E.N.FRENKEL
Chemistry tutorial
A guide for those who do not know, but want to learn and understand chemistry
Part I. Elements of General Chemistry
(first level of difficulty)
Continuation. See the beginning in No. 13, 18, 23/2007
Chapter 3. Elementary information about the structure of the atom.
Periodic law of D.I. Mendeleev
Remember what an atom is, what an atom consists of, whether an atom changes in chemical reactions.
An atom is an electrically neutral particle consisting of a positively charged nucleus and negatively charged electrons.
The number of electrons during chemical processes can change, but nuclear charge always stays the same. Knowing the distribution of electrons in an atom (the structure of an atom), it is possible to predict many properties of a given atom, as well as the properties of simple and complex substances of which it is a part.
The structure of the atom, i.e. the composition of the nucleus and the distribution of electrons around the nucleus can be easily determined by the position of the element in the periodic system.
In the periodic system of D.I. Mendeleev, chemical elements are arranged in a certain sequence. This sequence is closely related to the structure of the atoms of these elements. Each chemical element in the system is assigned serial number, in addition, for it you can specify the period number, group number, subgroup type.
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Knowing the exact "address" of a chemical element - a group, subgroup and period number, one can unambiguously determine the structure of its atom.
Period is a horizontal row of chemical elements. There are seven periods in the modern periodic system. The first three periods small, because they contain 2 or 8 elements:
1st period - H, He - 2 elements;
2nd period - Li ... Ne - 8 elements;
3rd period - Na ... Ar - 8 elements.
Other periods - large. Each of them contains 2-3 rows of elements:
4th period (2 rows) - K ... Kr - 18 elements;
6th period (3 rows) - Cs ... Rn - 32 elements. This period includes a number of lanthanides.
Group is a vertical row of chemical elements. There are eight groups in total. Each group consists of two subgroups: main subgroup and secondary subgroup. For example:
The main subgroup is formed by chemical elements of small periods (for example, N, P) and large periods (for example, As, Sb, Bi).
A side subgroup is formed by chemical elements of only large periods (for example, V, Nb,
Ta).
Visually, these subgroups are easy to distinguish. The main subgroup is “high”, it starts from the 1st or 2nd period. The secondary subgroup is “low”, starting from the 4th period.
So, each chemical element of the periodic system has its own address: period, group, subgroup, ordinal number.
For example, vanadium V is a chemical element of the 4th period, group V, secondary subgroup, serial number 23.
Task 3.1. Specify the period, group and subgroup for chemical elements with serial numbers 8, 26, 31, 35, 54.
Task 3.2. Specify the serial number and name of the chemical element, if it is known that it is located:
a) in the 4th period, group VI, secondary subgroup;
b) in the 5th period, group IV, main subgroup.
How can information about the position of an element in the periodic system be related to the structure of its atom?
An atom is made up of a nucleus (positively charged) and electrons (negatively charged). In general, the atom is electrically neutral.
Positive charge of the nucleus of an atom equal to the atomic number of the chemical element.
The nucleus of an atom is a complex particle. Almost all the mass of an atom is concentrated in the nucleus. Since a chemical element is a collection of atoms with the same nuclear charge, the following coordinates are indicated near the symbol of the element:
Based on these data, the composition of the nucleus can be determined. The nucleus is made up of protons and neutrons.
Proton p has a mass of 1 (1.0073 amu) and a charge of +1. Neutron n it has no charge (neutral), and its mass is approximately equal to the mass of a proton (1.0087 amu).
The nuclear charge is determined by the protons. And the number of protons is(by size) charge of the nucleus of an atom, i.e. serial number.
Number of neutrons N determined by the difference between the quantities: "mass of the nucleus" BUT and "serial number" Z. So, for an aluminum atom:
N = BUT – Z = 27 –13 = 14n,
Task 3.3. Determine the composition of the nuclei of atoms if the chemical element is in:
a) 3rd period, group VII, main subgroup;
b) 4th period, group IV, secondary subgroup;
c) 5th period, group I, main subgroup.
Attention! When determining the mass number of the nucleus of an atom, it is necessary to round off the atomic mass indicated in the periodic system. This is done because the masses of the proton and neutron are practically integer, and the mass of electrons can be neglected.
Let us determine which of the nuclei below belong to the same chemical element:
A (20 R + 20n),
B (19 R + 20n),
IN 20 R + 19n).
