Atom- the smallest particle of a substance that is indivisible by chemical means. In the 20th century, the complex structure of the atom was discovered. Atoms are made up of positively charged kernels and a shell formed by negatively charged electrons. The total charge of a free atom is zero, since the charges of the nucleus and electron shell balance each other. In this case, the nuclear charge is equal to the number of the element in the periodic table ( atomic number) and is equal to the total number of 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 in 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 top of a mountain, which has high potential energy, and the stable position of 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 - high.

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.

The number of electrons in the outer 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, in order to more clearly distinguish between a free atom and an atom in 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. Find the molar mass of hydrochloric acid: M (HCl) = 1 + 35.5 = 36.5 (g/mol)
   (the molar mass of each element, numerically equal to the relative atomic mass, is looked at in the periodic table under the sign of the element and rounded 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.

Topic – 1: Structure of the atom. Nuclear charge, atomic number and mass of the atom.

The student must:

Know:

· Modern formulation of the periodic law and structure of the table

Be able to:

· Identify elements by described properties, determine an element using an electronic formula.

· Determine by the serial number of the element the number of the period and the number of the group in which it is located, as well as the formulas and nature of the higher oxide and the corresponding hydroxide.

· Write down the electronic formula of a given element and compare it with the surrounding elements in the period and group.

1.1. The atomic number of a chemical element and the charge value of the nucleus of its atom. Isotopes

When classifying chemical elements, I used two of their characteristics: a) relative atomic mass b) properties of simple substances and compounds of elements.

The first sign is the leading one, the second one manifests itself in connection with the first one: the properties of the elements change periodically with an increase in the relative atomic mass.

But when constructing the periodic system, arranging chemical elements in order of increasing relative atomic mass, in some places he violated this rule: he changed cobalt and nickel, tellurium and iodine. Later, the same thing had to be done with two more pairs of chemical elements: argon - potassium and thorium - protactinium. After all, the active alkali metal potassium cannot be included in the family of chemically stable inert gases, which either do not form chemical compounds at all (helium, neon) or react with difficulty.

could not explain these exceptions to the general rule, as well as the reason for the periodicity in changes in the properties of chemical elements arranged in increasing relative atomic mass.

In the 20th century Scientists have established that an atom consists of a nucleus and electrons moving around it. Electrons moving around the nucleus form the electron shell of the atom. Atom – electro – neutral particle, i.e. having no charge. The nucleus is positively charged, and its charge is neutralized by the total negative charge of all electrons in the atom. For example, if the nucleus of an atom has a charge of +4, then four electrons move around it, each of which has a charge of -1.

It was experimentally established that the serial numbers of elements in the periodic table coincide with the values ​​of the charges of the nuclei of their atoms. The charge of the nucleus of a hydrogen atom is +1, helium +2, lithium +3, etc. d. The positive charge of the atom of each subsequent element is one more than that of the previous one, and there is one more electron in its electron shell.

The serial (atomic) number of a chemical element is numerically equal to the charge of its atom.

Since scientists discovered the physical meaning of the atomic number of an element, the periodic law has been formulated as follows: the properties of simple substances, as well as the composition and properties of compounds of chemical elements, periodically depend on the charge of the nucleus of atoms.

How can you explain why the nuclear charges of chemical elements in the periodic table increase, and the correct sequence of increase in relative atomic mass is disrupted in some cases? To answer this question you need draw on information about the composition of atomic nuclei that you know from a physics course.

The nuclei of atoms are positively charged because they contain protons. A proton is a particle with a charge of +1 and a relative mass equal to 1. The nucleus of a hydrogen atom having a relative atomic mass equal to 1 is a proton. There are two protons in the helium nucleus, but the relative atomic mass of helium is 4. This is due to the fact that the nucleus of a helium atom includes not only protons, but also neutrons - uncharged particles with a relative atomic mass equal to 1. Therefore, to find the number of neutrons in atom, the number of protons (charge of the atomic nucleus, atomic number) must be subtracted from the relative atomic mass. The mass of electrons is negligible, small, and is not taken into account.

It is by the number of protons in the nucleus that atoms of different elements differ. A chemical element is a type of atom with the same nuclear charge. The number of neutrons in the nuclei of atoms of the same element can be different.

Varieties of atoms of a chemical element that have different numbers of neutrons in their nuclei are called isotopes. It is the presence of isotopes that explains those rearrangements that at one time. Modern science has confirmed that he was right. Thus, natural potassium is formed mainly by atoms of its light isotopes, and argon - by heavy ones. Therefore, the relative atomic mass of potassium is less than that of argon, although the atomic number (charge) of potassium is greater.

Most chemical elements are mixtures of isotopes. For example, natural chlorine contains isotopes with atomic masses 35 and 37. The relative atomic mass of 35.5 was obtained by calculation, taking into account not only the mass of the isotopes, but also the content of each of them in nature. Due to the fact that chemical elements have isotopes, and the relative atomic masses of elements are values ​​averaged over the content of isotopes, they are fractions, not whole numbers.

