first one at a time and at the same time have same value back, and only then mate, but the backs, according to the Pauli principle, will already be in opposite directions.

Hund's rule and Pauli's principle

Hund's rule- rule quantum chemistry, which determines the order of filling the orbitals of a certain sublayer and is formulated in the following way: total value the spin quantum number of electrons of a given sublayer should be maximum. Formulated by Friedrich Hund in 1925.

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

Another wording: Lower in energy lies the atomic term for which two conditions are satisfied.

1. Multiplicity is maximum
2. If the multiplicities coincide, the total orbital moment L is maximum.

Let us analyze this rule using the example of filling p-sublevel orbitals p-elements of the second period (that is, from boron to neon (in the diagram below, horizontal lines indicate orbitals, vertical arrows indicate electrons, and the direction of the arrow indicates the spin orientation).

Klechkovsky's rule

Klechkovsky's rule - As the total number of electrons in atoms increases (with an increase in the charges of their nuclei, or the serial numbers of chemical elements), atomic orbitals are populated in such a way that the appearance of electrons in orbitals with more high energy depends only on the main quantum number n and does not depend on all the others quantum numbers, including from l. Physically, this means that in a hydrogen-like atom (in the absence of interelectron repulsion), the orbital energy of an electron is determined only by the spatial distance of the electron charge density from the nucleus and does not depend on the characteristics of its motion in the field of the nucleus.

The empirical Klechkovsky rule and the ordering scheme that follows from it are somewhat contradictory to the real energy sequence of atomic orbitals only in two similar cases: for atoms Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, Pt, Au, there is a “failure” of an electron with s -sublevel of the outer layer to the d-sublevel of the previous layer, which leads to an energetically more steady state atom, namely: after filling orbital 6 with two electrons s

As you know, everything material in the Universe consists of atoms. Atom is smallest unit matter, which carries its properties. In turn, the structure of the atom is made up of a magical trinity of microparticles: protons, neutrons and electrons.

Moreover, each of the microparticles is universal. That is, you cannot find two different protons, neutrons or electrons in the world. They are all absolutely similar to each other. And the properties of the atom will depend only on quantitative composition these microparticles in general structure atom.

For example, the structure of a hydrogen atom consists of one proton and one electron. The next most complex atom, helium, consists of two protons, two neutrons and two electrons. Lithium atom - made of three protons, four neutrons and three electrons, etc.

Atomic structure (from left to right): hydrogen, helium, lithium

Atoms combine to form molecules, and molecules combine to form substances, minerals, and organisms. The DNA molecule, which is the basis of all living things, is a structure assembled from the same three magical bricks of the universe as the stone lying on the road. Although this structure is much more complex.

Even more amazing facts are revealed when we try to take a closer look at the proportions and structure of the atomic system. It is known that an atom consists of a nucleus and electrons moving around it along a trajectory describing a sphere. That is, it cannot even be called a movement in the usual sense of the word. Rather, the electron is located everywhere and immediately within this sphere, creating an electron cloud around the nucleus and forming an electromagnetic field.

Schematic representations of the structure of an atom

The nucleus of an atom consists of protons and neutrons, and almost all the mass of the system is concentrated in it. But at the same time, the nucleus itself is so small that if its radius is increased to a scale of 1 cm, then the radius of the entire atomic structure will reach hundreds of meters. Thus, everything that we perceive as dense matter consists more than 99% of only energy connections between physical particles and less than 1% from the physical forms themselves.

But what are these physical forms? What are they made of, and how material are they? To answer these questions, let's take a closer look at the structures of protons, neutrons, and electrons. So, we descend one more step into the depths of the microworld - to the level of subatomic particles.

What does an electron consist of?

The smallest particle of an atom is an electron. An electron has mass but no volume. IN scientific idea The electron does not consist of anything, but is a structureless point.

