The principle of Pauli Chemistry. Quantum numbers. Principle Pauli. Rule Hund. I. Organizational moment
Introduction
In 1925, Pauli established a quantum - a mechanical principle (Pauli's prohibition principle).
In any atom, there can be no two electrons in the same stationary states determined by a set of four quantum numbers: N, M, MS.
For example, at the energy level there may be no more than two electrons, but with the opposite direction of spins.
The principle of Pauli gave the opportunity to theoretically justify the periodic system of Mendeleev elements, create quantum statisticians, modern theory of solid bodies, etc.
Powli principle
The state of each electron in the atom is characterized by four quantum numbers:
1. The main quantum number n (n \u003d 1, 2 ...).
2. Orbital (azimuthal) quantum number L (L \u003d 0, 1, 2, ... N-1).
3. Magnetic quantum number M (m \u003d 0, +/- 1, +/- 2, + / -... +/- L).
4. Spin quantum number MS (MS \u003d +/- 1/2).
For one fixed value of the main quantum number N, there are 2N2 different quantum electron states.
One of the laws of quantum mechanics, called Powli principle, claims:
In the same atom, there cannot be two electrons with the same set of quantum numbers (i.e., there can be no two electrons in the same state).
The principle of Pauli gives an explanation of the periodic repeatability of the properties of the atom, i.e. Periodic system of Mendeleev elements.
Periodic system of elements D. I. Mendeleev
In 1869, Mendeleev opened a periodic law of changing the chemical and physical properties of elements. He introduced the concept of the order number of the element and received complete frequency in changing the chemical properties of the elements.
In this case, part of the cells of the periodic system remained blank, because The corresponding elements were unknown by that time. In 1998, an isotope of the 114th element was synthesized in Russia.
Mendeleev predicted a number of new elements (Scandium, Germany, etc.) and described their chemical properties. Later, these elements were open, which fully confirmed the justice of his theory. It was even possible to clarify the values \u200b\u200bof atomic masses and some properties of elements.
The chemical properties of atoms and a number of their physical properties are explained by the behavior of external (valence) electrons.
Stationary quantum states of the electron in the atom (molecule) are characterized by a set of 4 quantum numbers: the main (N), orbital (L), magnetic (M) and magnetic spin (MS). Each of them characterizes quantization: energies (N), moment of impulse (L), the projections of the moment of impulse to the direction of the external magnetic field (M) and the projection of the back (MS).
According to the theory, the sequence number of the chemical element Z is equal to the total number of electrons in the atom.
If z is the number of electrons in an atom located in a state, which is set by a set of 4 quantum numbers N, L, M, MS, then z (n, l, m, ms) \u003d 0 or 1.
If z is the number of electrons in the atom located in states determined by the set of 3 quantum numbers n, l, m, then z (n, l, m) \u003d 2. Such electrons are characterized by the orientation of the spins.
If z is the number of electrons in the atom in the states determined by 2 quantum numbers N, L, then z (n, l) \u003d 2 (2L + 1).
If z is the number of electrons in the atom, which are in states determined by the value of the main quantum number n, then z (n) \u003d 2N2.
Electrons in the atom that occupy the set of states with the same values \u200b\u200bof the main quantum number n form the electronic layer: at n \u003d 1 to the layer; at n \u003d 2 l - layer; at n \u003d 3 m - layer; at n \u003d 4 n - layer; at n \u003d 5 o - layer, etc.
In each electronic layer of the atom, all electrons are distributed through the shells. The shell corresponds to a certain value of the orbital quantum number (Table 1 and Fig. 1).
| n. | Electronic layer | Number of electrons in shells | Total number of electrons | ||||
| s (L \u003d 0) | p (L \u003d 1) | d (L \u003d 2) | f (L \u003d 3) | g (L \u003d 4) | |||
| 1 | K. | 2 | - | - | - | - | 2 |
| 1 | L. | 2 | 6 | - | - | - | 8 |
| 3 | M. | 2 | 6 | 10 | - | - | 18 |
| 4 | N. | 2 | 6 | 10 | 14 | - | 32 |
| 5 | O. | 2 | 6 | 10 | 14 | 18 | 50 |
At a given L, the magnetic quantum number M accepts 2L + 1 values, and MS - two values. Therefore, the number of possible states in the electronic shell with a given L is 2 (2L + 1). So the shell L \u003d 0 (S - the shell) is filled with two electrons; Shell L \u003d 1 (P - shell) - six electrons; shell L \u003d 2 (D - shell) - ten electrons; Shell L \u003d 3 (F - shell) - fourteen electrons.
The sequence of filling the electron layers and shells in the periodic system of Mendeleev elements is explained by quantum mechanics and is based on 4 positions:
1. The total number of electrons in the atom of this chemical element is equal to the sequence of Z.
2. The state of the electron in the atom is determined by a set of 4 quantum numbers: N, L, M, MS.
3. The distribution of electrons in an atom of energy states should satisfy the minimum of energy.
4. Filling with electrons of energy states in the atom should occur in accordance with the principle of Pauli.
When considering atoms with a large z, due to the increase in the charge of the kernel, the electron layer is tightened to the kernel and begins to fill the layer with n \u003d 2, etc. At a given n, the state of S-electrons (L \u003d 0) is filled out, then P-electrons (L \u003d 1), D-electrons (L \u003d 2), etc. This leads to the frequency of chemical and physical properties of elements. For the elements of the first period, the 1S shell is first completed; For electrons of the second and third periods - 2S, 2P and 3S and 3r shells.
However, starting from the fourth period (element of potassium, z \u003d 19), the sequence of filling the shells is disturbed due to the competition of electrons close on energy. Reliable electrons with large N, but smaller L (for example, 4S electrons are stronger than 3D) can be stronger than (energetically more profitable).
The distribution of electrons in the atom of the shells determine its electronic configuration. To indicate the electronic configuration of the atom, they write to a number of symbols of filling the electronic states of the NL shells, starting close to the kernel. The index on the right is the number of electrons in the shell, which are in these states. For example, at the sodium atom 2311Na, where Z \u003d 11 is the sequence number of the element in the Mendeleev table; the number of electrons in the atom; the number of protons in the kernel; A \u003d 23 is a mass number (the number of protons and neutrons in the kernel). The electronic configuration is: 1S2 2S2 2P6 3S1, i.e. in the layer with n \u003d 1 and l \u003d 0 - two S-electrons; in the layer with n \u003d 2 and l \u003d 0 - two s electrons; in the layer with n \u003d 2 and l \u003d 1 - six p-electrons; In the layer with n \u003d 3 and l \u003d 0 - one s-electron.
Along with the normal electronic configuration of the atom corresponding to the most durable binding energy of all electrons, an excited electronic configuration occurs when one or more electrons is excited.
For example, in helium, all levels of energy are divided into two levels of levels: the system of levels of orthoglius, corresponding to the parallel orientation of the spins of electrons and the system of paraghelium levels corresponding to the anti-parallel spin orientation. The normal configuration of Helium 1s2 due to the principle of Pauli is possible only with an anti-parallel orientation of the spins of electrons corresponding to the paragelion.
Conclusion
So, the principle of ban on Pauli explains for a long time considered a mysterious, periodic structure of elements, open D.I. Medeleev.
Bibliography
1. Detlaf A.A., Yavorsky B.N. Course of physics. - M., 1989.
2. Kompanac A.S. What is a quantum mechanic? - M., 1977.
3. Orira J. Popular Physics. - M., 1964.
4. Trofimova T.I. Course of physics. - M., 1990.
The textbook is intended for students of non-chemical specialties of higher educational institutions. It can serve as a manual for individuals who have been studying the foundations of chemistry, and for students of chemical technical schools and high school classes.
