DEFINITION

Phosphorus located in the third period of group V of the main (A) subgroup Periodic table.

Phosphorus forms several allotropic changes: white, red and black phosphorus.

AT pure form white phosphorus completely colorless and transparent; technical white phosphorus is colored yellowish and appearance looks like wax. Density 1.83 g/cm 3 . In the cold, white phosphorus is brittle, but at temperatures above 15 o C it becomes soft and can be easily cut with a knife. In air, it is easily oxidized, as a result of which it glows in the dark. Has a molecular crystal lattice at the nodes of which are tetrahedral molecules P 4 . Poisonous.

Red phosphorus consists of several forms, which are polymeric substances, the composition of which is not fully understood. Slowly oxidizes in air, does not glow in the dark, non-toxic. Density 2.0-2.4g/cm 3 . Sublimates when heated. When red phosphorus vapor is cooled, white phosphorus is obtained.

Black phosphorus is formed from white by heating it under high pressure at 200-220 o C. In appearance it looks like graphite, greasy to the touch. Density - 2.7g / cm 3. Semiconductor.

Valency of phosphorus in compounds

Phosphorus is the fifteenth element in the Periodic Table of D.I. Mendeleev. He is in the third period in the VA group. The nucleus of a phosphorus atom contains 15 protons and 16 neutrons (the mass number is 31). There are three energy levels in the phosphorus atom, on which there are 15 electrons (Fig. 1).

Rice. 1. The structures of the phosphorus atom.

The electronic formula of the phosphorus atom in the ground state has next view:

1s 2 2s 2 2p 6 3s 2 3p 3 .

And the energy diagram (built only for electrons of the outer energy level, which are otherwise called valence):

The presence of three unpaired electrons indicates that phosphorus is capable of exhibiting valency III (P III 2 O 3 , Ca 3 P III 2 , P III H 3, etc.).

Since, in addition to the 3s and 3p sublevels, there is also a 3d sublevel on the third energy layer, the phosphorus atom is characterized by the presence of an excited state: a pair of electrons of the 3s sublevel is depaired and one of them occupies a vacant orbital of the 3d sublevel.

The presence of five unpaired electrons indicates that valence V is also characteristic of phosphorus (P V 2 O 5, H 3 P V O 4, P V Cl 5, etc.).

Examples of problem solving

EXAMPLE 1

In chemistry lessons, you already got acquainted with the concept of valence chemical elements. We have collected all in one place useful information about this question. Use it when preparing for the GIA and the Unified State Examination.

Valency and chemical analysis

Valence- the ability of atoms of chemical elements to enter into chemical compounds with atoms of other elements. In other words, it is the ability of an atom to form certain number chemical bonds with other atoms.

From Latin, the word "valence" is translated as "strength, ability." Very true name, right?

The concept of "valence" is one of the main ones in chemistry. It was introduced even before the structure of the atom became known to scientists (back in 1853). Therefore, as the structure of the atom was studied, it underwent some changes.

So, from the point of view of electronic theory, valency is directly related to the number of external electrons of an atom of an element. This means that by "valency" is meant the number of electron pairs by which an atom is bonded to other atoms.

Knowing this, scientists were able to describe the nature of the chemical bond. It lies in the fact that a pair of atoms of a substance shares a pair of valence electrons.

You may ask, how could chemists of the 19th century be able to describe valency even when they believed that there were no particles smaller than an atom? It cannot be said that it was so simple - they relied on chemical analysis.

way chemical analysis scientists of the past determined the composition of a chemical compound: how many atoms of various elements are contained in the molecule of the substance in question. To do this, it was necessary to determine what is the exact mass of each element in a sample of a pure (without impurities) substance.

Admittedly, this method is not without flaws. Because define In a similar way The valence of an element is possible only in its simple combination with always univalent hydrogen (hydride) or always divalent oxygen (oxide). For example, the valency of nitrogen in NH 3 - III, since one hydrogen atom is bonded to three nitrogen atoms. And the valency of carbon in methane (CH 4), according to the same principle, is IV.

This method for determining valency is only suitable for simple substances. But in acids, in this way we can only determine the valency of compounds like acid residues, but not all elements (except for the known hydrogen valence) separately.

As you have already noticed, valency is indicated by Roman numerals.