Atoms of the same chemical element have nuclei A and B, since they contain the same number of protons, i.e., the charges of these nuclei are the same. Studies show that the mass of an atom does not significantly affect its chemical properties.
Isotopes are called atoms of the same chemical element (the same number of protons), which differ in mass (a different number of neutrons).
Isotopes and their chemical compounds differ from each other in physical properties, but the chemical properties of isotopes of the same chemical element are the same. Thus, isotopes of carbon-14 (14 C) have the same chemical properties as carbon-12 (12 C), which enter the tissues of any living organism. The difference is manifested only in radioactivity (isotope 14 C). Therefore, isotopes are used for the diagnosis and treatment of various diseases, for scientific research.
Let us return to the description of the structure of the atom. As you know, the nucleus of an atom does not change in chemical processes. What is changing? The variable is the total number of electrons in the atom and the distribution of electrons. General number of electrons in a neutral atom it is easy to determine - it is equal to the serial number, i.e. charge of the nucleus of an atom:
Electrons have a negative charge of -1, and their mass is negligible: 1/1840 of the mass of a proton.
Negatively charged electrons repel each other and are at different distances from the nucleus. Wherein electrons having an approximately equal amount of energy are located at an approximately equal distance from the nucleus and form an energy level.
The number of energy levels in an atom is equal to the number of the period in which the chemical element is located. Energy levels are conventionally designated as follows (for example, for Al):
Task 3.4. Determine the number of energy levels in the atoms of oxygen, magnesium, calcium, lead.
Each energy level can contain a limited number of electrons:
On the first - no more than two electrons;
On the second - no more than eight electrons;
On the third - no more than eighteen electrons.
These numbers show that, for example, the second energy level can have 2, 5, or 7 electrons, but not 9 or 12 electrons.
It is important to know that regardless of the energy level number on external level(last) cannot be more than eight electrons. The outer eight-electron energy level is the most stable and is called complete. Such energy levels are found in the most inactive elements - the noble gases.
How to determine the number of electrons in the outer level of the remaining atoms? There is a simple rule for this: number of outer electrons equals:
For elements of the main subgroups - the number of the group;
For elements of secondary subgroups, it cannot be more than two.
For example (Fig. 5):
Task 3.5. Specify the number of external electrons for chemical elements with serial numbers 15, 25, 30, 53.
Task 3.6. Find chemical elements in the periodic table, in the atoms of which there is a completed external level.
It is very important to correctly determine the number of external electrons, because It is with them that the most important properties of the atom are associated. So, in chemical reactions, atoms tend to acquire a stable, completed external level (8 e). Therefore, atoms, on the outer level of which there are few electrons, prefer to give them away.
Chemical elements whose atoms can only donate electrons are called metals. Obviously, there should be few electrons at the outer level of the metal atom: 1, 2, 3.
If there are many electrons on the external energy level of an atom, then such atoms tend to accept electrons before the completion of the external energy level, i.e. up to eight electrons. Such elements are called non-metals.
Question. Do the chemical elements of the secondary subgroups belong to metals or non-metals? Why?
Answer. Metals and non-metals of the main subgroups in the periodic table are separated by a line that can be drawn from boron to astatine. Above this line (and on the line) are non-metals, below - metals. All elements of secondary subgroups are below this line.
Task 3.7. Determine whether metals or non-metals include: phosphorus, vanadium, cobalt, selenium, bismuth. Use the position of the element in the periodic table of chemical elements and the number of electrons in the outer level.
In order to compose the distribution of electrons over the remaining levels and sublevels, the following algorithm should be used.
1. Determine the total number of electrons in the atom (by serial number).
2. Determine the number of energy levels (by period number).
3. Determine the number of external electrons (according to the type of subgroup and group number).
4. Indicate the number of electrons at all levels except the penultimate one.
For example, according to points 1–4 for the manganese atom, it is determined:
Total 25 e; distributed (2 + 8 + 2) = 12 e; so, on the third level is: 25 - 12 = 13 e.
The distribution of electrons in the manganese atom was obtained:
Task 3.8. Work out the algorithm by drawing up atomic structure diagrams for elements No. 16, 26, 33, 37. Indicate whether they are metals or non-metals. Explain the answer.
When compiling the above diagrams of the structure of the atom, we did not take into account that the electrons in the atom occupy not only levels, but also certain sublevels each level. Types of sublevels are indicated by Latin letters: s, p, d.
The number of possible sublevels is equal to the level number. The first level consists of one
s-sublevel. The second level consists of two sublevels - s and R. The third level - from three sublevels - s, p and d.