The legendary textbook translated into many languages \u200b\u200bof Europe, Asia, Africa and issued by a total circulation over 5 million copies.
When making a file, the site http://alnam.ru/book_chem.php
Book:
| <<< Назад
|
Forward \u003e\u003e\u003e |
To determine the state of the electron in a lot of an electronic atom, a formulated V. Pauli is important ( powli principle), Whereby there can be no two electrons in the atom, in which all four quantum numbers would be the same. It follows from this that each atomic orbital characterized by certain values \u200b\u200bof N, L and M can be occupied by no more than two electrons whose backs have opposite signs. Two such electrons located on the same orbitals and possessing oppositely directed backs are called paired, in contrast to the single (i.e. unpaired) Electron, which occupies any orbital.
Using the Powli principle, we calculate what the maximum number of electrons can be located at various energy levels and sublevels in the atom.
At l \u003d 0, i.e. On S-sugro, the magnetic quantum number is also zero. Consequently, there is only one orbital on S-sugliner, which is customary to designate in the form of a cell ("Quantum cell") :?.
As mentioned above, no more than two electrons are placed on each atomic orbital, whose backs are oppositely directed. This can be symbolically present to the following scheme:
So, the maximum number of electrons on the S-lint of each electron layer is 2. at l \u003d 1 (p-sublayer) already three different values \u200b\u200bof the magnetic quantum number (-1, 0, +1) are possible. Hence. There are three orbitals on p-suds, each of which can be occupied by no more than two electrons. Total 6 electrons can accommodately accommodate
The sublayer D (L \u003d 2) consists of five orbital, corresponding to five different values \u200b\u200bm; Here, the maximum number of electrons is 10:
Finally, 14 electrons can be placed on f-supel (L \u003d 3); In general, the maximum number of electrons on a suite with an orbital quantum number L is 2 (2L + 1).
The first energy level (k-layer, n \u003d 1) contains only an S-sublayer, the second energy level (L-layer, n \u003d 2) consists of S- and p-lints, etc. Considering this, we will make a table of the maximum number of electrons placed in various electronic layers (Table 2).
As shown in the table. 2 Data, the maximum number of electrons at each energy level is 2N 2, where n is the corresponding value of the main quantum number. So, in the k-layer there may be a maximum of 2 electrons (2 · 1 2 \u003d 2), in the L-layer - 8 electrons (2 · 2 2 \u003d 8), in the m-layer - 18 electrons (2 · 3 2 \u003d 18 ) etc. Note that the obtained numbers coincide with the numbers of elements in the periodic periodic periods.
The most stable state of the electron in the atom corresponds to the minimum possible value of its energy. Any other of his condition is excitedUnstable: from it the electron is spontaneously moving into a state with lower energy. Therefore, in an unexcited atom of hydrogen (the charge of the nucleus Z \u003d 1) is the only electron is in the lowest possible energy states, i.e. on 1S-supro. The electronic structure of the hydrogen atom can be submitted by the scheme
or write like this: 1S 1 (one ES one is read).
Table 2. Maximum number of electrons on atomic energy levels and sublevels
In the helium atom (z \u003d 2), the second electron is also in 1s state. Its electronic structure (1S 2 - read "one ES two") is depicted by the scheme:
This element ends filling the K-layer nearest to the kernel and thus the construction of the first period of the electron system is completed.
In the following helium of the element - lithium (z \u003d 3), the third electron can no longer be located on the K-layer orbitals: this would contradict the principle of Pauli. Therefore, it occupies the S-state of the second energy level (L-layer, n \u003d 2). Its electronic structure is recorded by formula 1S 2 2S 1, which corresponds to the scheme:
The number and the mutual arrangement of quantum cells on the last scheme shows that 1) electrons in the lithium atom are located on two energy levels, and the first of which consists of one sublayer (1S) and is fully filled; 2) the second - the external-energy level corresponds to a higher energy and consists of two sublevels (2s and 2p); 3) 2S-sublayer includes one orbital, on which one electron is located in the lithium atom; 4) 2p-pylon includes three energetically equivalent orbital, which corresponds to higher energy than the energy corresponding to 2S orbital; In an unexcited, 2P orbital lithium atom remain unoccupied.
In the future, on electronic circuits, we will only specify non-fully occupied energy levels. In accordance with this, the structure of the electronic shell of the atom of the next element of the second period - beryllium (Z \u003d 4) - is expressed by the scheme
or 1s 2 2S 2 formula. Thus, as in the first period, the construction of the second period begins with the elements in which the S-electrons of the new electronic layer first appear. Due to the similarity in the structure of the outer electronic layer, such elements exhibit a lot in common and in their chemical properties. Therefore, they are customary to the general family s-elements.
The electronic structure of the atom of the following beryllium element - boron (Z \u003d 5) is depicted by the scheme
and can be expressed by 1S 2 2S 2 2P 1 formula 1.
With an increase in the charge of the kernel, another unit, i.e. When moving to carbon (z \u003d 6), the number of electrons by 2p-pylons increases to 2: the electronic structure of the carbon atom is expressed by 1S 2 2S 2 2P 2 formula. However, this formula could correspond to any of the three schemes:
According to the scheme (1), both 2p electrons in the carbon atom occupy the same orbital, i.e. Their magnetic quantum numbers are the same, and the directions of the spins are opposite; Scheme (2) means that 2p electrons occupy different orbitals (i.e., they have different values \u200b\u200bof M) and have oppositely directed backs; Finally, from the schema (3) it follows that different orbitals correspond to two 2p electrons, and the spins of these electrons are directed the same.
The analysis of the atomic spectrum of carbon shows that it is the last scheme for an unexcited carbon atom, which corresponds to the greatest possible value of the total spin of atom (the so-called the sum of the spins of all those part of the electron atom; for the carbon atom (1) and (2) schemes, this amount is zero and for the scheme (3) is equal to one).
This procedure for placing electrons in the carbon atom represents a special case of general patterns expressed rule Hund: the stable state of the atom corresponds to such a distribution of electrons within the energy sublayer, in which the absolute value of the total spin of the atom is maximum.
Note that the Hund rule does not prohibit another distribution of electrons within the subproduction. It only claims that sustainable, i.e. unexcited a state in which the atom has the lowest possible energy; With any other distribution of electrons, the energy of an atom will be greater, so it will be in excitedunstable.
Using the Rule of Hund, it is easy to make a circuit of an electronic structure for an atom of the element of the element - nitrogen (Z \u003d 7):
This scheme corresponds to formula 1S 2 2S 2 2P 3.
Now that each of the 2r-Oribals is occupied by one electron, the pairwise placement of electrons on 2p orbitals begins. The oxygen atom (Z \u003d 8) corresponds to the 1S 2 2S 2 2P 4 electronic structure formula and the following scheme:
The fluorine atom (Z \u003d 9) another 2r-electron appears. Its electronic structure is expressed, therefore, 1s 2 2S 2 2P 5 formula and scheme:
Finally, at the neon atom (Z \u003d 10), the filling of the 2P-suite ends, and thereby filling out the second energy level (L-layer) and the construction of the second period of the element system.
Thus, starting from the boron (z \u003d 5) and ending with neon (z \u003d 10), the p-sub-lineage of the outer electron layer is filling ;; The elements of this part of the second period relate, therefore, to the family of p-elements.
Sodium atom (Z \u003d 11) and magnesium (Z \u003d 12) is similar to the first element of the second period - lithium and beryllium - contain one or two S electrons in the outer layer. Their structure corresponds to electronic formulas 1S 2 2S 2 2P 6 3S 1 (sodium) and 1S 2 2S 2 2P 6 3S 2 (Magnesium) and the following schemes:
and 1S 2 2S 2 2P 6 3S 2 3P 6 formula 6.
