Exercise 1

1) DI Mendeleev's periodic law, its modern formulation. 2) The structure of the periodic system from the point of view of the structure of the atom. 3) The frequency of changes in the properties of the atom: ionization energy, electronegativeness, energy means to an electron. 4) The main classes of chemical compounds. 5) Classification of nutrients. 6) The qualitative and quantitative content of macro- and microelements in the human body. 7) Elements - organogens.

Periodic law- the fundamental law of nature, discovered by D.I.Mendeleev in 1869 when comparing the properties of the chemical elements known at that time and the values ​​of their atomic masses.

The wording of the periodic law given by D.I. Mendeleev, said: the properties of chemical elements are periodically dependent on the atomic masses of these elements. The modern formulation says: the properties of chemical elements are periodically dependent on the charge of the nucleus of these elements. Such a clarification was required, since at the time of the establishment of the periodic law by Mendeleev, it was not yet known about the structure of the atom. After clarifying the structure of the atom and establishing the patterns of distribution of electrons over the electronic levels, it became clear that the periodic recurrence of the properties of elements is associated with the repeatability of the structure of the electron shells.

Periodic system- a graphic representation of the periodic law, the essence of which is that with an increase in the nuclear charge, the structure of the electron shell of atoms is periodically repeated, which means that the properties of chemical elements and their compounds will periodically change.

The properties of elements, as well as the forms and properties of compounds of elements, are periodically dependent on the charges of nuclei and atoms.

Ionization energy- a kind of binding energy, represents the smallest energy required to remove an electron from a free atom in its lowest energy (ground) state to infinity.

The ionization energy is one of the main characteristics of the atom, on which the nature and strength of the chemical bonds formed by the atom largely depend. The reducing properties of the corresponding simple substance also substantially depend on the ionization energy of the atom. The ionization energy of elements is measured in electron volts per atom or joule per mole.

Electron affinity- energy that is released or absorbed due to the attachment of an electron to an isolated atom in a gaseous state. It is expressed in kilojoules per mole (kJ / mol) or electron volts (eV). It depends on the same factors as the ionization energy.

Electronegativity- the relative ability of the atoms of an element to attract electrons to themselves in any environment. It directly depends on the radius or size of the atom. The smaller the radius, the more it will attract electrons from another atom. Therefore, the higher and more to the right an element is in the periodic table, the smaller its radius and more electronegativity. Essentially, electronegativity determines the type of chemical bond.

Chemical compound- a complex substance consisting of chemically bonded atoms of two or more elements. Divided into classes: inorganic and organic.

Organic compounds- a class of chemical compounds that include carbon (there are exceptions). The main groups of organic compounds: hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, amides, amines.

Inorganic compounds- a chemical compound that is not organic, that is, it does not contain carbon. Inorganic compounds do not have a carbon skeleton characteristic of organic compounds. They are divided into simple and complex (oxides, bases, acids, salts).

Chemical element- a set of atoms with the same nuclear charge and the number of protons that coincide with the ordinal (atomic) number in the periodic table. Each chemical element has its own Latin name, a chemical symbol, consisting of one or a pair of Latin letters, regulated by IUPAC and listed in the table of the Periodic Table of the Elements of Mendeleev.

More than 70 elements were found in the composition of living matter.

Biogenic elements- the elements necessary for the body to build and function of cells and organs. There are several classifications of nutrients:

A) By their functional role:

1) organogens, there are 97% of them in the body (C, H, O, N, P, S);

2) elements of the electrolyte background (Na, K, Ca, Mg, Cl). These metal ions make up 99% of the total metal content in the body;

3) trace elements - biologically active atoms of the centers of enzymes, hormones (transition metals).

B) By the concentration of elements in the body:

1) macronutrients - the content exceeds 0.01% of body weight (Fe, Zn, I, Cu, Mn, Cr, F, Mo, Co, Ni, B, V, Si, Al, Ti, Sr, Se, Rb, Li)

2) trace elements - the content is about 0.01%. Most are found mainly in liver tissue. Some trace elements show an affinity for certain tissues (iodine - for the thyroid gland, fluorine - for tooth enamel, zinc - for the pancreas, molybdenum - for the kidneys). (Ca, Mg, Na, K, P, Cl, S).

