Located in the fourth period.
The atomic weight of iron is 55.84, nuclear charge +26. Distribution of electrons by energy levels (+26): 2, 8, 14, 2. Electronic configuration of the outer and pre-outer layer of iron 3s23p63d64s2.
Thus, the iron atom, in addition to two s-electrons of the fourth outer layer, there are six more d-electrons of the third pre-outer layer. Of these d-electrons are the most active 4 unpaired ones. Consequently, 6 electrons are especially actively involved in the formation of iron valence bonds - 2 from the outer and 4 from the pre-outer layers. The most common oxidation states of iron are Fe+2 and Fe+3. Iron is one of the most commonly found elements in nature. In terms of prevalence among other elements, it ranks fourth.
■ 57. Based on the structure of the iron atom, as well as the distribution of electrons in orbitals, indicate the possible oxidation states of this element.
Iron in its free state is a silvery-gray shiny metal with a density of 7.87, a melting point of 1535° and a boiling point of 2740°. Iron has pronounced ferromagnetic properties, i.e., under the influence of a magnetic field it becomes magnetized and when the field stops, it retains magnetic properties, becoming a magnet itself. All elements of the iron group have these properties.
In terms of its chemical properties, iron is a very active metal. In the absence of moisture, iron does not change in the air, but when exposed to moisture and oxygen in the air, it undergoes severe corrosion and becomes covered with a loose film of rust, which is iron that does not protect it from further oxidation, and the iron gradually oxidizes in its entire mass:
4Fe + 2H2O + 3O2 = 2Fe2O3 2H2O
A number of methods have been developed to protect this valuable metal from corrosion.
In the voltage series, iron is located to the left of hydrogen. In this regard, it is easily exposed to dilute acids, turning into a ferrous salt, for example:
Fe + 2HCl = FeCl2 + H2
Iron does not react with concentrated sulfuric and nitric acids. These acids create such a strong and dense film of oxide on the surface of the metal that the metal becomes completely passive and no longer enters into other reactions. At the same time, when directly interacting with such strong oxidizing agents as iron, iron always exhibits an oxidation state of +3:
2Fe + 3Сl2 = 2FeCl3
Iron reacts with superheated steam; in this case, is displaced from the water, and the hot iron turns into oxide, and this is always either ferrous oxide FeO or iron oxide Fe3O4(Fe2O3 FeO):
Fe + H2O = FeO + H2
3Fe + 4H2O = Fe3O4 + 4H2
Iron heated in pure oxygen burns vigorously to form iron scale (see Fig. 40).
3Fe + 2O2 = Fe3O4
When calcined, iron forms an alloy with carbon and at the same time iron carbide Fe3C.
■ 58. List the physical properties of iron.
59. What are the chemical properties of iron? Give a reasoned answer.
Iron forms two series of compounds - compounds Fe +2 and Fe +3. Iron is characterized by two oxides - oxide FeO and oxide Fe2O3. True, the mixed oxide Fe3O4 is known, the molecule of which is di- and trivalent iron: Fe2O3 · FeO. This oxide is also called iron scale, or iron oxide.
Ferrous iron compounds are less stable than iron oxide compounds, and in the presence of an oxidizing agent, even if it is only air, they usually turn into ferric iron compounds. For example, iron (II) hydroxide Fe(OH)2 is a white solid, but it can be obtained in pure form only when the solutions of the reacting substances do not contain dissolved oxygen and if the reaction is carried out in the absence of atmospheric oxygen:
FeSO4 + 2NaOH = Fe(OH)2 + Na2SO4
The salt from which iron (II) hydroxide is obtained, of course, should not contain the slightest admixture of oxide compounds. Since such conditions are very difficult to create in an ordinary educational laboratory, iron (II) hydroxide is obtained in the form of a more or less dark green precipitate of a gelatinous appearance, which indicates the oxidation of divalent iron compounds into ferric iron. If iron (II) hydroxide is kept in air for a long time, it gradually transforms into iron (III) hydroxide Fe(OH)3:
4Fe(OH)2 + O2 + 2H2O = 4Fe(OH)3
iron are typical insoluble hydroxides. Iron (II) hydroxide has basic properties, while Fe(OH)3 has very weakly expressed amphoteric properties.
■ 60. List the properties of iron oxide as a typical basic oxide. Give a reasoned answer. Write all reaction equations in full and abbreviated ionic forms.
61. List the properties of iron (II) hydroxide. Support your answer with reaction equations.
Among iron (II) salts, the most important is iron sulfate FeSO4 · 7H2O, which contains 7 molecules of water of crystallization. Iron sulfate dissolves well in water. It is used to control agricultural pests, as well as in the manufacture of dyes.
Of the trivalent iron salts, the most important is ferric chloride FeCl3, which is very hygroscopic orange crystals that absorb water during storage and dissolve into a brown paste.
Iron (II) salts can easily transform into iron (III) salts, for example when heated with nitric acid or potassium permanganate in the presence of sulfuric acid:
6FeSO4 + 2HNO3 + 3H2SO4 = 3Fe2(SO4)3 + 2NO + 4H2O
Oxidation of Fe +2 salts into Fe +3 salts can also occur under the influence of atmospheric oxygen during storage of these compounds, but this process is longer. Very characteristic specific reagents are used to recognize Fe 2+ and Fe 3+ cations. For example, to recognize divalent iron, take the red blood salt K3, which, in the presence of divalent iron ions, gives with them a characteristic intense blue precipitate of Turnboule blue:
3FeSO4 + 2K3 = Fe32 + 3K2SO4
or in ionic form
3Fe 2+ + 2 3- = Fe32
To recognize Fe3+ salts, a reaction with yellow blood salt K4 is used:
4FeCl3 + 3K4 = Fe43 + 12KCl
4Fe 3+ + 3 4- = Fe43
In this case, an intense blue precipitate of Prussian blue appears. Prussian blue and Turnboule blue are used as dyes.