Thus, the third period, like the second, begins with two S-elements, followed by six R-elements. The structure of the outer electronic layer of the corresponding elements of the second and third periods is consequently similar. Thus, at the atoms of lithium and sodium in the outer electron layer is one S-electron, in nitrogen and phosphorus atoms - two S- and three p-electrons, etc. In other words, with an increase in the charge of the kernel, the electronic structure of the outer electronic layers of atoms is periodically repeated. Below we will see that this is true for the elements of subsequent periods. Hence it follows that the location of the elements in the periodic system corresponds to the electronic structure of their atoms. But the electronic structure of atoms is determined by the charge of their nuclei and, in turn, determines the properties of the elements and their compounds. This is the essence of the periodic dependence of the properties of the elements from the charge of the core of their atoms expressed by periodic law.
Continue consideration of the electronic structure of atoms. We stopped at the Argon's atom, which is fully filled with 3s- and 3r-sucks, but remain unoccupied by all 3D-sublevels orbital. However, the next argon elements - potassium (z \u003d 19) and calcium (z \u003d 20) - the filling of the third electronic layer is temporarily stopped and the S-su-layer s-fourth layer begins to form: the electronic structure of the potassium atom is expressed by 1S 2 2S 2 2p 6 3S 2 3P 6 4S 1, calcium atom - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 and the following schemes:
The reason for this sequence of filling the electronic energy facilities is as follows. As indicated in § 31, the electron energy in a lot of electron atom is determined by the values \u200b\u200bof not only the main, but also the orbital quantum number. There was also a sequence of the location of energy suits that corresponds to an increase in the energy of an electron. The same sequence is presented in Fig. 22.
As shown fig. 22, 4S grain is characterized by lower energy than 3D sublayer, which is associated with stronger shielding of D-electrons in comparison with S-electrons. In accordance with this, the placement of the external electrons in potassium and calcium atoms on 4S pylons corresponds to the most stable state of these atoms.
The sequence of filling atomic electronic orbitals, depending on the importance of the main and orbital quantum numbers, was investigated by the Soviet scientist V. M. Klechkovsky, which found that the electron energy increases as the sum of these two quantum numbers increases, i.e. values \u200b\u200b(n + l). In accordance with this, they were formulated as the following position (the first rule of Clakovsky): with an increase in the charge of the atom nucleus, the sequential filling of electronic orbitals comes from orbitals with a lower value of the amount of the main and orbital quantum numbers (N + L) to orbitals with a large value of this amount.
The electronic structure of potassium and calcium atoms corresponds to this rule. Indeed, for 3D orbitals (n \u003d 3, L \u003d 2), the sum (n + L) is 5, and for 4S orbitals (n \u003d 4, l \u003d 0) - equal to 4. Therefore, 4S-sublevels should be filled earlier than 3D sublayer, which is actually happening.
So, the calcium atom completes the construction of 4S-supremies. However, when switching to the next element - Scandia (z \u003d 21) - the question arises: which of the sublevels with the same amount (n + L) - 3D (n \u003d 3, L \u003d 2), 4p (n \u003d 4, L \u003d 1) or 5s (n \u003d 5, l \u003d 0) - should be filled? It turns out that with the same amounts of the amount (N + L) the electron energy is higher, the greater the greater the value of the main quantum number n. Therefore, in such cases, the order of filling by electrons of energy suits is determined the second rule of Clekkovsky, Whereby with the same values \u200b\u200bof the amount (N + L), the filling of the orbital occurs sequentially in the direction of the increase in the value of the main quantum number N.
Fig. 22. The sequence of filling the electronic energy suite in the atom.
In accordance with this rule, in the case (n + l) \u003d 5, the 3D sublayer (n \u003d 3) must be filled, then the sublayer 4p (n \u003d 4) and, finally, the sublayer 5s (n \u003d 5). At the scandium atom, therefore, the filling of 3D orbitals should begin, so its electronic structure corresponds to the formula 1S 2 2S 2 2p 6 3S 2 3P 6 3D 1 4S 2 * and the scheme:
Filling 3D-sublevels continues with the following scanda elements - titanium, vanadium, etc. - and completely ends in zinc (z \u003d 30), the structure of the atom of which is expressed by the scheme
what corresponds to 1S 2 2 3P 6 3P 6 3S 2 3P 6 34 4S 2 formula 2.
* In the formulas of the electronic structure, it is customary to first sequentially record all states with this value n, and then move to states with a higher value n. Therefore, the recording procedure does not always coincide with the procedure for filling the energy prying. Thus, in the record of the electronic formula of the Scandium atom, the 3D sublayer was previously placed earlier than the sublayer of 4S, although these supertures are filled in in reverse sequence.
Ten D-elements, starting with scandium and ending with zinc, belong to transition elements. The feature of the construction of electronic shells of these elements compared to the preceding (S- and P-elements) is that when switching to each subsequent D-element, the new electron appears not in the external (n \u003d 4), but in the second outside (N \u003d 3) electronic layer. In this connection, it is important to note that the chemical properties of the elements are primarily determined by the structure of the outer electron layer of their atoms and only to a lesser extent depends on the structure of the preceding (internal) electronic layers. At the atoms of all transitional elements, the outer electron layer is formed by two S electrons *; Therefore, the chemical properties of D-elements with an increase in the atomic number are changed not as sharp as the properties of the S and P-elements. All D-elements belong to metals, while the filling of an external p-sublayer leads to a transition from metal to typical non-metalla and, finally, to a noble gas.
After filling the 3D-sublayer (n \u003d 3, L \u003d 2) electrons, in accordance with the second rule of the clerk, occupy a grain 4p (n \u003d 4, L \u003d 1), thereby resizing the construction of the N-layer. This process begins at the gallium atom (Z \u003d 31) and ends at the crypton atom (Z \u003d 36), the electron structure of which is expressed by 1S 2 2 2P 6 3S 2 34 4S 2 4P 6 formula 2. Like the atoms of the preceding noble gases - neon and argon, the crypton atom is characterized by an external electron structure of the NS 2NP6 layer, where N is the main quantum number (neon - 2S 2 2p 6, Argon - 3S 2 3P 6, Crypton - 4S 2 4P 6 ).
Starting from Rubidia, 5S-sublevels filled; This also corresponds to the second rule of Clachkovsky. In a rubidium atom (z \u003d 37), a structure with one S-electron in the outer electronic layer appears at the alkali metal. Thus, the construction of a new-fifth - period of the system of elements begins. At the same time, as when constructing the fourth period, it remains unfilled by the D-sublayer of the antisomine electronic layer. Recall that in the fourth electronic layer there is already a F-subline, the fillings of which in the fifth period also does not occur.
At the strontium atom (Z \u003d 38), the 5s 5s is occupied by two electrons, after which the 4D filling is filling, so the following ten elements - from yttrium (z \u003d 39) to cadmium (z \u003d 48) - belong to transient D-elements. Then, six p-elements are located from India to the noble gas xenon, which completes the fifth period. Thus, the fourth and fifth periods in their structure are quite similar.
* There are D-elements (for example, chromium, molybdenum, elements of the copper subgroup), at the atoms of which there is only one S-electron in the external electronic layer. The reasons for these deviations from the "normal" order of filling out electronic energy facilities are considered at the end of the paragraph.