Valency and acids

Since the valence of hydrogen remains unchanged and is well known to you, you can easily determine the valency of the acid residue. So, for example, in H 2 SO 3 the valency of SO 3 is I, in HClO 3 the valency of ClO 3 is I.

Similarly, if the valency of the acid residue is known, it is easy to write correct formula acids: NO 2 (I) - HNO 2, S 4 O 6 (II) - H 2 S 4 O 6.

Valency and formulas

The concept of valence makes sense only for substances of a molecular nature and is not very suitable for describing chemical bonds in compounds of a cluster, ionic, crystalline nature, etc.

Indices in the molecular formulas of substances reflect the number of atoms of the elements that make up their composition. Knowing the valency of the elements helps to correctly arrange the indices. In the same way, looking at molecular formula and indices, you can name the valencies of the constituent elements.

You perform such tasks in chemistry lessons at school. For example, having chemical formula a substance in which the valency of one of the elements is known, the valence of another element can be easily determined.

To do this, you just need to remember that in a substance of molecular nature, the number of valencies of both elements are equal. Therefore, use the least common multiple (corresponding to the number of free valences required for the connection) to determine the valence of the element that you do not know.

To make it clear, let's take the formula of iron oxide Fe 2 O 3. Here, two iron atoms with valence III and 3 oxygen atoms with valence II participate in the formation of a chemical bond. Their least common multiple is 6.

• Example: you have formulas Mn 2 O 7 . You know the valence of oxygen, it is easy to calculate that the least common multiple is 14, hence the valency of Mn is VII.

Similarly, you can do the opposite: write down the correct chemical formula of a substance, knowing the valencies of its constituent elements.

• Example: in order to correctly write down the formula of phosphorus oxide, we take into account the valency of oxygen (II) and phosphorus (V). Hence, the least common multiple for P and O is 10. Therefore, the formula has the following form: P 2 O 5.

Knowing well the properties of the elements that they exhibit in various compounds, one can determine their valence even by the appearance of such compounds.

For example: copper oxides are red (Cu 2 O) and black (CuO) in color. Copper hydroxides are colored yellow (CuOH) and blue (Cu(OH) 2).

And to make covalent bonds in substances more clear and understandable for you, write their structural formulas. The dashes between the elements depict the bonds (valencies) that arise between their atoms:

Valency characteristics

Today, the determination of the valency of elements is based on knowledge about the structure of the outer electron shells of their atoms.

Valence can be:

• constant (metals of the main subgroups);
• variable (non-metals and metals of side groups):
• highest valence;
• lower valency.

The constant in various chemical compounds remains:

• valency of hydrogen, sodium, potassium, fluorine (I);
• valency of oxygen, magnesium, calcium, zinc (II);
• valency of aluminum (III).

But the valency of iron and copper, bromine and chlorine, as well as many other elements, changes when they form various chemical compounds.

Valence and electronic theory

Within the framework of the electronic theory, the valence of an atom is determined on the basis of the number of unpaired electrons that participate in the formation of electron pairs with the electrons of other atoms.

Only electrons located on the outer shell of the atom participate in the formation of chemical bonds. Therefore, the maximum valence of a chemical element is the number of electrons in the outer electron shell of its atom.

The concept of valence is closely related to Periodic law, discovered by D. I. Mendeleev. If you look closely at the periodic table, you can easily notice: the position of an element in the periodic table and its valency are inextricably linked. The highest valency of elements that belong to the same group corresponds to serial number groups in the periodic table.

You will find out the lowest valency when you subtract the group number of the element that interests you from the number of groups in the periodic table (there are eight of them).

For example, the valency of many metals matches the group numbers in the table periodic elements to which they belong.