When they want to emphasize which isotope we are talking about, near the chemical sign at the top left they write the value of the relative atomic mass of an atom of this isotope, and at the bottom left - the charge of the nucleus, For example 37Cl17.

1.2. State of electrons in an atom

The state of an electron in an atom is understood as the totality of information about energy a certain electron and aboutwandering, in which he is located. We already know that an electron in an atom does not have a trajectory of motion, that is, we can only talk about probabilities its location 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 electron cloud with a certain negative charge density.

W. Heisenberg introduced the concept of the uncertainty principle that is, he showed that it is impossible to determine simultaneously and accurately the energy and location of the electron. The more precisely the energy of an electron is determined, the more uncertain its position will be, and vice versa, having determined the position, it is impossible to determine the energy of the electron. The probability range for detecting an electron does not have clear boundaries. However, it is possible to select a space where the probability of finding an electron will be maximum.

The space around the atomic nucleus in which an electron is most likely to be found is called an orbital.

Number of energy levels (electronic layers) inatom is equal to the period number in the system,to which the chemical element belongs: y atomov of elements of the first period- one energylevel, second period- two, seventh period - seven.

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

N = 2 n 2 ,

Where N - maximum number of electrons; P - level number or main quantum number. Hence, on the first, damnthe energy level closest to the nucleus may beno 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.

And how, in turn, are energy levels (electronic layers) arranged?

Starting from the second energy level (P= 2), each of the levels is divided into sublevels (sublayers), slightly different from each other in the binding energy with the core.

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. Sublevels, in turn, are formed by orbitals.

Each value P corresponds to the number of orbitals equal to p2. According to the data presented in Table 1, it is possible to trace the connection between the main quantum number P with the number of sublevels, the type and number of orbitals, and the maximum number of electrons per sublevel and level.

s-Sublevel- the first sublevel of each energy level closest to the atomic nucleus consists of one s-orbital;

p-sublevel- the second sublevel of each energy level, except the first, consists of three-p orbitals;

d-sublevel- the third sublevel of each, starting from the third energy level, consists of five d-orbitals;

f-sublevel each, starting from the fourth energy level, consists of seven orbitals.

The figure shows a diagram showing the number, shape and position in space of the electron orbitals of the first four electron layers of an individual atom.

1.3. Electronic configurations in chemical atoms elements

Swiss physicist W. Pauli in 1925 established that in an atom there can be no more than one orbitaltwo electrons, having opposite (antiparallel) backs(translated from English as “spindle”), that is, having properties that can be conventionally 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 an orbital, it is called unpaired, if two, then this paired electrons, that is, electrons with opposite spins.

The s-orbital, as you already know, has a spherical shape. Electron of the hydrogen atom ( P= 1) is located in this orbital and is unpaired. Therefore it electronic formula, or elekthrone configuration, will be written like this: 1s1. In electronic formulas, the number of the energy level is indicated by the number preceding the letter (1...), the Latin letter indicates the sublevel (type of orbital), and the number written to the upper right of the letter (as an exponent) shows the number of electrons in the sublevel.

At the second energy level (n = 2) there are four orbitals: one s and three p. The electrons of the s-orbital of the second level (2p-orbitals) have higher energy, since they are at a greater distance from the nucleus than the electrons of the ls-orbital (n = 2)

In general, for each value P there is one s orbital, but with a corresponding supply of electron energy on it and therefore with a corresponding diameter, growing as the value increases P.

The p-Orbital has the shape of a dumbbell or a three-dimensional figure eight. All three p-orbitals are located in the atom mutually perpendicular along the spatial coordinates drawn through the nucleus of the atom. It should be emphasized once again that each energy level (electronic layer), starting from n = 2, has three p orbitals. With increasing value P electrons are occupied. p-orbitals located at large distances from the nucleus and directed along the axes x, y, g.

For elements of the second period (P= 2) first one s-orbital is filled, and then three p-orbitals.

For elements of the third period, the 3s and 3p orbitals are filled, respectively. Five d-orbitals of the third level remain free:

For elements of large periods (fourth and fifth), the first two electrons occupy the 4s and 5s orbitals, respectively.

Starting from the third element of each major period, the next ten electrons will enter the previous 3d and 4d orbitals, respectively.

For elements of large periods - the sixth and incomplete seventh - electronic levels and sublevels are filled with electrons, as a rule, like this: the first two electrons will go to the outer s-sublevel, the next one electron (for La and Ac) to the previous d-sublevel. Then the next 14 electrons will go to the third outer energy level at 4 f - and 5f orbitals, respectively, for lanthanides and actinides:

Then the second external energy level (d-sublevel) will begin to build up again: for elements of secondary subgroups: 73Ta 2, 8, 18, 32, 11, 2; 104Rf 2, 8, 18, 32, 32, 10, 2, - and finally, only after the d-sublevel is completely filled with ten electrons will the outer p-sublevel be filled again:

86Rn 2, 8, 18, 32, 18, 8.