In addition, ferric iron can be recognized using soluble salts - potassium thiocyanate KCNS or ammonium thiocyanate NH4CNS. When these substances interact with Fe(III) salts, the solution acquires a blood-red color.
■ 62. List the properties of Fe +3 and Fe +2 salts. Which oxidation state is more stable?
63. How to convert Fe +2 salt into Fe +3 salt and vice versa? Give examples.
The reaction follows the equation:
FeCl3 + 3KCNS = Fe(CNS)3 + 3КCl
or in ionic form
Fe 3+ + 3CNS - = Fe(CNS),
Iron compounds play an important role in the life of organisms. For example, it is part of the main blood protein - hemoglobin, as well as green plants - chlorophyll. Iron enters the body mainly as part of organic matter in food products. Apples, eggs, spinach, and beets contain a lot of iron. As medicines, iron is used in the form of salts of organic acids. Ferric chloride serves as a hemostatic agent.
■ 64. Three test tubes contain: a) iron (II) sulfate, b) iron (III) sulfate and c) iron (III) chloride. How to determine which test tube contains which salt?
65. How to carry out a series of transformations:
Fe → FeCl2 → FeSO4 → Fe2(SO4)3 → Fe(OH)3 → Fe2O3.
66. The following are given: iron, caustic soda. How, using only these substances, can one obtain iron (II) hydroxide and iron (III) hydroxide?
67. A solution containing chromium (III) chloride and iron (III) chloride was treated with excess alkali. The resulting precipitate was filtered. What remained on the filter and what went into the filtrate? Give a reasoned answer using reaction equations in molecular, full ionic, and reduced ionic forms.
Iron is the basis of ferrous metallurgy, so it is mined in huge quantities. The new program for the extensive construction of communism provides for the production of 250 million tons of steel in 1980. This is 3.8 times more than in 1960.
Iron is almost never used in its pure form, but only in the form of alloys. The most important alloys of iron are its with carbon - various cast irons and steels. The main difference between cast iron and steel is the carbon content: cast iron contains more than 1.7% carbon, and steel contains less than 1.7%.
Ferroalloys (an alloy of iron and silicon), ferrochrome (an alloy of iron and chromium), and ferromanganese (an alloy of iron and manganese) are of great practical importance. Ferroalloys are cast irons containing more than 10% iron and at least 10% of the corresponding component. In addition, they contain the same elements as cast iron. Ferroalloys are used mainly in the “deoxidation” of steel and as alloying impurities.
Among cast irons, a distinction is made between linear and pigment. Foundry cast iron is used for castings of various parts; pig iron is remelted into steel, as it has very high hardness and cannot be processed. Pig iron is white, and foundry iron is gray. Pig iron contains more manganese.
Steels are carbon and alloyed. Carbon steels are usually an alloy of iron and carbon, while alloy steels contain alloying additives, i.e., admixtures of other metals that give the steel more valuable properties. gives steel ductility, elasticity, stability during hardening, and - hardness and heat resistance. Steels with zirconium additives are very elastic and ductile; they are used to make armor plates. Manganese impurities make steel resistant to impact and friction. Boron improves the cutting properties of steel in the manufacture of tool steels.
Sometimes even minor impurities of rare metals give steel new properties. If you keep a steel part in beryllium powder at a temperature of 900-1000°, the hardness of the steel and its wear resistance increase greatly.
Chromium-nickel steel, or, as they are also called, stainless steel, is resistant to corrosion. Impurities of sulfur and phosphorus are very harmful to steel - they make the metal brittle.
■ 68. What important glands do you know?
69. What is the main difference between steel and cast iron?
70. What properties of cast iron and what types of cast iron do you know?
71. What are alloy steels and alloying additives?
Cast iron is obtained by reduction smelting in blast furnaces. These are huge structures thirty meters high, producing more than 2000 tons of cast iron per day. A diagram of the blast furnace structure is shown in Fig. 83.
The upper part of the blast furnace, through which the charge is loaded, is called the top. Through the furnace the charge
Rice. 83. Scheme of a blast furnace.
falls into a long furnace shaft that widens downwards, which facilitates the movement of the loaded material from top to bottom. As the charge moves to the widest part of the furnace - the steam - a series of transformations occur with it, as a result of which cast iron is formed, flowing into the hearth - the hottest part of the furnace. This is where the slag collects. Pig iron and slag are discharged from the furnace through special holes in the forge, called tapholes. Air is blown into the blast furnace through the top of the furnace to keep the fuel burning in the furnace.
Let us consider the chemical processes that occur during the smelting of cast iron. The blast furnace charge, i.e., the complex of substances loaded into it, consists of iron ore, fuel and fluxes, or fluxes. There are many iron ores. The main ores are magnetic iron ore Fe3O4, red iron ore Fe2O3, brown iron ore 2Fe2O8 · 3H2O. In the blast furnace process, siderite FeCO3 and sometimes FeS2 are used as iron ore, which, after firing in pyrite furnaces, turns into cinder Fe2O3, which can be used in metallurgy. Such ore is less desirable due to its high sulfur content. Not only cast iron, but also ferroalloys are smelted in a blast furnace. The fuel loaded into the furnace serves both to maintain a high temperature in the furnace and to reduce iron from ore, and also takes part in the formation of an alloy with carbon. The fuel is usually coke.