An electron cannot be seen under a microscope. It is visible only in the form of an electron cloud, which looks like a blurry sphere around the atomic nucleus. At the same time, it is impossible to say with accuracy where the electron is at a moment in time. Instruments are capable of capturing not the particle itself, but only its energy trace. The essence of the electron is not embedded in the concept of matter. It is rather like some empty form that exists only in movement and due to movement.

No structure in the electron has yet been discovered. It is the same point particle as an energy quantum. In fact, an electron is energy, however, it is a more stable form of it than the one represented by photons of light.

IN currently The electron is considered indivisible. This is understandable, because it is impossible to divide something that has no volume. However, the theory already has developments according to which the electron contains a trinity of such quasiparticles as:

• Orbiton – contains information about the orbital position of the electron;
• Spinon – responsible for spin or torque;
• Holon – carries information about the charge of the electron.

However, as we see, quasiparticles have absolutely nothing in common with matter, and carry only information.

Photos of atoms different substances in an electron microscope

Interestingly, an electron can absorb energy quanta, such as light or heat. In this case, the atom moves to a new energy level, and the boundaries of the electron cloud expand. It also happens that the energy absorbed by an electron is so great that it can jump out of the atomic system and continue its movement as an independent particle. At the same time, it behaves like a photon of light, that is, it seems to cease to be a particle and begins to exhibit the properties of a wave. This was proven in an experiment.

Jung's experiment

During the experiment, a stream of electrons was directed at a screen with two slits cut in it. Passing through these slits, the electrons collided with the surface of another projection screen, leaving their mark on it. As a result of this “bombardment” of electrons, an interference pattern appeared on the projection screen, similar to the one that would appear if waves, but not particles, passed through two slits.

This pattern occurs because a wave passing between two slits is divided into two waves. As a result of further movement, the waves overlap each other, and in some areas they are mutually cancelled. The result is many lines on the projection screen, instead of just one, as would be the case if the electron behaved like a particle.

Structure of the nucleus of an atom: protons and neutrons

Protons and neutrons make up the nucleus of an atom. And despite the fact that in total volume the core occupies less than 1%; it is in this structure that almost the entire mass of the system is concentrated. But physicists are divided on the structure of protons and neutrons, and this moment There are two theories at once.

• Theory No. 1 - Standard

The Standard Model says that protons and neutrons are made up of three quarks connected by a cloud of gluons. Quarks are point particles, just like quanta and electrons. And gluons are virtual particles, ensuring the interaction of quarks. However, neither quarks nor gluons were ever found in nature, so this model is subject to severe criticism.

• Theory #2 - Alternative

But according to alternative theory single field, developed by Einstein, the proton, like the neutron, like any other particle physical world, is an electromagnetic field rotating at the speed of light.

Electromagnetic fields man and planet

What are the principles of atomic structure?

Everything in the world - thin and dense, liquid, solid and gaseous - is just the energy states of countless fields that permeate the space of the Universe. The higher the energy level in the field, the thinner and less perceptible it is. The lower the energy level, the more stable and tangible it is. In the structure of the atom, as in the structure of any other unit of the Universe, lies the interaction of such fields - different in energy density. It turns out that matter is just an illusion of the mind.

Atom - smallest particle substances, indivisible chemically. In the 20th century it was found out complex structure atom. Atoms are made up of positively charged kernels and a shell formed by negatively charged electrons. Total charge of a free atom equal to zero, since the nuclear charges and electron shell balance each other. In this case, the magnitude of the nuclear charge is equal to the number of the element in periodic table (atomic number ) and equal total number electrons (electron charge is −1).

The atomic nucleus consists of positively charged protons and neutral particles - neutrons, having no charge. Generalized characteristics of elementary particles in an atom can be presented in the form of a table:

The number of protons is equal to the charge of the nucleus, therefore equal to the atomic number. To find the number of neutrons in an atom, you need to subtract the charge of the nucleus (the number of protons) from the atomic mass (consisting of the masses of protons and neutrons).