Very often, the structure of the electronic shells of atoms is depicted using energy or quantum cells - the so-called graphic electronic formulas. 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 principle , according to which there can be no more than two electrons in a cell (orbital), but with antiparallel spins, and F. Hund's rule , according to which electrons occupy free cells (orbitals), are located in them first one at a time and have the same spin value, and only then pair, but the spins will be oppositely directed according to the Pauli principle.

1.4. Structure of the electronic shell of atoms

During chemical reactions, the nuclei of atoms do not change. This conclusion can be drawn from the fact that you know that the reaction products consist of atoms of the same chemical elements as the starting substances. But what happens to atoms during chemical reactions? Is there a connection between the structure of an atom and the manifestation of certain physical and chemical properties? To answer the questions, we must first consider the structure of the electron shell of atoms of different chemical elements.

The number of electrons in an atom is equal to the charge of its nucleus. Electrons are located at different distances from the nucleus of an atom, grouping into electronic layers. The closer the electrons are to the nucleus, the more tightly they are bound to the nucleus.

The nucleus of a hydrogen atom has a charge of +1. An atom has only one electron and, naturally, one electron layer.

Next to hydrogen is helium. It does not form compounds with other elements, which means it does not exhibit valence. The nucleus of a helium atom has a charge of +2, two electrons move around it, forming one electron layer. Helium atoms do not form compounds with atoms of other chemical elements, and this indicates the great stability of its electronic shell. The electron shells of helium and other noble gas atoms are called completed.

The next element is lithium. A lithium atom has three electrons. Two of them are located on the first electron layer closest to the nucleus, and the third forms the second outer electronic layer. A second electron layer has appeared in the lithium atom. The electron located on it is more distant from the nucleus and weaker bound to the nucleus than the other two.

Find the chemical sign for lithium in the periodic table. From lithium to neon, the charge of atomic nuclei naturally increases. The second electronic layer is gradually filled with electrons, and with an increase in the number of electrons on it, the metallic properties of the elements gradually weaken and are replaced by increasing non-metallic ones.

Fluorine is the most active non-metal, the charge of its nucleus is +9, its atom has two electron layers containing 2 and 7 electrons. Fluorine is followed by neon.

The properties of the elements fluorine and neon differ sharply. Neon is inert and, like helium, does not form compounds. This means the second electron layer, containing eight electrons is complete: electrons formed a stable system, giving the atom inertia.

If this is so, then the next element, the atoms of which should differ from the neon atoms by an additional proton in the nucleus and an electron, will have three electron layers. An atom of this element will thus have a third, outer electron layer, populated by one electron. This element will have sharply different properties from neon; it must be an active metal, like lithium, and exhibit a valency of 1 in compounds.

The element sodium fits this description. It opens the third period. Sodium is an alkali metal, even more active than lithium. This means that our assumptions turned out to be correct. The single electron in the outer electron layer of the sodium atom is located further from the nucleus than the outer electron of lithium, and is therefore even more weakly bound to the nucleus.

In the series of elements from sodium to argon, the above-mentioned pattern again appears: the number of electrons forming the outer electronic layer of atoms increases, the metallic properties of simple substances from sodium to aluminum weaken, non-metallic properties increase in the transition from silicon to phosphorus and sulfur and are most pronounced in the halogens . At the end of the third period there is an element - argon, in the atom of which there is a complete, eight-electron outer layer. When moving from chlorine to argon, the properties of the atoms of the elements change sharply, and with them the properties of simple substances and compounds of this element. It is known that argon is an inert gas. It does not combine with other substances.

The properties also change sharply when moving from argon, the last element of the third period, to the first element of the fourth period, potassium. Potassium is an alkali metal and is chemically very active.

Thus, quantitative changes in the composition of an atom (the number of protons in the nucleus and electrons in the outer electronic layer) associated with quality (properties of simple substances and compounds formed by a chemical element).

Systematizing knowledge.

1. In the electron shell of an atom, electrons are arranged in layers. The first layer from the nucleus is complete when it contains two electrons, the second complete layer contains eight electrons.

2. The number of electron layers in an atom coincides with the number of the period in which the chemical element is located

3. The electron shell of the atom of each subsequent element in the periodic table repeats the structure of the electron shell of the previous element, but differs from it by one electron.

What you have studied is enough to draw conclusions about the relationship between the structure of atoms and the properties of chemical elements, to understand the reasons for the periodic changes in their properties, similarities and differences. Formulate these conclusions.

1. The properties of chemical elements, arranged in order of increasing charges of atomic nuclei, change periodically because a similar structure of the outer electronic layer of atoms is periodically repeated.