During the iron smelting process, coke is gasified, turning, as in a gas generator, first into dioxide and then into carbon monoxide:
C + O2 = CO3 CO2 + C = 2CO
The resulting carbon monoxide is a good gaseous reducing agent. With its help, iron ore is recovered:
Fe2O3 + 3СО = 3СО2 + 2Fe
Along with the ore containing iron, waste rock impurities necessarily enter the furnace. They can be very refractory and can clog a furnace that has been operating continuously for many years. In order for waste rock to be easily removed from the furnace, it is converted into a low-melting compound, turning it into slag using fluxes (fluxes). To convert base rock containing, for example, limestone into slag, which decomposes in a furnace according to the equation
CaCO3 = CaO + CO2
add sand. Fusion with calcium oxide, sand forms silicate:
CaO + SiO3 = CaSiO3
This is a substance with an incomparably lower melting point. In a liquid state, it can be released from the oven.
If the rock is acidic, containing a large amount of silicon dioxide, then, on the contrary, limestone is loaded into the furnace, which converts the silicon dioxide into silicate, and the result is the same slag. Previously, slag was a waste, but now it is cooled with water and used as a building material.
To maintain fuel combustion, heated, oxygen-enriched air is continuously supplied to the blast furnace. It is heated in special air heaters - kiupers. Cowper is a high tower made of refractory bricks, where hot gases escaping from the blast furnace are diverted. Blast furnace gases contain carbon dioxide CO2, N2 and carbon monoxide CO. Carbon monoxide burns in the cowper, thereby increasing its temperature. Then the blast furnace gases are automatically directed to another cowper, and through the first one begins to blow air directed into the blast furnace. In a hot cowper, the air is heated, and thus fuel is saved, which in large quantities would be spent on heating the air entering the blast furnace. Each blast furnace has several cowpers.
■ 72. What is the composition of the blast furnace charge?
73. List the main chemical processes that occur during the smelting of cast iron.
74. What is the composition of blast furnace gas and how is it used in cowpers?
75. How much cast iron containing 4% carbon can be obtained from 519.1 kg of magnetic iron ore containing 10% impurities?
76. What amount of coke gives a volume of carbon monoxide sufficient to reduce 320 kg of iron oxide if the coke contains 97% pure carbon?
77. How should siderite be processed so that iron can be obtained from them?
Steel is smelted in three types of furnaces - open-hearth regenerative furnaces, Bessemer converters and electric furnaces.
The open hearth furnace is the most modern furnace designed for smelting the bulk of steel (Fig. 84). An open hearth furnace, unlike a blast furnace, is not a continuously operating furnace.
Rice. 84. Diagram of an open-hearth furnace
Its main part is the bathtub, into which the necessary materials are loaded through the windows using a special machine. The bath is connected by special passages to regenerators, which serve to heat combustible gases and air supplied to the furnace. Heating occurs due to the heat of combustion products, which are passed through regenerators from time to time. Since there are several of them, they work in turn and heat up in turn. An open hearth furnace can produce up to 500 tons of steel per melt.
The charge of an open-hearth furnace is very diverse: the charge includes cast iron, scrap metal, ore, fluxes (fluxes) of the same nature as in the blast furnace process. As in the blast furnace process, during steel smelting, air and combustible gases are heated in regenerators using the heat of waste gases. The fuel in open-hearth furnaces is either fuel oil sprayed by nozzles or combustible gases, which are currently used especially widely. The fuel here serves only to maintain a high temperature in the furnace.
The process of steel smelting is fundamentally different from the blast furnace process, since the blast furnace process is a reducing process, and steel smelting is an oxidative process, the purpose of which is to reduce the carbon content by oxidizing it in the metal mass. The processes that take place are quite complex.
Contained in the ore and supplied with air to the furnace for burning gaseous fuel, it oxidizes, as well as a significant amount of iron, converting it mainly into iron (II) oxide: 2Fe + O2 = 2FeO
Contained in cast iron, or any impurities of other metals at high temperatures reduce the resulting iron (II) oxide again to metallic iron according to the equation: Si + 2FeO = SiO2 + 2Fe Mn + FeO = MnO + Fe
Reacts similarly with iron (II) oxide and: C + FeO = Fe + CO
At the end of the process, “deoxidizers” - ferroalloys - are added to restore the remaining iron (II) oxide (or, as they say, to “deoxidize” it). The additives of manganese and silicon present in them reduce the remaining iron (II) oxide according to the above equations. After this, the melting ends. Melting in open hearth furnaces lasts 8-10 hours.
Rice. 85. Bessemer converter design diagram
The Bessemer converter (Fig. 85) is an older type furnace, but with very high productivity. Since the converter operates without fuel consumption, this method of steel production occupies a significant place in metallurgy. The converter is a pear-shaped steel vessel with a capacity of 20-30 tons, lined on the inside with refractory bricks. Each melting in the converter lasts 12-15 minutes. The converter has a number of disadvantages: it can only operate on liquid cast iron. This is due to the fact that carbon oxidation is carried out by air passed from below through the entire mass of liquid cast iron, which significantly speeds up melting and increases the intensity of oxidation. Naturally, the “waste” of iron in this case is especially great. At the same time, the short melting time does not allow it to be regulated or alloyed to be added, so mainly carbon steels are smelted in converters. At the end of the melting, the air supply is stopped and, as in the open-hearth process, “deoxidizers” are added.
In electric furnaces (Fig. 86) alloy steel of special grades is smelted, mainly with a high melting point, containing and other additives. The finished steel is sent to rolling. There, on huge rolling mills - blooming and slab mills - hot steel ingots are compressed using rolls, which make it possible to produce various shapes from the steel ingot.
Figure 86. Diagram of an electric arc furnace. 1 - electrodes, 2 - loading window, 3 - chute for steel release, 4 - rotary mechanism
Iron in the form of alloys is widely used in the national economy. Not a single sector of the national economy can do without it. In order to save ferrous metals, currently, whenever possible, they are trying to replace them with synthetic materials.