For example, in the sodium atom 23 Na the number of protons is p = 11, and the number of neutrons is n = 23 − 11 = 12

The number of neutrons in atoms of the same element can be different. Such atoms are called isotopes .

The electron shell of an atom also has a complex structure. Electrons are located on energy levels(electronic layers).

The level number characterizes the energy of the electron. This is due to the fact that elementary particles can transmit and receive energy not in arbitrarily small quantities, but in certain portions - quanta. The higher the level, the more energy the electron has. Since the lower the energy of the system, the more stable it is (compare the low stability of a stone on the top of a mountain, which has a large potential energy, And stable position the same stone below on the plain, when its energy is much lower), the levels with low electron energy are filled first and only then the high ones.

The maximum number of electrons that a level can accommodate can be calculated using the formula:
N = 2n 2, where N is the maximum number of electrons at the level,
n - level number.

Then for the first level N = 2 1 2 = 2,

for the second N = 2 2 2 = 8, etc.

Number of electrons per external level for elements of the main (A) subgroups is equal to the group number.

In most modern periodic tables, the arrangement of electrons by level is indicated in the cell with the element. Very important understand that the levels are readable down up, which corresponds to their energy. Therefore, the column of numbers in the cell with sodium:
1
8
2

at the 1st level - 2 electrons,

at the 2nd level - 8 electrons,

at the 3rd level - 1 electron
Be careful, this is a very common mistake!

The electron level distribution can be represented as a diagram:
11 Na)))
2 8 1

If the periodic table does not indicate the distribution of electrons by level, you can use:

• maximum number of electrons: at the 1st level no more than 2 e − ,
  on the 2nd - 8 e − ,
  at the external level - 8 e − ;
• number of electrons in the outer level (for the first 20 elements coincides with the group number)

Then for sodium the line of reasoning will be as follows:

1. The total number of electrons is 11, therefore, the first level is filled and contains 2 e − ;
2. The third, outer level contains 1 e − (I group)
3. The second level contains the remaining electrons: 11 − (2 + 1) = 8 (completely filled)

* A number of authors, for a clearer distinction between a free atom and an atom as part of a compound, propose to use the term “atom” only to designate a free (neutral) atom, and to designate all atoms, including those in compounds, propose the term “ atomic particles" Time will tell what the fate of these terms will be. From our point of view, an atom by definition is a particle, therefore, the expression “atomic particles” can be considered as a tautology (“oil”).

2. Task. Calculation of the amount of substance of one of the reaction products if the mass of the starting substance is known.
Example:

What amount of hydrogen substance will be released when zinc reacts with hydrochloric acid weighing 146 g?

Solution:

1. We write the reaction equation: Zn + 2HCl = ZnCl 2 + H 2
2. We find molar mass of hydrochloric acid: M (HCl) = 1 + 35.5 = 36.5 (g/mol)
   (molar mass of each element, numerically equal to the relative atomic mass, look in the periodic table under the sign of the element and round to whole numbers, except for chlorine, which is taken as 35.5)
3. Find the amount of hydrochloric acid: n (HCl) = m / M = 146 g / 36.5 g/mol = 4 mol
4. We write down the available data above the reaction equation, and below the equation - the number of moles according to the equation (equal to the coefficient in front of the substance):
   4 mol x mol
   Zn + 2HCl = ZnCl 2 + H 2
   2 mole 1 mole
5. Let's make a proportion:
   4 mol - x mole
   2 mol - 1 mol
   (or with an explanation:
   from 4 moles of hydrochloric acid you get x mole of hydrogen,
   and from 2 moles - 1 mole)
6. We find x:
   x= 4 mol 1 mol / 2 mol = 2 mol

Answer: 2 mol.

(Lecture notes)

The structure of the atom. Introduction.

The object of study in chemistry is chemical elements and their compounds. Chemical element called a collection of atoms with the same positive charge. Atom- is the smallest particle of a chemical element that preserves it Chemical properties. Bonding with each other, atoms of one or different elements form more complex particles - molecules. A collection of atoms or molecules form chemical substances. Each individual chemical substance is characterized by a set of individual physical properties, such as boiling and melting points, density, electrical and thermal conductivity, etc.

