Chemical properties of metals using sodium as an example. General chemical properties of metals. with non-metals of groups IV–VI

First of all, remember that metals are generally divided into three groups:

1) Reactive metals: These metals include all alkali metals, alkaline earth metals, as well as magnesium and aluminum.

2) Metals of intermediate activity: these include metals located between aluminum and hydrogen in the activity series.

3) Low-active metals: metals located in the activity series to the right of hydrogen.

First of all, you need to remember that low-active metals (i.e. those located after hydrogen) do not react with water under any conditions.

Alkali and alkaline earth metals react with water under any conditions (even at ordinary temperatures and in the cold), and the reaction is accompanied by the release of hydrogen and the formation of metal hydroxide. For example:

2Na + 2H 2 O = 2NaOH + H 2

Ca + 2H 2 O = Ca(OH) 2 + H 2

Magnesium, due to the fact that it is covered with a protective oxide film, reacts with water only when boiled. When heated in water, the oxide film consisting of MgO is destroyed and the magnesium underneath begins to react with water. In this case, the reaction is also accompanied by the release of hydrogen and the formation of metal hydroxide, which, however, in the case of magnesium is insoluble:

Mg + 2H 2 O = Mg(OH) 2 ↓ + H 2

Aluminum, like magnesium, is covered with a protective oxide film, but in this case it cannot be destroyed by boiling. To remove it, either mechanical cleaning (with some kind of abrasive) or its chemical destruction with alkali, solutions of mercury salts or ammonium salts is required:

2Al + 6H 2 O = 2Al(OH) 3 + 3H 2

Medium activity metals react with water only when it is in a state of superheated water vapor. The metal itself must be heated to a red-hot temperature (about 600-800 o C). Unlike active metals, metals with intermediate activity react with water to form metal oxides instead of hydroxides. The reduction product in this case is hydrogen:

Zn + H 2 O = ZnO + H 2

3Fe + 4H 2 O = Fe 3 O 4 + 4H 2 or

Fe + H 2 O = FeO + H 2 (depending on the degree of heating)

Properties of metals.

1. Basic properties of metals.

The properties of metals are divided into physical, chemical, mechanical and technological.

Physical properties include: color, specific gravity, fusibility, electrical conductivity, magnetic properties, thermal conductivity, expansion when heated.

Chemical properties include oxidation, solubility and corrosion resistance.

Mechanical - strength, hardness, elasticity, viscosity, plasticity.

Technological ones include hardenability, fluidity, malleability, weldability, machinability.

1. Physical and chemical properties.

Color. Metals are opaque, i.e. do not let light pass through them, and in this reflected light, each metal has its own special shade - color.

Of the technical metals, only copper (red) and its alloys are painted. The color of other metals ranges from steel-gray to silver-white. The thinnest films of oxides on the surface of metal products give them additional colors.

Specific gravity. The weight of one cubic centimeter of a substance, expressed in grams, is called specific gravity.

Based on their specific gravity, light metals and heavy metals are distinguished. Of the technical metals, the lightest is magnesium (specific gravity 1.74), the heaviest is tungsten (specific gravity 19.3). The specific gravity of metals depends to some extent on the method of their production and processing.

Fusibility. The ability to transform from a solid to a liquid state when heated is the most important property of metals. When heated, all metals pass from a solid to a liquid state, and when a molten metal is cooled, from a liquid to a solid state. The melting point of technical alloys does not have one specific melting point, but a temperature range, sometimes quite significant.

Electrical conductivity. Electrical conductivity involves the transfer of electricity by free electrons. The electrical conductivity of metals is thousands of times higher than the electrical conductivity of non-metallic bodies. As the temperature rises, the electrical conductivity of metals decreases, and as it decreases, it increases. When approaching absolute zero (- 273 0 C), the electrical conductivity of infinite metals ranges from +232 0 (tin) to 3370 0 (tungsten). Most increase (resistance drops to almost zero).

The electrical conductivity of alloys is always lower than the electrical conductivity of one of the components that make up the alloys.

Magnetic properties. Only three metals are clearly magnetic (ferromagnetic): iron, nickel, and cobalt, as well as some of their alloys. When heated to certain temperatures, these metals also lose their magnetic properties. Some iron alloys are not ferromagnetic even at room temperature. All other metals are divided into paramagnetic (attracted by magnets) and diamagnetic (repelled by magnets).

Thermal conductivity. Thermal conductivity is the transfer of heat in a body from a more heated place to a less heated place without visible movement of particles of this body. The high thermal conductivity of metals allows them to be heated and cooled quickly and evenly.

Of the technical metals, copper has the highest thermal conductivity. The thermal conductivity of iron is much lower, and the thermal conductivity of steel varies depending on the content of components in it. As the temperature increases, thermal conductivity decreases, and as the temperature decreases, it increases.

Heat capacity. Heat capacity is the amount of heat required to increase body temperature by 1 0 .

The specific heat capacity of a substance is the amount of heat in kilograms - calories that must be imparted to 1 kg of a substance in order to increase its temperature by 1 0.

The specific heat capacity of metals is low compared to other substances, which makes it relatively easy to heat them to high temperatures.

Expandability when heated. The ratio of the increase in the length of a body when it is heated by 1 0 to its original length is called the coefficient of linear expansion. For different metals, the coefficient of linear expansion varies widely. For example, tungsten has a linear expansion coefficient of 4.0·10 -6, and lead 29.5·10 -6.

