Periodic law.
Atomic structure
The article provides test tasks on the topic from the bank of test tasks compiled by the authors for thematic control in the 8th grade. (The capacity of the bank is 80 tasks for each of the six topics studied in the 8th grade, and 120 tasks on the topic “Basic classes of inorganic compounds.”) Currently, chemistry in the 8th grade is taught using nine textbooks. Therefore, at the end of the article there is a list of controlled knowledge elements indicating task numbers. This will allow teachers working in different programs to choose both the appropriate sequence of tasks from one topic, and a set of combinations of test tasks from different topics, including for final control.
The proposed 80 test tasks are grouped into 20 questions into four versions, in which similar tasks are repeated. To compile a larger number of options from the list of knowledge elements, we select (randomly) task numbers for each studied element in accordance with our thematic planning. This presentation of tasks for each topic allows for a quick element-by-element analysis of errors and their timely correction. Using similar tasks in one version and alternating one or two correct answers reduces the likelihood of guessing the answer. The complexity of questions, as a rule, increases from the 1st and 2nd options to the 3rd and 4th options.
There is an opinion that tests are a “guess game”. We invite you to check if this is true. After testing, compare the results with the marks in the log. If the test results are lower, it may be due to the following reasons.
Firstly, this (test) form of control is unusual for students. Secondly, the teacher places emphasis differently when studying the topic (determining the main thing in the content of education and teaching methods).
Option 1
Assignments.
1. In the 4th period, VIa group there is an element with a serial number:
1) 25; 2) 22; 3) 24; 4) 34.
2. An element with atomic nuclear charge +12 has an atomic number:
1) 3; 2) 12; 3) 2; 4) 24.
3. The serial number of an element corresponds to the following characteristics:
1) charge of the atomic nucleus;
2) the number of protons;
3) the number of neutrons;
4. Six electrons in the outer energy level of atoms of elements with group number:
1) II; 2) III; 3) VI; 4) IV.
5. Superior Chlorine Oxide Formula:
1) Cl 2 O; 2) Cl 2 O 3;
3) Cl 2 O 5; 4) Cl 2 O 7.
6. The valence of an aluminum atom is:
1) 1; 2) 2; 3) 3; 4) 4.
7. General formula of volatile hydrogen compounds of group VI elements:
1) EN 4; 2) EN 3;
3) NE; 4) N 2 E.
8. Number of outer electron layer in calcium atom:
1) 1; 2) 2; 3) 3; 4) 4.
9.
1) Li; 2) Na; 3) K; 4) Cs.
10. Specify metal elements:
1) K; 2) Cu; 3) O; 4) N.
11. Where in D.I. Mendeleev’s table are located the elements whose atoms are in chemical reactions do they just give up electrons?
1) In group II;
2) at the beginning of the 2nd period;
3) in the middle of the 2nd period;
4) in group VIa.
12.
2) Be, Mg; Al;
3) Mg, Ca, Sr;
13. Specify non-metal elements:
1) Cl; 2) S; 3) Mn; 4) Mg.
14. Non-metallic properties increase in the following order:
15. What characteristic of an atom changes periodically?
1) Charge of the nucleus of an atom;
2) number energy levels in an atom;
3) the number of electrons at the external energy level;
4) number of neutrons.
16.
1) K; 2) Al; 3) P; 4) Cl.
17. In the period with increasing nuclear charge, the radii of atoms of elements:
1) decrease;
2) do not change;
3) increase;
4) change periodically.
18. Isotopes of atoms of the same element differ in:
1) the number of neutrons;
2) the number of protons;
3) the number of valence electrons;
4) position in the table of D.I. Mendeleev.
19. Number of neutrons in the nucleus of a 12 C atom:
1) 12; 2) 4; 3) 6; 4) 2.
20. Distribution of electrons by energy levels in a fluorine atom:
1) 2, 8, 4; 2) 2,6;
3) 2, 7; 4) 2, 8, 5.
Option 2
Assignments. Choose one or two correct answers.
21. The element with serial number 35 is located in:
1) 7th period, group IV;
2) 4th period, VIIa group;
3) 4th period, VIIb group;
4) 7th period, IVb group.
22. An element with atomic nuclear charge +9 has the atomic number:
1) 19; 2) 10; 3) 4; 4) 9.
23. The number of protons in a neutral atom coincides with:
1) the number of neutrons;
2) atomic mass;
3) serial number;
4) the number of electrons.
24. Five electrons in the outer energy level of atoms of elements with group number:
1) I; 2) III; 3) V; 4) VII.
25. Supreme Nitric Oxide Formula:
1) N 2 O; 2) N 2 O 3;
3) N 2 O 5; 4) NO;
26. The valency of the calcium atom in its higher hydroxide is:
1) 1; 2) 2; 3) 3; 4) 4.
