Lecture: The structure of the electron shells of atoms of the elements of the first four periods: s-, p- and d-elements
The structure of the atom
The 20th century is the time of the invention of the "model of the structure of the atom". Based on the provided structure, it was possible to develop the following hypothesis: around a nucleus that is small enough in volume and size, electrons make movements similar to the movement of planets around the Sun. Subsequent study of the atom showed that the atom itself and its structure are much more complex than previously established. And at present, with enormous opportunities in the scientific field, the atom is not fully explored. Such components as an atom and molecules are considered to be objects of the microworld. Therefore, a person is not able to consider these parts on his own. In this world, completely different laws and rules are established, which differ from the macrocosm. Proceeding from this, the study of the atom is carried out on its model.
Each atom is assigned a serial number, fixed in Periodic table Mendeleeva D.I. For example, the serial number of the phosphorus atom (P) is 15.
So an atom is made up of protons (p + ) , neutrons (n 0 ) and electrons (e - ). Protons and neutrons form the nucleus of an atom, it has a positive charge. And the electrons moving around the nucleus "construct" the electron shell of the atom, which has a negative charge.
How many electrons are in an atom? It's easy to know. It is enough to look at the ordinal number of the element in the table.
So, the number of electrons in phosphorus is 15 . The number of electrons contained in the shell of an atom is strictly equal to the number of protons contained in the nucleus. So the protons in the nucleus of the phosphorus atom 15 .
The mass of protons and neutrons that make up the mass of the nucleus of an atom is the same. And electrons are 2000 times smaller. This means that the entire mass of the atom is concentrated in the nucleus, the mass of electrons is neglected. We can also find out the mass of the nucleus of an atom from the table. Look at the image of phosphorus in the table. Below we see the designation 30, 974 - this is the mass of the phosphorus nucleus, its atomic mass. When writing, we round this figure. Based on the foregoing, we write the structure of the phosphorus atom as follows:
(at the bottom left they wrote the charge of the nucleus - 15, at the top left the rounded value of the mass of the atom - 31).
The nucleus of a phosphorus atom:
(at the bottom left we write the charge: protons have a charge equal to +1, and neutrons are not charged, that is, charge 0; at the top left, the mass of a proton and a neutron, equal to 1, is a conventional unit of mass of an atom; the charge of an atom's nucleus is equal to the number of protons in the nucleus, which means p = 15, and the number of neutrons must be calculated: from atomic mass subtract the charge, i.e. 31 - 15 = 16).
The electron shell of the phosphorus atom is 15 negatively charged electrons that balance positively charged protons. Therefore, an atom is an electrically neutral particle.
Energy levels
Fig.1
Next, we need to analyze in detail how electrons are distributed in an atom. Their movement is not chaotic, but is subject to a specific order. Some of the available electrons are attracted to the nucleus with enough great strength, while others, on the contrary, attract weakly. The root cause of this behavior of electrons lies in varying degrees distance of electrons from the nucleus. That is, an electron closer to the nucleus will become more strongly interconnected with it. These electrons simply cannot be detached from the electron shell. The farther the electron is from the nucleus, the easier it is to "pull" it out of the shell. Also, the energy of an electron increases as it moves away from the nucleus of an atom. The electron energy is determined by the main quantum number n, which is equal to any natural number (1,2,3,4…). Electrons having the same value of n form one electron layer, as if fencing off other electrons moving at a remote distance. Figure 1 shows the electron layers contained in the electron shell at the center of the atom's nucleus.
You can notice how the volume of the layer increases as you move away from the core. Therefore, the farther the layer is from the nucleus, the more electrons it contains.
The electron layer contains electrons that are similar in terms of energy. Because of this, such layers are often referred to as energy levels. How many levels can an atom contain? The number of energy levels is equal to the number of the period in the periodic table D.I. in which the element is located. For example, phosphorus (P) is in the third period, so the phosphorus atom has three energy levels.
Rice. 2
How to find out the maximum number of electrons located on one electron layer? For this we use the formula Nmax = 2n 2
, where n is the level number. We get that the first level contains only 2 electrons, the second - 8, the third - 18, the fourth - 32.
Everyone energy level contains sublevels. Their letters are: s-, p-, d- and f-. Look at fig. 2:
Energy levels are marked with different colors, and sublevels with stripes of different thicknesses.
The thinnest sublevel is denoted by the letter s. 1s is the s-sublevel of the first level, 2s is the s-sublevel of the second level, and so on.
The p-sublevel appeared at the second energy level, the d-sublevel appeared at the third one, and the f-sublevel appeared at the fourth one.