Each sublevel can contain a strictly limited number of electrons:
at the s-sublevel - no more than 2e;
at the p-sublevel - no more than 6e;
at the d-sublevel - no more than 10e.
Sublevels of one level are filled in a strictly defined order: spd.
Thus, R- sublevel can't start to fill if not full s-sublevel of a given energy level, etc. Based on this rule, it is easy to compose the electronic configuration of the manganese atom:
Generally electronic configuration of an atom manganese is written like this:
25 Mn 1 s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2 .
Task 3.9. Make electronic configurations of atoms for chemical elements No. 16, 26, 33, 37.
Why is it necessary to make electronic configurations of atoms? To determine the properties of these chemical elements. It should be remembered that only valence electrons.
Valence electrons are in the outer energy level and incomplete
d-sublevel of the pre-outer level.
Let's determine the number of valence electrons for manganese:
or abbreviated: Mn ... 3 d 5 4s 2 .
What can be determined by the formula for the electronic configuration of an atom?
1. What element is it - metal or non-metal?
Manganese is a metal, because the outer (fourth) level contains two electrons.
2. What process is typical for metal?
Manganese atoms always donate electrons in reactions.
3. What electrons and how many will give a manganese atom?
In reactions, the manganese atom gives up two outer electrons (they are farthest from the nucleus and are weaker attracted by it), as well as five pre-outer d-electrons. The total number of valence electrons is seven (2 + 5). In this case, eight electrons will remain at the third level of the atom, i.e. complete outer level is formed.
All these reasoning and conclusions can be reflected using the scheme (Fig. 6):
The resulting conditional charges of an atom are called oxidation states.
Considering the structure of the atom, in a similar way it can be shown that the typical oxidation states for oxygen are -2, and for hydrogen +1.
Question. With which of the chemical elements can manganese form compounds, if we take into account the degrees of its oxidation obtained above?
Answer: Only with oxygen, tk. its atom has the opposite charge in its oxidation state. The formulas of the corresponding manganese oxides (here, the oxidation states correspond to the valences of these chemical elements):
The structure of the manganese atom suggests that manganese cannot have a higher degree of oxidation, because in this case, one would have to touch upon the stable, now completed, pre-outer level. Therefore, the +7 oxidation state is the highest, and the corresponding Mn 2 O 7 oxide is the highest manganese oxide.
To consolidate all these concepts, consider the structure of the tellurium atom and some of its properties:
As a non-metal, the Te atom can accept 2 electrons before the completion of the outer level and donate "extra" 6 electrons:
Task 3.10. Draw the electronic configurations of Na, Rb, Cl, I, Si, Sn atoms. Determine the properties of these chemical elements, the formulas of their simplest compounds (with oxygen and hydrogen).
Practical Conclusions
1. Only valence electrons participate in chemical reactions, which can only be in the last two levels.
2. Metal atoms can only donate valence electrons (all or a few), taking positive oxidation states.
3. Non-metal atoms can accept electrons (missing - up to eight), while acquiring negative oxidation states, and donate valence electrons (all or a few), while they acquire positive oxidation states.
Let us now compare the properties of the chemical elements of one subgroup, for example, sodium and rubidium:
Na...3 s 1 and Rb...5 s 1 .
What is common in the structure of the atoms of these elements? At the outer level of each atom, one electron is active metals. metal activity associated with the ability to donate electrons: the easier an atom gives off electrons, the more pronounced its metallic properties.
What holds electrons in an atom? attraction to the nucleus. The closer the electrons are to the nucleus, the stronger they are attracted by the nucleus of the atom, the more difficult it is to “tear them off”.
Based on this, we will answer the question: which element - Na or Rb - gives away an external electron more easily? Which element is the more active metal? Obviously, rubidium, because its valence electrons are farther away from the nucleus (and are less strongly held by the nucleus).
Conclusion. In the main subgroups, from top to bottom, the metallic properties are enhanced, because the radius of the atom increases, and valence electrons are weaker attracted to the nucleus.
Let's compare the properties of chemical elements of group VIIa: Cl …3 s 2 3p 5 and I...5 s 2 5p 5 .
Both chemical elements are non-metals, because. one electron is missing before the completion of the outer level. These atoms will actively attract the missing electron. Moreover, the stronger the missing electron attracts a non-metal atom, the stronger its non-metallic properties (the ability to accept electrons) are manifested.