27. The valency of the arsenic atom in its hydrogen compound is:
1) 1; 2) 2; 3) 3; 4) 4.
28. Number of the outer electron layer in the potassium atom:
1) 1; 2) 2; 3) 3; 4) 4.
29. The largest atomic radius of an element is:
1) B; 2) O; 3) C; 4) N.
30. Specify metal elements:
1) K; 2) H; 3) F; 4) Cu.
31. Atoms of elements that can both accept and donate electrons are located:
1) in group Ia;
2) in group VIa;
3) at the beginning of the 2nd period;
4) at the end of the 3rd period.
32.
1) Na, K, Li; 2) Al, Mg, Na;
3) P, S, Cl; 4) Na, Mg, Al.
33. Specify non-metal elements:
1) Na; 2) Mg; 3) Si; 4) P.
34.
35. Main characteristics of the chemical element:
1) atomic mass;
2) nuclear charge;
3) number of energy levels;
4) number of neutrons.
36. Symbol of an element whose atoms form an amphoteric oxide:
1) N; 2) K; 3) S; 4) Zn.
37. In the main subgroups (a) of the periodic system of chemical elements, with increasing nuclear charge, the radius of the atom is:
1) increases;
2) decreases;
3) does not change;
4) changes periodically.
38. The number of neutrons in the nucleus of an atom is:
1) number of electrons;
2) the number of protons;
3) the difference between the relative atomic mass and the number of protons;
4) atomic mass.
39. Hydrogen isotopes differ in number:
1) electrons;
2) neutrons;
3) protons;
4) position in the table.
40. Distribution of electrons by energy levels in the sodium atom:
1) 2, 1; 2) 2, 8, 1;
3) 2, 4; 4) 2, 5.
Option 3
Assignments. Choose one or two correct answers.
41. Indicate the serial number of the element that is in group IVa, the 4th period of D.I. Mendeleev’s table:
1) 24; 2) 34; 3) 32; 4) 82.
42. The charge of the nucleus of an atom of element No. 13 is equal to:
1) +27; 2) +14; 3) +13; 4) +3.
43. The number of electrons in an atom is:
1) the number of neutrons;
2) the number of protons;
3) atomic mass;
4) serial number.
44. For atoms of group IVa elements, the number of valence electrons is equal to:
1) 5; 2) 6; 3) 3; 4) 4.
45. Oxides with the general formula R 2 O 3 form elements of the series:
1) Na, K, Li; 2) Mg, Ca, Be;
3) B, Al, Ga; 4) C, Si, Ge.
46. The valency of the phosphorus atom in its higher oxide is:
1) 1; 2) 3; 3) 5; 4) 4.
47. Hydrogen compounds of group VIIa elements:
1) HClO 4; 2) HCl;
3) HBrO; 4) HBr.
48. The number of electron layers in a selenium atom is equal to:
1) 1; 2) 2; 3) 3; 4) 4.
49. The largest atomic radius of an element is:
1) Li; 2) Na; 3) Mg;
50. Specify metal elements:
1) Na; 2) Mg; 3) Si; 4) P.
51. Atoms of which elements easily give up electrons?
1) K; 2) Cl; 3) Na; 4) S.
52. A number of elements in which metallic properties increase:
1) C, N, B, F;
2) Al, Si, P, Mg;
53. Specify non-metal elements:
1) Na; 2) Mg; 3) N; 4) S.
54. A number of elements in which non-metallic properties increase:
1) Li, Na, K, H;
2) Al, Si, P, Mg;
3) C, N, O, F;
4) Na, Mg, Al, K.
55. With increasing charge of the atomic nucleus, non-metallic properties of elements:
1) change periodically;
2) intensify;
3) do not change;
4) weaken.
56. Symbol of the element whose atoms form an amphoteric hydroxide:
1) Na; 2) Al; 3) N; 4) S.
57. The frequency of changes in the properties of elements and their compounds is explained:
1) repetition of the structure of the outer electronic layer;
2) increasing the number of electronic layers;
3) an increase in the number of neutrons;
4) increase in atomic mass.
58. The number of protons in the nucleus of a sodium atom is:
1) 23; 2) 12; 3) 1; 4) 11.
59. How do atoms of isotopes of the same element differ?
1) The number of protons;
2) the number of neutrons;
3) number of electrons;
4) nuclear charge.
60. Distribution of electrons by energy levels in a lithium atom:
1) 2, 1; 2) 2, 8, 1;
3) 2, 4; 4) 2, 5;
Option 4
Assignments. Choose one or two correct answers.
61. The element with serial number 29 is located in:
1) 4th period, group Ia;
2) 4th period, group Ib;
3) 1st period, group Ia;
4) 5th period, group Ia.
62. The charge of the nucleus of an atom of element No. 15 is:
1) +31; 2) 5; 3) +3; 4) +15.