Remember what you saw: the first energy level includes one s-sublevel, the second two s- and p-sublevels, the third three s-, p- and d-sublevels, and the fourth level four s-, p-, d- and f-sublevels.
On the Only 2 electrons can be in the s-sublevel, a maximum of 6 electrons in the p-sublevel, 10 electrons in the d-sublevel, and up to 14 electrons in the f-sublevel.
Electronic orbitals
The area (place) where an electron can be located is called an electron cloud or orbital. Keep in mind that we are talking about the probable region where the electron is located, since the speed of its movement is hundreds of thousands of times greater than the speed of the needle of a sewing machine. Graphically, this area is displayed as a cell:
One cell can contain two electrons. Judging by Figure 2, we can conclude that the s-sublevel, which includes no more than two electrons, can contain only one s-orbital, is denoted by one cell; The p-sublayer has three p-orbitals (3 slots), the d-sublayer has five d-orbitals (5 slots), and the f-sublayer has seven f-orbitals (7 slots).
The shape of the orbital depends on orbital quantum number (l - el) atom. Atomic energy level originates from s- an orbital that has l= 0. The presented orbital has a spherical shape. At the levels after s- orbitals are formed p- orbitals with l = 1. P Orbitals are shaped like dumbbells. There are only three orbitals with this shape. Each possible orbital contains no more than 2 electrons. Next are more complex structure d-orbitals ( l= 2), and after them f-orbitals ( l = 3).
Rice. 3 The shape of the orbitals
Electrons in orbitals are shown as arrows. If the orbitals contain one electron each, then they are unidirectional - arrow up: 
If there are two electrons in the orbital, then they have two directions: an arrow up and an arrow down, i.e. electrons are in opposite directions: 
This structure of electrons is called valence.
There are three conditions for filling atomic orbitals with electrons:
1 condition: The principle of the minimum amount of energy. The filling of orbitals starts from the sublevel having the minimum energy. According to this principle, the sublevels are filled in the following order: take a place in a sub-level of a higher level, although the sub-level of a lower level is not filled. For example, the valence configuration of a phosphorus atom looks like this:
Rice. 4
2 condition: Pauli principle. One orbital includes 2 electrons (electron pair) and no more. But the content of only one electron is also possible. It is called unpaired.
3 condition: Hund's rule. Each orbital of one sublevel is first filled with one electron, then a second electron is added to them. In life, we have seen a similar situation when unfamiliar bus passengers first occupy all the free seats one at a time, and then take two seats.
Electronic configuration of an atom in the ground and excited state
The energy of an atom in its ground state is the lowest. If atoms begin to receive energy from outside, for example, when a substance is heated, then they pass from the ground state to an excited one. This transition is possible in the presence of free orbitals to which electrons can move. But this is temporary, giving off energy, the excited atom returns to its ground state.
Let's consolidate our knowledge with an example. Consider the electronic configuration, i.e. the concentration of electrons in the orbitals of the phosphorus atom in the ground (unexcited state). Let us turn again to Fig. 4. So, remember that the phosphorus atom has three energy levels, which are represented by half-arcs: +15)))
Let's distribute the available 15 electrons into these three energy levels:
Such formulas are called electronic configurations. There are also electronic - graphic, they illustrate the placement of electrons inside the energy levels. The electronic-graphic configuration of phosphorus looks like this: 1s 2 2s 2 2p 6 3s 2 3p 3 (here the large numbers are the numbers of energy levels, the letters are the sublevels, and the small numbers are the number of electrons in the sublevel, if you add them up, you get the number 15).
In the excited state of the phosphorus atom 1, the electron moves from the 3s orbital to the 3d orbital, and the configuration looks like this: 1s 2 2s 2 2p 6 3s 1 3p 3 3d 1
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Electrons
The concept of an atom originated in the ancient world to denote the particles of matter. In Greek, atom means "indivisible".
The Irish physicist Stoney, on the basis of experiments, came to the conclusion that electricity is carried by the smallest particles that exist in the atoms of all chemical elements. In 1891, Stoney proposed to call these particles electrons, which in Greek means "amber". 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 a unit (-1). Thomson even managed to determine the speed of the electron (the speed of an electron in orbit is inversely proportional to the orbit number n. The radii of the orbits grow 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 / c, that is, about a hundred times less than the speed of light c=3 108 m/s.) and the mass of an electron (it is almost 2000 times less than the mass of a hydrogen atom).