Ferrous metals are used to make machine tools and cars, airplanes and tools, reinforcement for reinforced concrete structures, tin for cans and roofing sheets, ships and bridges, agricultural machines and beams, pipes and a whole range of household products.
■ 78. What is the fundamental difference between the steel smelting process and the blast furnace process?
79. What furnaces are used to smelt steel?
80. What are regenerators in an open hearth furnace?
81. Indicate the composition of the open-hearth furnace charge and its difference from the composition of the blast furnace charge?
82. What are “deoxidizers”?
83. Why is steel smelting called oxidative smelting?
84. How much steel containing 1% carbon can be produced from 116.7 kg of cast iron containing 4% carbon?
85. How much ferromanganese containing 80% manganese is needed to “deoxidize” 36 kg of ferrous oxide?
Article on the topic Iron, a secondary subgroup of group VIII
IRON AND ELECTRICITY The properties of steels are varied. There are steels designed to last long in sea water, steels that can withstand high temperatures and...
MINISTRY OF EDUCATION AND SCIENCE OF THE RF FEDERAL STATE BUDGET EDUCATIONAL INSTITUTION OF HIGHER PROFESSIONAL EDUCATION “VORONEZH STATE UNIVERSITY”
CHEMISTRY OF ELEMENTS OF GROUP VIII OF THE PERIODIC SYSTEM
Tutorial
Publishing and Printing Center of Voronezh State University
Approved by the scientific and methodological council of the Faculty of Chemistry on December 12, 2012, protocol No. 9
Compiled by: I.Ya. Mittova, E.V. Tomina, B.V. Sladkopevtsev, D.O. Solodukhin
Reviewer Dr. Chem. Sciences, Professor V.N. Semenov
The textbook was prepared at the Department of Materials Science and Nanosystems Industry, Faculty of Chemistry, Voronezh State University.
For directions: 020300 – Chemistry, physics and mechanics of materials, 020100 – Chemistry
PREFACE
This textbook is a continuation of the first three parts, in which the Periodic Law as the basis of inorganic chemistry, the chemistry of elements of groups I–VI of the Periodic Table were considered. The fourth part examines the chemistry of elements of group VIII of the Periodic Table of Chemical Elements by D.I. Mendeleev.
The manual is intended to help a first-year student in studying the discipline “Inorganic Chemistry” and is essentially a lecture course outline, which displays all the main key points that need to be taken into account when studying it.
As a continuation of the series of manuals for the course “Inorganic Chemistry”, this publication generally retains the structure and consistency of the presentation of the material. The description begins with a general description of simple substances, their prevalence in nature, methods of preparation and chemical properties; in separate subsections, the properties of compounds of group elements are considered. Particular attention is paid to the use of chemical elements and their compounds as a variety of modern materials.
To implement the principle of clarity, the manual contains a large amount of illustrative material and tables, which make it possible to present large volumes of material in a compact form and reflect the main patterns in changes in the properties of chemical elements and their compounds.
When writing, modern literary sources were used, a list of which is given at the end of the manual. The illustrative material is mostly taken from the textbooks “Inorganic Chemistry” (edited by Yu.D. Tretyakov, M.: Asademia, 2004) and “Chemistry of Elements” (N. Greenwood, A. Earnshaw. M.: BINOM. Lab. Knowledge , 2008).
This manual is primarily intended for first-year students of the Faculty of Chemistry, but it can also be useful for senior students, in particular master’s students studying the disciplines “Modern Inorganic Chemistry” and “Modern Problems of Inorganic Chemistry” to update previously acquired knowledge.
CHAPTER 1. VIII-A GROUP
1.1. Simple substances
1.1.1. Element properties
Group VIII-A elements: helium 2 He, neon 10 Ne, argon 18 Ar, krypton 36 Kr, xenon 54 Xe and radon 86 Rn are called noble gases. Electron-
This configuration of the first representative of the group, helium, is 1s 2 . The atoms of the remaining noble gases at the outer level have eight valence electrons (Table 1), which corresponds to a stable electronic configuration.
Table 1
Properties of Group VIII-A elements
Property |
|||||||||||
Core charge Z |
|||||||||||
Electronic configuration |
4f 14 |
||||||||||
the walkie-talkie is mainly |
[Not]2s 2p |
3s 3p |
|||||||||
4 s 4 p |
5 s 5 p |
5p 6 |
|||||||||
Atomic radius, nm |
|||||||||||
The first ion energy |
|||||||||||
tions I 1, kJ/mol |
|||||||||||
Excitation energy |
|||||||||||
ns2 np6 →ns2 np5 (n + 1) s1, |
|||||||||||
Electronegative |
|||||||||||
The fully completed configuration of the outer electron layer (in the case of helium and neon) or the presence of an octet of electrons determines the high ionization energies of noble gas atoms and, as a consequence, their low chemical activity. The ability of atoms of these elements to enter into chemical reactions increases with increasing atomic radius due to the weakening of the attraction of valence electrons to the nucleus. To date, chemical compounds of only heavy noble gases have been obtained: krypton, xenon and radon.
1.1.2. Being in nature, receiving
Helium is the second most abundant element (after hydrogen) in the Universe. At the same time, the mass of “earthly” helium is only one millionth the mass of the earth’s crust. On the Sun, a significant number of helium nuclei are formed during the nuclear “burning” of hydrogen, so the content of this element in the Universe is gradually increasing. Helium is also formed during the α-decay of radionuclides. It fills voids in radioactive rocks and minerals, and from there it enters the atmosphere. Helium accompanies methane as an impurity. The main source of helium is natural gas.
All noble gases contained in the air, which is the raw material for their industrial production.
Radon is a radioactive element. The longest-lived isotope 222 Rn, formed from the α decay of 226 Ra, has a half-life of 3.82 days. One gram of radium-226 releases 6.6 × 10–4 ml of radon per day. Thorium minerals contain some amount of the 220 Rn isotope.