2. A smooth change in the properties of elements within one period is due to a gradual increase in the number of electrons in the outer layer of atoms.

3. Completion of the outer electron layer of the atom leads to a sharp jump in properties when going from halogen to an inert gas; the appearance of a new outer electron layer in an atom is the reason for a sharp jump in properties during the transition from an inert gas to an alkali metal.

4. The properties of chemical elements belonging to the same family are similar because the outer electron layer of their atoms contains the same number of electrons.

1.5. Valence possibilities of atoms of chemical elements

The structure of the outer energy levels of atoms of chemical elements mainly determines the properties of their atoms. Therefore these levels are called valence. Electrons of these levels, and sometimes of pre-external levels, can take part in the formation of chemical bonds. These electrons are also called valence.

The valency of an atom of a chemical element is determined primarily by the number of unpaired electrons participating in the formation of a chemical bond .

The valence electrons of the atoms of the elements of the main subgroups are located on s- and p-orbitals of the outer electron layer. For elements of side subgroups, except for lanthanides and actinides, valence electrons are located in the s-orbital of the outer and d-orbitals of the pre-outer layer.

In order to correctly assess the valence capabilities of atoms of chemical elements, it is necessary to consider the distribution of electrons in them across energy levels and sublevels and determine the number of unpaired electrons in accordance with the Pauli principle and Hund’s rule for the unexcited (ground, or stationary) state of the atom and for the excited (then that has received additional energy, as a result of which the electrons of the outer layer are paired and transferred to free orbitals). An atom in an excited state is designated by the corresponding element symbol with an asterisk.

https://pandia.ru/text/80/139/images/image003_118.gif" height="757"> For example, Let's consider the valence possibilities of phosphorus atoms in stationary and excited states:

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The energy expended on the excitation of carbon atoms is more than compensated by the energy released during the formation of two additional covalent bonds. Thus, to transfer carbon atoms from the stationary state 2s22p2 to the excited state - 2s12p3, it is necessary to expend about 400 kJ/mol of energy. But when a C-H bond is formed in saturated hydrocarbons, 360 kJ/mol is released. Consequently, when two moles of C-H bonds are formed, 720 kJ will be released, which exceeds the energy of transfer of carbon atoms to the excited state by 320 kJ/mol.

In conclusion, it should be noted that the valence capabilities of atoms of chemical elements are far from being limited to the number of unpaired electrons in the stationary and excited states of atoms. If you remember the donor-acceptor mechanism for the formation of covalent bonds, then two other valence possibilities of atoms of chemical elements will become clear to you, which are determined by the presence of free orbitals and the presence of lone electron pairs that can give a covalent chemical bond through the donor-acceptor mechanism. Remember the formation of the ammonium ion NH4+ (We will consider in more detail the implementation of these valence possibilities by atoms of chemical elements when studying chemical bonds.)

Let's draw a general conclusion.

The valence capabilities of atoms of chemical elements are determined by: 1) the number of unpaired electrons (one-electron orbitals); 2) the presence of free orbitals; 3) the presence of lone pairs of electrons.

As you know, everything material in the Universe consists of atoms. An atom is the smallest unit of matter that 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 the quantitative composition of these microparticles in the overall structure of the 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 the 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 of more than 99% of the energetic bonds between physical particles alone and less than 1% of 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 the scientific concept, an 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.

At the moment, 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.

Photographs of atoms of 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 the core occupies less than 1% of the total volume, 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 at the moment there are two theories.

• 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 that ensure 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 the alternative theory of the unified field, developed by Einstein, the proton, like the neutron, like any other particle of the physical world, is an electromagnetic field rotating at the speed of light.

Electromagnetic fields of 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. The structure of the atom, as well as the structure of any other unit of the Universe, lies in the interaction of such fields - different in energy density. It turns out that matter is just an illusion of the mind.

Chemicals are what the world around us is made of.

The properties of each chemical substance are divided into two types: chemical, which characterize its ability to form other substances, and physical, which are objectively observed and can be considered in isolation from chemical transformations. For example, the physical properties of a substance are its state of aggregation (solid, liquid or gaseous), thermal conductivity, heat capacity, solubility in various media (water, alcohol, etc.), density, color, taste, etc.

The transformation of some chemical substances into other substances is called chemical phenomena or chemical reactions. It should be noted that there are also physical phenomena that are obviously accompanied by a change in any physical properties of a substance without its transformation into other substances. Physical phenomena, for example, include the melting of ice, freezing or evaporation of water, etc.

The fact that a chemical phenomenon is taking place during a process can be concluded by observing characteristic signs of chemical reactions, such as color changes, the formation of precipitates, the release of gas, the release of heat and (or) light.

For example, a conclusion about the occurrence of chemical reactions can be made by observing:

Formation of sediment when boiling water, called scale in everyday life;

The release of heat and light when a fire burns;

Change in color of a cut of a fresh apple in air;

Formation of gas bubbles during dough fermentation, etc.