The state of electrons in an atom
The state of an electron in an atom is 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., one can only speak of 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 as follows: if it were possible to photograph the position of an electron in an atom in hundredths or millionths of a second, as in a photo finish, then the electron in such photographs would be represented as points. Overlaying countless such photographs would result in a picture of an electron cloud with the highest density where there will be most of these points.
space around atomic nucleus where an electron is most likely to be found is called an orbital. It contains approximately 90% e-cloud, and this means that about 90% of the time the electron is in this part of space. Distinguished by shape 4 currently known types of orbitals, which are denoted by Latin letters s, p, d and f. Graphic image some forms of electron orbitals are shown in the figure.
The most important characteristic of the motion of an electron in a certain orbit is the 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.
An integer n, denoting the number of the energy level, is called the main quantum number. It characterizes the energy of electrons occupying a given energy level. The electrons of the first energy level, closest to the nucleus, have the lowest energy. Compared with the electrons of the first level, the electrons of the next levels will be characterized by a large amount of energy. Consequently, the electrons of the outer level are the least strongly bound to the nucleus of the atom.
The largest number of electrons in the energy level is determined by the formula:
N = 2n2,
where N is the maximum number of electrons; n is the level number, or the main quantum number. Consequently, the first energy level closest to the nucleus can contain 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 subdivided into sublevels (sublayers), which differ somewhat 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. Sublevels, in turn, are formed by orbitals. Each valuen corresponds to the number of orbitals equal to n.
It is customary to designate sublevels in Latin letters, as well as the shape of the orbitals of which they consist: s, p, d, f.
Protons and neutrons
Atom of any chemical element comparable to tiny solar system. Therefore, such a 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 the charge of electrons, but opposite in sign (+1), and a mass equal to the mass of a hydrogen atom (it is accepted in chemistry as a unit). Neutrons carry no charge, they are neutral and have a mass equal to that of a proton.
Protons and neutrons are collectively 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:
13 + 14 = 27
number of protons 13, number of neutrons 14, mass number 27
Since the mass of the electron, which is negligible, can be neglected, it is obvious that the entire mass of the atom is concentrated in the nucleus. Electrons represent e - .
Because the atom electrically neutral, it is also obvious that the number of protons and electrons in an atom is the same. It is equal to the ordinal number of the chemical element assigned to it in Periodic system. The mass of an atom is made up of the mass of protons and neutrons. Knowing the serial 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 the same nuclear charge but different mass numbers are called isotopes. Chemical elements found in nature are a mixture of isotopes. So, carbon has three isotopes with a mass of 12, 13, 14; oxygen - three isotopes with a mass of 16, 17, 18, etc. Usually given in the Periodic system, the relative atomic mass of a chemical element is the average value of the atomic masses of a natural mixture of isotopes of a given element, taking into account their relative content in nature. Chemical properties The isotopes of most chemical elements are exactly the same. However, hydrogen isotopes differ greatly in properties due to the dramatic fold increase in their relative atomic mass; they were even given individual titles and chemical signs.
Elements of the first period
Scheme of the electronic structure of the hydrogen atom:
Schemes of the electronic structure of atoms show the distribution of electrons over electronic layers (energy levels).
The graphical electronic formula of the hydrogen atom (shows the distribution of electrons over energy levels and sublevels):
Graphic electronic formulas of atoms show the distribution of electrons not only in levels and sublevels, but also in orbits.
In a helium atom, the first electron layer is completed - it has 2 electrons. Hydrogen and helium are s-elements; for these atoms, the s-orbital is filled with electrons.
All elements of the second period the first electron layer is filled, and the 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 rules of Pauli and Hund.
In the neon atom, the second electron layer is completed - it has 8 electrons.
For atoms of elements of the third period, the first and second electron layers are completed, so the third electron layer is filled, in which electrons can occupy 3s-, 3p- and 3d-sublevels.
A 3s electron orbital is completed at the magnesium atom. Na and Mg are s-elements.
For aluminum and subsequent elements, the 3p sublevel is filled with electrons.
The elements of the third period have unfilled 3d orbitals.
All elements from Al to Ar are p-elements. s- and p-elements form the main subgroups in the Periodic system.
Elements of the fourth - seventh periods
A fourth electron layer appears at the potassium and calcium atoms, the 4s sublevel is filled, since it has less 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 the secondary subgroups, they have a pre-external electron layer filled, they are referred to as transition elements.
Pay attention to the structure of the electron shells of chromium and copper atoms. In them, a “failure” of one electron from the 4s- to the 3d-sublevel occurs, 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 completed - all the 3s, 3p and 3d sublevels are filled in it, in total there are 18 electrons on them. In the elements following zinc, the fourth electron layer continues to be filled, the 4p sublevel.