63. The charge of the nucleus of an atom is determined by:
1) the serial number of the element;
2) group number;
3) period number;
4) atomic mass.
64. For atoms of group III elements, the number of valence electrons is equal to:
1) 1; 2) 2; 3) 3; 4) 5.
65. Higher sulfur oxide has the formula:
1) H 2 SO 3; 2) H 2 SO 4;
3) SO 3; 4) SO 2.
66. Formula of superior phosphorus oxide:
1) R 2 O 3; 2) H 3 PO 4;
3) NRO 3; 4) R 2 O 5.
67. Valency of the nitrogen atom in its hydrogen compound:
1) 1; 2) 2; 3) 3; 4) 4.
68. The period number in D.I. Mendeleev’s table corresponds to the following characteristic of the atom:
1) the number of valence electrons;
2) higher valence in combination with oxygen;
3) the total number of electrons;
4) the number of energy levels.
69. The largest atomic radius of an element is:
1) Cl; 2) Br; 3) I; 4) F.
70. Specify metal elements:
1) Mg; 2) Li; 3) H; 4) S.
71. Which element gives up an electron more easily?
1) Sodium; 2) cesium;
3) potassium; 4) lithium.
72. Metallic properties increase in the order:
1) Na, Mg, Al; 2) Na, K, Rb;
3) Rb, K, Na; 4) P, S, Cl.
73. Specify non-metal elements:
1) Cu; 2) Br; 3) N; 4) Cr.
74. Non-metallic properties in the series N–P–As–Sb:
1) decrease;
2) do not change;
3) increase;
4) decrease and then increase.
75. What characteristics of an atom change periodically?
1) Relative atomic mass;
2) nuclear charge;
3) the number of energy levels in an atom;
4) the number of electrons in the external level.
76. Atoms of which element form an amphoteric oxide?
1) K; 2) Be; 3) C; 4) Sa.
77. In the period with increasing charge of the atomic nucleus, the attraction of electrons to the nucleus and metallic properties increase:
1) intensify;
2) change periodically;
3) weaken;
4) do not change.
78. The relative atomic mass of an element is numerically equal to:
1) the number of protons in the nucleus;
2) the number of neutrons in the nucleus;
3) the total number of neutrons and protons;
4) the number of electrons in an atom.
79. The number of neutrons in the nucleus of a 16 O atom is:
1) 1; 2) 0; 3) 8; 4) 32.
80. Distribution of electrons by energy levels in a silicon atom:
1) 2, 8, 4; 2) 2, 6;
3) 2, 7; 4) 2, 8, 5.
List of controlled knowledge elements on the topic
"Periodic law. Structure of the atom"
(end-to-end task numbers are given in parentheses)
The atomic number (1, 3, 21, 41, 61), the charge of the atomic nucleus (2, 22, 42, 62, 63), the number of protons (23) and the number of electrons (43) in the atom.
Group number, number of electrons in the outer energy level (4, 24, 44, 64), formulas of the higher oxide (5, 25, 45, 65), highest valence element (6, 26, 46, 66), formulas of hydrogen compounds (7, 27, 47, 67).
Period number, number of electronic levels (8, 28, 48, 68).
Change in atomic radius (9, 17, 29, 37, 49, 67, 69).
The position in D.I. Mendeleev’s table of metal elements (10, 30, 50, 70) and non-metal elements (13, 33, 53, 73).
The ability of atoms to give and accept electrons (11, 31, 51, 71).
Changes in the properties of simple substances: by groups (12, 14, 34, 52, 54, 74) and periods (32, 72, 77).
Periodic changes in the electronic structure of atoms and the properties of simple substances and their compounds (15, 35, 55, 57, 75, 77).
Amphoteric oxides and hydroxides (16, 36, 56, 76).
Mass number, number of protons and neutrons in an atom, isotopes (18, 19, 38, 39, 58, 59, 78, 79).
Distribution of electrons by energy levels in an atom (20, 40, 60, 80).