1.1.3. Physical properties
All noble gases are colorless, tasteless and odorless and have low melting and boiling points. Their molecules are monatomic. Argon, krypton and xenon form clathrates based on water and hydroquinone, for example Xe · 3C6 H4 (OH)2, in which the noble gas atoms are located in the cavities of the structure of the “host” substance. Smaller helium and argon atoms are not able to be retained in cavities. The main physical properties of simple substances are given in table. 2.
Properties of simple substances |
Table 2 |
||||||
Property |
|||||||
Standard en- |
|||||||
talpia vapor- |
|||||||
niya, kJ/mol |
|||||||
tpl, °C |
|||||||
t kip, ° C |
|||||||
5.2 10–4 |
1.8 10–3 |
1.1 10–3 |
8.7 10–6 |
6.0 10–18 |
|||
in the air, % |
|||||||
Solubility in |
|||||||
water at 20 °C, |
|||||||
1.2. Chemical properties
True chemical compounds have been obtained only for krypton, xenon and radon. The chemistry of xenon is best studied, since krypton compounds are extremely unstable, and radon is radioactive.
The interaction of xenon with fluorine leads to the formation of a mixture of fluorides. A convenient method for the synthesis of difluoride, which avoids direct fluorination, is the oxidation of xenon with silver (II) fluoride in the presence of a Lewis acid:
2AgF2 + 2BF3 + Xe = XeF2 + 2AgBF4.
Xenon fluorides are colorless, volatile crystalline substances that easily hydrolyze. Xenon difluoride forms stable solutions that decompose within a few hours:
2XeF2 + 2H2 O = 2Xe + 4HF + O2.
Xenon tetra- and hexafluoride are much more sensitive to air moisture - when they get into water, they instantly hydrolyze to form XeO3:
6XeF4 + 12H2 O = 2XeO3 + 4Xe + 3O2 + 24HF, XeF6 + 3H2 O = XeO3 + 6HF.
Xenon fluorides have a molecular structure (Fig. 1). XeF2 is a linear molecule with three lone electron pairs lying in the equatorial plane (AB2 E3 type); XeF4 has the shape of a square with two lone pairs (AB4 E2 type), and XeF6 has the shape of a distorted octahedron with one lone pair of electrons (AB6 E type). Free XeF6 molecules are known in pairs.
Rice. 1. Structure of molecules XeF2 (a), XeF4 (b), XeF6 (dynamic model with a migrating electron pair) (c)
The molecular orbital method describes the formation of xenon fluorides from the position of three-center four-electron bonds. For example, the p x orbitals of a xenon atom and two fluorine atoms participate in the formation of the XeF2 molecule (Fig. 2). Their interaction leads to the appearance of trex molecular σ orbitals: bonding, nonbonding and antibonding, the first two of which are filled with electrons. The bond order thus turns out to be equal to unity. Compounds containing three-center four-electron bonds are called hypervalent.
Rice. 2. Diagram of molecular orbitals of the XeF2 molecule. Shown on the right are the combinations of atomic orbitals involved in the formation of each of the molecular orbitals of the molecule.
Xenon fluorides are strong oxidizing agents. They convert bromates into perbromates, iodates into periodates, sulfur into hexafluoride, manganese (II) salts into permanganates:
3XeF2 + S = 3Xe + SF6,
5XeF2 + 2Mn(NO3)2 + 16KOH = 2KMnO4 + 10KF + 4KNO3 + 8H2 O + 5Xe.
This is the basis for the use of xenon fluorides in the synthesis of higher transition metal fluorides:
XeF2 + 2CeF3 → Xe + 2CeF4.
Another important property of xenon fluorides is their ability to act as both donors and acceptors of fluoride ions. Donor properties decrease in the order XeF2 > XeF6 > XeF4. Xenon difluoride most easily interacts with typical Lewis acids PF5, AsF5, SbF5, PtF5 and others, forming salts + –, + –:
XeF2 + AsF5 = + – .
By reacting XeF2 with an excess of antimony pentafluoride at a pressure of 3 atm, it was possible to obtain dark green crystals containing the paramagnetic dixenon cation Xe2 +:
4XeF2 + 8SbF5 = 2Xe2 + – + 3F2.
The Xe–Xe distance in the cation is 0.309 nm, indicating only a very weak interaction.
The acceptor properties decrease in the order XeF6 > XeF4 > XeF2. They are most typical for xenon hexafluoride, which easily reacts with fluorides of heavy alkali metals (rubidium and cesium):
XeF6 + CsF = Cs+ – .
For krypton, only compounds with fluorine in the +2 oxidation state are known. Fluoride KrF2 is formed from simple substances at liquid temperature
whom nitrogen. It is usually produced by passing an electrical discharge through a mixture of krypton and fluorine in a reactor cooled with liquid nitrogen. In structure and properties, KrF2 resembles xenon difluoride, being an even stronger oxidizing agent in comparison. KrF2 oxidizes gold trifluoride to pentafluoride and chlorine pentafluoride to + ion, converting metallic gold into gold (V):
7KrF2 + 2Au = 2KrF+ – + 5Kr.
Interestingly, free fluorine, unlike krypton difluoride, is not capable of oxidizing gold to AuF5.
Oxygen compounds are known only for xenon. Xenon forms two oxides: XeO3 and XeO4 (Fig. 3), both are extremely unstable and easily explode from the slightest shock. XeO3 oxide is formed by the hydrolysis of tetra- and hexafluorides or by the action of hexafluoride on silicon oxide:
2XeF6 + 3SiO2 = 2XeO3 + 3SiF4.
In its free form, it is colorless crystals, highly soluble in water.