Elements from Ga to Kr are p-elements.
The outer layer (fourth) of the krypton atom is complete and has 8 electrons. But there can only be 32 electrons in the fourth electron layer; the 4d- and 4f-sublevels of the krypton atom still remain unfilled. The elements of the fifth period are filling the sub-levels 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 outer electronic layer are filled, respectively.
4f elements are called lanthanides.
5f elements are called actinides.
The order of filling of 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 even here there are elements in which the order of filling of electronic orbitals is “violated”, which, for example, is associated with greater energy stability of half and completely 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 electronic 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 III-VIII groups.
- d-elements. The d-sublevel of the preexternal level of the atom is filled with electrons; d-elements include elements of secondary subgroups of groups I-VIII, i.e., elements of intercalary decades of large periods located between s- and p-elements. They are also called transition elements.
- f-elements. The f-sublevel of the third outside level of the atom is filled with electrons; these include the 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 - “spindle”), i.e. having such properties that can be conditionally 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, that is, 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 electron shells of atoms is depicted using energy or quantum cells - they write down the so-called graphic electronic formulas. For this record, the following notation is used: each quantum cell is denoted by a cell that corresponds to one orbital; each electron is indicated by an arrow corresponding to the direction of the spin. When writing a graphical electronic formula, two rules should be remembered: Pauli principle and F. Hund's rule, according to which electrons occupy free cells first one at a time and at the same time have the same spin value, and only then they pair, but the spins, according to the Pauli principle, will already be oppositely directed.
Hund's rule and Pauli's principle
Hund's rule- the rule of quantum chemistry, which determines the order of filling the orbitals of a certain sublayer and is formulated as follows: the total value of the spin quantum number of electrons of this sublayer should be maximum. Formulated by Friedrich Hund in 1925.
This means that in each of the orbitals of the sublayer, one electron is first filled, and only after the exhaustion of unfilled orbitals, a second electron is added to this orbital. In this case, there are two electrons with half-integer spins of the opposite sign in one orbital, which pair (form a two-electron cloud) and, as a result, the total spin of the orbital becomes equal to zero.
Other wording: Below in energy lies the atomic term for which two conditions are satisfied.
- Multiplicity is maximum
- When the multiplicities coincide, the total orbital momentum L is maximum.
Let's analyze this rule using the example of filling the orbitals of the p-sublevel 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 orientation of the spin).
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 ordinal numbers of chemical elements), atomic orbitals are populated in such a way that the appearance of electrons in higher-energy orbitals depends only on the principal quantum number n and does not depend on all other quantum numbers. numbers, including those 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 remoteness of the electron charge density from the nucleus and does not depend on the features of its motion in the field of the nucleus.
The empirical rule of Klechkovsky and the sequence of sequences of a somewhat contradictory real energy sequence of atomic orbitals arising from it only in two cases of the same type: 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 stable state of the atom, namely: after filling the orbital 6 with two electrons s
Chemicals are the things that make up the world around us.
The properties of each chemical substance are divided into two types: these are 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 environments(water, alcohol, etc.), density, color, taste, etc.
Transformations of some chemical substances into other substances are called chemical phenomena or chemical reactions. It should be noted that there are also physical phenomena, which, obviously, are accompanied by a change in some physical properties substances without being converted into other substances. To physical phenomena, for example, include the melting of ice, the freezing or evaporation of water, etc.
The fact that in the course of any process a chemical phenomenon takes place can be concluded by observing characteristics chemical reactions such as color change, precipitation, gas evolution, heat and/or light evolution.
So, for example, a conclusion about the course of chemical reactions can be made by observing:
The formation of sediment when boiling water, called scale in everyday life;
The release of heat and light during the burning of a fire;
Changing the color of a slice of a fresh apple in the air;
The formation of gas bubbles during the fermentation of dough, etc.
The smallest particles of matter, which in the process of chemical reactions practically do not undergo changes, but only in a new way are connected to each other, 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 the ancient Greek philosophers, atoms are not the absolute minimum of matter, i.e. themselves have a complex structure.
Each atom consists of the so-called subatomic particles - protons, neutrons and electrons, denoted 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 the atom, each atom has all the protons and neutrons concentrated in the so-called nucleus, around which the electrons form an electron shell.
The proton and neutron have practically the same masses, i.e. m p ≈ m n , and the electron mass is almost 2000 times less than the mass of each of them, i.e. m p / m e ≈ m n / m e ≈ 2000.