Answers to test tasks on the topic
"Periodic law. Structure of the atom"
| Option 1 | Option 2 | Option 3 | Option 4 | ||||
|---|---|---|---|---|---|---|---|
| Job No. | Answer no. | Job No. | Answer no. | Job No. | Answer no. | Job No. | Answer no. |
| 1 | 4 | 21 | 2 | 41 | 3 | 61 | 2 |
| 2 | 2 | 22 | 4 | 42 | 3 | 62 | 4 |
| 3 | 1, 2 | 23 | 3, 4 | 43 | 2, 4 | 63 | 1 |
| 4 | 3 | 24 | 3 | 44 | 4 | 64 | 3 |
| 5 | 4 | 25 | 3 | 45 | 3 | 65 | 3 |
| 6 | 3 | 26 | 2 | 46 | 3 | 66 | 4 |
| 7 | 4 | 27 | 3 | 47 | 2, 4 | 67 | 3 |
| 8 | 4 | 28 | 4 | 48 | 4 | 68 | 4 |
| 9 | 4 | 29 | 1 | 49 | 5 | 69 | 3 |
| 10 | 1, 2 | 30 | 1, 4 | 50 | 1, 2 | 70 | 1, 2 |
| 11 | 1, 2 | 31 | 2, 4 | 51 | 1, 3 | 71 | 2 |
| 12 | 3 | 32 | 2 | 52 | 3 | 72 | 2 |
| 13 | 1, 2 | 33 | 3, 4 | 53 | 3, 4 | 73 | 2, 3 |
| 14 | 1 | 34 | 4 | 54 | 3 | 74 | 1 |
| 15 | 3 | 35 | 2 | 55 | 1 | 75 | 4 |
| 16 | 2 | 36 | 4 | 56 | 2 | 76 | 2 |
| 17 | 1 | 37 | 1 | 57 | 1 | 77 | 3 |
| 18 | 1 | 38 | 3 | 58 | 4 | 78 | 3 |
| 19 | 3 | 39 | 2 | 59 | 2 | 79 | 3 |
| 20 | 3 | 40 | 2 | 60 | 1 | 80 | 1 |
Literature
Gorodnicheva I.N.. Tests and tests in chemistry. M.: Aquarium, 1997; Sorokin V.V., Zlotnikov E.G.. Chemistry tests. M.: Education, 1991.
It was said above (p. 172) about the periodicity of changes in the most important property of atoms for chemistry - valence. There are other important properties, the changes of which are characterized by periodicity. These properties include the size (radius) of an atom. Atom has no surfaces, and its boundary is vague, since the density of the outer electron clouds smoothly decreases with distance from the nucleus. Data on the radii of atoms is obtained from determining the distances between their centers in molecules and crystal structures. Calculations based on the equations of quantum mechanics were also carried out. In Fig. 5.10 pre-
Rice. 5.10. Periodicity of changes in atomic radii
a curve of changes in atomic radii depending on the charge of the nucleus is plotted.
From hydrogen to helium the radius decreases and then increases sharply for lithium. This is explained by the appearance of an electron at the second energy level. In the second period from lithium to neon, as the nuclear charge increases, the radii decrease.
At the same time, an increase in the number of electrons at a given energy level leads to an increase in their mutual repulsion. Therefore, towards the end of the period the decrease in radius slows down.
When moving from neon to sodium - the first element of the third period - the radius again increases sharply, and then gradually decreases to argon. After this it happens again sharp increase radius of potassium. A characteristic periodic sawtooth curve is obtained. Each section of the curve from an alkali metal to a noble gas characterizes a change in radius in a period: a decrease in radius is observed when moving from left to right. It is also interesting to find out the nature of the change in radii in groups of elements. To do this, you need to draw a line through the elements of one group. From the position of the maxima in alkali metals it is immediately clear that the radii of atoms increase when moving from top to bottom in a group. This is due to an increase in the number of electron shells.
task 5.17. How do the radii of atoms change from F to Br? Determine this from Fig. 5.10.
Many other properties of atoms, both physical and chemical, depend on radii. For example, an increase in atomic radii can explain the decrease in the melting temperatures of alkali metals from lithium to cesium:
The sizes of atoms are related to their energetic properties. The larger the radius of the outer electron clouds, the easier the atom loses an electron. At the same time, it turns into a positively charged ion.
An ion is one of the possible states of an atom in which it has electric charge due to the loss or gain of electrons.
The ability of an atom to transform into a positively charged ion is characterized by ionization energy E I. This is the minimum energy required to remove an outer electron from an atom in the gas state:
The resulting positive ion can also lose electrons, becoming doubly charged, triply charged, etc. In this case, the ionization energy increases greatly.
The ionization energy of atoms increases in a period when moving from left to right and decreases in groups when moving from top to bottom.
Many, but not all, atoms are capable of adding an additional electron, becoming a negatively charged ion A~. This property is characterized electron affinity energy E Wed This is the energy released when an electron attaches to an atom in the gas state:
Both ionization energy and electron affinity energy are usually referred to as 1 mole of atoms and express in kJ/mol. Consider the ionization of the sodium atom as a result of the addition and loss of an electron (Fig. 5.11) . From the figure it is clear that to remove an electron from a sodium atom it is required 10 times more energy than is released when an electron is added. The negative sodium ion is unstable and almost never occurs in complex substances.
Rice. 5.11. Ionization of the sodium atom
The ionization energy of atoms changes in periods and groups in the direction opposite to the change in the radius of the atoms. The change in electron affinity energy over a period is more complex, since elements IIA- and VIIIA-rpynn do not have electron affinity. It can be approximately assumed that the electron affinity energy is similar to E k, increases in periods (up to group VII inclusive) and decreases in groups from top to bottom (Fig. 5.12).
exercise 5 .18. Can magnesium and argon atoms form negatively charged ions in the gaseous state?