What causes the attraction of an electron? Due to the positive charge of the nucleus of the atom. In addition, the closer the electron to the nucleus, the stronger their mutual attraction, the more active the non-metal.
Question. Which element has more pronounced non-metallic properties: chlorine or iodine?
Answer: Obviously, chlorine, because. its valence electrons are closer to the nucleus.
Conclusion. The activity of non-metals in subgroups decreases from top to bottom, because the radius of the atom increases and it is more and more difficult for the nucleus to attract the missing electrons.
Let us compare the properties of silicon and tin: Si …3 s 2 3p 2 and Sn…5 s 2 5p 2 .
Both atoms have four electrons at the outer level. Nevertheless, these elements in the periodic table are on opposite sides of the line connecting boron and astatine. Therefore, for silicon, the symbol of which is above the B–At line, nonmetallic properties are more pronounced. On the contrary, tin, whose symbol is below the B–At line, has stronger metallic properties. This is due to the fact that in the tin atom, four valence electrons are removed from the nucleus. Therefore, the attachment of the missing four electrons is difficult. At the same time, the return of electrons from the fifth energy level occurs quite easily. For silicon, both processes are possible, with the first (acceptance of electrons) predominating.
Conclusions on chapter 3. The fewer external electrons in an atom and the farther they are from the nucleus, the stronger the metallic properties are manifested.
The more external electrons in an atom and the closer they are to the nucleus, the more non-metallic properties are manifested.
Based on the conclusions formulated in this chapter, a "characteristic" can be compiled for any chemical element of the periodic system.
Property Description Algorithm
chemical element by its position
in the periodic system
1. Draw up a diagram of the structure of the atom, i.e. determine the composition of the nucleus and the distribution of electrons by energy levels and sublevels:
Determine the total number of protons, electrons and neutrons in an atom (by serial number and relative atomic mass);
Determine the number of energy levels (by period number);
Determine the number of external electrons (by type of subgroup and group number);
Indicate the number of electrons at all energy levels except the penultimate one;
2. Determine the number of valence electrons.
3. Determine which properties - metal or non-metal - are more pronounced for a given chemical element.
4. Determine the number of given (received) electrons.
5. Determine the highest and lowest oxidation states of a chemical element.
6. Compose for these oxidation states the chemical formulas of the simplest compounds with oxygen and hydrogen.
7. Determine the nature of the oxide and write an equation for its reaction with water.
8. For the substances indicated in paragraph 6, draw up equations of characteristic reactions (see Chapter 2).
Task 3.11. According to the above scheme, make descriptions of the atoms of sulfur, selenium, calcium and strontium and the properties of these chemical elements. What are the general properties of their oxides and hydroxides?
If you have completed exercises 3.10 and 3.11, then it is easy to see that not only the atoms of the elements of one subgroup, but also their compounds have common properties and a similar composition.
Periodic law of D.I. Mendeleev:the properties of chemical elements, as well as the properties of simple and complex substances formed by them, are in a periodic dependence on the charge of the nuclei of their atoms.
The physical meaning of the periodic law: the properties of chemical elements are periodically repeated because the configurations of valence electrons (the distribution of electrons of the outer and penultimate levels) are periodically repeated.
So, the chemical elements of the same subgroup have the same distribution of valence electrons and, therefore, similar properties.
For example, the chemical elements of the fifth group have five valence electrons. At the same time, in the atoms of chemical elements of the main subgroups- all valence electrons are in the outer level: ... ns 2 np 3 , where n– period number.
At atoms elements of secondary subgroups only 1 or 2 electrons are in the outer level, the rest are in d- sublevel of the pre-external level: ... ( n – 1)d 3 ns 2 , where n– period number.
Task 3.12. Make short electronic formulas for atoms of chemical elements No. 35 and 42, and then make up the distribution of electrons in these atoms according to the algorithm. Make sure your prediction comes true.
Exercises for chapter 3
1. Formulate the definitions of the concepts "period", "group", "subgroup". What do the chemical elements that make up: a) period; b) a group; c) subgroup?
2. What are isotopes? What properties - physical or chemical - do isotopes have in common? Why?
3. Formulate the periodic law of DIMendeleev. Explain its physical meaning and illustrate with examples.
4. What are the metallic properties of chemical elements? How do they change in a group and in a period? Why?
5. What are the non-metallic properties of chemical elements? How do they change in a group and in a period? Why?
6. Make brief electronic formulas of chemical elements No. 43, 51, 38. Confirm your assumptions by describing the structure of the atoms of these elements according to the above algorithm. Specify the properties of these elements.