The smallest particles of a substance that undergo virtually no changes during chemical reactions, but only combine with each other in a new way, are called atoms.

The very idea of ​​the existence of such units of matter arose in ancient Greece in the minds of ancient philosophers, which actually explains the origin of the term “atom,” since “atomos” literally translated from Greek means “indivisible.”

However, contrary to the idea of ​​​​ancient Greek philosophers, atoms are not the absolute minimum of matter, i.e. themselves have a complex structure.

Each atom consists of so-called subatomic particles - protons, neutrons and electrons, designated respectively by the symbols p +, n o and e -. The superscript in the notation used indicates that the proton has a unit positive charge, the electron has a unit negative charge, and the neutron has no charge.

As for the qualitative structure of an atom, in each atom all protons and neutrons are concentrated in the so-called nucleus, around which the electrons form an electron shell.

The proton and neutron have almost the same masses, i.e. m p ≈ m n, and the mass of the electron is almost 2000 times less than the mass of each of them, i.e. m p /m e ≈ m n /m e ≈ 2000.

Since the fundamental property of an atom is its electrical neutrality, and the charge of one electron is equal to the charge of one proton, from this we can conclude that the number of electrons in any atom is equal to the number of protons.

For example, the table below shows the possible composition of atoms:

Type of atoms with the same nuclear charge, i.e. with the same number of protons in their nuclei is called a chemical element. Thus, from the table above we can conclude that atom1 and atom2 belong to one chemical element, and atom3 and atom4 belong to another chemical element.

Each chemical element has its own name and individual symbol, which is read in a certain way. So, for example, the simplest chemical element, the atoms of which contain only one proton in the nucleus, is called “hydrogen” and is denoted by the symbol “H”, which is read as “ash”, and a chemical element with a nuclear charge of +7 (i.e. containing 7 protons) - “nitrogen”, has the symbol “N”, which is read as “en”.

As you can see from the table above, atoms of one chemical element can differ in the number of neutrons in their nuclei.

Atoms that belong to the same chemical element, but have a different number of neutrons and, as a result, mass, are called isotopes.

For example, the chemical element hydrogen has three isotopes - 1 H, 2 H and 3 H. The indices 1, 2 and 3 above the symbol H mean the total number of neutrons and protons. Those. Knowing that hydrogen is a chemical element, which is characterized by the fact that there is one proton in the nuclei of its atoms, we can conclude that in the 1 H isotope there are no neutrons at all (1-1 = 0), in the 2 H isotope - 1 neutron (2-1=1) and in the 3 H isotope – two neutrons (3-1=2). Since, as already mentioned, the neutron and proton have the same masses, and the mass of the electron is negligibly small in comparison with them, this means that the 2 H isotope is almost twice as heavy as the 1 H isotope, and the 3 H isotope is even three times heavier . Due to such a large scatter in the masses of hydrogen isotopes, the isotopes 2 H and 3 H were even assigned separate individual names and symbols, which is not typical for any other chemical element. The 2H isotope was named deuterium and given the symbol D, and the 3H isotope was given the name tritium and given the symbol T.

If we take the mass of the proton and neutron as one, and neglect the mass of the electron, in fact the upper left index, in addition to the total number of protons and neutrons in the atom, can be considered its mass, and therefore this index is called the mass number and is designated by the symbol A. Since the charge of the nucleus of any Protons correspond to the atom, and the charge of each proton is conventionally considered equal to +1, the number of protons in the nucleus is called the charge number (Z). By denoting the number of neutrons in an atom as N, the relationship between mass number, charge number and number of neutrons can be expressed mathematically as:

According to modern concepts, the electron has a dual (particle-wave) nature. It has the properties of both a particle and a wave. Like a particle, an electron has mass and charge, but at the same time, the flow of electrons, like a wave, is characterized by the ability to diffraction.

To describe the state of an electron in an atom, the concepts of quantum mechanics are used, according to which the electron does not have a specific trajectory of motion and can be located at any point in space, but with different probabilities.

The region of space around the nucleus where an electron is most likely to be found is called an atomic orbital.

An atomic orbital can have different shapes, sizes, and orientations. An atomic orbital is also called an electron cloud.

Graphically, one atomic orbital is usually denoted as a square cell:

Quantum mechanics has an extremely complex mathematical apparatus, therefore, in the framework of a school chemistry course, only the consequences of quantum mechanical theory are considered.

According to these consequences, any atomic orbital and the electron located in it are completely characterized by 4 quantum numbers.

• The principal quantum number, n, determines the total energy of an electron in a given orbital. The range of values ​​of the main quantum number is all natural numbers, i.e. n = 1,2,3,4, 5, etc.
• The orbital quantum number - l - characterizes the shape of the atomic orbital and can take any integer value from 0 to n-1, where n, recall, is the main quantum number.