Ions with positive and negative charges attract each other, which leads to various transformations. The simplest case is the formation of ionic bonds, i.e., the combination of ions into a substance under the influence of electrostatic attraction. Then an ionic crystal structure appears, characteristic of table salt NaCl and many other salts. But maybe
Rice. 5.12. The nature of changes in ionization energy and electron affinity energy in groups and periods
so that the negative ion does not hold its extra electron very firmly, and the positive ion, on the contrary, strives to restore its electrical neutrality. Then the interaction between the ions can lead to the formation of molecules. It is obvious that the ions different sign charge C1 + and C1~ attract each other. But due to the fact that these are ions of identical atoms, they form a C1 2 molecule with zero charges on the atoms.
QUESTIONS AND EXERCISES
1. How many protons, neutrons and electrons do bromine atoms consist of?
2.
Calculate the mass fractions of isotopes in nature. 
3. How much energy is released during the formation of 16 G oxygen by reaction 
flowing in the depths of stars?
4. Calculate the energy of an electron in an excited hydrogen atom at n =3.
5. Write the full and abbreviated electronic formulas of the iodine atom.
6. Write the abbreviated electronic formula of the G ion.
7. Write the full and abbreviated electronic formulas of the Ba atom and Ba 2 ion.
8. Construct energy diagrams of phosphorus and arsenic atoms.
9. Construct complete energy diagrams of zinc and gallium atoms.
10. Arrange the following atoms in order of increasing radius: aluminum, boron, nitrogen.
11. Which of the following ions form ionic crystal structures among themselves: Br + Br - , K + , K - , I + , I - , Li + , Li - ? What can be expected when ions interact in other combinations?
12. Suggest the possible nature of the change in the radius of atoms during a transition in the periodic system in the diagonal direction, for example Li - Mg - Sc.
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3. Periodic law and periodic system of chemical elements
3.3. Periodic change in the properties of atoms of elements
The frequency of changes in the properties (characteristics) of atoms of chemical elements and their compounds is due to periodic repetition through certain number structural elements of valence energy levels and sublevels. For example, for atoms of all elements of the VA group, the configuration of valence electrons is ns 2 np 3. That is why phosphorus is close in chemical properties to nitrogen, arsenic and bismuth (similarity of properties, however, does not mean their identity!). Let us recall that the periodicity of changes in properties (characteristics) means their periodic weakening and strengthening (or, conversely, periodic strengthening and weakening) as the charge of the atomic nucleus increases.
Periodically, as the charge of the atomic nucleus increases by unit, the following properties (characteristics) of isolated or chemically bonded atoms change: radius; ionization energy; electron affinity; electronegativity; metallic and non-metallic properties; redox properties; higher covalency and highest degree oxidation; electronic configuration.
Trends in changes in these characteristics are most pronounced in groups A and small periods.
Atomic radius r is the distance from the center of the atomic nucleus to the outer electron layer.
The atomic radius in groups A increases from top to bottom as the number of electronic layers increases. The radius of an atom decreases as it moves from left to right across a period, since the number of layers remains the same, but the charge of the nucleus increases, and this leads to compression of the electron shell (electrons are more strongly attracted to the nucleus). The He atom has the smallest radius, the Fr atom has the largest.
The radii of not only electrically neutral atoms, but also monatomic ions change periodically. The main trends in this case are as follows:
- the anion radius is larger, and the cation radius is smaller than the radius of the neutral atom, for example, r (Cl − ) > r (Cl ) > r (Cl + );
- the greater the positive charge of the cation of a given atom, the smaller its radius, for example r (Mn +4)< r (Mn +2);
- if ions or neutral atoms different elements have the same electronic configuration (and therefore the same number of electron layers), then the radius is smaller for the particle whose nuclear charge is greater, for example
r (Kr) > r (Rb +), r (Sc 3+)< r (Ca 2+) < r (K +) < r (Cl −) < r (S 2−); - in groups A, from top to bottom, the radius of ions of the same type increases, for example, r (K +) > r (Na +) > r (Li +), r (Br −) > r (Cl −) > r (F −).
Example 3.1. Arrange the Ar, S 2− , Ca 2+ and K + particles in a row as their radii increase.
Solution. The radius of a particle is affected primarily by the number of electron layers, and then by the charge of the nucleus: than larger number electron layers and the smaller (!) the charge of the nucleus, the larger the radius of the particle.
In the listed particles, the number of electron layers is the same (three), and the nuclear charge decreases by next order: Ca, K, Ar, S. Therefore, the required series looks like this:
r(Ca2+)< r (K +) < r (Ar) < r (S 2−).