7. By short electronic formulas
a) ...4 s 2 4p 1 ;
b) …4 d 1 5s 2 ;
in 3 d 5 4s 1
determine the position of the corresponding chemical elements in the periodic system of D.I. Mendeleev. Name these chemical elements. Confirm your assumptions with a description of the structure of the atoms of these chemical elements according to the algorithm. Specify the properties of these chemical elements.
To be continued
The closer to the atomic nucleus is the electron shell of the atom, the stronger the electrons are attracted to the nucleus and the greater their binding energy with the nucleus. Therefore, the arrangement of electron shells is conveniently characterized by energy levels and sublevels and the distribution of electrons over them. The number of electronic energy levels is equal to the number of the period, in which the element is located. The sum of the numbers of electrons at the energy levels is equal to the ordinal number of the element.
The electronic structure of the atom is shown in fig. 1.9 in the form of a diagram of the distribution of electrons over energy levels and sublevels. The diagram consists of electronic cells depicted by squares. Each cell symbolizes one electron orbital capable of accepting two electrons with opposite spins, indicated by the up and down arrows.
Rice. 1.9.
The electronic diagram of an atom is built in the sequence increasing the energy level number. In the same direction the energy of the electron increases and the energy of its connection with the nucleus decreases. For clarity, we can imagine that the nucleus of the atom is "at the bottom" of the diagram. The number of electrons in an atom of an element is equal to the number of protons in the nucleus, i.e. element's atomic number in the periodic table.
The first energy level consists of only one orbital, which is denoted by the symbol s. This orbital is filled with hydrogen and helium electrons. Hydrogen has one electron, and hydrogen is monovalent. Helium has two paired electrons with opposite spins, helium has zero valency and does not form compounds with other elements. The energy of a chemical reaction is not enough to excite a helium atom and transfer an electron to the second level.
The second energy level consists of. "-sublevel and /. (-sublevel, which has three orbitals (cells). Lithium sends the third electron to the 2"-sublevel. One unpaired electron causes lithium to be monovalent. Beryllium fills the same sublevel with the second electron, therefore, in In the unexcited state, beryllium has two paired electrons.However, an insignificant excitation energy turns out to be sufficient to transfer one electron to the ^-sublevel, which makes beryllium bivalent.
The further filling of the 2p-sublevel proceeds in a similar way. Oxygen in compounds is divalent. Oxygen does not exhibit higher valences due to the impossibility of pairing second-level electrons and transferring them to the third energy level.
In contrast to oxygen, sulfur located under oxygen in the same subgroup can exhibit valences 2, 4 and 6 in its compounds due to the possibility of depairing the electrons of the third level and moving them to the ^-sublevel. Note that other valence states of sulfur are also possible.
Elements whose s-sublevel is filled are called “-elements. Similarly, the sequence is formed R- elements. Elements s- and p-sublevels are included in the main subgroups. Elements of secondary subgroups are ^-elements (wrong name - transitional elements).
It is convenient to denote subgroups by the symbols of electrons, due to which the elements included in the subgroup were formed, for example s"-subgroup (hydrogen, lithium, sodium, etc.) or //-subgroup (oxygen, sulfur, etc.).
If the periodic table is constructed in such a way that the period numbers increase from bottom to top, and first one and then two electrons are placed in each electron cell, a long-period periodic table will be obtained, resembling a diagram of the distribution of electrons over energy levels and sublevels.
| Parameter name | Meaning |
| Article subject: | ENERGY LEVELS |
| Rubric (thematic category) | Education |
STRUCTURE OF THE ATOM
1. Development of the theory of the structure of the atom. With
2. The nucleus and electron shell of the atom. With
3. The structure of the nucleus of an atom. With
4. Nuclides, isotopes, mass number. With
5. Energy levels.
6. Quantum-mechanical explanation of the structure.
6.1. Orbital model of the atom.
6.2. Rules for filling orbitals.
6.3. Orbitals with s-electrons (atomic s-orbitals).
6.4. Orbitals with p-electrons (atomic p-orbitals).
6.5. Orbitals with d-f electrons
7. Energy sublevels of a multielectron atom. quantum numbers.
ENERGY LEVELS
The structure of the electron shell of an atom is determined by the different energy reserves of individual electrons in the atom. In accordance with the Bohr model of the atom, electrons can occupy positions in the atom that correspond to precisely defined (quantized) energy states. These states are called energy levels.