1. Atomic structure and the Periodic Table of Elements

DI. Mendeleev.

Knowledge and understanding of the laws of the order of filling the Periodic Table of Elements D.I. Mendeleev allows us to understand the following:

1. the physical essence of the existence of certain elements in nature,

2. the nature of the chemical valence of the element,

3. the ability and “lightness” of an element to give or accept electrons when interacting with another element,

4.the nature of the chemical bonds that can form this element when interacting with other elements, the spatial structure of simple and complex molecules, etc., etc.

The structure of the atom.

An atom is a complex microsystem of elementary particles in motion and interacting with each other.

In the late 19th and early 20th centuries, it was discovered that atoms are made up of smaller particles: neutrons, protons and electrons. The last two particles are charged particles, the proton carries positive charge, electron - negative. Since the atoms of an element in the ground state are electrically neutral, this means that the number of protons in an atom of any element is equal to the number of electrons. The mass of atoms is determined by the sum of the masses of protons and neutrons, the number of which is equal to the difference between the mass of atoms and its serial number in the periodic table D.I. Mendeleev.

In 1926, Schrödinger proposed describing the movement of microparticles in the atom of an element using the wave equation he derived. When solving the Schrödinger wave equation for the hydrogen atom, three integer quantum numbers appear: n, ℓ And m ℓ , which characterize the state of the electron in three-dimensional space in the central field of the nucleus. Quantum numbers n, ℓ And m ℓ take integer values. Wave function defined by three quantum numbers n, ℓ And m ℓ and obtained as a result of solving the Schrödinger equation is called an orbital. An orbital is a region of space in which an electron is most likely to be found, belonging to an atom of a chemical element. Thus, solving the Schrödinger equation for the hydrogen atom leads to the appearance of three quantum numbers, physical meaning which is that they characterize three different types of orbitals that an atom can have. Let's take a closer look at each quantum number.

Principal quantum number n can take any positive integer values: n = 1,2,3,4,5,6,7...It characterizes the energy of the electron level and the size of the electron “cloud”. It is characteristic that the number of the main quantum number coincides with the number of the period in which the element is located.

Azimuthal or orbital quantum numberℓ can take integer values ​​from ℓ = 0….to n – 1 and determines the moment of electron motion, i.e. orbital shape. For various numerical valuesℓ use the following notation: ℓ = 0, 1, 2, 3, and are indicated by the symbols s, p, d, f, respectively for ℓ = 0, 1, 2 and 3. In the periodic table of elements there are no elements with a spin number ℓ = 4.

Magnetic quantum numberm ℓ characterizes the spatial arrangement of electron orbitals and, consequently, the electromagnetic properties of the electron. It can take values ​​from – ℓ to + ℓ , including zero.

The shape, or more precisely, the symmetry properties of atomic orbitals depend on quantum numbers ℓ And m ℓ . "Electronic cloud" corresponding s- the orbitals have, have the shape of a ball (at the same time ℓ = 0).

Fig.1. 1s orbital

The orbitals defined by the quantum numbers ℓ = 1 and m ℓ = -1, 0 and +1 are called p-orbitals. Since m ℓ in this case has three different meanings, then the atom has three energetically equivalent p-orbitals (the principal quantum number for them is the same and can have the value n = 2,3,4,5,6 or 7). p-Orbitals have axial symmetry and look like three-dimensional figure eights, oriented along the x, y and z axes in an external field (Fig. 1.2). Hence the origin of the symbolism p x , p y and p z .

Fig.2. p x, p y and p z orbitals

In addition, there are d- and f- atomic orbitals, for the first ℓ = 2 and m ℓ = -2, -1, 0, +1 and +2, i.e. five AOs, for the second ones ℓ = 3 and m ℓ = -3, -2, -1, 0, +1, +2 and +3, i.e. 7 JSC.