Rice. 3. Structure of XeO3 (a) and XeO4 (b) molecules
It was possible to isolate only acidic alkali metal xenates (M) of the composition MHXeO4, which, when adding excess alkali, disproportionately:
2NaHXeO4 + 2NaOH = Na4 XeO6 + Xe + O2 + 2H2 O.
This is how perxenates are obtained - salts of perxenonic acid H4 XeO6. They contain the [XeO6]4– ion, which has an octahedral structure.
By treating perxenates with 100% sulfuric acid, higher xenon oxide XeO4 is obtained:
Na4 XeO6 + 2H2 SO4 = 2Na2 SO4 + XeO4 + 2H2 O.
It is a colorless gas that explodes spontaneously; its solutions in donor solvents (BrF5, HF) are more stable and can be stored at a temperature of –33 °C. Xenon tetroxide and perxenates are among the most powerful oxidizing agents.
1.3. Application
The initial use of helium as a non-flammable gas for filling balloons (its lifting force is approximately 1 kg/m3) was lost -
lost its importance, although it is still used for weather balloons. Helium is used as a cryogenic liquid to maintain temperatures of the order of 4.2 K and below (30% of the He produced is used for these purposes); 2/3 are spent on spectrometers and NMR tomographs. Other important applications include arc welding (21%) and sealing and cleaning (11%). The choice between Ar and He for these purposes is determined by the cost of gas, and everywhere except the United States they usually prefer to use argon. Small but important applications of helium include:
a) to replace N2 in artificial gas mixtures when breathing at great depths (the low solubility of helium in the blood minimizes the outgassing that occurs in the case of nitrogen - when a diver undergoes decompression - and sometimes leads to death);
b) as a working medium in gas leak detectors; c) as a coolant in the cooling system of high-temperature
nuclear reactors; d) as a carrier gas in gas-liquid chromatography;
e) for deaeration of solutions and generally as an inert diluent or inert atmosphere.
Ar is used mainly as an inert gas medium in high-temperature metallurgical processes and, in smaller quantities, to fill incandescent lamps. Together with Ne, Kr and Xe, which are obtained in much smaller quantities, Ar is also used in discharge tubes - the resulting color of the tube depends on the composition of the gas mixture. Noble gases are also used in fluorescent tubes, although in this case the color depends not on the gas filling the tube, but on the phosphorus coating the inside of the tube walls. Another important application is lasers, although compared to other applications the amount of gas used is small.
Other noble gases are significantly more expensive, so their use is limited to highly specialized areas. Radon was used in the treatment of cancer and as a source of radioactivity in flaw detection of metal castings, but due to its short half-life (3.824 days) it was replaced by other materials. The small amount of radon that is required in practice is obtained as a decay product of 226 Ra (1 g of which gives 0.64 cm3 of radon over 30 days).
CHAPTER 2. VIII-B GROUP
2.1. Simple substances
2.1.1. Electronic structure
Group VIII-B includes nine elements at once: iron 26 Fe, ruthenium 44 Ru, osmium 76 Os, cobalt 27 Co, rhodium 45 Rh, iridium 77 Ir, nickel 28 Ni, palladium 46 Pd and platinum 78 Pt.
The properties of the chemical elements of group VIII-B do not differ too much, which was the reason for their combination into triads. The similarity in properties is due to the preservation of the composition and structure of the outer electron shell of atoms with a consistent increase in the atomic number of the element and, accordingly, the total number of electrons in an isolated atom. For elements of triads, with a constant structure of the outer electron shell (principal quantum number n = 4, 5, 6), the corresponding d-sublevel (electronic n – 1-layer) is completed (with increasing atomic number), the degree of filling of which does not have a decisive effect on the dimensions atoms and ions, as well as on the properties of compounds - at least if the chemical bond in them is predominantly ionic in nature.
At the same time, the properties of compounds of elements of the iron triad differ from the properties of compounds of elements of the triads of palladium and platinum (the family of platinum elements) with similar compositions.
One of the reasons for the greater similarity between compounds of platinum elements (PE) compared to compounds of the iron triad is the influence of lanthanide compression. Thus, the atomic radii of the elements of the palladium and platinum triads are almost the same, but differ significantly from the atomic radii of the elements of the iron triad.
As you move from top to bottom through the group, the stability of compounds containing an element in the highest oxidation state increases (see diagram below). If for iron the most characteristic oxidation states are +2 and +3, and the states +6 and especially +8 are unstable, then for osmium compounds containing the element in the highest possible oxidation state +8 are quite stable. A similar pattern is observed when moving from Co and Ni to their heavy analogues. Thus, for nickel the most stable compounds are those where it has an oxidation state of +2, while palladium and especially platinum have an oxidation state of +4.
It is the only substance that remains liquid at temperatures down to 0 K. It crystallizes only under a pressure of 25 atm. has the lowest boiling point. at temperatures below 2.2 K, liquid helium exists as a mixture of two liquids, one of which has anomalous properties - in particular, superfluidity (viscosity is 10 billion times lower than that of water).
Helium is the second most abundant element (after hydrogen) in the Universe. About 10% of the Sun consists of it (discovered in 1868). On earth, helium was found in 1895 in reaction gases when the mineral kleveite was dissolved in acids. The remaining noble gases were isolated from the air.
Neon is a light gas: it is 1.44 times lighter than air, almost 2 times lighter than argon, but 5 times heavier than helium. In terms of its properties, it is closer to helium than to argon. The spectrum of neon is rich: it contains more than 900 lines. The brightest lines form a beam in the red, orange and yellow parts of the spectrum at waves from 6599 to 5400 Ǻ. These rays are much less absorbed and scattered by air and particles suspended in it than short-wave rays - blue, indigo, violet.