Table of valency of chemical elements

Serial number chem. element (atomic number)	Name	chemical symbol	Valence
1	Hydrogen Helium / Helium Lithium / Lithium Beryllium / Beryllium Carbon / Carbon Nitrogen / Nitrogen Oxygen / Oxygen Fluorine / Fluorine Neon / Neon Sodium Magnesium / Magnesium Aluminum Silicon / Silicon Phosphorus / Phosphorus Sulfur Chlorine / Chlorine Argon / Argon Potassium / Potassium Calcium / Calcium Scandium / Scandium Titanium / Titanium Vanadium / Vanadium Chromium / Chromium Manganese / Manganese Iron / Iron Cobalt / Cobalt Nickel / Nickel Copper Zinc / Zinc Gallium / Gallium Germanium /Germanium Arsenic / Arsenic Selenium / Selenium Bromine / Bromine Krypton / Krypton Rubidium / Rubidium Strontium / Strontium Yttrium / Yttrium Zirconium / Zirconium Niobium / Niobium Molybdenum / Molybdenum Technetium / Technetium Ruthenium / Ruthenium Rhodium Palladium / Palladium Silver / Silver Cadmium / Cadmium Indium / Indium Tin / Tin Antimony / Antimony Tellurium / Tellurium Iodine / Iodine Xenon / Xenon Cesium / Cesium Barium / Barium Lanthanum / Lanthanum Cerium / Cerium Praseodymium / Praseodymium Neodymium / Neodymium Promethium / Promethium Samaria / Samarium Europium / Europium Gadolinium / Gadolinium Terbium / Terbium Dysprosium / Dysprosium Holmium / Holmium Erbium / Erbium Thulium / Thulium Ytterbium / Ytterbium Lutetium / Lutetium Hafnium / Hafnium Tantalum / Tantalum Tungsten / Tungsten Rhenium / Rhenium Osmium / Osmium Iridium / Iridium Platinum / Platinum Gold / Gold Mercury / Mercury Waist / Thallium Lead / Lead Bismuth / Bismuth Polonium / Polonium Astatine / Astatine Radon / Radon Francium / Francium Radium / Radium Actinium / Actinium Thorium / Thorium Proactinium / Protactinium Uranus / Uranium	H	I (I), II, III, IV, V I, (II), III, (IV), V, VII II, (III), IV, VI, VII II, III, (IV), VI (I), II, (III), (IV) I, (III), (IV), V (II), (III), IV (II), III, (IV), V (II), III, (IV), (V), VI (II), III, IV, (VI), (VII), VIII (II), (III), IV, (VI) I, (III), (IV), V, VII (II), (III), (IV), (V), VI (I), II, (III), IV, (V), VI, VII (II), III, IV, VI, VIII (I), (II), III, IV, VI (I), II, (III), IV, VI (II), III, (IV), (V) No data No data (II), III, IV, (V), VI

In brackets are given those valences that the elements possessing them rarely show.

Valency and oxidation state

So, speaking of the degree of oxidation, they mean that an atom in a substance of an ionic (which is important) nature has a certain conditional charge. And if valence is a neutral characteristic, then the oxidation state can be negative, positive or equal to zero.

It is interesting that for an atom of the same element, depending on the elements with which it forms a chemical compound, the valency and oxidation state can be the same (H 2 O, CH 4, etc.) and differ (H 2 O 2, HNO 3 ).

Conclusion

Deepening your knowledge of the structure of atoms, you will learn more deeply and in more detail about valency. This characterization of chemical elements is not exhaustive. But it has great applied value. What you yourself have seen more than once, solving problems and conducting chemical experiments in the classroom.

This article is designed to help you organize your knowledge of valency. And also to recall how it can be determined and where valence is used.

We hope that this material will be useful for you in preparing homework and self-preparation for tests and exams.

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Phosphorus valency

Phosphorus P (Is 2s 2/f 3s Zr) is analogous to nitrogen in terms of the number of valence electrons. However, as an element of the 3rd period, it differs significantly from nitrogen, an element of the 2nd period. This difference is that phosphorus larger size atom, less ionization energy, greater electron affinity and greater polarizability of the atom than nitrogen. The maximum coordination number of phosphorus is six. As for other elements of the 3rd period, rl - rl binding is not typical for the phosphorus atom, and therefore, unlike nitrogen, the sp- and sp-hybrid states of the phosphorus orbitals are unstable. Phosphorus in compounds exhibits oxidation states from -3 to +5. The most typical oxidation state is +5.

Let's write the formula of the compound that consists of and. phosphorus (V valence) and oxygen (II valence).

In which compounds does phosphorus have the highest valency?

What are the valence capabilities of phosphorus How does it differ in this respect from its counterpart - nitrogen

The electronic structure of the phosphorus atom corresponds to the formula 16F 5 25 2p 33 3p. Phosphorus has valence electrons in the third (outer) energy level, in which, in addition to 5- and three p-orbitals, there are five free -orbitals.