Insofar as 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.
So, for example, the table below shows the possible composition of atoms:
The 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, has the name "hydrogen" and is denoted by the symbol "H", which is read as "ash", and the 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, the atoms of one chemical element can differ in the number of neutrons in the nuclei.
Atoms belonging to the same chemical element, but having a different number of neutrons and, as a result, mass, are called isotopes.
So, for example, the chemical element hydrogen has three isotopes - 1 H, 2 H and 3 H. The indices 1, 2 and 3 above the H symbol 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 there are no neutrons at all in the 1 H isotope (1-1 = 0), in the 2 H isotope - 1 neutron (2-1=1) and in the isotope 3 H - two neutrons (3-1=2). Since, as already mentioned, a neutron and a proton have the same masses, and the mass of an electron is negligible compared to 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 as heavy. . In connection with such a large spread in the masses of hydrogen isotopes, the 2 H and 3 H isotopes were even given separate individual names and symbols, which is not typical of any other chemical element. The 2 H isotope was named deuterium and given the symbol D, and the 3 H isotope was given the name tritium and given the symbol T.
If we take the mass of the proton and neutron as unity, 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 denoted 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). Denoting the number of neutrons in an atom with the letter N, mathematically the relationship between mass number, charge number and number of neutrons can be expressed 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 a mass and a 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, representations are used quantum mechanics, 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 the atomic orbital.
An atomic orbital can have a different shape, size and orientation. 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, within the framework of school course chemistry, only the consequences of quantum mechanical theory are considered.
According to these consequences, any atomic orbital and an electron located on it are completely characterized by 4 quantum numbers.
- The main 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 integers, 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 values 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 and do not have a direction in space:
Orbitals with l = 1 are called p-orbitals. These orbitals have the shape of a three-dimensional figure eight, i.e. the shape obtained by rotating the figure eight around the 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) The magnetic quantum number - m l - determines the spatial orientation of a particular atomic orbital and expresses the projection of the orbital angular momentum on the direction 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, with l = 0 m l = 0 (one value), with l = 1 m l = -1, 0, +1 (three values), with l = 2 m l = -2, -1, 0, +1 , +2 (five values of the 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 eight”, correspond to three values of the magnetic quantum number (-1, 0, +1), which, in turn, corresponds to three directions in space perpendicular to each other.
4) The spin quantum number (or simply spin) - m s - can be conditionally considered responsible for the direction of rotation of an electron in an atom, it can take on values. Electrons with different spins are indicated by vertical arrows pointing in different sides: ↓ and .
The set of all orbitals in an atom that have the same value of the principal quantum number is called the energy level or electron shell. Any arbitrary energy level with some number n consists of n 2 orbitals.
The set of orbitals with the same values of the principal quantum number and the orbital quantum number is an energy sublevel.
Each energy level, which corresponds to the main quantum number n, contains n sublevels. In turn, each energy sublevel with an orbital quantum number l consists of (2l + 1) orbitals. Thus, the s-sublayer consists of one s-orbital, the p-sublayer - three p-orbitals, the d-sublayer - five d-orbitals, and the f-sublayer - 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 depicted as follows:
Each orbital corresponds to an individual strictly defined set of three quantum numbers n, l and m l .
The distribution of electrons in orbitals is called the electron configuration.
The filling of atomic orbitals with electrons occurs in accordance with three conditions:
- The principle of minimum energy: electrons fill orbitals starting from the lowest energy sublevel. The sequence of sublevels in order of increasing energy is as follows: 1s<2s<2p<3s<3p<4s≤3d<4p<5s≤4d<5p<6s…;
In order to make it easier to remember this sequence of filling electronic sublevels, the following graphic illustration is very convenient:
- Pauli principle: Each orbital can hold at most two electrons.
If there is one electron in the 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 the 1st, 2nd, 3rd and 4th electrons on three orbitals of the p-sublevel will be carried out as follows:
The filling of atomic orbitals from hydrogen, which has a charge number equal to 1, to krypton (Kr) with a charge number of 36, will be carried out as follows:
A similar representation of the order in which atomic orbitals are filled is called an energy diagram. Based on the electronic diagrams of individual elements, you can write down their so-called electronic formulas (configurations). So, for example, an element with 15 protons and, as a result, 15 electrons, i.e. phosphorus (P) will have the following energy diagram:
When translated into an electronic formula, the phosphorus atom will take the form:
15 P = 1s 2 2s 2 2p 6 3s 2 3p 3
Normal-sized digits to the left of the sublevel symbol show the number of the energy level, and 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 D.I. Mendeleev.