3) ultramicroelements - the content is less than 10-5%. Data on the amount and biological role of many elements have not been fully identified.

Depo organs of microelements:

Fe - Accumulates in erythrocytes, spleen, liver

K - Accumulates in the heart, skeletal and smooth muscles, blood plasma, nervous tissue, kidneys.

Mn - depot organs: bones, liver, pituitary gland.

P - depot organs: bones, protein substances.

Ca - depot organs: bones, blood, teeth.

Zn - depot organs: liver, prostate, retina.

I - Depot organs: thyroid gland.

Si - depot organs: liver, hair, lens of the eye.

Mg - depot organs: biological fluids, liver

Cu - depot organs: bones, liver, gallbladder

S - depot organs: connective tissue

Ni - depot organs: lungs, liver, kidneys, pancreas, blood plasma.

The biological role of macro- and microelements:

Fe - participates in hematopoiesis, respiration, immunobiological and redox reactions. With a deficiency, anemia develops.

K - participates in urination, the emergence of an action potential, maintenance of osmotic pressure, protein synthesis.

Mn - Influences the development of the skeleton, participates in immune reactions, in hematopoiesis and tissue respiration.

P - combines sequential nucleotides in DNA and RNA strands. ATP serves as the main energy carrier of cells. Forms cell membranes. The strength of bones is determined by the presence of phosphates in them.

Ca - participates in the occurrence of nervous excitement, in the coagulation functions of the blood, provides osmotic pressure of the blood.

Co - Tissues in which a trace element usually accumulates: blood, spleen, bone, ovaries, liver, pituitary gland. Stimulates hematopoiesis, participates in protein synthesis and carbohydrate metabolism.

Zn - participates in hematopoiesis, participates in the activity of the endocrine glands.

I - Needed for the normal functioning of the thyroid gland, affects mental abilities.

Si - promotes collagen synthesis and cartilage formation.

Mg - participates in various metabolic reactions: synthesis of enzymes, proteins, other coenzyme of synthesis of B vitamins.

Cu - Influences the synthesis of hemoglobin, erythrocytes, proteins, coenzyme of the synthesis of B vitamins.

S - Affects the condition of the skin.

Ag - Antimicrobial activity

Ni - stimulates the synthesis of amino acids in the cell, increases the activity of pepsin, normalizes the hemoglobin content, and improves the generation of plasma proteins.

Organogenic elements- chemical elements that form the basis of organic compounds (C, H, O, N, S, P). In biology, four elements are called organogenic, which together make up about 96-98% of the mass of living cells (C, H, O, N).

Carbon- the most important chemical element for organic compounds. Organic compounds are, by definition, carbon compounds. It is tetravalent and capable of forming strong covalent bonds with each other.

Role hydrogen in organic compounds, it mainly consists in the binding of those electrons of carbon atoms that are not involved in the formation of intercarbon bonds in the composition of polymers. However, hydrogen is involved in the formation of non-covalent hydrogen bonds.

Together with carbon and hydrogen, oxygen is included in many organic compounds in the composition of such functional groups as hydroxyl, carbonyl, carboxyl and the like.

Nitrogen is often included in organic substances in the form of an amino group or a heterocycle. It is an essential chemical element in the composition. Nitrogen is also a part of nitrogenous bases, the residues of which are contained in nucleosides and nucleotides.

Sulfur is part of some amino acids, in particular methionine and cysteine. In the composition of proteins, disulfide bonds are established between the sulfur atoms of cysteine ​​residues, providing the formation of a tertiary structure.

Phosphate groups, that is, phosphoric acid residues are part of such organic substances as nucleotides, nucleic acids, phospholipids, phosphoproteins.

Task 2,3,4

Biogenic s- and p-elements. The relationship between the electronic structure of s- and p-elements and their biological functions. Compounds s- and p- in medicine.

1. How many and what values ​​can a magnetic quantum number take m e with an orbital quantum number l = 0,1,2 and 3? What elements in the periodic table are called s-, p-, d- and f-elements? Give examples.