According to another point of view, the difference in the properties of phosphorus and nitrogen is explained by the presence of valence 3-orbitals in the phosphorus atom,

Explain the difference between the first ionization energy of phosphorus, P (1063 kJ mol) and sulfur, 8 (1000 kJ mol), based on a comparison of the valence orbital electronic configurations of the P and 8 atoms.

But in phosphorus, as an element of the 3rd period, the 3-orbitals also play the role of valences. Therefore, along with the commonality of properties in the chemistry of these typical elements of group V, significant differences appear. For phosphorus, sp-, sp-, and 5p types of hybridization of valence orbitals are possible. The maximum coordination number of phosphorus is 6. In contrast to nitrogen, phosphorus is characterized by n - rl binding due to the acceptance of free 3d (-orbitals of electron pairs of the corresponding atoms

The stable coordination number of phosphorus (V) is 4, which corresponds to the sp hybridization of its valence orbitals. The coordination numbers 5 and 6 appear less frequently; in these cases sp4 and sp4 hybrid states are assigned to the phosphorus atom, respectively (p. 415).

A similar behavior is found in the elements of the VA group, but the boundary between metals and nonmetals in this group is lower. Nitrogen and phosphorus are non-metals, the chemistry of their covalent compounds and possible oxidation states are determined by the presence of five valence electrons in the configuration. Nitrogen and phosphorus most often have oxidation states - 3, -b 3 and +5. Arsenic As and antimony Sb are semimetals forming amphoteric oxides, and only bismuth has metallic properties. For As and Sb, the oxidation state + 3 is the most important. For Bi, this is the only possible one, except for the oxidation states that appear under some extremely specific conditions. Bismuth cannot lose all five valence electrons, the energy required for this is too high. However, it loses three br-electrons, forming a Bi ion.

Mendeleev was doing his dissertation work in Germany, in Heidelberg, just in time for the International Chemical Congress in Karlsruhe. He attended the congress and heard Cannizzaro's speech, in which he clearly stated his point of view on the problem of atomic weight. Returning to Russia, Mendeleev began to study the list of elements and drew attention to the periodicity of the change in valence for elements arranged in ascending order of atomic weights: valency of hydrogen 1, lithium I, beryllium 2, boron 3, carbon 4, magnesium 2, nitrogen 3, sulfur 2 , fluorine 1, sodium 1, aluminum 3, silicon 4, phosphorus 3, k1 oxygen 2, chlorine I, etc.

Phosphorus in terms of the number of valence electrons (35 3p) is an analogue of nitrogen

Oxygen atoms bond to at least two different atoms. So do calcium, sulfur, magnesium and barium. These elements have a valence of two, Nitrogen, phosphorus, aluminum and gold have a valence of three. Iron can have a valence of two or three. In principle, the question of valency turned out to be not as simple as it seemed at first, but even such the simplest option This theory led to important conclusions.

In the transition from lithium to fluorine G, a regular weakening of the metallic properties and an increase in non-metallic properties occur with a simultaneous increase in valence. The transition from fluorine G to the next element in terms of atomic mass, sodium Na, is accompanied by an abrupt change in properties and valence, and sodium largely repeats the properties of lithium, being a typical monovalent metal, although more active. Magnesium, which follows sodium, is in many respects similar to beryllium Be (both are divalent, exhibit metallic properties, but the chemical activity of both is less pronounced than that of the N-Na pair). Aluminum A1, following magnesium, resembles boron B (valence is 3). Silicon 81 and carbon C, phosphorus P and nitrogen N, sulfur 8 and oxygen O, chlorine C1 and fluorine G are similar to each other as close relatives. valency and chemical properties. Potassium, like lithium and sodium, opens a series of elements (the third in a row), the representatives of which show a deep analogy with the elements of the first two rows.

The effectiveness of the additive depends on the valence state and position of the elements in the additive molecule, the presence of functional groups, their synergism, and other factors. The use of phosphorus-, sulfur-, oxygen- and nitrogen-containing compounds as additives to lubricating oils is closely related to the feature electronic structure these elements. Their interaction with the metal surface of engine parts leads to modification of the latter (change in structure) and due to the formation of protective films, the anticorrosion, antiwear and extreme pressure properties of these compounds in the oil solution are provided. In addition, additives containing these elements stabilize the oil by terminating the oxidation chain by reaction with peroxide radicals and destroying hydroperoxides.