The sixth period, like the previous ones, begins with two S-elements (cesium and barium), which completes the filling of orbitals with the amount (N + L), equal to 6. Now, in accordance with the Rules of Clakovsky, the sublayer 4F (N \u003d 4, must be filled. L \u003d 3) With the sum (N + L), equal to 7b and with the smallest possible value of the main quantum number. In fact, Lanthan (Z \u003d 57), located immediately after the barium, appears not 4F, but a 5D electron, so that its electronic structure corresponds to the formula 1S 2 2S 2 2p 6 3S 2 3P 6 3D 10 4S 2 4p 6 4D 10 5S 2 5P 6 5D 1 6S 2. However, the construction of the cerium element (z \u003d 58) is really beginning to build a 16F sublayer on which the only 5D electron, extended in the Lanthan atom; In accordance with this, the electronic structure of the cerium atom is expressed by 1S 2 2 2 2p 6 3P 6 3P 6 3P 6 4D 10 4P 6 4P 6 4D 10 4F 2 4P 6 4D 10 4F 2 5S 2 5P 6 6S 2. Thus, the retreat from the second rule of Clekkovsky, which takes place in Lanthan, is temporary: starting with cerium, consistently filling all orbitals 4F-sublevel. Fourteen lanthanides located in this part of the sixth period belong to F-elements and are close by properties to Lanthan. A characteristic feature of constructing electronic shells of their atoms is that in the transition to the subsequent F-element, the new electron occupies not in the external (n \u003d 6) and not in the preceding (n \u003d 5), but even more deeply located, the third outside electronic layer (n \u003d 4).
Due to the absence of lanthanide atoms, there are significant differences in the structure of the external and pretended electronic layers, all lanthanoids show great similarity in the chemical properties.
Filling a 5D-suite, started in Lanthan, is resumed in Hafnia (Z \u003d 72) and ends at mercury (Z \u003d 80). After that, as in previous periods, six P-elements are located. Here is a construction of a 6P sublevel: it begins at thallium (Z \u003d 81) and ends at the noble gas of radon (z \u003d 86), which completes the sixth period.
The seventh while the unfinished period of the element system is built similarly to the sixth. After two S-elements (France and Radium) and one D-element (ACTING), 14 F-elements are located here, whose properties exhibit known proximity to the properties of the actinium. These elements, starting with thorium (z \u003d 90) and ending with an element 103, are usually combined under the overall name of actinoids. Among them - Mendeli (Z \u003d 101), artificially obtained by American physicists in 1955 and named after D. I. Mendeleev. Directly behind the actinoids is Kurchatov (Z \u003d 104) and element 105. Both of these elements are artificially obtained by a group of scientists led by Academician N. Flerov; They belong to the D-elements and are completed by the known part of the periodic system of elements.
The distribution of electrons by energy levels (layers) in atoms of all known chemical elements is given in the periodic system of elements placed at the beginning of the book.
The sequence of filling by electrons by electrons of energy levels and under the atoms is schematically represented in Fig. 23, graphically expressing Clachekovsky rules. Filling comes from smaller sum values \u200b\u200b(N + L) to large in the order specified by the arrows. It is easy to notice that this sequence coincides with the sequence of filling the atomic orbitals shown in Fig. 22.
Fig. 23. Scheme of the sequence of filling electron energy pillies in the atom.
Fig. 24. The dependence of the energy of 4F- and 5D-electrons from the charge of the Zero Z.
It should be borne in mind that the last scheme (as well as the rules of the Clekkovsky) does not reflect the private features of the electronic structure of atoms of certain elements. For example, in the transition from the nickel atom (z \u003d 28) to the copper atom (Z \u003d 29), the number of 3D electrons is increasing not one, but at once to two at the expense of the "slippoint" of one of the 4S electrons to the 3D sublayer. Thus, the electronic structure of the copper atom is expressed in formula 1S 2 2S 2 2P 6 3S 2 3P 6 3D 10 4S 1. A similar "spock" of an electron from an external S- D-superer of the previous layer occurs in the atoms of the analogs of copper - silver and gold. This phenomenon is associated with the increased energy stability of electronic structures that meet fully engaged in energy subcoins (see § 34). The electron transition in the copper atom with 4S sublevel on the 3D sublayer (and similar transitions in silver and gold atoms) leads to the formation of a fully filled D-sublayer and therefore it turns out to be energetically beneficial.
As will be shown in § 34, electronic configurations with exactly half-filled with suicide (for example, structures containing three P electrons in the outer layer, five D-electrons in the forever layer or a network of F-electrons in an even more deeply located layer). This explains the "Squad" of one 4S electrone in the chromium atom (z \u003d 24) on a 3D-pricken, as a result of which the chromium atom acquires a steady electronic structure (1S 2 2S 2 2P 6 3S 2 3P 6 3D 5 4S 1) with exactly half filled with 3D sublayer; A similar period of 5S electrone on a 4D-pylon occurs in the molybdenum atom (Z \u003d 42).
The above-mentioned violations of the "normal" order of filling the energy states in the lanthanum atoms (the appearance of 5d-, and not 4F electrons) and the cerium (the appearance of two 4F-electrons at once) and similar features in the construction of electronic structures of atoms of the seventh period elements are explained as follows. With an increase in the charge of the kernel, the electrostatic attraction to the electron core, which is in this energy pylon, becomes stronger, and the electron energy decreases.
At the same time, the energy of electrons, which are on various sublevels, changes unequal, since with respect to these electrons the nucleus charge is shielded to varying degrees. In particular, the energy of 4F-electrons decreases with increasing the charge of the kernel more dramatically than the energy of 5D electrons (see Fig. 24). Therefore, it turns out that lanthanne (z \u003d 57) the energy of 5D electrons is lower, and the cerium (Z \u003d 58) is higher than the energy of 4F-electrons. In accordance with this, the electron, which was in Lantan on a superer 5D, moves to cerium to the 4F sublayer.
| <<< Назад
|
Forward \u003e\u003e\u003e |
In atoms according to states
If identical particles have the same quantum numbers, their wave function is symmetric relative to the permutation of particles. It follows that two identical fermion included in one system cannot be in the same states, since for fermions, the wave function must be antisymmetric. Summarizing experienced data, V. Pauli formulated the principle according to which the fermion systems are found only in conditions described by antisymmetric wave functions (quantum-mechanical formulation of Pauli principle).
From this situation, there is a simpler formulation of the Pauli principle, which was introduced into a quantum theory (1925) before building quantum mechanics: in the system of identical fermions, any two of them cannot simultaneously be in the same condition. Note that the number of one-type bosons in the same state is not limited.
Recall that the state of the electron in the atom is uniquely determined by a set of four quantum numbers:
the main N (n \u003d 1, 2, 3, ...),
orbital l. (l. \u003d 0, 1, 2, ..., n-1),
magnetic M. L.(M. L. = - l., .... - 1, 0, +1, ..., + l.),
magnetic spin (m s \u003d + 1/2, - 1/2).
The distribution of electrons in the atom obeys the principle of Pauli, which can be used in its simple formulation: in the same atom there can be no more than one electron with the same set of four quantum numbers N , L,m. L.and m s, t. e.
where z (n, L., M. L., m s) - the number of electrons in quantum state, described by a set of four quantum numbers: n , L,m. L., M s. In the way, Pauli principle argues that two electrons associated in the same atom differ by the values \u200b\u200bof at least one quantum number.
According to formula (223.8), this N Interfaces 2 various states that differ in values l. and M. L.. Quantum number M. , may take only two values \u200b\u200b(± 1/2).
Therefore, the maximum number of electrons in the states determined by this main quantum number is equal
The combination of electrons in a multi-electrone atom having the same main quantum number N , called electronic shell. In each of the shells, electrons are distributed across the subordrodes corresponding to this l.. Since. The bidded quantum number takes values \u200b\u200bfrom 0 to n - 1, the number of subcases is equal to the sequence number of the Nobolochka. The number of electrons in the suburbs is determined by magnetic and magnetic spin quantum numbers: the maximum number of electrons in the submarine with the data l. Equal 2 (2 l. + 1). The designations of the shells, as well as the distribution of electrons by shells and subcomms are presented in Table. 6.