Solution:

at l =0, m e= 0; (1value)

at l = 1, m e= -1, 0, +1; (3 values)

at l =3, m e= -3, -2, -1, 0, +1, +2, +3. (7values)

s-elements - elements in which the s-sublevel is filled with electrons last. The s-elements are the first two elements of each period.

p-elements - elements in which the p-sublevel is filled with electrons last. The p-elements include elements of the second period (except for the first two).

d-elements - elements in which the d-sublevel is filled with electrons last. The d-elements include elements from yttrium to cadmium.

f-elements - elements in which the f-sublevel is filled with electrons last. The f-elements include lanthanides from lanthanum to lutetium.

36. How do amphoteric oxides differ from basic and acidic oxides? (Examples).

Solution:

Amphoteric oxides have a dual nature and interact with alkali solutions and with acid solutions to form salt and water. That is, they exhibit both basic and acidic properties.

Amphoteric oxides: t

Al 2 O 3 + 2NaOH + 7H 2 O 2Na Al (OH) 4 * 2H 2 O

Al 2 O 3 + 6HCI = AlCI 3 = 3 H 2 O

Acidic oxides:

SO 3 + 2NaOH = Na 2 SO 4 + H 2 O

Basic oxides:

CaO + H 2 = Ca SO 4 + H 2 O

67. How can one explain that under standard conditions the exothermic reaction H 2 (g) + CO 2 (g) = H 2 O (g) + CO (g) is impossible; DH = -2.85 kJ. Knowing the thermal effect of the reaction and the standard absolute entropies of the corresponding substances, determine the DG 298 of this reaction.

H 2 (g) + CO 2 (g) = H 2 O (l) + CO (g)

DG 0 x. p. = DH 0 x. p. -TDS 0 x. p.

Evaluate DS 0 x.p. = (DS 0 H 2 O + DS 0 CO) - (DS 0 CO 2 + DS 0 H2);

DS 0 x. p = (69.96 + 197.4) - (213.6 +130.6) = 267.36-344.2 = -76.84 J / mol.grad = - 0.7684 kJ / mol.grad

The change in free energy (Gibbs energy) is calculated:

DG 0 x. p. = -2.85 - 298 * (- 0.7684) = -2.85 + 22.898 = +20.048 kJ.

Exothermic reaction (DH 0 0) does not occur spontaneously if at

DS 0 0 it turns out that G 0 x.p. > 0.

In our case DH 0 0 (-2.85 kJ)

DS 0 0 (-0.07684 kJ / mol.grad)

G 0 x. p. > 0. (+20.048 kJ)

100. What happens when sodium hydroxide acts on a mixture of equal volumes of nitric oxide (11) and nitric oxide (1V), reacting according to the equation

NO + NO 2 N 2 O 3?

Solution:

N 2 O 3 + 2NaOH = 2NaNO 2 + H 2 O

Since sodium hydroxide reacts with nitric oxide (III), the amount of the reaction product decreases in the system. Le Chatelier's principle indicates that the removal of any substance from the equilibrium system leads to a shift in equilibrium in the direction corresponding to the formation of an additional amount of this substance. In this case, the equilibrium will shift towards the formation of reaction products.

144. Make up the ionic-molecular and molecular equations of joint hydrolysis that occurs when mixing solutions of K 2 S and. Each of the salts taken is irreversibly hydrolyzed to the end.

Solution:

The K 2 S salt is hydrolyzed at the anion. The CrCl 3 salt is cationically hydrolyzed.