| period | Item No. | symbol | title | electronic formula |
| I | 1 | H | hydrogen | 1s 1 |
| 2 | He | helium | 1s2 | |
| II | 3 | Li | lithium | 1s2 2s1 |
| 4 | Be | beryllium | 1s2 2s2 | |
| 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 s on the 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 s on the 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 arranged according to the principle of least energy. Nevertheless, in the presence of empty p-orbitals in the ground state of an atom, often, when excess energy is imparted to it, the atom can be transferred to the so-called excited state. So, 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 the excited state (*), i.e. when imparting some energy to the boron atom, its electronic 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:
- 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 for the first and seventh, as well as elements of the main subgroups of III-VIII groups.
- d-elements are located between s- and p-elements in large periods.
- The f-elements are called lanthanides and actinides. They are placed at the bottom of the table by D.I. Mendeleev.
An atom is the smallest particle of a chemical substance that is capable of retaining its properties. The word "atom" comes from the ancient Greek "atomos", which means "indivisible". Depending on how many and what particles are in the atom, you can determine the chemical element.
Briefly about the structure of the atom
As you can briefly list the basic information about is a particle with one nucleus, which is positively charged. Around this nucleus is a negatively charged cloud of electrons. Every atom in its normal state is neutral. The size of this particle can be completely determined by the size of the electron cloud that surrounds the nucleus.
The nucleus itself, in turn, also consists of smaller particles - protons and neutrons. Protons are positively charged. Neutrons carry no charge. However, protons, along with neutrons, are combined into one category and are called nucleons. If you need basic information about the structure of the atom briefly, then this information can be limited to the listed data..
The first information about the atom
The fact that matter can consist of small particles was suspected even by the ancient Greeks. They believed that everything that exists is made up of atoms. However, this view was purely philosophical in nature and cannot be interpreted scientifically.
An English scientist was the first to obtain basic information about the structure of the atom. It was this researcher who was able to discover that two chemical elements can enter into different ratios, and each such combination will represent a new substance. For example, eight parts of the element oxygen give rise to carbon dioxide. Four parts of oxygen is carbon monoxide.
In 1803, Dalton discovered the so-called law of multiple ratios in chemistry. With the help of indirect measurements (since not a single atom could then be examined under the then microscopes), Dalton concluded about the relative weight of atoms.
Rutherford's research
Almost a century later, the basic information about the structure of atoms was confirmed by another English chemist - the scientist proposed a model of the electron shell of the smallest particles.
At that time, Rutherford's "Planetary Model of the Atom" was one of the most important steps that chemistry could take. Basic information about the structure of the atom testified that it is similar to the solar system: particles-electrons rotate around the nucleus in strictly defined orbits, just as the planets do.
Electronic shell of atoms and formulas of atoms of chemical elements
The electron shell of each of the atoms contains exactly as many electrons as there are protons in its nucleus. That is why the atom is neutral. In 1913, another scientist received basic information about the structure of the atom. Niels Bohr's formula was similar to Rutherford's. According to his concept, electrons also revolve around the nucleus located in the center. Bohr finalized Rutherford's theory, introduced harmony into its facts.
Even then, the formulas of some chemicals were drawn up. For example, schematically the structure of the nitrogen atom is denoted as 1s 2 2s 2 2p 3, the structure of the sodium atom is expressed by the formula 1s 2 2s 2 2p 6 3s 1. Through these formulas, you can see how many electrons move in each of the orbitals of a particular chemical.
Schrödinger model
However, then this atomic model became outdated. Basic information about the structure of the atom, known to science today, has largely become available thanks to the research of the Austrian physicist
He proposed a new model of its structure - a wave one. By this time, scientists had already proved that the electron was endowed not only with the nature of a particle, but had the properties of a wave.
However, the Schrödinger and Rutherford model also has some general provisions. Their theories are similar in that electrons exist at certain levels.
Such levels are also called electronic layers. The level number can be used to characterize the energy of an electron. The higher the layer, the more energy it has. All levels are counted from bottom to top, so the level number corresponds to its energy. Each of the layers in the electron shell of an atom has its own sublevels. In this case, the first level can have one sublevel, the second - two, the third - three, and so on (see the above electronic formulas of nitrogen and sodium).
Even smaller particles
At the moment, of course, even smaller particles have been discovered than the electron, proton and neutron. It is known that the proton consists of quarks. There are even smaller particles of the universe - for example, a neutrino, which is a hundred times smaller than a quark and a billion times smaller than a proton.