Table 6.
Periodic system of elements
Mendeleev
The Powli principle underlying the systematics of filling electron states in atoms allows to explain the periodic system of elements D. I. Mendeleev (1869) - fundamental Lawnature, which is the basis of modern chemistry, atomic and nuclear physics.
D. I. Mendeleev introduced the concept of the sequence number of the Z chemical element equal to the number of protons in the kernel and, accordingly, the total number of electrons in the electron shell of the atom. By placing chemical elements as the ordinal numbers increase, it received frequency in changing the chemical properties of the elements. However, for those known at that time, 64 chemical elements, some table cells turned out to be empty, since the elements corresponding to them (for example, GA, SE, GE) were not yet known. D. I. Mendeleev, therefore, not only positioned the well-known elements, but also predicted the existence of new, not yet open elements and their basic properties. In addition, D. I. Mendeleev managed to clarify the atomic weights of some elements. For example, atomic weights BE and U, calculated on the basis of the Mendeleev table, turned out to be correct, and previously obtained experimentally erroneous.
Since the chemical and some physical properties of elements are explained by external (valence) electrons in atoms, the frequency of properties of chemical elements should be associated with a certain periodicity in the location of electrons in atoms. Therefore, to explain the table, we assume that each subsequent element is formed from the previous addition to the kernel of one proton and, according to the addition of one electron in the electron sheath of the atom. Electron interaction neglect, bringing where necessary, appropriate amendments. Consider atoms of chemical elements that are mainly state.
The only electron of the hydrogen atom is in 1s state. , characterized by quantum numbers n \u003d 1, l. \u003d 0, m L. \u003d 0 and m s \u003d ± 1/2 (orientation of its back is arbitrary). Both electrons atom are not in 1s , but with anti-parallel reference orientation. The electronic configuration for an atom is not written as 1s 2 (two 1S electrons). Atom does not end the filling of the K-shell, which corresponds to the completion of the first period of the periodic system of Mendeleev elements (Table 7).
The third electron of the Li atom (z \u003d 3), according to the principle of Pauli, can no longer be located in the entirely filled with a-shell and occupies the lowest energy state with n \u003d 2 (L-shell), i.e. 2S-state. An electronic configuration for an atom Li: 1S 2 2S. Li begins the second period of the periodic system of elements. The fourth electron B (z \u003d 4) ends filling the submarine 2s. The following six elements from in (2 \u003d 5) to NE (z \u003d 10) are filling the submarine 2p (Table 7). The II period of the periodic system ends with neon - inert gas for which the submarine is filled with a 2rzelik.
The eleventh electron Na (Z \u003d 11) is placed in the M-shell (n \u003d 3), occupying the lowest state of 3S. The electronic configuration has the appearance of 1S 2 2S 2 2P 6 3S.CS-electron (as well as 2S elscTrone Li) is a valence electron , Therefore, the optical properties of Na are similar to the properties of Li. With Z \u003d 12 there is a consistent filling of the M-shell. AG (Z \u003d 18) turns out to be similar to NE: in its outer shell, all S- and P states are filled. AH is chemically inert and completes the III period of the periodic system.
The nineteenth electron K (Z \u003d 19) would have to take the ZD-Condition in the M-Shell. However, in the optical, and in the chemical relations, the atom to similar to Li and Na atoms, which have an external valence electron in S-state. Therefore, the 19th valence electron K should also be in S-state, but it can only be the S-state of a new shell (N-shell), i.e., the filling of the N-shell for K starts with an empty M-shell. This means that as a result of the interaction of electrons, the state N \u003d 4, l.\u003d 0 and less energy than the state n \u003d 3, l.\u003d Spectroscopic and chemical properties of Ca (z \u003d 20) show that its 20th electron is also in the 4S state of the N-shell. In the subsequent elements, the M-shell is filling (from SC (Z \u003d 21) to Zn (z \u003d 30)). Next n-shell is filled to kg (z \u003d 36), which again, as in the case of NE and AG, S - and the p-state of the outer shell is filled with entirely. Crypton ends the IV period of the periodic system. Similar arguments are applicable to the other elements of the Mendeleev table, however, this data can be found in reference books. We only note that the initial elements of subsequent RB periods, Cs, FR are alkaline metals, and their last electron is in S-state. In addition, the atoms of inert gases (not, ne, at, kg, x, rn) occupy a special position in the table - in each of them S- and P-status of the outer shell are fully filled and the next periodic periodic periods are completed.
| ON | Z. | Element | K. | L. | M. | N. | Period | Z. | Element | K. | L. | M. | N. | ||||||||||||
| 1s. | 2s. | 2p. | 3s. | 3P. | 3D | 4S. | 4p. | 4d. | 4f. | 1s. | 2s. | 2p. | 3s. | 3P. | 3D | 4S. | 4p. | 4d. | 4f. | ||||||
| H He. | IV. | K CA SC TI V CR MN FE CO NI | - - | ||||||||||||||||||||||
| III | Na VG Al Si P S Cl Ar | Cu Zn GA GE AS SE BR KR |
Table 7.
Each of the two groups of elements - lanthanides (from Lanthan (Z \u003d 57) to Lutection (Z \u003d 71)) and actinides (from Actinia (Z \u003d 89) to Laurerencia (Z \u003d 103)) - you have to put in one cell table, so As the chemical properties of elements within these groups are very close. This is explained by the fact that for lanthanides filling the submarine 4f, which may contain 14 electrons, begins only after the submarine 5s, 5p and 6s are fully filled . Therefore, for these elements, the outer p-shell (6S 2) turns out to be the same. Similarly, the same for actinides is the Q-shell (7S 2).
Thus, the periodicity in the chemical properties of the elements is expandable in the chemical properties of elements in the structure of the outer shells in the atoms of the related elements. Thus, the inert gases have the same outer shells of 8 electrons (filled with S- and P states); in the outer shell of alkali metals (Li, Na, K, Rb, CS, FR) there is only one s-electron; In the outer shell of alkaline earth metals (BE, MG, CA, SR, BA, RA) there are two S electrons; Haloids (F, C1, VG, I, AT) have external shells in which one electron is lacking to an inert gas shell, etc.
X-ray spectra
A large role in finding out the structure of the atom, namely the distribution of electrons by the shells, played radiation, opened in 1895 by the German physicist V. X-ray (1845-1923) and called X-ray. The most common source of X-ray radiation is an X-ray tube, in which electrons are highly accelerated by an electric field bombard the anode (metal target of heavy metals, such as W or Pt), testing sharp braking on it. At the same time, X-ray radiation occurs, which is electromagnetic waves with a wavelength of approximately 10 12 -10 -8 m. The wave of X-ray radiation is proved by experiments on its diffraction, discussed in § 182.
The study of the spectral composition of the X-ray radiation shows that its spectrum has a complex structure (Fig. 306) and depends on both the electron energy and the anode material. The spectrum is the imposition of a solid spectrum bounded by short wavelengths by some boundary L min, called the boundary of the solid spectrum, and the line spectrum - the set of individual lines appearing against the background of a solid spectrum.
Studies have shown that the nature of the solid spectrum is completely independent of the material of the anode, but is determined only by the energy of the bombarding anode of electrons. A detailed study of the properties of this radiation showed that it is emitted by bombing anode by electrons as a result of their braking when interacting with target atoms. A solid X-ray spectrum is therefore called the brake spectrum. This conclusion is in harmony with the classical theory of radiation, since when braking moving charges, radiation with a solid spectrum should really occur.