S 2- + H 2 O HS - + OH -

Cr 3+ + H 2 O CrOH 2+ + H +

If the salt solutions are in one vessel, then there is a mutual strengthening of the hydrolysis of each of them, because the H + and OH - ions form a molecule of a weak electrolyte H 2 0. In this case, the hydrolytic equilibrium shifts to the right and the hydrolysis of each of the salts taken goes to the end with the formation of Cr (OH) s and H 2 S. Ionic-molecular equation

2Cr 3+ + ЗS 2- + 6Н 2 О = 2Cr (OH) З + ЗH 2 S,

molecular equation

2CrCl 3 + 3K 2 S + 6H 2 O = 2Cr (OH) h + 3H 2 S + 6KL

162. Based on the electronic structure of atoms, indicate if they can be oxidizing agents:

d) hydrogen cation;

h) sulfide ions;

d) H 1 1s 1 the hydrogen atom lacks one electron until the last electronic level is filled, so it can be an oxidizing agent.

h) S 16 1s 2 2s 2 2p 6 3s 2 3p 4

Nonmetal anions (acidic residues of anoxic acids) can exhibit high reducibility. This is due to the fact that they can donate not only electrons, which cause the negative charge of the anions, but also their own valence electrons.

182g, y does not exist, so they made 181. Write the equations for the reactions occurring during the electrolysis of the following solutions.

The belonging of an element to the electronic family is determined by the nature of the filling of the energy sublevels:

s-elements - filling of the external s - sublevel in the presence of two or eight electrons at the pre-external level, for example:

Li 1s 2 2s 2

s-elements are active metals, the characteristic oxidation states of which are numerically equal to the number of electrons at the last level:

1 for alkali metals and +2 for elements of the second group

p-elements - filling the outer p-sublevel, for example:

F 1s 2 2s 2 2p 5

Elements from B to Ne inclusive form the first series p-elements (elements of the main subgroups), in whose atoms the electrons farthest from the nucleus are located on the second sublevel of the external energy level.

d-elements - filling in the pre-outer d-sublevel, for example:

V 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3

d- elements refer to metals.

f- elements - filling in the f- sublevel of the second outside the level, for example:

Nd 1s 2 2s 2 2p 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 4

f- elements are elements of the actinide and lanthanide families.

Quantum mechanics, comparing the electronic configurations of atoms, comes to the following theoretical conclusions:

1. The structure of the outer shell of an atom is a periodic function of the charge number of the atom Z.

2. Since the chemical properties of the atom are determined by the structure of the outer shell, it follows from the previous paragraph: the chemical properties of the elements are periodically dependent on the charge of the nucleus.

Control questions

1. Nuclear model of the structure of the atom. Isotopes (radionuclides).

2. Quantum - mechanical model of the structure of the atom.

3. Quantum numbers (main, orbital, magnetic, spin).

4. The structure of the electron shells of atoms. Pauli's principle. Least Energy Principle. Gund's rule.

5. Electronic-structural formulas of atoms. Hybridization of atomic orbitals.

6. Characteristics of the atom. Atomic radius. Electronegativity. Electron affinity. Ionization energy. S, p, d, f - electronic families of atoms.

Typical tasks

Problem No. 1. The radii of the Na + and Cu + ions are the same (0.098 nm). Explain the difference between the melting points of sodium chloride (801 ° C) and copper (I) chloride (430 ° C).

With the same charges and sizes of Na + and Cu + ions, the Cu + ion has an 18 - electron outer shell and polarizes the Cl - anion more strongly than the Na + ion, which has the electronic structure of a noble gas. Therefore, in copper (I) chloride, as a result of polarization from the anion to the cation, a greater part of the electronic charge is transferred than in sodium chloride. The effective charges of ions in the CuCl crystal become less than that of NaCl, and the electrostatic interaction between them is weaker. This explains the lower melting point of CuCl in comparison with NaCl, the crystal lattice of which is close to the purely ionic type.

Problem number 2. As indicated by the state of the electron a) with n = 4, L = 2; b) with n = 5, L = 3.

Solution: When recording the energy state, the number indicates the level number (n), and the letter indicates the nature of the sublevel (s, p, d, f). For n = 4 and L = 2, write 4d; for n = 5 and L = 3, write 5f.

Problem number 3. How many orbitals in total correspond to the third energy level? How many electrons are there at this level? How many sublevels is this level split into?

Solution: For the third energy level n = 3, the number of atomic orbitals is 9 (3 2), which is

is the sum of 1 (s) +3 (p) +5 (d) = 9. According to Pauli's principle, the number of electrons at this level is 18. The third energy level is split into three sublevels: s, p, d (the number of sublevels coincides with the number of values ​​of the principal quantum number).