Answer: Ca 2+, K +, Ar, S 2−.
Ionization energy E and is the minimum energy that must be expended to remove the electron most weakly bound to the nucleus from an isolated atom:
E + E u = E + + e.
Ionization energy is calculated experimentally and is usually measured in kilojoules per mole (kJ/mol) or electronvolts (eV) (1 eV = 96.5 kJ).
In periods from left to right, the ionization energy generally increases. This is explained by a consistent decrease in the radius of the atoms and an increase in the nuclear charge. Both factors lead to the fact that the binding energy of the electron with the nucleus increases.
In groups A, as the atomic number of an element increases, E and, as a rule, decreases, since the radius of the atom increases, and the binding energy of the electron with the nucleus decreases. The ionization energy of atoms of noble gases, in which the outer electron layers are complete, is especially high.
Ionization energy can serve as a measure of the reducing properties of an isolated atom: the lower it is, the easier it is to tear off an electron from the atom, the more pronounced the reducing properties of the atom are. Sometimes ionization energy is considered a measure of the metallic properties of an isolated atom, meaning the ability of the atom to give up an electron: the lower E and, the more pronounced the metallic properties of the atom are.
Thus, the metallic and reducing properties of isolated atoms increase in groups A from top to bottom, and in periods - from right to left.
Electron affinity Eav is the change in energy during the process of adding an electron to a neutral atom:
E + e = E − + E avg.
Electron affinity is also an experimentally measured characteristic of an isolated atom, which can serve as a measure of its oxidizing properties: the higher E avg, the more pronounced oxidizing properties atom. In general, across the period, from left to right, electron affinity increases, and in groups A it decreases from top to bottom. Halogen atoms are characterized by the highest electron affinity; for metals, the electron affinity is low or even negative.
Sometimes electron affinity is considered a criterion for the non-metallic properties of an atom, meaning the ability of an atom to accept an electron: the greater E avg, the more pronounced the non-metallic properties of the atom are.
Thus, the nonmetallic and oxidizing properties of atoms in periods as a whole increase from left to right, and in groups A - from bottom to top.
Example 3.2. According to the position in the periodic table, indicate which atom of the element has the most pronounced metallic properties, if the electronic configurations of the external energy level of the atoms of the elements (ground state):
1) 2s 1 ;
2) 3s 1 ;
3) 3s 2 3p 1 ;
4) 3s 2.
Solution. The electronic configurations of Li, Na, Al and Mg atoms are indicated. Since the metallic properties of atoms increase from top to bottom in group A and from right to left across the period, we come to the conclusion that the sodium atom has the most pronounced metallic properties.
Answer: 2).
Electronegativityχ is a conditional value that characterizes the ability of an atom in a molecule (i.e., a chemically bonded atom) to attract electrons.
Unlike E and and E avg, electronegativity is not determined experimentally, therefore in practice a number of scales of χ values are used.
In periods 1–3, the value of χ increases naturally from left to right, and in each period the most electronegative element is halogen: among all elements, the fluorine atom has the highest electronegativity.
In groups A, electronegativity decreases from top to bottom. Lowest valueχ is characteristic of alkali metal atoms.
For atoms of non-metal elements, as a rule, χ > 2 (exceptions: Si, At), and for atoms of metal elements, χ< 2.
A series in which the χ of atoms increases from left to right - alkali and alkaline earth metals, metals of the p- and d-families, Si, B, H, P, C, S, Br, Cl, N, O, F
Atomic electronegativity values are used, for example, to estimate the degree of polarity of a covalent bond.
Highest covalency atoms vary in period from I to VII (sometimes to VIII), and highest oxidation state varies from left to right over a period from +1 to +7 (sometimes up to +8). However there are exceptions:
- fluorine, as the most electronegative element, exhibits a single oxidation state in compounds equal to −1;
- the highest covalency of the atoms of all elements of the 2nd period is IV;
- for some elements (copper, silver, gold) the highest oxidation state exceeds the group number;
- The highest oxidation state of an oxygen atom is less than the group number and is equal to +2.
Lesson 2
The quantum numbers discussed above may seem like abstract concepts and far from chemistry. Indeed, they can be used to calculate the structure of real atoms and molecules only with special mathematical training and a powerful computer. However, if we add one more principle to the schematically presented concepts of quantum mechanics, quantum numbers “come to life” for chemists.
In 1924, Wolfgang Pauli formulated one of the most important postulates of theoretical physics, which did not follow from known laws: in one orbital (in one energy state) there cannot be more than two electrons at the same time, and even then only if their spins are in opposite directions. Other formulations: two identical particles cannot be in the same quantum state; One atom cannot have two electrons with the same values of all four quantum numbers.
Let's try to “create” the electron shells of atoms using the latest formulation of the Pauli principle.