Halogenation. The most commonly used catalysts for chlorination are metallic iron, copper oxide, bromine, sulfur, iodine, iron halides, antimony, tin, arsenic, phosphorus, aluminum and copper, vegetable and animal charcoal, activated bauxite and other clays. Most of these catalysts are halogen carriers. So, Fe, Sb and P in halogen compounds are able to exist in two valence states in the presence of free chlorine, they alternately add and donate chlorine to active form. Similarly, iodine, bromine and sulfur form unstable compounds with chlorine. Bromination catalysts are similar to chlorination catalysts. Phosphorus is the best accelerator for iodination. No catalyst is required for the fluorination process. In the presence of oxygen, halogenation slows down.

Catalytic chlorination is based on the use of a chlorine carrier, such as iodine, sulfur, phosphorus, antimony, and others, in the form of the corresponding chlorides, which are dissolved in the chlorinated hydrocarbon or, when chlorinating gaseous paraffinic hydrocarbons, in a solvent. Only elements with at least two valency values. Radical generating substances such as diazomethap, tetraethyl lead and hexaphenylethane can also be used as homogeneous catalysts. They have the ability to split the chlorine molecule into atoms, which immediately cause a chain reaction.

When an element forms several rows of compounds corresponding to different oxidation states, after the name of the compound in brackets, an indication is given either of the valency of the cation (in Roman numerals) or of the number of halogen, oxygen, sulfur or acid residue atoms in the compound molecule (in words). For example, iron chloride (P1), phosphorus chloride three), manganese oxide (two). In this case, the designation of valence is usually given for less characteristic valence states. For example, for copper in the case of a divalent state, the indication of valence is omitted, while monovalent copper is designated as copper iodide (I).

The conductivity of substances such as silicon and germanium can be increased by introducing small amounts of certain impurities into them. For example, the introduction of boron or phosphorus impurities into silicon crystals effectively narrows the interband gap. Small amounts of boron or phosphorus (several ppm) can be incorporated into the silicon structure during crystal growth. The phosphorus atom has five valence electrons, and therefore, after four of them are used-

Phosphorus, arsenic, antimony and bismuth form stoichiometric compounds that correspond to formal valency, only with s-elements and d-elements of the zinc subgroup.

The fact that the dye and adsorbent constitute a single quantum system is evident from many facts. The most obvious of them is that the absorption of radiation of any, for example, the smallest, frequency within the absorption band of a given phosphorus causes the emission of its entire radiation spectrum, including frequencies much higher than the frequencies of the absorbed light. This means that radiation quanta come into common use, and the energy insufficient to emit frequencies that exceed the low frequency of the absorbed light also comes at the expense of common resources solid body. The fact that although the dye is undoubtedly only on the surface does not allow other interpretations, the absorption of light characteristic of it long waves(for which the crystal adsorbing this dye is practically transparent) is accompanied by the formation of metallic silver in the bulk of the silver bromide crystal. In this case, the sensitivity of silver bromide shifts the further towards long waves, the longer the chain of conjugated bonds in the structure of the dye molecule (Fig. 44). The fact is that the electrons of the dye are in wave motion and that the dye molecule, connecting with the crystal by a valence bond, forms a single whole with it. Crystal and dye form a single quantum system. It is not surprising, therefore, that the mechanism of photolysis of pure

Phosphorus, P, has the valence configuration 3x 3p, and sulfur, 8, has the valence configuration 3x 3p. The atom P, therefore, has a half-filled 3p shell, while atom 8 has an additional electron forced to pair with one of the electrons already present in the 3p orbitals.

SA for the formation of covalent bonds in the crystal structure of silicon, phosphorus has one more electron left. When an electric field is applied to the crystal, this electron can move away from the phosphorus atom; therefore, phosphorus is said to be an electron donor in the silicon crystal. Only 1.05 kJ mol is required to release donated electrons; this energy turns a silicon crystal with a small admixture of phosphorus into a conductor. When a boron impurity is introduced into a silicon crystal, the opposite phenomenon occurs. The boron atom lacks one electron to build the required number of covalent bonds in a silicon crystal. Therefore, for each boron atom in a silicon crystal, there is one vacancy in the bonding orbital. The valence electrons of silicon can be excited into these vacant orbitals associated with boron atoms, which allows the electrons to move freely through the crystal. Such conduction occurs as a result of the fact that an electron of the neighboring silicon atom jumps to the vacant orbital of the boron atom. A newly formed vacancy in the orbital of the silicon atom is immediately filled with an electron from another silicon atom following it. A cascade effect occurs, in which electrons jump from one atom to the next. Physicists prefer to describe this phenomenon as the movement of a positively charged hole in the opposite direction. But regardless of how this phenomenon is described, it is firmly established that less energy is required to activate the conductivity of a substance such as silicon if the crystal contains a small amount of an electron donor such as phosphorus or an electron acceptor such as boron.