From the classic theory, however, does not follow the existence of a short-wave limit of a solid spectrum. From experiments it follows that the greater the kinetic energy of electrons causing braking X-ray radiation, the less L min. This circumstance, as well as the presence of the border itself, is explained by quantum theory. It is obvious that the limit energy of the quantum corresponds to this case of braking, in which all the kinetic electron energy goes into the energy of the quantum, i.e.
where the u is the potential difference, at the expense of which the electron is reported to Energy E MAX, V MAX - the frequency corresponding to the boundary of the solid spectrum. Hence the boundary wavelength
what fully complies with experimental data. Measuring the boundary of the X-ray solid spectrum, according to formula (229.1), you can determine the experimental value of the constant plank h,which most accurately coincides with modern data.
With a sufficiently large energy of bombarding anode of electrons against the background of a solid spectrum, separate sharp lines appear - a strollery spectrum, determined by the anode material and called the characteristic X-ray spectrum (radiation).
Compared to the optical spectra, the characteristic X-ray spectra of the elements are completely the same type and consist of several episodes, denoted to, L, M, N and O . Each series, in turn, contains a small set of individual lines denoted in descending order of wavelengths by indexes a, b, g ... (to A, to b, to G, .... L A, L B, L G , ...). When moving from light elements to severe, the characteristic spectrum structure does not change, only the entire spectrum shifts towards short waves. The peculiarity of these spectra is that the atoms of each chemical element, regardless of whether they are in free state or are included in the chemical compound, they have a certain characteristic radiation inherent in this element. So, if the anode consists of several elements, then the characteristic X-ray radiation is the imposition of the spectra of these elements.
Consideration of the structure and features of characteristic X-ray spectra leads to the conclusion that their occurrence is associated with processes occurring in internal, built-up electronic shells of atoms that have a similar structure.
We will analyze the mechanism of the occurrence of X-ray series, which is schematically shown in Fig. 307.
Suppose that under the influence of an external electron or high energy photon, one of the two electrons of an IT-shell of an atom is broken. Then the electron can be moved to its place with more removed shells L, M, N, .... such transitions are accompanied by emission of X-ray quanta and the occurrence of spectral lines of the K-series: to A (L®K), to B (M® K), to g (n®k), etc. The longer-wave line K-series is the line to A . The frequencies of the lines increase in the row to A ®K B ®k G, since the energy released during the transition of the electron to the K-shell with more remote shells increases. On the contrary, the intensity of the lines in a row to A ®K B ®K g decreases, since the probability of electrons transitions from the L-shell on the K-shell is greater than with more remote shells M and N. K-sketching necessarily by other series, since Embossing its lines Appears vacancies in shells L, M, ..., which will be filled with electrons located at higher levels.
Similarly, there are other series observed, however, only for heavy elements. The considered characteristic radiation lines may have a thin structure, since the levels determined by the main quantum number are cleaved according to the values \u200b\u200bof orbital and magnetic quantum numbers.
Exploring the X-ray spectra of elements, the English physicist of Mosli (1887-1915) established in 1913 the ratio, called the law of Mosli:
(229.2)
where V is the frequency corresponding to this line of the characteristic X-ray radiation, R-constant readberg, S- constant shielding, M \u003d 1.2, 3, ... (determines the X-ray series), nims the integer values \u200b\u200bfrom +1 (determines the separate value line of the corresponding series). The law of Moslos (229.2) is similar to the generalized formula of Balmer (209.3) for the hydrogen atom.
The meaning of constant shielding is that an electron, which makes a transition corresponding to some PINIAN, is not valid Zeand charge (z - s) e , weakened by the shielding effect of other electrons. For example, for A -Line S = 1, and the law of Moslos will be recorded in the form
The main quantum number, N -determines the electron energy and the size of electronic orbitals, receives discrete values:
n. = 1, 2, 3, 4, 5, . . . . . , +∞.
The electron energy depends on the distance between the electron and the nucleus: the electron is closer, the less energy that is defined as E. \u003d -13,6, eV, where n. - The main quantum number.
Electrons in the atom can only be in defined quantum statesthat correspond specificthe values \u200b\u200bof its communication energy with the kernel. Electron transition from one quantum state to another is connected with hopping Change of energy. Therefore, energy levels and energy communication with the main quantum number n. can be submitted by the scheme (Fig. 2.1).
 |
Fig. 2.1. Energy level diagram and energy connection
with the main quantum number
In this way, n. It characterizes the electron belonging to one or another energy level and, accordingly, the size of the orbital.
Orbital quantum number, ℓ N(ℓ ) determines the form of orbital (more precisely symmetry), characterizes the rotational component of the electron movement. The different form of electron clouds is caused by a change in an electron energy within one energy level, that is, the splitting of it on the slope.
The electronic cloud is represented in different ways, but more often as boundary surface Within which most of the cloud is located (~ 95%).
The orbital quantum number may vary within: ℓ N. = 0, 1, . . . , (n. – 1), Where n. - The main quantum number. In addition to numerical values, an alphabetic designation of the orbital quantum number is possible: s, P, D, F . If you bind the numerical value of the orbital quantum number with the letter and spatial image, the information will be presented as a table (Table 2.2). The spherical form of the electronic cloud is characterized by the minimum value of energy ( ℓ N. \u003d 0), and this cloud is indicated as s. -Orbital, etc.
Table 2.2.
The values \u200b\u200bof the orbital quantum number and
spatial image of orbital
| An image of orbital |  |   | ||
| Value ℓ N. | ||||
| Letter notation | s. | p. | d. | f. |
Obviously, with this n. The orbital quantum number takes a number of values, i.e. Within one energy level, the presence of various forms of orbitals is possible. The relationship of the orbital and main quantum numbers is presented on
 |
Energy diagram (Fig. 2.2).
Fig. 2.2.Energy diagram of levels and sublevels in multielectronic atoms (relationship of orbital and main quantum numbers)
For the first energy level, the only value is possible. ℓ N. , and it is zero, i.e. The form of orbit is spherical. To refer to the state of an electron for which n.\u003d 1 I. ℓ N. \u003d 0, Used Record 1 s. (Table 2.3).
With the transition to the second energy level ( n.=2), ℓ N. Takes values \u200b\u200b0 and 1, therefore, status 2 may be possible. s. and 2 p.; We conclude about the possibility of the existence of two types of forms of orbitals, etc.
Table 2.3.
The value and relationship of the orbital and main quantum numbers, the designation of sublevels
| Level No. | N. | Value ℓ N. | Designation of prying |
| I. | n.=1 | 1 s. | |
| II. | n.=2 | 2 s. 2 p. | |
| III | n.=3 | 3 s. 3 p. 3 d. | |
| IV. | n.=4 | 4 s. 4 p. 4 d. 4 f. |
Thus, different values ℓ N. in the multielectronic atoms, they characterize energy suits within each energy level, and the energy s. -, p. -, d. -, f. - The sublevel consistently increase.
The amount of sublevels at this level corresponds to the level number. Each subsequent level contains all kinds of supreme plus one.
Magnetic quantum number, m ℓ, characterizes the spatial orientation of electronic clouds (determines the value of the projection of the orbital moment of the amount of movement on the selected direction).
Magnetic quantum number m ℓ For a given meaning ℓ N. takes a set of values \u200b\u200bfrom – ℓ N., ... ,0, …, + ℓ N.. Those. The specific form of the electronic cloud is orbital, in space oriented strictly in a certain way.
For ℓ N. \u003d 0, the form of the orbital spherical ( s.- Sorbital) and in space can be oriented the only way, therefore, the magnetic quantum number M ℓ may take the only value equal to 0.