The minimum value of the principal quantum number n is 1. It corresponds to only one value of the orbital number l, equal to 0 (s-orbital). The spherical symmetry of s-orbitals is expressed in the fact that at l = 0 in a magnetic field there is only one orbital with m l = 0. This orbital can contain one electron with any spin value (hydrogen) or two electrons with opposite spin values (helium) . Thus, with n = 1, no more than two electrons can exist.
Now let's start filling the orbitals with n = 2 (there are already two electrons in the first level). The value n = 2 corresponds to two values of the orbital number: 0 (s-orbital) and 1 (p-orbital). At l = 0 there is one orbital, at l = 1 there are three orbitals (with m l values: -1, 0, +1). Each orbital can contain no more than two electrons, so the value n = 2 corresponds to a maximum of 8 electrons. Total number electrons at a level with a given n can thus be calculated using the formula 2n 2:
Let us denote each orbital by a square cell, the electrons by oppositely directed arrows. For further “construction” of the electronic shells of atoms, it is necessary to use one more rule, formulated in 1927 by Friedrich Hund (Hund): the most stable states for a given l are those with the largest total spin, i.e. the number of filled orbitals at a given sublevel should be maximum (one electron per orbital).
The beginning of the periodic table will look like this:
Scheme of filling the external level of elements of the 1st and 2nd periods with electrons.
Continuing the “construction”, you can reach the beginning of the third period, but then you will have to introduce the order of filling the d and f orbitals as a postulate.
From the diagram constructed on the basis of minimal assumptions, it is clear that quantum objects (atoms of chemical elements) will relate differently to the processes of giving and receiving electrons. He and Ne objects will be indifferent to these processes due to a fully occupied electron shell. The F object will most likely actively accept the missing electron, and the Li object will be more likely to give up the electron.
Object C must have unique properties - it has the same number of orbitals and the same number of electrons. Perhaps he will strive to form connections with himself due to such high symmetry of the external level.
It is interesting to note that the concepts of the four principles of constructing the material world and the fifth that connects them have been known for at least 25 centuries. IN Ancient Greece and Ancient China, philosophers spoke of four first principles (not to be confused with physical objects): “fire”, “air”, “water”, “earth”. The connecting principle in China was “wood”, in Greece it was “quintessence” (fifth essence). The relationship of the “fifth element” with the other four is demonstrated in the science fiction film of the same name.
Game "Parallel World"
In order to better understand the role of “abstract” postulates in the world around us, it is useful to move to the “Parallel World”. The principle is simple: the structure of quantum numbers is slightly distorted, then, based on their new values, we build a periodic system of a parallel world. The game will be successful if only one parameter changes, which does not require additional assumptions about the relationship between quantum numbers and energy levels.
For the first time, a similar problem-game was offered to schoolchildren at the All-Union Olympiad in 1969 (9th grade):
“What would a periodic system of elements look like if the maximum number of electrons in a layer was determined by the formula 2n 2 -1, and the outer level could not have more than seven electrons? Draw a table of such a system for the first four periods (designating the elements by their atomic numbers). What oxidation states could element N 13 exhibit? What properties of the corresponding simple substance and compounds of this element could you assume?
This task is too difficult. In the answer, it is necessary to analyze several combinations of postulates establishing the values of quantum numbers with postulates about the relationship between these values. After a detailed analysis of this problem, we came to the conclusion that the distortions in the “parallel world” are too large, and we cannot correctly predict the properties of the chemical elements of this world.
We at the Scientific Research Center of Moscow State University usually use a simpler and more visual problem, in which the quantum numbers of the “parallel world” are almost no different from ours. In this parallel world live analogues of people - homozoids(the description of the homozoids themselves should not be taken seriously).
Periodic law and atomic structure
Task 1.
Homozoids live in a parallel world with the following set of quantum numbers:
n = 1, 2, 3, 4, ...
l= 0, 1, 2, ... (n – 1)
m l = 0, +1, +2,...(+ l)
m s = ± 1/2
Construct the first three periods of their periodic table, keeping our names for the elements with corresponding numbers.
1. How do homozoids wash themselves?
2. What do homozoids get drunk on?
3. Write the equation for the reaction between Their sulfuric acid and aluminum hydroxide.
Solution Analysis
Strictly speaking, you cannot change one of the quantum numbers without affecting the others. Therefore, everything described below is not the truth, but an educational task.
The distortion is almost imperceptible - the magnetic quantum number becomes asymmetric. However, this means the existence of unipolar magnets in a parallel world and other serious consequences. But let's get back to chemistry. In the case of s-electrons, no changes occur ( l= 0 and m 1 = 0). Therefore, hydrogen and helium are the same there. It is useful to remember that according to all data, hydrogen and helium are the most common elements in the Universe. This allows us to assume the existence of such parallel worlds. However, for p-electrons the picture changes. At l= 1 we get two values instead of three: 0 and +1. Therefore, there are only two p orbitals that can accommodate 4 electrons. The length of the period has decreased. We build “arrow cells”:
Construction of the Periodic Table of a Parallel World:
The periods, naturally, have become shorter (in the first there are 2 elements, in the second and third - 6 instead of 8. The changed roles of the elements are perceived very cheerfully (we deliberately keep the names behind the numbers): inert gases O and Si, alkali metal F. In order not to get confused, we will denote their elements are symbols only, and our- in words.