The number of electrons that can be on a separate energy level is determined by the formula 2n 2, where n is the number of the level, which is denoted by Arabic numerals 1 - 7. The maximum filling of the first four energy levels in. in accordance with the formula 2n 2 is: for the first level - 2 electrons, for the second - 8, for the third -18 and for the fourth level - 32 electrons. The maximum filling of higher energy levels in atoms of known elements with electrons has not been achieved.
Rice. 1 shows the filling of the energy levels of the first twenty elements with electrons (from hydrogen H to calcium Ca, black circles). By filling in the energy levels in the indicated order, the simplest models of the atoms of the elements are obtained, while observing the order of filling (from bottom to top and from left to right in the figure) in such a way that the last electron points to the symbol of the corresponding element At the third energy level M(maximum capacity is 18 e -) for elements Na - Ar contains only 8 electrons, then the fourth energy level begins to build up N- two electrons appear on it for the elements K and Ca. The next 10 electrons again occupy the level M(elements Sc – Zn (not shown), and then the filling of the N level with six more electrons continues (elements Ca-Kr, white circles).
| Rice. one |  Rice. 2 |
If the atom is in the ground state, then its electrons occupy levels with a minimum energy, i.e., each subsequent electron occupies the energetically most favorable position, such as in Fig. 1. With an external impact on an atom associated with the transfer of energy to it, for example, by heating, electrons are transferred to higher energy levels (Fig. 2). This state of the atom is called excited. The place vacated at the lower energy level is filled (as an advantageous position) by an electron from a higher energy level. During the transition, the electron gives off a certain amount of energy, ĸᴏᴛᴏᴩᴏᴇ corresponds to the energy difference between the levels. As a result of electronic transitions, characteristic radiation arises. From the spectral lines of the absorbed (emitted) light, one can make a quantitative conclusion about the energy levels of the atom.
In accordance with the Bohr quantum model of the atom, an electron having a certain energy state moves in a circular orbit in the atom. Electrons with the same energy reserve are at equal distances from the nucleus, each energy level corresponds to its own set of electrons, called the electron layer by Bohr. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, according to Bohr, the electrons of one layer move along a spherical surface, the electrons of the next layer along another spherical surface. all spheres are inscribed one into another with the center corresponding to the atomic nucleus.
ENERGY LEVELS - concept and types. Classification and features of the category "ENERGY LEVELS" 2017, 2018.
Let us briefly recall what we already know about the structure of the electron shell of atoms:
the number of energy levels of an atom = the number of the period in which the element is located;
the maximum capacity of each energy level is calculated by the formula 2n 2
the outer energy shell cannot contain more than 2 electrons for elements of period 1, more than 8 electrons for elements of other periods
Once again, let us return to the analysis of the scheme for filling energy levels in elements of small periods:
Table 1. Filling of energy levels
For elements of small periods
| Period number | Number of energy levels = period number | Element symbol, its ordinal number | Total electrons | Distribution of electrons by energy levels | Group number |
|
| Scheme 1 | Scheme 2 |
|||||
| 1 | 1 | 1 N | 1 | H +1) 1 | +1 H, 1e - | I (VII) |
| 2 Not | 2 | He + 2 ) 2 | +2 no, 2nd - | VIII |
||
| 2 | 2 | 3Li | 3 | Li + 3 ) 2 ) 1 | + 3 Li, 2e - , 1e - | I |
| 4 Be | 4 | Be +4) 2 ) 2 | + 4 Be, 2e - , 2 e - | II |
||
| 5B | 5 | B +5) 2 ) 3 | +5 B, 2e - , 3rd - | III |
||
| 6C | 6 | C +6) 2 ) 4 | +6 C, 2e - , 4th - | IV |
||
| 7 N | 7 | N + 7 ) 2 ) 5 | + 7 N, 2e - , 5 e - | V |
||
| 8 O | 8 | O + 8 ) 2 ) 6 | + 8 O, 2e - , 6 e - | VI |
||
| 9F | 9 | F + 9 ) 2 ) 7 | + 9 F, 2e - , 7 e - | VI |
||
| 10 Ne | 10 | Ne+ 10 ) 2 ) 8 | + 10 Ne, 2e - , 8 e - | VIII |
||
| 3 | 3 | 11 Na | 11 | Na+ 11 ) 2 ) 8 ) 1 | +1 1 Na, 2e - , 8e - , 1e - | I |
| 12 mg | 12 | mg+ 12 ) 2 ) 8 ) 2 | +1 2 mg, 2e - , 8e - , 2 e - | II |
||
| 13 Al | 13 | Al+ 13 ) 2 ) 8 ) 3 | +1 3 Al, 2e - , 8e - , 3 e - | III |
||
| 14 Si | 14 | Si+ 14 ) 2 ) 8 ) 4 | +1 4 Si, 2e - , 8e - , 4 e - | IV |
||
| 15p | 15 | P+ 15 ) 2 ) 8 ) 5 | +1 5 P, 2e - , 8e - , 5 e - | V |
||
| 16S | 16 | S+ 16 ) 2 ) 8 ) 6 | +1 5 P, 2e - , 8e - , 6 e - | VI |
||
| 17Cl | 17 | Cl+ 17 ) 2 ) 8 ) 7 | +1 7 Cl, 2e - , 8e - , 7 e - | VI |
||
| 18 Ar | 18 | Ar+ 18 ) 2 ) 8 ) 8 | +1 8 Ar, 2e - , 8e - , 8 e - | VIII |
||
Analyze table 1. Compare the number of electrons in the last energy level and the number of the group in which the chemical element is located.