White phosphorus consists of P4 tetrahedral molecules, shown schematically in fig. 21.25. As noted in sect. 8.7, part 1, bond angles of 60 ", as in the P4 molecule, are quite rare in other molecules. They indicate the presence of very tense bonds, which is consistent with a high reactivity

Although phosphorus is an electronic analog of nitrogen, the presence of free /-orbitals in the valence mectron layer of the atom makes phosphorus compounds unlike nitrogen compounds.

The electronic structure of organophosphorus compounds and the nature of chemical bonds;

To an even greater extent, aromatic properties are inherent in the phosphorine ring. 2,4,6-Triphenylphosphoric acid does not auto-oxidize and does not quaternize under the action of methyl iodide or triethyloxonium borofluoride. At the same time, its interaction with nucleophilic reagents - alkyl or aryllithium compounds, easily proceeds in benzene already at room temperature". In this case, the attack occurs at phosphorus, the valence shell of which expands to decet, and a resonance-stabilized phosphorine anion (1) appears. The formation of anion (I) was proved using PMR and UV spectra. Hydrolysis of the reaction mixture, which has a deep blue -violet color, leads to 1-alkyl(aryl)-2,4,6-tri-

Preparation of silicate phosphors. Chemical composition phosphorus, structure of phosphorus, valence Mn. There is a significant number various techniques preparation of crystal phosphors on a silicate basis. Let's take one of them as an example. Well-purified ammonia solution of zinc oxide, water solution manganese nitrate and an alcoholic solution of silicic acid (ethyl silicate) are poured together and a gel is formed. The gel is dried, triturated and calcined to 1200°C in quartz vessels and cooled rapidly after calcination. When the Mn content is low, calcination can always be carried out in air at a large Mn content, in order to avoid its oxidation, calcination is carried out in an atmosphere of carbon dioxide.

Catalytic oxidation of oil residues. There are many attempts to accelerate the process of oxidation of raw materials, improve the quality or give certain properties to the oxidized bitumen using various catalysts and initiators. It is proposed to use salts as catalysts for redox reactions. of hydrochloric acid and metals of variable valency (iron, copper, tin, titanium, etc.). As catalysts for dehydration, alkylation and cracking (transfer of protons), chlorides of aluminum, iron, tin, phosphorus pentoxide as oxidation initiators - peroxides are proposed. Most of these catalysts initiate reactions of densification of feedstock molecules (oils and resins) into asphaltenes without enriching bitumen with oxygen. The possibilities of accelerating the process of oxidation of raw materials and improving the properties of bitumen (mainly in the direction of increasing penetration at a given softening temperature), cited in numerous patent literature, are summarized in, but since the authors of the patents make their proposals without disclosing the chemistry of the process, their conclusions are in this monograph are not considered. Research by A. Heuberg

In most cases, halogenation is accelerated by light irradiation (wavelength 3000-5000 A) or high temperature(with or without a catalyst). As catalysts, halogen compounds of metals are usually used, having two valence states, capable of donating halogen atoms upon transition from one valence state to another, - P I5, P I3, Fe lg. Antimony chloride or manganese chloride are also used, as well as non-metallic catalysts - iodine, bromine or phosphorus.

Lithium and sodium have a moderate electron affinity, the electron affinity of beryllium is negative, while that of magnesium is close to zero. In the Be and M atoms, the valence x-orbital is completely filled, and the attached electron must populate the p-orbital located higher in energy. Nitrogen and phosphorus have little electron affinity because the electron to be added must pair in these atoms with one of the electrons in the half-filled p orbitals.

Atoms of elements of the third and subsequent periods often do not obey the octet rule. Some of them show an amazing ability to communicate with a large number atoms (i.e., be surrounded by more electron pairs) than the octet rule predicts. For example, phosphorus and sulfur form compounds PF5 and SF, respectively. In the Lewis structures of these compounds, all the valence electrons of a heavy element are used by it to form bonds with other atoms.