Problem number 4. What electronic families are chemical elements classified into?

Solution: All chemical elements can be classified into 4 types depending on the nature of the sublevels being filled:

s-elements-fill ns sublevel with electrons;

p-elements - fill the np sublevel with electrons;

d-elements-fill with electrons (n-1) d sublevel;

f-elements - fill the (n-2) f sublevel with electrons;

Problem No. 5. What sublevel is filled in the atom with electrons after filling the sublevel: a) 4p; b) 4s

Solution: A) the sum (n + 1), equal to 4 + 1 = 5, corresponds to the sublevel 4p. The sublevels 3d (3 + 2 = 5) and 5s (5 + 0 = 5) are characterized by the same sum. However, the 3d state corresponds to a smaller value of n (n = 3) than the 4p state, so the 3d sublevel will be filled earlier than the 4p sublevel. Consequently, after filling the 4p sublevel, the 5s sublevel will be filled, which corresponds to one greater value of n (n = 5).

B) the sum n + 1 = 4 + 0 = 4 corresponds to the sublevel 4s. The same sum n + 1 characterizes sublevel 3p, but filling of this sublevel precedes filling of sublevel 4s, because the latter corresponds to a larger value of the principal quantum number. Consequently, after sublevel 4s, the sublevel will be filled with the sum (n + 1) = 5, and of all possible combinations n + l corresponding to this sum (n = 3, l = 2; n = 4; l = 1; n = 5 ; l = 0), the combination with the lowest value of the principal quantum number will be realized first, that is, after the sublevel 4s, the sublevel 3d will be filled.

Conclusion: thus, filling of the sublevel d lags behind by one quantum level, filling of the sublevel f lags behind by two quantum levels.

To write an electronic formula of an element, it is necessary: ​​indicate the number of the energy level in Arabic numerals, write the letter value of the sublevel, write the number of electrons as an exponent.

For example: 26 Fe 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

The electronic formula is made taking into account the competition of sublevels, i.e. minimum energy rules. Without taking into account the latter, the electronic formula will be written: 26 Fe 4 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2.

Problem No. 6. The electronic structure of an atom is described by the formula 1s22s22p63s23d74s2. What element is it?

Solution: This element belongs to the electronic type of d-elements of the 4th period, because electrons build up the 3d sublevel; the number of electrons 3d 7 indicates that this is the seventh element in order. The total number of electrons is 27, which means the ordinal number is 27. This element is cobalt.

Test tasks

Choose the correct answer

01. ELECTRONIC FORMULA OF THE ELEMENT HAS THE FORM ... 5S 2 4D 4. SPECIFY THE NUMBER OF ELECTRONS IN THE OUTDOOR LEVEL

02. CAN THERE BE TWO ELECTRONS WITH THE SAME SET OF ALL FOUR QUANTUM NUMBERS IN AN ATOM?

1) cannot

Can

3) can only in an excited state

4) can only be in a normal (unexcited) state

03. WHAT SUB-LEVEL IS FILLED AFTER SUB-LEVEL 4D?

04. ELECTRONIC FORMULA OF THE ELEMENT IS: 1S 2 2S 2 2P 6 3S 2. SPECIFY NUMBER OF VALENT ELECTRONS

05. ELECTRONIC FORMULA OF THE ELEMENT IS: 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 7. WHAT IS THIS ELEMENT?

06. WHAT IS THE SUB-LEVEL FILLED BEFORE THE 4D SUB-LEVEL?

07. AMONG THE ELECTRONIC CONFIGURATIONS BELOW, IT IS IMPOSSIBLE TO SPECIFY

08. ELECTRONIC STRUCTURE OF THE ATOM OF THE ELEMENT IS EXPRESSED BY THE FORMULA: 5S 2 4D 3. DETERMINE WHAT IT IS AN ELEMENT.