Have you noticed that the number of electrons in the outer energy level of atoms is the same as the group number, in which the element is located (the exception is helium)?
!!! This rule is trueonly for elementsmajor subgroups.
Each period of the D.I. Mendeleev ends with an inert element(helium He, neon Ne, argon Ar). The external energy level of these elements contains the maximum possible number of electrons: helium -2, the remaining elements - 8. These are elements of group VIII of the main subgroup. The energy level similar to the structure of the energy level of an inert gas is called completed. This is a kind of strength limit of the energy level for each element of the Periodic system. Molecules of simple substances - inert gases, consist of one atom and are distinguished by chemical inertness, i.e. practically do not enter into chemical reactions.
For the remaining elements of the PSCE, the energy level differs from the energy level of the inert element, such levels are called unfinished. The atoms of these elements tend to complete their outer energy level by donating or accepting electrons.
Questions for self-control
What energy level is called external?
What energy level is called internal?
What energy level is called complete?
The elements of which group and subgroup have a completed energy level?
What is the number of electrons in the outer energy level of the elements of the main subgroups?
How are the elements of one main subgroup similar in the structure of the electronic level
How many electrons at the outer level contain the elements of a) group IIA;
View answer
Last
Any but the last
The one that contains the maximum number of electrons. As well as the outer level, if it contains 8 electrons for period I - 2 electrons.
Group VIIIA elements (inert elements)
The number of the group in which the element is located
All elements of the main subgroups on the outer energy level contain as many electrons as the group number
a) elements of group IIA have 2 electrons in the outer level; b) group IVA elements have 4 electrons; c) elements of group VII A have 7 electrons.
Tasks for independent solution
Determine the element according to the following features: a) it has 2 electronic levels, on the outer - 3 electrons; b) has 3 electronic levels, on the outer - 5 electrons. Write down the distribution of electrons over the energy levels of these atoms.
Which two atoms have the same number of filled energy levels?
How many electrons are in the outer energy level of magnesium?
How many electrons are there in a neon atom?
What two atoms have the same number of electrons at the external energy level: a) sodium and magnesium; b) calcium and zinc; c) arsenic and phosphorus d) oxygen and fluorine.
At the external energy level of the sulfur atom of electrons: a) 16; b) 2; c) 6 d) 4
What do sulfur and oxygen atoms have in common: a) the number of electrons; b) the number of energy levels c) the number of the period d) the number of electrons in the outer level.
What do magnesium and phosphorus atoms have in common: a) the number of protons; b) the number of energy levels c) the group number d) the number of electrons in the outer level.
Choose an element of the second period, which has one electron at the outer level: a) lithium; b) beryllium; c) oxygen; d) sodium
There are 4 electrons at the outer level of an atom of an element of the third period. Specify this element: a) sodium; b) carbon c) silicon d) chlorine
An atom has 2 energy levels and 3 electrons. Specify this element: a) aluminum; b) boron c) magnesium d) nitrogen
View answer:
1. a) Let's establish the "coordinates" of the chemical element: 2 electronic levels - II period; 3 electrons at the outer level - III A group. This is boron 5 B. Scheme of distribution of electrons by energy levels: 2nd - , 3rd -
B) III period, VA group, element phosphorus 15 R. Scheme of distribution of electrons by energy levels: 2nd - , 8e - , 5e -
2. d) sodium and chlorine.