The location of the dumbbell electronic cloud ( p-orbital) in space is possible in three ways, therefore, a magnetic quantum number m ℓ can take three values \u200b\u200bequal to -1; 0; +1.
Taking for the symbol of the orbital, the relationship between ℓ N. and M ℓ you can show in the form of the table. 2.4.
Table 2.4.
Distribution of orbitals on sublevels
| ℓ N. | m ℓ | Number of orbitals |
| 0 (s.) | 1 | |
| 1 (p.) | -1 0 +1 | 3 |
| 2 (d.) | -2 -1 0 +1 +2 |  5
|
| 3 (f.) | -3 -2 -1 0 +1 +2 +3 | 7 |
From the table it is clear that s.-provine has one orbital, p.-Provers - three orbitals, d.-provine - five orbitals, f.-provine has seven orbitals (Fig. 2.3). Each of such orbital is characterized by a certain combination of quantum numbers. n, ℓ N and m ℓ.
 |
Fig. 2.3. Energy diagram of levels and sublevels in multielectronic atoms (the relationship of the main, orbital and magnetic quantum numbers)
Spin quantum number, m s.The electron has its own magnetic moment due to its back. The projection in space may have a positive or negative sign. If the electron is indicated , value m S. =+½. If the electron is indicated ↓ then value m S. = – ½.
Thus, the combination of the position of the electron in the atom is characterized by certain values \u200b\u200bof quantum numbers. They determine the spin, electron energy, the volume and form of space near the kernel, in which its stay is likely.
For example, The electron shown below is characterized by the following set of quantum numbers: n. = 5; ℓ N. =3; m ℓ = -1; m S. = – ½.
 |
Those. This electron is located at 5 energy levels, d. -Porovna. The electron occupies the second orbital and is denoted ↓.
In the transition of an atom from one quantum state to another, the adjustment of the electronic cloud occurs, which means that the values \u200b\u200bof quantum numbers are changed:
The state of electrons in the atom is responsible powli's principle:there can be no two electrons in the atom that would be the same all four quantum numbers. The principle of Pauli limits the number of electrons possessing a certain value of the main quantum number n. : if a n.\u003d 1, the number of electrons is 2; if a n.\u003d 2, the number of electrons 8, etc. Therefore, two electrons can occupy one orbital if they have opposite spins. Two electrons located on the same orbitals are called paired. Sparnoelectrons are electrons with opposite (anti-parallel) backs.
When filling out energy prying, it is observed hund rule: In this supro, the electrons seek to occupy energy states in such a way that the total spin would be maximum.
for example, atom 6 s valence electrons are: 2 s. 2 2p. 2. We define what location of electrons on p-slovers meets sustainable state. For this, according to rule Hund calculate the absolute value of the total spin for two options for the location of the electrons shown below.
|
|
For case but | 1/2 - 1/2 | \u003d 0 I. b. |1/2 + 1/2| = 1.
The maximum value of the value of the total spin is characterized by the state B, it is it that corresponds to the steady state of the atom of 6 C.
- Number: Lesson Theme: Quantum Numbers. Powli principle, Gund rule, Clakovsky rules. Settlement challenges (definition of the structure of atoms of chemical elements. Placing electrons by energy levels and orbitals, electronic configurations of atoms and ions). The purpose of the lesson: to form students on the structure of an atom electronic shell on the example of the chemical elements of 1-3 periodic periodic system periods. Secure the concepts of "Periodic Law" and "Periodic System".
1. Powli principle. In atom, there can be no two electrons, in which the values \u200b\u200bof all quantum numbers (N, L, M, S) would be the same, i.e. Each orbital may contain no more than two electrons (with opposite spins).
2. Clekkovsky rule (the principle of least energy). In the ground state, each electron is located so that its energy is minimal. The smaller the sum (N + L), the less the energy of the orbit. For a given value (N + L), the smallest energy has an orbital with less n. Energy of orbitals increases in a series:
3. Hund rule. The atom basically must have the highest possible number of unpaired electrons within a certain sublevel.
Recording reflecting the distribution of electrons in the atom of the chemical element for energy levels and sublayers is called the electronic configuration of this atom. Basically (unexcited) the state of the atom, all electrons satisfy the principle of minimal energy. This means that the supertures are filled first for which:
1) the main quantum number n is minimal;
2) inside the level is first filled with S-, then p- and only then D-sublayer;
3) filling occurs so that (N + L) was minimal (Clakovsky rule);
4) within a single sublayer electrons are arranged so that their total spin is maximum, i.e. contained the greatest number of unpaired electrons (Hinda rule).
5) When filling atomic orbitals, Pauli principle is performed. Its consequence is that the energy level with the number N can belong to no more than 2n 2 electrons located on N 2 suits.
Cesium (CS) is in 6 periods, its 55 electrons (sequence number 55) is distributed through 6 energy levels and their refinery. Cutting sequence filling the electrons of orbitals we get:
55 CS 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 4P 6 4D 10 5S 2 5P 6 5D 10 6S 1
Principle Pauli Rule Gund Rules Clakovsky
Fundamentals of the structure of the substance
Chapter 3. Multi-Electronic Atoms
The exact solution of the Schrödinger equation can be found only in rare cases, for example, for atom of hydrogen and hypothetical one-electron ions, such as HE +, LI 2+, BE 3+. The atom of the following hydrogen element is helium - consists of a kernel and two electrons, each of which is attracted to both cores and is repelled from another electron. In this case, the wave equation has no accurate solution.
Therefore, various approximate methods have great importance. Using such methods, it was possible to establish the electronic structure of atoms of all known elements. These calculations show that orbitals in multi-electrone atoms are not very different from the orbital hydrogen atom (these orbital is called hydrogen-like). The main difference is some compressedness of orbitals due to the larger charge of the kernel. In addition, for multi-electronic atoms found that for everyone energy level (with this value of the main quantum number n.) splitting on sill. Electron energy depends not only from n., but also from the orbital quantum number l.. It increases in row s.-, p.-, d.-, f.-Evubitals (Fig. 7).
For high energy levels, the differences in the energy of sublevel is large enough, so that one level can penetrate into another, for example
6s. 2 2s. 2 2p. 6 3s. 2 3p. 6. The number of electrons on the orbital lines of this sublayer is indicated in the upper index to the right of the letter, for example 3 d. 5 is 5 electrons by 3 d.-Porovna.
For brief recording of an atom electron configuration instead of orbitals, a noble gas symbol with an appropriate electronic formula is sometimes recorded.
For example, the electronic formula of the chlorine atom 1 s. 2 2s. 2 2p. 6 3s. 2 3p. 5, or 3 s. 2 3p. five . The brackets carried out valence electrons involved in the formation of chemical bonds.
For large periods (especially sixth and seventh), the construction of electronic configurations of atoms has more complex. For example, 4. f.-Electron appears not in the lanthanne atom, but in the atom of the next cerium behind him. Sequential filling 4. f.-Production is interrupted in the gadolinium atom, where there are 5 d.-electron.
Principle Pauli Rule Gund Rules Clakovsky
Especially stable also fully filled d.-probel, therefore, electronic configuration of valence electrons of copper, silver and gold atoms (IB-group) ( n.−1)d. 10 nS. 1 will fit lower energy than ( n.−1)d. 9 nS. 2 .
All elements are divided into four types.:
1. Atoms s-elements S-shells of the outer layer NS are filled. These are the first two elements of each period.
2. Atoms p-elements Electrons are filled with the P-shell of the external level NP. These include the last 6 elements of each period (except for the first and seventh).
3. U. d-elements Filled by electrons d-suite of the second level (N-1) d. These are the elements of the plug-in decades of large periods located between S- and P-elements.