A neutrino is such a small particle that it is 10 septillion times smaller than, for example, a Tyrannosaurus rex. The tyrannosaurus itself is as many times smaller than the entire observable universe.
Basic information about the structure of the atom: radioactivity
It has always been known that no chemical reaction can change one element into another. But in the process of radioactive emission, this happens spontaneously.
Radioactivity is called the ability of the nuclei of atoms to turn into other nuclei - more stable. When people received basic information about the structure of atoms, isotopes could, to a certain extent, serve as the embodiment of the dreams of medieval alchemists.
During the decay of isotopes, radioactive radiation is emitted. This phenomenon was first discovered by Becquerel. The main type of radioactive radiation is alpha decay. It releases an alpha particle. There is also beta decay, in which a beta particle is ejected from the nucleus of an atom, respectively.
Natural and artificial isotopes
Currently, about 40 natural isotopes are known. Most of them are located in three categories: uranium-radium, thorium and actinium. All these isotopes can be found in nature - in rocks, soil, air. But besides them, about a thousand artificially derived isotopes are also known, which are obtained in nuclear reactors. Many of these isotopes are used in medicine, especially in diagnostics..
Proportions within an atom
If we imagine an atom, the size of which will be comparable to the size of an international sports stadium, then we can visually obtain the following proportions. The electrons of an atom in such a "stadium" will be located at the very top of the stands. Each one will be smaller than a pinhead. Then the nucleus will be located in the center of this field, and its size will be no larger than the size of a pea.
Sometimes people ask what an atom really looks like. In fact, it literally does not look like anything - not for the reason that insufficiently good microscopes are used in science. The dimensions of an atom are in those areas where the concept of "visibility" simply does not exist.
Atoms are very small. But how small are these dimensions really? The fact is that the smallest grain of salt barely visible to the human eye contains about one quintillion atoms.
If we imagine an atom of such a size that could fit in a human hand, then next to it there would be viruses 300 meters long. Bacteria would be 3 km long and a human hair would be 150 km thick. In the supine position, he could go beyond the boundaries of the earth's atmosphere. And if such proportions were real, then a human hair in length could reach the moon. This is such a complex and interesting atom, the study of which scientists continue to study to this day.
laboratory works
workshops
independent classroom work
independent homework (standard calculation)
control (defenses, colloquia, test, exam)
Textbooks and study guides
N.V. Korovin. general chemistry
General chemistry course. Theory and problems (under the editorship of N.V. Korovin, B.I. Adamson)
N.V. Korovin and others. Laboratory work in chemistry
Calendar plan
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Introduction to Chemistry
Chemistry at the Energy Institute is a fundamental general theoretical discipline.
Chemistry is a natural science that studies the composition, structure, properties and transformations of substances, as well as the phenomena that accompany these transformations.
M.V. Lomonosov |
D.I. Mendeleev |
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“Chemical |
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"Fundamentals of Chemistry" 1871 |
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properties |
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d.) – “Chemistry – |
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the doctrine of the elements and |
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chemical |
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transformations are taking place."
"Golden Age of Chemistry" (late XIX - early XX centuries)
Periodic law of D.I. Mendeleev (1896)
The concept of valency introduced by E. Frankland (1853)
Theory of the structure of organic compounds A.M.Butlerov (1861-1863)
Theory of complex compounds A. Werner
The law of mass action by M. Gultberg and L. Waage
Thermochemistry, developed mainly by G.I. Hess
Theory of electrolytic dissociation by S. Arrhenius
The principle of moving equilibrium by A. Le Chatelier
J.W. Gibbs phase rule
The theory of the complex structure of the atom Bohr-Sommerfeld (1913-1916)
Significance of the modern stage of development of chemistry
Understanding the laws of chemistry and their application allows you to create new processes, machines, installations and devices.
Obtaining electricity, fuel, metals, various materials, food, etc. directly related to chemical reactions. For example, electrical and mechanical energy is currently mainly obtained by converting the chemical energy of natural fuel (combustion reactions, the interaction of water and its impurities with metals, etc.). Without an understanding of these processes, it is impossible to ensure the efficient operation of power plants and internal combustion engines.
Knowledge of chemistry is necessary for:
- formation of scientific outlook,
- for the development of figurative thinking,
- creative growth of future specialists.
The modern stage in the development of chemistry is characterized by the widespread use of quantum (wave) mechanics for the interpretation and calculation of the chemical parameters of substances and systems of substances and is based on a quantum mechanical model of the structure of the atom.
An atom is a complex electromagnetic microsystem, which is the carrier of the properties of a chemical element.