Orbitals with l = 0 are called s-orbitals. s-Orbitals are spherical in shape and have no directionality in space:

Orbitals with l = 1 are called p-orbitals. These orbitals have the shape of a three-dimensional figure eight, i.e. a shape obtained by rotating a figure eight around an axis of symmetry, and outwardly resemble a dumbbell:

Orbitals with l = 2 are called d-orbitals, and with l = 3 – f-orbitals. Their structure is much more complex.

3) Magnetic quantum number – m l – determines the spatial orientation of a specific atomic orbital and expresses the projection of the orbital angular momentum onto the direction of the magnetic field. The magnetic quantum number m l corresponds to the orientation of the orbital relative to the direction of the external magnetic field strength vector and can take any integer values ​​from –l to +l, including 0, i.e. the total number of possible values ​​is (2l+1). So, for example, for l = 0 m l = 0 (one value), for l = 1 m l = -1, 0, +1 (three values), for l = 2 m l = -2, -1, 0, +1 , +2 (five values ​​of magnetic quantum number), etc.

So, for example, p-orbitals, i.e. orbitals with an orbital quantum number l = 1, having the shape of a “three-dimensional figure of eight,” correspond to three values ​​of the magnetic quantum number (-1, 0, +1), which in turn correspond to three directions perpendicular to each other in space.

4) The spin quantum number (or simply spin) - m s - can conventionally be considered responsible for the direction of rotation of the electron in the atom; it can take on values. Electrons with different spins are indicated by vertical arrows directed in different directions: ↓ and .

The set of all orbitals in an atom that have the same principal quantum number is called the energy level or electron shell. Any arbitrary energy level with some number n consists of n 2 orbitals.

A set of orbitals with the same values ​​of the principal quantum number and orbital quantum number represents an energy sublevel.

Each energy level, which corresponds to the principal quantum number n, contains n sublevels. In turn, each energy sublevel with orbital quantum number l consists of (2l+1) orbitals. Thus, the s sublevel consists of one s orbital, the p sublevel consists of three p orbitals, the d sublevel consists of five d orbitals, and the f sublevel consists of seven f orbitals. Since, as already mentioned, one atomic orbital is often denoted by one square cell, the s-, p-, d- and f-sublevels can be graphically represented as follows:

Each orbital corresponds to an individual strictly defined set of three quantum numbers n, l and m l.

The distribution of electrons among orbitals is called the electron configuration.

The filling of atomic orbitals with electrons occurs in accordance with three conditions:

• Minimum energy principle: Electrons fill orbitals starting from the lowest energy sublevel. The sequence of sublevels in increasing order of their energies is as follows: 1s<2s<2p<3s<3p<4s≤3d<4p<5s≤4d<5p<6s…;

To make it easier to remember this sequence of filling out electronic sublevels, the following graphic illustration is very convenient:

• Pauli principle: Each orbital can contain no more than two electrons.

If there is one electron in an orbital, then it is called unpaired, and if there are two, then they are called an electron pair.

• Hund's rule: the most stable state of an atom is one in which, within one sublevel, the atom has the maximum possible number of unpaired electrons. This most stable state of the atom is called the ground state.

In fact, the above means that, for example, the placement of 1st, 2nd, 3rd and 4th electrons in three orbitals of the p-sublevel will be carried out as follows:

The filling of atomic orbitals from hydrogen, which has a charge number of 1, to krypton (Kr), with a charge number of 36, will be carried out as follows:

Such a representation of the order of filling of atomic orbitals is called an energy diagram. Based on the electronic diagrams of individual elements, it is possible to write down their so-called electronic formulas (configurations). So, for example, an element with 15 protons and, as a consequence, 15 electrons, i.e. phosphorus (P) will have the following energy diagram:

When converted into an electronic formula, the phosphorus atom will take the form:

15 P = 1s 2 2s 2 2p 6 3s 2 3p 3

The normal size numbers to the left of the sublevel symbol show the energy level number, and the superscripts to the right of the sublevel symbol show the number of electrons in the corresponding sublevel.

Below are the electronic formulas of the first 36 elements of the periodic table by D.I. Mendeleev.