4. U. f-elements Filled by electrons F-subrinking third outside level (N-2) F. These are lanthanoids and actinoids.
Changes in the acid-base properties of connections of elements by groups and periodic system periods (Scheme of Kossel)
To explain the nature of the changes in the acid-base properties of the compounds of the Kossel elements (Germany, 1923), proposed to use a simple scheme based on the assumption that there is a purely ion connection in molecules and the Coulomb interaction occurs between ions. The Kossel scheme describes the acid-basic properties of compounds containing e-n and e-o-H connections, depending on the charge of the kernel and the radius of the forming item.
The cossel scheme for two metal hydroxides (for LiOH and KOH molecules) is shown in Fig. 6.2. As can be seen from the submitted scheme, the radius of the Li ion + is less than the radius of the ion to + and it is a group, the group is stronger with the lithium ion than with the potassium ion. As a result, it will be easier to dissociate in the solution and the basic properties of potassium hydroxide will be expressed stronger. The periodic system of elements is a graphical image of a periodic law and reflects the structure of the atoms of the elements
"Quantum numbers. Powli principle, Gund rule, Clakovsky rules. Settlement tasks (definition of the structure of atoms of chemical elements. Placing electrons by energy levels and orbital, electronic configurations of atoms and ions). "
Hurry up to take advantage of up to 60% for infourok courses
Number:
Theme lesson: Quantum numbers. Powli principle, Gund rule, Clakovsky rules. Settlement tasks ( determination of the structure of atoms of chemical elements. Placement of electrons for energy levels and orbitals, electronic configurations of atoms and ions).
The purpose of the lesson: to form students on the structure of an atom electronic shell on the example of the chemical elements of 1-3 periodic periodic system periods. Secure the concepts of "Periodic Law" and "Periodic System".
Tasks lesson: To learn how to make electronic formulas of atoms, to determine the elements by their electronic formulas, to determine the composition of the atom.
Equipment: Periodic system of chemical elements D.I. Mendeleev, cool board, multimedia projector, personal computer, layout and presentation "Compilation of electronic formulas for the structure of atoms".
Type of lesson: combined
Methods: Sensual, visual.
I. Organizational moment.
Greeting. Mark of missing. Activation of a class for the assimilation of a new topic.
The teacher welcomes and records the subject of the lesson on the board "The structure of an atom electronic shells".
II. Explanation of the new material
Teacher: The structure of electronic shells of atoms has an important role for chemistry, since it is the electrons that determine the chemical properties of substances. The most important characteristic of the electron motion on a certain orbital is the energy of its connection to the core. Electrons in the atom differ in a certain energy, and, as experiments show, some are stronger to the kernel is stronger, others are weaker. This is explained by the remoteness of electrons from the kernel. The closer the electrons to the kernel, the greater the connection of them with the core, but less energy supply. As the atom is removed from the nucleus, the power of the electron attraction to the kernel is reduced, and the energy supply increases. So form electronic layers in an electronic shell atom. Electrons with close energy values \u200b\u200bform a single electronic layer, or energy level . Energy of electrons in the atom and the energy level is determined by the main quantum number n. and takes the integer values \u200b\u200bof 1, 2, 3, 4, 5, 6 and 7. The greater the value N, the greater the electron energy in the atom. The maximum number of electrons that can be on a thom or different energy level is determined by the formula:
Where N. - the maximum number of electrons at the level;
n. - Energy level number.
It was established that no more than two electrons are located on the first shell, on the second - no more than eight, on the third - not more than 18, on the fourth - not more than 32. Filling out more distant shells we will not consider. It is known that at the external energy level may be no more than eight electrons, it is called completed . Electronic layers that do not contain the maximum number of electrons are called unfinished .
The number of electrons at the external energy level of the electronic shell of the atom is equal to the number of the group for the chemical elements of the main subgroups.
As previously said, the electron is moving not in orbit, but according to orbitals and does not have the trajectory.
Space around the kernel where the most likely to find this electron, is called an orbital of this electron, or an electronic cloud.
Principle Pauli Rule Gund Rules Clakovsky
Ticket number 2. Electronic structure of atom, quantum numbers, types of orbital. The procedure for filling the energy levels and sublevels (minimum energy, the principle of Pauli, the Rule of Hund, the rule of Clakovsky, degenerate orbital). Electronic formulas of elements. Formulas in the form of energy cells. Valuation of the element for the main and excited states of the atom.
Atom is the smallest particle of the chemical element, the carrier of its properties. It is the most simple electrical chemical microsystem, subject to quantum mechanics.
For an electron in the atom, the principle of duality is true: the electron is both a material particle of small mass and an electromagnetic wave.
Geisenberg's uncertainty principle: at each specific point in time, it is impossible to determine the location of the electrons (X, Y, Z) coordinates (or impulse) with the same accuracy.
The movement of the electorone in the atom can be represented as an electronic cloud.
The region of the electronic cloud in which the electron holds more than 95% of the time is revealed by an electronic orbital (E.O.). The larger size of the orbital characterizes the high electron energy. The orbital size orbitals form energy levels that consist of sublevels.
To describe the state of the electron in the atom, 4 quantum numbers (N, L, M, S) are used. The first three correspond to the three degrees of the electron freedom in three-dimensional space, and the fourth corresponds to the probability of rotation of the electron around the imaginary own axis. Quantum numbers:
- "N" - the main quantum number. It characterizes the level of electron energy in the atom field (remoteness from the kernel). Mathematical dependence of communication energy with the nucleus: E a \u003d -13.6 / n 2 eV, n \u003d 1,2, ... for real elements n \u003d 1, ..., 7. n \u003d period number.
- "L" is an orbital quantum number. It characterizes the type of sublevel (form of an electronic cloud). L \u003d 0,1,2, ..., (n-1). Denoted by letters. In this case, L \u003d 0 corresponds to S, 1-P, 2-D, 3-F, 4-Q, 5-h.
- "M" - magnetic quantum number. Characterizes the spatial location of the orbital. m \u003d ± 0, ± 1, ± 2, ..., ± l. Summa orbitals on supro: E \u003d 2L + 1.
- "S" - spin quantum number. It characterizes the likelihood of an electron rotation around its axis in two opposite directions. S \u003d ± 1/2. "+" - clockwise, "-" - counterclockwise. Rotation reports an electron of its own magnetic moment, which is called an electron back.
The principle of Pauli (prohibition): Atoms having more than one electron cannot be two electrons with the same values \u200b\u200bof all four quantum numbers. Or so: on the same orbital there may be only two electrons, and with the opposite spins.
The principle of the minimum of energy: the sequential filling of electrons in the atom must be responding both at the low energy of the electron itself and the atom's minimum energy in general. Or so: minimum energy corresponds to maximum stability. Filution goes in accordance with the energy equation of orbital: NSRIKLY Clekkovsky: First, those subcoins are filled out, the sum of N + L which is the smallest. If for two supertons, the sum N + L is equal, then the sublayer with smaller n is filled first.
Hinda rule: basically (unexcited) the state of the atom on the sublayers NP, ND and NF there is always a maximum number of unpaired electrons (maximum unpaired spin).
The p, d and f suite consist of several orbital, the energy of which is the same, so these sublevels are called "degenerate": P sublayer degenerate three times, D five times and F seventies. For electrons of these sublevels, Hinda rule is observed.
Valence is the ability to form chemical connections.
The main state is a state with minimal energy, i.e. electrons are closer to the kernel.
The excited state is a state at which all or part of electrons in the atom is sparkled and are on superts with greater energy, that is, on the kernel.
The maximum valence is observed in the excited state and as a rule coincides with the number of the group in which the element is located.