In 1898, in the Old World, when studying with a spectroscope the first portions of gas evaporating from liquid air, the Scottish chemist William Ramsay (Ramsay), together with Morris William Traver, discovered in them a new gas, Neon (Ne 6), an inert gas contained in the air in microscopic quantities.
Argon is a monatomic gas with a boiling point (at normal pressure) of -185.9 °C (slightly lower than oxygen, but slightly higher than nitrogen), melting point -189.3 °C In 100 ml of water at 20 °C 3.3 ml of argon dissolves; argon dissolves much better in some organic solvents than in water.
Discovered by J. Rayleigh and English physicist W. Ramsay in 1894 from the air. The gas was distinguished by a monatomic composition of molecules and almost complete chemical inactivity (argon does not enter into any chemical reactions). the new gas got its name (Greek argos inactive).
Krypton is an inert monatomic gas without color, taste or smell. 3 times heavier than air.t pl = - 157.3 o C, t boil = -152.0 o C, density at normal conditions. equal to 3.74 g/l. Opened in 1898 by W. Ramsay (England) Application: for filling incandescent lamps. Krypton compounds are oxidizing agents and fluorinating agents in chemical synthesis reactions.
Xenon is an inert monatomic gas without color, taste or smell. Tmelt 112 °C, Tt 108 °C, glow in the discharge violet. In 1889, the English scientist Wu Ramsay isolated a mixture from liquid air in which two gases were discovered by spectral method: krypton (“hidden”, “secret”) and xenon (“alien”, “unusual”).
Radon is a radioactive monatomic gas, colorless and odorless. Solubility in water 460 ml/l; in organic solvents and in human adipose tissue, the solubility of radon is tens of times higher than in water. Radon's own radioactivity causes it to fluoresce. Gaseous and liquid radon fluoresces with blue light. The color of the glow in a gas discharge in radon is blue.
Colorless crystals, soluble in water. The molecule is linear. A solution in water is a very strong oxidizing agent, especially in an acidic environment, where it oxidizes bromine and manganese to the highest oxidation states of +7. In an alkaline environment, it hydrolyzes according to the equation: XeF 2 + 4KOH = 2Xe + 4KF + O 2 + 2H 2 O
When interacting with water, XeF 4 disproportionates: 6XeF H 2 O = 2XeО НF + 4Xe + 3О 2
It is formed during the hydrolysis of XeF 4. It is a white, non-volatile, highly explosive substance, highly soluble in water, and the solution has a slightly alkaline reaction. When such a solution is exposed to ozone, a salt of xenonic acid is formed, in which xenon has an oxidation state of +8: XeO 3 + O 3 + 4NaOH = Na 4 XeO 6 + O H 2 O
Can be obtained by reacting barium perxenate with anhydrous sulfuric acid at low temperatures: Ba 2 XeO 6 + 2H 2 SO 4 = 2 BaSO 4 + XeO H 2 O XeO 4 is a colorless gas that is very explosive and decomposes at temperatures above 0 ° C : 3XeО 4 = 2XeО 3 + Xe + 3О 2
In the IB group (copper group) there are transition metals Cu, Ag, Au, which have a similar distribution of electrons, determined by the phenomenon of “breakthrough” or “failure” of electrons.
The “breakthrough” phenomenon is a symbolic transfer of one of the two valence s electrons to the d sublevel, which reflects the uneven retention of outer electrons by the nucleus.
The transition of one s-electron to the outer level leads to stabilization of the d-sublevel. Therefore, depending on the degree of excitation, group IB atoms can donate from one to three electrons to form a chemical bond. As a result, elements of group IB can form compounds with oxidation states +1, +2 and +3. However, there are differences: for copper the most stable oxidation states are +1 and +2; for silver +1, and for gold +1 and +3. The most characteristic coordination numbers in this group are 2, 3, 4.
Group 1B elements are relatively inert. In the electrochemical series they come after hydrogen, which is manifested in their weak reducing ability. Therefore, they are found in nature in native form. They are among the first metals that ancient man discovered and used. The following compounds are found as fossils: Cu 2 O - cuprite, Cu 2 S - chalcocite, Ag 2 S - argentite, acanthite, AgCl - cerargyrite, AuTe 2 - calaverite, (Au,Ag)Te 4 - sylvanite .
In group IB, the reducing and basic properties decrease from copper to gold.
Chemical properties of compounds of copper, silver, gold.
Silver (I) oxide is obtained by heating silver with oxygen or treating AgNO3 solutions with alkalis:
2 AgNO 3 + 2KOH > Ag 2 O + 2KNO 3 + H 2 O
Silver (I) oxide dissolves slightly in water, however, due to hydrolysis, the solutions have an alkaline reaction
Ag 2 O + H 2 O > 2Ag + + 2OH -
in cyanide solutions it turns into a complex:
Ag 2 O + 4KN + H 2 O > 2K[Ag(CN) 2 ] + 2KON
Ag 2 O is an energetic oxidizing agent. Oxidizes chromium (III) salts:
3Ag 2 O + 2Cr(OH) 3 + 4NaOH > 2Na 2 CrO 4 + 6Ag + 5H 2 O,
as well as aldehydes and halogenated hydrocarbons.
The oxidative properties of silver (I) oxide determine the use of its suspension as an antiseptic.
In the electrochemical series of normal redox potentials, silver comes after hydrogen. Therefore, metallic silver reacts only with oxidizing concentrated nitric and sulfuric acids:
2Аg + 2Н 2 SO 4 > Аg 2 SO 4 + 5О 2 + 2Н 2 О
Most silver salts are slightly or poorly soluble. Halides and phosphates are practically insoluble. Silver sulfate and silver carbonate are poorly soluble. Solutions of silver halides decompose under the influence of ultraviolet and X-rays:
2АgСl -- hн > 2Аg + Сl 2
AgCl crystals with an admixture of bromides are even more sensitive to the action of ultraviolet and X-rays. Under the influence of a quantum of light, reactions occur in a crystal
Br -- + hn > Br° + e -
Аg + + e ~ > Аg°
2АgВr > 2Аg 0 + Вr 2
This property of silver halides is used in the manufacture of photosensitive materials, in particular photographic films and X-ray films.