STRUCTURE OF THE ATOM
Isotopes are varieties of atoms of the same chemical
elements that have the same atomic number but different atomic numbers
Mr (Cl) \u003d 35 * 0.7543 + 37 * 0.2457 \u003d 35.491
Fundamentals of quantum mechanics
Quantum mechanics- behavior of moving micro-objects (including electrons) is
the simultaneous manifestation of both the properties of particles and the properties of waves is a dual (corpuscular-wave) nature.
Energy quantization: Max Planck (1900, Germany) -
substances emit and absorb energy in discrete portions (quanta). The energy of a quantum is proportional to the frequency of radiation (oscillations) ν:
h is Planck's constant (6.626 10-34 J s); ν=с/λ , с – speed of light, λ – wavelength
Albert Einstein (1905): any radiation is a flux of energy quanta (photons) E = m v 2
Louis de Broglie (1924, France): electron is also characterizedcorpuscular-waveduality - radiation propagates like a wave and consists of small particles (photons)
Particle - m, |
mv , E=mv 2 |
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Wave - , |
E 2 \u003d h \u003d hv / |
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uncertainty |
Werner Heisenberg (1927, |
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less than h/2
x (mv) h/2 (- error, uncertainty) I.e. the position and momentum of a particle cannot be determined in principle at any time with absolute accuracy.
Electron Cloud Atomic Orbital (AO)
That. the exact location of a particle (electron) is replaced by the concept of the statistical probability of finding it in a certain volume (near the nuclear) space.
The movement e- has a wave character and is described
2 dv is the probability density of finding e- in a certain volume near the nuclear space. This space is called atomic orbital (AO).
In 1926, Schrödinger proposed an equation that mathematically describes the state of e in an atom. Solving it
find the wave function. In a simple case, it depends on 3 coordinates
An electron carries a negative charge, its orbital represents a certain charge distribution and is called electron cloud
QUANTUM NUMBERS
Introduced to characterize the position of an electron in an atom in accordance with the Schrödinger equation
1. Principal quantum number(n)
Determines the energy of an electron - energy level
shows the size of the electron cloud (orbitals)
takes values from 1 to
n (energy level number): 1 2 3 4 etc.
2. Orbital quantum number(l) :
determines - the orbital angular momentum of the electron
shows the shape of the orbital
takes values - from 0 to (n -1)
Graphically, the AO is represented by the Orbital quantum number: 0 1 2 3 4
Energy sublevel: s p d f g
E increases
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Each n corresponds to a certain number of l values, i.e. each energy level is split into sublevels. The number of sublevels is equal to the level number.
1st energy level → 1 sublevel → 1s 2nd energy level → 2 sublevels → 2s2p 3rd energy level → 3 sublevels → 3s 3p 3d
4th energy level → 4 sublevels → 4s 4p 4d 4f etc.
3. Magnetic quantum number(ml)
defines – the value of the projection of the orbital angular momentum of the electron on an arbitrarily selected axis
shows - the spatial orientation of the AO
takes values – from –l to + l
Any value of l corresponds to (2l +1) values of the magnetic quantum number, i.e. (2l +1) possible locations of an electron cloud of a given type in space.
s - state - one orbital (2 0+1=1) - m l = 0, because l = 0
p - state - three orbitals (2 1+1=3)
m l : +1 0 -1, because l=1
ml =+1 |
m l =0 |
m l = -1 |
All orbitals belonging to the same sublevel have the same energy and are called degenerate.
Conclusion: AO is characterized by a certain set of n, l, m l , i.e. certain sizes, shape and orientation in space.
4. Spin quantum number (m s )
"spin" - "spindle"
determines - the intrinsic mechanical moment of an electron associated with its rotation around its axis
takes the values - (-1/2 h/2) or (+1/2 h/2)
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Principles and rules
Electronic configurations of atoms
(in the form of electronic configuration formulas)
Indicate the numbers of the energy level number
The letters indicate the energy sublevel (s, p, d, f);
Sublevel exponent means number
electrons at a given sublevel
19 K 1s2 2s2 2p 6 3s 2 3p 6 4s 1
minimum
Electrons in an atom occupy the lowest energy state corresponding to its most stable state.
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
Increase E
Klechkovsky
Electrons are placed sequentially in orbitals characterized by an increase in the sum of the main and orbital quantum numbers (n + l) ; for the same values of this sum, the orbital with a lower value of the principal quantum number n is filled earlier
1s<2 s < 2 p = 3 s < 3 p = 4 s < 3 d = 4 p и т. д