1) s-block in the periodic table of elements - an electron shell, which includes the first two layers of s-electrons. This block includes alkali metals, alkaline earth metals, hydrogen and helium. These elements differ in that, in the atomic state, a high-energy electron is in the s-orbital. Excluding hydrogen and helium, these electrons are very easily converted and formed into positive ions in a chemical reaction. The configuration of helium is chemically very stable, therefore, this is why helium does not have stable isotopes; sometimes, due to this property, it is combined with inert gases. The rest of the elements that have this block, without exception, are all strong reducing agents and therefore do not occur in free form in nature. An element in metallic form can only be obtained by electrolysis of salt dissolved in water. Davy Humphrey, in 1807 and 1808, was the first to separate acid salts from s-block metals, with the exception of lithium, beryllium, rubidium and cesium. Beryllium was first separated from salts independently by two scientists: F. Wooler and A. A. Bazi in 1828, while lithium was separated by R. Bunsen only in 1854, who, after studying rubidium, separated it 9 years later. Cesium was not isolated in pure form until 1881, after Karl Setterberg electrolyzed cesium cyanide. The hardness of elements with an s-block in a compact form (under normal conditions) can vary from very low (all alkali metals - they can be cut with a knife) to quite high (beryllium). Except for beryllium and magnesium, metals are highly reactive and can be used in small amounts of lead alloys (<2 %). Бериллий и магний, ввиду их высокой стоимости, могут быть ценными компонентами для деталей, где требуется твёрдость и лёгкость. Эти металлы являются чрезвычайно важными, поскольку позволяют сэкономить средства при добыче титана, циркония, тория и тантала из их минеральных форм; могут находить своё применение как восстановители в органической химии.

Danger and storage

All s-shell elements are hazardous substances. They are fire hazardous and require special fire extinguishing, excluding beryllium and magnesium. Should be stored in an inert atmosphere of argon or hydrocarbons. Reacts violently with water, the reaction product is hydrogen, for example:

Excluding magnesium, which reacts slowly, and beryllium, which only reacts when its oxide film is removed with mercury. Lithium has similar properties to magnesium, as it is located, relative to the periodic table, next to magnesium.

The P-block in the periodic table of elements is the electron shell of atoms, the valence electrons of which with the highest energy occupy the p-orbital.

The p-block includes the last six groups, excluding helium (which is in the s-block). This block contains all non-metals (excluding hydrogen and helium) and semimetals, as well as some metals.

The P-block contains elements that have different properties, both physical and mechanical. P-block non-metals are, as a rule, highly reactive substances with strong electronegativity, p-metals are moderately active metals, and their activity increases towards the bottom of the table of chemical elements

Properties of d- and f-elements. Give examples.

The D-block in the periodic table of elements is the electron shell of atoms, the valence electrons of which with the highest energy occupy the d-orbital.

This block is part of the periodic table; it includes elements from 3 to 12 groups. The elements of this block fill the d-shell with d-electrons, which for the elements begins s2d1 (third group) and ends with s2d10 (twelfth group). However, there are some irregularities in this sequence, for example, in chromium s1d5 (but not s2d4), the entire eleventh group has the s1d10 configuration (but not s2d9). The eleventh group has filled s and d electrons.

D-block elements are also known as transition metals or transition elements. However, the exact boundaries that separate transition metals from other groups of chemical elements have not yet been drawn. Although some authors believe that the elements included in the d-block are transition elements in which the d-electrons are partially filled either in neutral atoms or ions, where the oxidation state is zero. IUPAC currently accepts such studies as valid, and reports that this applies only to 3-12 groups of chemical elements. The metals of the 12th group do not have pronounced chemical and physical properties; this is explained by the incomplete filling of the d subshell; therefore, they can also be considered post-transition metals. The historical use of the term "transition elements" and the d-block has also been revised.

In the s-box and p-box of the periodic table, similar properties are usually not observed through periods: the most important properties are enhanced vertically at the lower elements of these groups. It is noteworthy that the differences of the elements included in the d-block horizontally, through periods, become more pronounced.

Lutetium and lawrennium are in the d-block, and they are not considered transition metals, but lanthanides and actinides, which are remarkable, are considered from the IUPAC point of view. Although the twelfth group of chemical elements is located in the d-block, it is believed that the elements included in it are post-transition elements.