Insoluble silver chloride and silver bromide dissolve in ammonia to form ammonia:
AgСl + 2NН 3 > [Аg(NH 3) 2 ]Сl
The dissolution of AgCl is possible because silver ions bind into a very strong complex ion. There are so few silver ions remaining in the solution that there are not enough of them to form a precipitate, since the product of concentrations is less than the solubility constant.
The bactericidal properties of AgCl are used in preparations for treating gas mucous membranes. For sterilization and preservation of food products, “silver water” is used - distilled water treated with AgCl crystals.
Just like silver, copper (I) forms insoluble halides. These salts dissolve in ammonia and form complexes:
СuСl + 2NН 3 > [Сu(NН 3) 2 ]Сl
Insoluble in water are oxides and hydroxides of copper (II), which are basic in nature and dissolve in acids:
Cu(OH) 2 + 2HCl + 4H 2 O > [Cu(H 2 O) 6 ]Cl 2
The resulting aquacation [Cu(H 2 O) 6 ] 2+ gives the solutions a bright blue color.
Copper (II) hydroxide dissolves in ammonia and forms a complex that turns the solution blue:
Cu(OH) 2 + 4NH 3 + 2H 2 O > [Cu(NH 3) 4 (H 2 O) 2 ](OH) 2
This reaction is used for the qualitative reaction of copper(II) ions.
Salts of copper, silver and gold interact with alkali metal sulfides and hydrogen sulfide to form water-insoluble precipitates - Ag 2 S, Cu 2 S, CuS, Au 2 S 3.
The high affinity of group IB metals for sulfur determines the high binding energy of M--S, and this, in turn, determines the specific nature of their behavior in biological systems.
The cations of these metals easily interact with substances that contain groups containing sulfur. For example, Ag + and Cu + ions react with dithiol enzymes of microorganisms according to the following scheme:
The inclusion of metal ions in protein inactivates enzymes and destroys proteins.
The same mechanism underlies the action of drugs containing silver and gold used in dermatology.
The most common gold(III) compound is AuCl 3 chloride, which is highly soluble in water.
Gold(III) oxide and hydroxide are amphoteric compounds with more pronounced acidic properties. Gold(III) hydroxide is insoluble in water, but dissolves in alkalis to form a hydroxo complex:
AuO(OH) + NaOH + H 2 O > Na[Au(OH) 4 ]
Reacts with acids to form an acid complex:
AuO(OH) + 2H 2 SO 4 > H[Au(SO 4) 2 ] + 2H 2 O
A large number of complex compounds are known for gold and its analogues. The famous reaction of dissolving gold in aqua regia (1 volume of conc. HMO3 and 3 volumes of conc. HCl) is the formation of a complex acid:
Au + 4HCl + HNO 3 > H[AuCl 4 ] + NO + 2H 2 O
In the body, copper functions in oxidation states + 1 and +2. Cu + and Cu 2+ ions are part of “blue” proteins isolated from bacteria. These proteins have similar properties and are called azurins.
Copper (I) binds more firmly to sulfur-containing ligands, and copper (II) to carboxyl, phenolic, and amino groups of proteins. Copper(I) gives complexes with a coordination number of 4. A tetrahedral structure is formed (if an even number of d-electrons are involved). For copper (II) the coordination number is 6, which corresponds to the orthorhombic geometry of the complex.
General characteristics of the elements of group VIII of the secondary subgroup of the Periodic Table of D. I. Mendeleev.
Iron subgroup- chemical elements of the 8th group of the periodic table of chemical elements. The group includes iron Fe, ruthenium Ru and osmium Os. Based on the electronic configuration of the atom, the artificially synthesized element also belongs to the same group Hassiy Hs.
All group 8 elements contain 8 electrons in their valence shells. Two elements of the group - ruthenium and osmium - belong to the platinum metal family. As with other groups, members of group 8 elements exhibit patterns of electronic configuration, especially in outer shells, although, surprisingly, ruthenium does not follow this trend. However, the elements of this group also exhibit similarities in physical properties and chemical behavior.
Iron as a tool material has been known since ancient times. The history of the production and use of iron dates back to the prehistoric era, most likely with the use of meteorite iron.
Ruthenium was discovered by Kazan University professor Karl Klaus in 1844. Klaus isolated it from Ural platinum ore in its pure form and pointed out the similarities between the triads ruthenium - rhodium - palladium and osmium - iridium - platinum. He named the new element ruthenium in honor of Rus' (Ruthenia is the Latin name for Rus').
Osmium was discovered in 1804 by the English chemist Smithson Tennant in the precipitate remaining after dissolving platinum in aqua regia.
Iron is rarely found in nature in its pure form; most often it is found in iron-nickel meteorites. The prevalence of iron in the earth's crust is 4.65% (4th place after oxygen, silicon and aluminum). It is also believed that iron makes up most of the earth's core.
Ruthenium is the most abundant platinum metal in humans, but almost the rarest of all. Has no biological role. Concentrated mainly in muscle tissue. Higher ruthenium oxide is extremely toxic and, being a strong oxidizing agent, can cause combustion of flammable substances. Osmium may also exist in humans in imperceptibly small quantities.
General characteristics of the elements of group VIII of the secondary subgroup of the Periodic Table of D. I. Mendeleev. - concept and types. Classification and features of the category "General characteristics of elements of group VIII of the secondary subgroup of the Periodic Table of D. I. Mendeleev." 2017, 2018.
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