Fourth quantum m s called the spin quantum number, was introduced to explain certain subtle effects in the spectrum of the hydrogen atom by Goudsmit and Uhlenbeck in 1925. The spin of an electron is the angular momentum of a charged elementary particle of an electron, the orientation of which is quantized, i.e. strictly limited to certain angles. This orientation is determined by the value of the spin magnetic quantum number (s), which for the electron is equal to ½ , therefore for the electron according to the quantization rules m s = ± ½. In this regard, to the set of three quantum numbers we should add the quantum number m s . Let us emphasize once again that four quantum numbers determine the order of construction of Mendeleev’s periodic table of elements and explain why there are only two elements in the first period, eight in the second and third, 18 in the fourth, etc. However, in order to explain the structure of many-electron atoms, the order of filling electronic levels as the positive charge of the atom increases, it is not enough to have an idea of ​​the four quantum numbers that “control” the behavior of electrons when filling electron orbitals, but you need to know some more simple rules, namely, Pauli's principle, Hund's rule and Kleczkowski's rules.

According to the Pauli principle In the same quantum state, characterized by certain values ​​of four quantum numbers, there cannot be more than one electron. This means that one electron can, in principle, be placed in any atomic orbital. Two electrons can be in the same atomic orbital only if they have different spin quantum numbers.

When filling three p-AOs, five d-AOs and seven f-AOs with electrons, one should be guided, in addition to the Pauli principle, by Hund’s rule: The filling of the orbitals of one subshell in the ground state occurs with electrons with identical spins.

When filling the subshells (p, d, f)the absolute value of the sum of spins must be maximum.

Klechkovsky's rule. According to Klechkovsky’s rule, when fillingd And felectron orbital must be respectedprinciple of minimum energy. According to this principle, electrons in the ground state fill orbitals with minimum levels energy. The energy of a sublevel is determined by the sum of quantum numbersn + ℓ = E .

Klechkovsky's first rule: First, those sublevels for whichn + ℓ = E minimal.

Klechkovsky's second rule: in case of equalityn + ℓ for several sublevels, the sublevel for which is filledn minimal .

Currently, 109 elements are known.

2. Ionization energy, electron affinity and electronegativity.

The most important characteristics of the electronic configuration of an atom are ionization energy (IE) or ionization potential (IP) and the atom's electron affinity (EA). Ionization energy is the change in energy during the removal of an electron from a free atom at 0 K: A = + + ē . The dependence of ionization energy on the atomic number Z of an element and the size of the atomic radius has a pronounced periodic character.

Electron affinity (EA) is the change in energy that accompanies the addition of an electron to an isolated atom to form a negative ion at 0 K: A + ē = A - (the atom and ion are in their ground states). In this case, the electron occupies the lowest free space atomic orbital(HCAO), if the HCAO is occupied by two electrons. The SE strongly depends on their orbital electronic configuration.

Changes in EI and SE correlate with changes in many properties of elements and their compounds, which is used to predict these properties from EI and SE values. The highest absolute value Halogens have an affinity for electrons. In each group of the periodic table of elements, the ionization potential or EI decreases with increasing element number, which is associated with an increase in atomic radius and with an increase in the number of electronic layers and which correlates well with an increase in the reducing power of the element.

Table 1 of the Periodic Table of Elements shows the values ​​of EI and SE in eV/per atom. Note that exact values SEs are known only for a few atoms; their values ​​are highlighted in Table 1.

Table 1

First ionization energy (EI), electron affinity (EA) and electronegativity χ) of atoms in the periodic table.