In these diagrams, the full arrow indicates the position of the coordination bond. The donor elements appearing here (sulfur, arsenic and nitrogen), as well as selenium, phosphorus and others, do not form compounds with the properties of catalytic poisons if they are in the highest valence state, since in this case the molecules do not have pairs of free electrons. The same is true for the ions of these elements. For example, the sulfite ion is a poison, while the sulfate ion is not.

The number of electrons in the outer shell determines the valence states inherent in given element, and consequently, the types of its compounds - hydrides, oxides, hydroxides, salts, etc. So, in the outer shells of the atoms of phosphorus, arsenic, antimony and bismuth is the same number(five) electrons. This determines the identity of their main valence states (-3, -f3, -b5), the uniformity of EN3 hydrides, E2O3 and EaO3 oxides, hydroxides, etc. This circumstance is ultimately the reason that these elements are located in one subgroup periodic system.

Thus, the number of unpaired electrons in the excited state of beryllium, boron, and carbon atoms corresponds to the actual valency of these elements. As regards the atoms of nitrogen, oxygen, and fluorine, their excitation cannot lead to an increase in the number of non-ionic electrons in the second level of their electron shells. However, the analogs of these elements - phosphorus, sulfur and chlorine - since at the third level they

The number of unpaired electrons in a phosphorus atom upon excitation reaches five, which corresponds to its actual maximum palency. When a sulfur atom is excited, the number of unpaired electrons increases to four and even up to [yes, and for a chlorine atom, up to three, five, and, at most, up to seven, which also corresponds to actual values their valency.                      Basics of General Chemistry Volume 2 Edition 3 (1973) -

2. VALENCE POSSIBILITIES

ATOMS OF CHEMICAL ELEMENTS

Structure of external energy levels atoms of chemical elements determines mainly the properties of their atoms. These levels are calledvalence. The electrons of the outer levels (sometimes the pre-outer ones) take part in the formation of chemical bonds. These electrons are also calledvalence.

Valence - this is the ability of atoms of chemical elements to form a certain number of chemical bonds.

The valence possibilities of atoms are defined in two ways:

The number of unpaired electrons that participate in the formation of a bond by the exchange mechanism:

in the stationary (basic) state;

in an excited state.

Consider the valence possibilities of the carbon atom.

Scheme of the structure of the carbon atom:
6 C +6) 2 ) 4

excited state

Electronic configuration

1 s 2 2 s 2 2 p 2

1 s 2 2 s 1 2 p 3

Graphic formula

Add suggestions:

The number of unpaired electrons of a carbon atom in a stationary state: _____. These are ____ electrons.

The valence of the carbon atom in the ground state is ____.

The number of unpaired electrons of an excited carbon atom: _____. These are ____ electron and ____ electrons.

The valency of an excited carbon atom is ______.

The number of unshared electron pairs that can participate in the formation of a chemical bond by the donor-acceptor mechanism.

Consider the valence possibilities of the nitrogen atom.

Scheme of the structure of the nitrogen atom:
7 N +7) 2 ) 5

excited state

(the atom has received additional energy)

Electronic configuration

1 s 2 2 s 2 2 p 3

Not typical, since there are no more free orbitals in the second level and paired electrons cannot be paired.

Graphic formula

Unpaired electrons participate in the formation of a chemical bond by the exchange mechanism.

In this case, the nitrogen valency is III.

But the nitrogen atom at the second outer level has two more paireds-electron. This is an unshared electron pair.

The lone pair of electrons is involved in the formation of a chemical bond by the donor-acceptor mechanism.

Then the valency increases by one more and will be equal to IV.

Tasks for fixing:

Exercise 1.

Determine the valence possibilities of sulfur and chlorine atoms in the ground and excited states.

Goals.

• To develop ideas about valence as the main property of an atom, to identify patterns of change in the radii of atoms of chemical elements in periods and groups of the periodic system.
• Using an integrated approach, develop students' skills to compare, contrast, find analogies, predict a practical result based on theoretical reasoning.
• By creating situations of success, to overcome the psychological inertia of students.
• Develop creative thinking ability to reflect.

Equipment: Table “Valency and electronic configurations of elements”, multimedia.