Explanation: a) sodium: +11 ) 2 ) 8 ) 1 (filled 2) ←→ hydrogen: +1) 1
B) helium: +2 ) 2 (filled 1) ←→ hydrogen: hydrogen: +1) 1
C) helium: +2 ) 2 (filled 1) ←→ neon: +10 ) 2 ) 8 (filled 2)
*G) sodium: +11 ) 2 ) 8 ) 1 (filled 2) ←→ chlorine: +17 ) 2 ) 8 ) 7 (filled 2)
4. Ten. Number of electrons = serial number
c) arsenic and phosphorus. Atoms located in the same subgroup have the same number of electrons.
A) sodium and magnesium (in different groups); b) calcium and zinc (in the same group, but different subgroups); * c) arsenic and phosphorus (in one, main, subgroup) d) oxygen and fluorine (in different groups).
7. d) the number of electrons in the outer level
8. b) the number of energy levels
9. a) lithium (located in group IA of period II)
10. c) silicon (IVA group, III period)
11. b) boron (2 levels - IIperiod, 3 electrons in the outer level - IIIAGroup)
An atom is an electrically neutral particle consisting of a positively charged nucleus and a negatively charged electron shell. The nucleus is at the center of the atom and is made up of positively charged protons and uncharged neutrons held together by nuclear forces. The nuclear structure of the atom was experimentally proved in 1911 by the English physicist E. Rutherford.
The number of protons determines the positive charge of the nucleus and is equal to the ordinal number of the element. The number of neutrons is calculated as the difference between the atomic mass and the ordinal number of the element. Elements that have the same nuclear charge (same number of protons) but different atomic mass (different number of neutrons) are called isotopes. The mass of an atom is mainly concentrated in the nucleus, because the negligibly small mass of electrons can be neglected. The atomic mass is equal to the sum of the masses of all protons and all neutrons of the nucleus.
An element is a type of atom with the same nuclear charge. Currently, 118 different chemical elements are known.
All the electrons of an atom form its electron shell. The electron shell has a negative charge equal to the total number of electrons. The number of electrons in the shell of an atom coincides with the number of protons in the nucleus and is equal to the ordinal number of the element. The electrons in the shell are distributed among the electron layers according to the energy reserves (electrons with similar energies form one electron layer): electrons with lower energy are closer to the nucleus, electrons with higher energy are farther from the nucleus. The number of electronic layers (energy levels) coincides with the number of the period in which the chemical element is located.
Distinguish between completed and incomplete energy levels. The level is considered complete if it contains the maximum possible number of electrons (the first level - 2 electrons, the second level - 8 electrons, the third level - 18 electrons, the fourth level - 32 electrons, etc.). The incomplete level contains fewer electrons.
The level farthest from the nucleus of an atom is called the outer level. Electrons in the outer energy level are called outer (valence) electrons. The number of electrons in the outer energy level coincides with the number of the group in which the chemical element is located. The outer level is considered complete if it contains 8 electrons. Atoms of elements of the 8A group (inert gases helium, neon, krypton, xenon, radon) have a completed external energy level.
The region of space around the nucleus of an atom, in which the electron is most likely to be found, is called the electron orbital. Orbitals differ in energy level and shape. The shape distinguishes s-orbitals (sphere), p-orbitals (volumetric eight), d-orbitals and f-orbitals. Each energy level has its own set of orbitals: at the first energy level - one s-orbital, at the second energy level - one s- and three p-orbitals, at the third energy level - one s-, three p-, five d-orbitals , at the fourth energy level one s-, three p-, five d-orbitals and seven f-orbitals. Each orbital can hold a maximum of two electrons.
The distribution of electrons in orbitals is reflected using electronic formulas. For example, for a magnesium atom, the distribution of electrons over energy levels will be as follows: 2e, 8e, 2e. This formula shows that 12 electrons of a magnesium atom are distributed over three energy levels: the first level is completed and contains 2 electrons, the second level is completed and contains 8 electrons, the third level is not completed, because contains 2 electrons. For a calcium atom, the distribution of electrons over energy levels will be as follows: 2e, 8e, 8e, 2e. This formula shows that 20 calcium electrons are distributed over four energy levels: the first level is completed and contains 2 electrons, the second level is completed and contains 8 electrons, the third level is not completed, because contains 8 electrons, the fourth level is not completed, because contains 2 electrons.