χ	0.747 2. 1 0 0, 3 7																	1,2 2
χ	0.54 1. 55	-0.3 1. 1 3											0.2 0. 91	1.2 5	-0. 1 0, 55	1.47 0. 59	3.45 0. 64	1 ,60
χ	0. 7 4 1. 89	-0.3 1 . 3 1 1 . 6 0											0. 6	1.63	0.7	2.07	3.61
χ	2.3 6	- 0 .6						1.26(α)				-0.9 1 . 39	0. 18	1.2	0. 6	2.07	3.36
χ	2.4 8											-0.6 1 . 56	0. 2			2.2
χ	2.6 7	2, 2 1						ABOUTs

χ – electronegativity according to Pauling

r- atomic radius, (from “Laboratory and seminar classes in general and inorganic chemistry”, N.S. Akhmetov, M.K. Azizova, L.I. Badygina)

An atom is the smallest particle of matter. Its study began in Ancient Greece, when the structure of the atom attracted the attention of not only scientists, but also philosophers. What is it like electronic structure atom, and what basic information is known about this particle?

Atomic structure

Already ancient Greek scientists guessed about the existence of the smallest chemical particles that make up any object and organism. And if in the XVII-XVIII centuries. chemists were sure that the atom is an indivisible elementary particle, then turn of XIX-XX centuries, it was experimentally possible to prove that the atom is not indivisible.

An atom, being a microscopic particle of matter, consists of a nucleus and electrons. The nucleus is 10,000 times smaller than an atom, but almost all of its mass is concentrated in the nucleus. The main characteristic The atomic nucleus is that it has a positive charge and consists of protons and neutrons. Protons are positively charged, while neutrons have no charge (they are neutral).

They are connected to each other through a strong nuclear interaction. The mass of a proton is approximately equal to the mass of a neutron, but 1840 times more mass electron. Protons and neutrons have in chemistry common name– nucleons. The atom itself is electrically neutral.

An atom of any element can be designated electronic formula and electronic graphic formula:

Rice. 1. Electronic graphic formula of the atom.

The only chemical element from periodic table, the nucleus of which does not contain neutrons, is light hydrogen (protium).

An electron is a negatively charged particle. The electron shell consists of electrons moving around the nucleus. Electrons have the property of being attracted to the nucleus, and between each other they are influenced by the Coulomb interaction. To overcome the attraction of the nucleus, electrons must receive energy from external source. The further the electron is from the nucleus, the less energy is needed.

Atom models

For a long time, scientists have sought to understand the nature of the atom. On early stage The ancient Greek philosopher Democritus made a major contribution. Although now his theory seems banal and too simple to us, at a time when ideas about elementary particles just beginning to emerge, his theory about pieces of matter was taken quite seriously. Democritus believed that the properties of any substance depend on the shape, mass and other characteristics of the atoms. So, for example, fire, he believed, has sharp atoms - that’s why fire burns; Water has smooth atoms, so it can flow; In solid objects, in his opinion, the atoms were rough.

Democritus believed that absolutely everything is made of atoms, even the human soul.

In 1904, J. J. Thomson proposed his model of the atom. The main provisions of the theory boiled down to the fact that the atom was represented as a positively charged body, inside of which there were electrons with negative charge. This theory was later refuted by E. Rutherford.

Rice. 2. Thomson's model of the atom.

Also in 1904 Japanese physicist H. Nagaoka proposed an early planetary model of the atom by analogy with the planet Saturn. According to this theory, electrons are united in rings and rotate around a positively charged nucleus. This theory turned out to be wrong.

In 1911, E. Rutherford, having carried out a series of experiments, concluded that the atom in its structure is similar to planetary system. After all, electrons, like planets, move in orbits around a heavy, positively charged nucleus. However, this description contradicted classical electrodynamics. Then the Danish physicist Niels Bohr introduced postulates in 1913, the essence of which was that an electron, being in some special conditions, does not emit energy. Thus, boron's postulates showed that for atoms classical mechanics not applicable. The planetary model described by Rutherford and supplemented by Bohr was called the Bohr-Rutherford planetary model.

Rice. 3. Bohr-Rutherford planetary model.

Further study of the atom led to the creation of such a section as quantum mechanics, with the help of which many were explained scientific facts. Modern representations about the atom developed from the Bohr-Rutherford planetary model. Evaluation of the report

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