Epigraph.Logic, if it is reflected in truth and common sense, always leads to the goal, to the correct result.

The lesson is combined, with elements of integration. Teaching methods used: explanatory-illustrated, heuristic and problematic.

I stage. Approximate motivational

The lesson begins with “tuning” (music sounds - symphony No. 3 by J. Brahms).

Teacher: The word “valency” (from Latin valentia) originated in mid-nineteenth century, during the completion of the second chemical-analytical stage in the development of chemistry. By that time, more than 60 elements had been discovered.

The origins of the concept of “valency” are contained in the works of various scientists. J. Dalton established that substances consist of atoms connected in certain proportions. E. Frankland, in fact, introduced the concept of valence as a connecting force. F. Kekule identified valence with chemical bond. A.M. Butlerov drew attention to the fact that valency is related to the reactivity of atoms. DI. Mendeleev created periodic system chemical elements, in which the highest valence of atoms coincided with the group number of the element in the system. He also introduced the concept of “variable valency”.

Question. What is valence?

Read the definitions taken from different sources (the teacher shows slides through multimedia):

“Valency of a chemical element- the ability of its atoms to combine with other atoms in certain ratios.

"Valence- the ability of atoms of one element to attach a certain number of atoms of another element.

"Valence- a property of atoms, entering into chemical compounds, donate or accept a certain number of electrons (electrovalence) or combine electrons to form electron pairs common to two atoms (covalence).

Which definition of valency do you think is more perfect, and where do you see the shortcomings of others? (Discussion in groups.)

Valency and valence capabilities are important characteristics of a chemical element. They are determined by the structure of atoms and periodically change with increasing nuclear charges.

Teacher. Thus, we conclude that:

What do you think the concept of “valence possibility” means?

Students express their opinion. They recall the meaning of the words “possibility”, “possible”, clarify the meaning of these words in the explanatory dictionary of S.I. Ozhegov:

"Possibility- a means, a condition necessary for the implementation of something ”;

"Possible- such that can happen, feasible, permissible, permissible, conceivable.

(teacher shows next slide)

Then the teacher sums up.

Teacher. The valence possibilities of atoms are the allowable valences of an element, the whole range of their values ​​in various compounds.

II stage. Operational executive

Working with the table “Valency and electronic configurations of elements”.

Teacher. Since the valence of an atom depends on the number of unpaired electrons, it is useful to consider the structures of atoms in excited states, taking into account the valence possibilities. Let us write down the electron diffraction formulas for the distribution of electrons over orbitals in the carbon atom. With their help, we determine what valence carbon C exhibits in compounds. An asterisk (*) denotes an atom in an excited state:

Thus, carbon exhibits valence IV due to pairing
2s 2 – electrons and the transition of one of them to a vacant orbital. (Vacant - unoccupied, empty (S. I. Ozhegov))

Why valency C-II and IV, and H-I, He-O, Be - II, B - III, P-V?

Compare the electron diffraction formulas of the elements (scheme No. 1) and establish the reason for the different valency.

Group work:

Teacher. So, what do the valence and valence possibilities of atoms depend on? Let's consider these two concepts in interrelation (diagram No. 2).

The energy consumption (E) for the transfer of an atom to an excited state is compensated by the energy released during the formation of a chemical bond.

What is the difference between an atom in the ground (stationary) state and an atom in an excited state (scheme No. 3)?

Teacher . Can the elements have the following valences: Li -III, O - IV, Ne - II?

Explain your answer using the electronic and electron diffraction formulas of these elements (Scheme No. 4).

Group work.

Answer. No, since in this case the energy costs for moving an electron

(1s -> 2p or 2p -> 3s) are so large that they cannot be compensated for by the energy released during the formation of a chemical bond.

Teacher. There is another type of valence possibility of atoms - this is the presence of lone electron pairs (the formation of a covalent bond by the donor-acceptor mechanism):

Stage III. Evaluative-reflexive

The results are summed up, the work of students in the lesson is characterized (return to the epigraph of the lesson). Then a summary is given - the attitude of the children to the lesson, subject, teacher.

1. What did you not like about the lesson?

2. What did you like?

3. What questions remain unclear to you?

4. Evaluation of the work of the teacher and his work? (justified).

Homework(according to the textbook by O.S. Gabrielyan, Chemistry-10; profile level, paragraph No. 4, exercise 4)