Analysis of the problem questions allows one to analyze the meaning of the distribution of electrons at the external level for chemical properties element. The first question is simple - hydrogen = H, and C becomes oxygen. Everyone immediately agrees that the parallel world cannot exist without halogens (N, Al, etc.). The answer to the second question is related to solving the problem - why carbon is an “element of life” for us and what will be its parallel analogue. During the discussion, we find out that such an element should give the “most covalent” bonds with analogues of oxygen, nitrogen, phosphorus, and sulfur. We have to go ahead a little and analyze the concepts of hybridization, ground and excited states. Then the element of life becomes an analogue of our carbon in symmetry (B) - it has three electrons in three orbitals. The result of this discussion is an analogue of ethyl alcohol BH 2 BHCH.
At the same time, it becomes obvious that in the parallel world we have lost direct analogues of our 3rd and 5th (or 2nd and 6th) groups. For example, period 3 elements correspond to:
Maximum oxidation states: Na (+3), Mg (+4), Al (+5); however, the priority is the chemical properties and their periodic change, and the length of the period has decreased.
Then the answer to the third question (if there is no analogue of aluminum):
Sulfuric acid + aluminum hydroxide = aluminum sulfate + water
H 2 MgC 3 + Ne(CH) 2 = NeMgC 3 + 2 H 2 C
Or as an option (there is no direct analogue of silicon):
H 2 MgC 3 + 2 Na(CH) 3 = Na 2 (MgC 3) 3 + 6 H 2 C
The main result of the described “journey to parallel world" - the understanding that the endless diversity of our world stems from not very large set relatively simple laws. An example of such laws are the analyzed postulates of quantum mechanics. Even a small change in one of them dramatically changes the properties of the material world.
Test yourself
Select the correct answer (or answers)
Atomic structure, periodic law
1. Eliminate the unnecessary concept:
1) proton; 2) neutron; 3) electron; 4) ion
2. The number of electrons in an atom is equal to:
1) the number of neutrons; 2) the number of protons; 3) period number; 4) group number;
3. Of the following, the characteristics of atoms of elements change periodically as the atomic number of the element increases:
1) the number of energy levels in an atom; 2) relative atomic mass;
3) the number of electrons at the external energy level;
4) charge of the atomic nucleus
4. At the outer level of an atom of a chemical element, there are 5 electrons in the ground state. What element could this be:
1) boron; 2) nitrogen; 3) sulfur; 4) arsenic
5. The chemical element is located in the 4th period, group IA. The distribution of electrons in an atom of this element corresponds to a series of numbers:
1) 2, 8, 8, 2 ; 2) 2, 8, 18, 1 ; 3) 2, 8, 8, 1 ; 4) 2, 8, 18, 2
6. P-elements include:
1) potassium; 2) sodium; 3) magnesium; 4) aluminum
7. Can the electrons of the K+ ion be in the following orbitals?
1) 3p; 2) 2f ; 3) 4s; 4) 4p
8. Select the formulas of particles (atoms, ions) with the electron configuration 1s 2 2s 2 2p 6:
1) Na+; 2) K + ; 3) Ne; 4) F –
9. How many elements would there be in the third period if the spin quantum number had a single value of +1 (the remaining quantum numbers have ordinary values)?
1) 4 ; 2) 6 ; 3) 8 ; 4) 18
10. In which row chemical elements arranged in increasing order of their atomic radius?
1) Li, Be, B, C;
2) Be, Mg, Ca, Sr;
3) N, O, F, Ne;
4) Na, Mg, Al, Si
© V.V.Zagorsky, 1998-2004
ANSWERS
- 4) ion
- 2) number of protons
- 3) the number of electrons in the outer energy level
- 2) nitrogen; 4) arsenic
- 3) 2, 8, 8, 1
- 4) aluminum
- 1) 3p; 3) 4s; 4) 4p
- 1) Na+; 3) Ne; 4) F –
- 2) Be, Mg, Ca, Sr
- Zagorsky V.V. A version of the presentation in the physics and mathematics school of the topic “Structure of the Atom and the Periodic Law”, Russian Chemical Journal (ZhRKhO named after D.I. Mendeleev), 1994, v. 38, N 4, p. 37-42
- Zagorsky V.V. The structure of the atom and the Periodic Law / "Chemistry" N 1, 1993 (supplement to the newspaper "First of September")