Elements in the periodic system of Mendeleev are divided into s-, p-, d-elements. This subdivision is carried out on the basis of how many levels the electron shell of an atom of an element has and which level ends with the filling of the shell with electrons.

TO s-elements include elements IA-groups - alkali metals... Electronic formula of the valence shell of alkali metal atoms ns1... The stable oxidation state is +1. The elements IA groups have similar properties due to the similar structure of the electron shell. With an increase in the radius in the Li-Fr group, the bond of the valence electron with the nucleus weakens and the ionization energy decreases. The atoms of alkaline elements easily donate their valence electron, which characterizes them as strong reducing agents.

The restorative properties are enhanced with an increase in the serial number.

TO p-elements includes 30 elements IIIA-VIIIA-groups periodic system; p-elements are located in the second and third small periods, as well as in the fourth to sixth large periods. The elements IIIIA-group have one electron in the p-orbital. V IVА-VIIIА-groups the filling of the p-sublevel up to 6 electrons is observed. General electronic formula of p-elements ns2np6... In periods with an increase in the nuclear charge, the atomic radii and ionic radii of the p-elements decrease, the ionization energy and the electron affinity increase, the electronegativity increases, the oxidative activity of the compounds and the non-metallic properties of the elements increase. In groups, the atomic radii increase. The ionization energy decreases from 2p to 6p elements. The metallic properties of the p-element in the group are enhanced with an increase in the serial number.

TO d-elements include 32 elements of the periodic system IV-VII large periods... V IIIB-group atoms have the first electron in the d-orbital, in subsequent B-groups the d-sublevel is filled up to 10 electrons. General formula of the outer electron shell (n-1) dansb, where a = 1 × 10, b = 1 × 2... With an increase in the ordinal number, the properties of d-elements change insignificantly. The atomic radius of the d-elements slowly increases, and they also have a variable valence associated with the incompleteness of the pre-external d-electron sublevel. In the lowest oxidation states, d-elements exhibit metallic properties; with an increase in the serial number in groups B, they decrease. In solutions, d-elements with the highest oxidation state exhibit acidic and oxidizing properties, while at lower oxidation states, vice versa. Elements with an intermediate oxidation state exhibit amphoteric properties.

8. Covalent bond. Valence bond method

The chemical bond carried out by common electron pairs arising in the shells of the bonded atoms having antiparallel spins is called atomic, or covalent bond. The covalent bond is two-electron and two-center (holds the nuclei). It is formed by atoms of one type - covalent non-polar- a new electron pair, arising from two unpaired electrons, becomes common for two chlorine atoms; and atoms of different types, similar in chemical nature - covalent polar. Elements with more electronegativity (Cl) will pull shared electrons from elements with less electronegativity (H). Atoms with unpaired electrons having parallel spins repel - no chemical bond arises. The method of forming a covalent bond is called exchange mechanism.

Properties of a covalent bond. Link length - internuclear distance. The shorter the distance, the stronger the chemical bond. Communication energy - the amount of energy required to break the bond. The magnitude of the bond multiplicity is directly proportional to the bond energy and inversely proportional to the bond length. Communication direction - a certain arrangement of electron clouds in a molecule. Saturability- the ability of an atom to form a certain number of covalent bonds. The chemical bond formed by the overlapping of electron clouds along the axis connecting the centers of the atoms is called ? -connection. The bond formed by the overlapping of electron clouds perpendicular to the axis connecting the centers of the atoms is called ? -connection... The spatial directionality of a covalent bond is characterized by the angles between the bonds. These angles are called bond angles. Hybridization - the process of restructuring of electron clouds of unequal shape and energy, leading to the formation of hybrid clouds with the same parameters. Valence- the number of chemical bonds (covalent ), through which the atom is connected to others. The electrons involved in the formation of chemical bonds are called valence... The number of bonds between atoms is equal to the number of its unpaired electrons participating in the formation of common electron pairs, so the valence does not take into account the polarity and has no sign. In compounds in which there is no covalent bond, there is oxidation state - conditional charge of an atom, starting from the assumption that it consists of positively or negatively charged ions. For most inorganic compounds, the concept of the oxidation state is applicable.