period	Item no.	symbol	Name	electronic formula
I	1	H	hydrogen	1s 1
	2	He	helium	1s 2
II	3	Li	lithium	1s 2 2s 1
	4	Be	beryllium	1s 2 2s 2
	5	B	boron	1s 2 2s 2 2p 1
	6	C	carbon	1s 2 2s 2 2p 2
	7	N	nitrogen	1s 2 2s 2 2p 3
	8	O	oxygen	1s 2 2s 2 2p 4
	9	F	fluorine	1s 2 2s 2 2p 5
	10	Ne	neon	1s 2 2s 2 2p 6
III	11	Na	sodium	1s 2 2s 2 2p 6 3s 1
	12	Mg	magnesium	1s 2 2s 2 2p 6 3s 2
	13	Al	aluminum	1s 2 2s 2 2p 6 3s 2 3p 1
	14	Si	silicon	1s 2 2s 2 2p 6 3s 2 3p 2
	15	P	phosphorus	1s 2 2s 2 2p 6 3s 2 3p 3
	16	S	sulfur	1s 2 2s 2 2p 6 3s 2 3p 4
	17	Cl	chlorine	1s 2 2s 2 2p 6 3s 2 3p 5
	18	Ar	argon	1s 2 2s 2 2p 6 3s 2 3p 6
IV	19	K	potassium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 1
	20	Ca	calcium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2
	21	Sc	scandium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1
	22	Ti	titanium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2
	23	V	vanadium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3
	24	Cr	chromium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 here we observe the jump of one electron with s on d sublevel
	25	Mn	manganese	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5
	26	Fe	iron	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6
	27	Co	cobalt	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7
	28	Ni	nickel	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8
	29	Cu	copper	1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 here we observe the jump of one electron with s on d sublevel
	30	Zn	zinc	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10
	31	Ga	gallium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 1
	32	Ge	germanium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2
	33	As	arsenic	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3
	34	Se	selenium	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4
	35	Br	bromine	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5
	36	Kr	krypton	1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6

As already mentioned, in their ground state, electrons in atomic orbitals are located according to the principle of least energy. However, in the presence of empty p-orbitals in the ground state of the atom, often, by imparting excess energy to it, the atom can be transferred to the so-called excited state. For example, a boron atom in its ground state has an electronic configuration and an energy diagram of the following form:

5 B = 1s 2 2s 2 2p 1

And in an excited state (*), i.e. When some energy is imparted to a boron atom, its electron configuration and energy diagram will look like this:

5 B* = 1s 2 2s 1 2p 2

Depending on which sublevel in the atom is filled last, chemical elements are divided into s, p, d or f.

Finding s, p, d and f elements in the table D.I. Mendeleev:

• The s-elements have the last s-sublevel to be filled. These elements include elements of the main (on the left in the table cell) subgroups of groups I and II.
• For p-elements, the p-sublevel is filled. The p-elements include the last six elements of each period, except the first and seventh, as well as elements of the main subgroups of groups III-VIII.
• d-elements are located between s- and p-elements in large periods.
• f-Elements are called lanthanides and actinides. They are listed at the bottom of the D.I. table. Mendeleev.

DEFINITION

Atom– the smallest chemical particle.

The variety of chemical compounds is due to the different combinations of atoms of chemical elements into molecules and non-molecular substances. The ability of an atom to enter into chemical compounds, its chemical and physical properties are determined by the structure of the atom. In this regard, for chemistry, the internal structure of the atom and, first of all, the structure of its electronic shell are of paramount importance.

Atomic structure models

At the beginning of the 19th century, D. Dalton revived the atomic theory, relying on the fundamental laws of chemistry known by that time (constancy of composition, multiple ratios and equivalents). The first experiments were carried out to study the structure of matter. However, despite the discoveries made (atoms of the same element have the same properties, and atoms of other elements have different properties, the concept of atomic mass was introduced), the atom was considered indivisible.

After obtaining experimental evidence (late 19th - early 20th century) of the complexity of the structure of the atom (photoelectric effect, cathode and x-rays, radioactivity), it was found that the atom consists of negatively and positively charged particles that interact with each other.

These discoveries gave impetus to the creation of the first models of atomic structure. One of the first models was proposed J. Thomson(1904) (Fig. 1): the atom was imagined as a “sea of ​​positive electricity” with electrons oscillating in it.

After experiments with α-particles, in 1911. Rutherford proposed the so-called planetary model atomic structure (Fig. 1), similar to the structure of the solar system. According to the planetary model, at the center of the atom there is a very small nucleus with a charge Z e, the dimensions of which are approximately 1,000,000 times smaller than the dimensions of the atom itself. The nucleus contains almost the entire mass of the atom and has a positive charge. Electrons move in orbits around the nucleus, the number of which is determined by the charge of the nucleus. The external trajectory of the electrons determines the external dimensions of the atom. The diameter of an atom is 10 -8 cm, while the diameter of the nucleus is much smaller -10 -12 cm.

Rice. 1 Models of atomic structure according to Thomson and Rutherford

Experiments on studying atomic spectra showed the imperfection of the planetary model of the structure of the atom, since this model contradicts the line structure of atomic spectra. Based on Rutherford's model, Einstein's doctrine of light quanta and Planck's quantum theory of radiation Niels Bohr (1913) formulated postulates, which consists theory of atomic structure(Fig. 2): an electron can rotate around the nucleus not in any, but only in some specific orbits (stationary), moving along such an orbit it does not emit electromagnetic energy, radiation (absorption or emission of a quantum of electromagnetic energy) occurs during a transition (jump-like) electron from one orbit to another.

Rice. 2. Model of the structure of the atom according to N. Bohr

The accumulated experimental material characterizing the structure of the atom has shown that the properties of electrons, as well as other micro-objects, cannot be described on the basis of the concepts of classical mechanics. Microparticles obey the laws of quantum mechanics, which became the basis for the creation modern model of atomic structure.

The main theses of quantum mechanics:

- energy is emitted and absorbed by bodies in separate portions - quanta, therefore, the energy of particles changes abruptly;

- electrons and other microparticles have a dual nature - they exhibit the properties of both particles and waves (wave-particle duality);

— quantum mechanics denies the presence of certain orbits for microparticles (for moving electrons it is impossible to determine the exact position, since they move in space near the nucleus, you can only determine the probability of finding an electron in different parts of space).

The space near the nucleus in which the probability of finding an electron is quite high (90%) is called orbital.

Quantum numbers. Pauli's principle. Klechkovsky's rules

The state of an electron in an atom can be described using four quantum numbers.

n– main quantum number. Characterizes the total energy reserve of an electron in an atom and the number of the energy level. n takes on integer values ​​from 1 to ∞. The electron has the lowest energy when n=1; with increasing n – energy. The state of an atom when its electrons are at such energy levels that their total energy is minimal is called ground. States with higher values ​​are called excited. Energy levels are indicated by Arabic numerals according to the value of n. Electrons can be arranged in seven levels, therefore, n actually exists from 1 to 7. The main quantum number determines the size of the electron cloud and determines the average radius of an electron in an atom.

l– orbital quantum number. Characterizes the energy reserve of electrons in the sublevel and the shape of the orbital (Table 1). Accepts integer values ​​from 0 to n-1.

l depends on n. If n=1, then l=0, which means that there is a 1st sublevel at the 1st level.– magnetic quantum number. Characterizes the orientation of the orbital in space. Accepts integer values ​​from –l through 0 to +l. Thus, when l=1 (p-orbital), m e takes on the values ​​-1, 0, 1 and the orientation of the orbital can be different (Fig. 3).

Rice. 3. One of the possible orientations in space of the p-orbital

s– spin quantum number. Characterizes the electron's own rotation around its axis. Accepts values ​​-1/2(↓) and +1/2(). Two electrons in the same orbital have antiparallel spins.

The state of electrons in atoms is determined Pauli principle: an atom cannot have two electrons with the same set of all quantum numbers. The sequence of filling the orbitals with electrons is determined Klechkovsky rules: the orbitals are filled with electrons in increasing order of the sum (n+l) for these orbitals, if the sum (n+l) is the same, then the orbital with the smaller n value is filled first.

However, an atom usually contains not one, but several electrons, and to take into account their interaction with each other, the concept of effective nuclear charge is used - an electron in the outer level is subject to a charge that is less than the charge of the nucleus, as a result of which the internal electrons screen the external ones.

Basic characteristics of an atom: atomic radius (covalent, metallic, van der Waals, ionic), electron affinity, ionization potential, magnetic moment.

Electronic formulas of atoms

All the electrons of an atom form its electron shell. The structure of the electron shell is depicted electronic formula, which shows the distribution of electrons across energy levels and sublevels. The number of electrons in a sublevel is indicated by a number, which is written to the upper right of the letter indicating the sublevel. For example, a hydrogen atom has one electron, which is located in the s-sublevel of the 1st energy level: 1s 1.

The electronic formula of helium containing two electrons is written as follows: 1s 2.

For elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:

5 B 1s 2 2s 2 2p 1

The electronic formula of an element is determined by its position in the Periodic Table D.I. Mendeleev. Thus, the period number corresponds to In elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill In elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:

For elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:

In atoms of some elements, the phenomenon of electron “leap” from the outer energy level to the penultimate one is observed. Electron leakage occurs in atoms of copper, chromium, palladium and some other elements. For example:

24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1

an energy level that can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:

For elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:

The group number for elements of the main subgroups is equal to the number of electrons in the outer energy level; such electrons are called valence electrons (they participate in the formation of a chemical bond). Valence electrons for elements of side subgroups can be electrons of the outer energy level and the d-sublevel of the penultimate level. The group number of elements of secondary subgroups III-VII groups, as well as for Fe, Ru, Os, corresponds to the total number of electrons in the s-sublevel of the outer energy level and the d-sublevel of the penultimate level

Tasks:

Draw the electronic formulas of the phosphorus, rubidium and zirconium atoms. Indicate the valence electrons.

Answer:

15 P 1s 2 2s 2 2p 6 3s 2 3p 3 Valence electrons 3s 2 3p 3

37 Rb 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 5s 1 Valence electrons 5s 1

40 Zr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 2 5s 2 Valence electrons 4d 2 5s 2