Corrosion resistance. Corrosion is the destruction of a metal due to its chemical or electrochemical interaction with the external environment. An example of corrosion is the rusting of iron.

High resistance to corrosion (corrosion resistance) is an important natural property of some metals: platinum, gold and silver, which is why they are called noble. Nickel and other non-ferrous metals also resist corrosion well. Ferrous metals corrode more strongly and faster than non-ferrous metals.

2. Mechanical properties.

Strength. The strength of a metal is its ability to resist external forces without breaking.

Hardness. Hardness is the ability of a body to resist the penetration of another, harder body.

Elasticity. The elasticity of a metal is its ability to restore its shape after the cessation of the action of external forces that caused a change in shape (deformation.)

Viscosity. Toughness is the ability of a metal to resist rapidly increasing (impact) external forces. Viscosity is the opposite property of brittleness.

Plastic. Plasticity is the property of a metal to deform without destruction under the influence of external forces and retain new uniform after the force ceases. Plasticity is the opposite property of elasticity.

In table 1 shows the properties of technical metals.

Table 1.

Properties of technical metals.

Metal name	Specific gravity (density) gsm 3	Melting point 0 C	Brinell hardness	Tensile strength (temporary resistance) kgmm 2	Relative extension %	Relative narrowing of the cross section %
AluminumTungstenIronCobaltMagnesiumManganeseCopperNickelTinLeadChromiumZinc	2,7 19,3 7,87 8,9 1,74 7,44 8,84 8,9 7,3 11,34 7,14 7,14	658 3370 1530 1490 651 1242 1083 1452 232 327 1550 419	20-37 160 50 125 25 20 35 60 5-10 4-6 108 30-42	8-11 110 25-33 70 17-20 Fragile22 40-50 2-4 1,8 Fragile11,3-15	40 - 21-55 3 15 Fragile60 40 40 50 Fragile5-20	85 - 68-55 - 20 Fragile75 70 74 100 Fragile-

3. The importance of the properties of metals.

Mechanical properties. The first requirement for any product is sufficient strength.

Metals have higher strength compared to other materials, so loaded parts of machines, mechanisms and structures are usually made of metals.

Many products, in addition to general strength, must also have special properties characteristic of the operation of this product. For example, cutting tools must have high hardness. Tool steels and alloys are used for the manufacture of other cutting tools.

For the manufacture of springs and springs, special steels and alloys with high elasticity are used

Viscous metals are used in cases where parts are subject to shock loads during operation.

The plasticity of metals makes it possible to process them by pressure (forging, rolling).

Physical properties. In aircraft, automobile and carriage construction, the weight of parts is often the most important characteristic, therefore aluminum and especially magnesium alloys are irreplaceable here. Specific strength (the ratio of tensile strength to specific gravity) for some, such as aluminum, alloys is higher than for mild steel.

Fusibility used to produce castings by pouring molten metal into molds. Low-melting metals (for example, lead) are used as a quenching medium for steel. Some complex alloys have such a low melting point that they melt in hot water. Such alloys are used for casting typographic matrices and in devices used to protect against fires.

Metals with high electrical conductivity(copper, aluminum) are used in electrical engineering, for the construction of power lines, and alloys with high electrical resistance are used for incandescent lamps and electric heating devices.

Magnetic properties metals play a primary role in electrical engineering (dynamos, motors, transformers), for communication devices (telephone and telegraph devices) and are used in many other types of machines and devices.

Thermal conductivity metals makes it possible to produce them physical properties. Thermal conductivity is also used in soldering and welding of metals.

Some metal alloys have linear expansion coefficient, close to zero; Such alloys are used for the manufacture of precision instruments and radio tubes. Expansion of metals must be taken into account when constructing long structures such as bridges. It should also be taken into account that two parts made of metals with different expansion coefficients and fastened together can bend and even break when heated.

Chemical properties. Corrosion resistance is especially important for products operating in highly oxidizing environments (grids, parts of chemical machines and instruments). To achieve high corrosion resistance, special stainless, acid-resistant and heat-resistant steels are produced, and protective coatings are also used.

There are technological, physical, mechanical and chemical properties of metals. Physical properties include color and electrical conductivity. The characteristics of this group also include thermal conductivity, fusibility and density of the metal.

Mechanical characteristics include plasticity, elasticity, hardness, strength, and toughness.

Chemical properties of metals include corrosion resistance, solubility, and oxidability.

Characteristics such as fluidity, hardenability, weldability, and malleability are technological.

Physical properties

1. Color. Metals do not transmit light through themselves, that is, they are opaque. In reflected light, each element has its own shade - color. Among technical metals, only copper and its alloys have color. The remaining elements are characterized by a shade ranging from silver-white to steel-gray.
2. Fusibility. This characteristic indicates the ability of an element to transform into a liquid state from a solid state under the influence of temperature. Fusibility is considered the most important property of metals. During the heating process, all metals change from a solid state to a liquid state. When the molten substance is cooled, a reverse transition occurs - from the liquid to the solid state.
3. Electrical conductivity. This characteristic indicates the ability of free electrons to transfer electricity. The electrical conductivity of metallic bodies is thousands of times greater than that of non-metallic bodies. As the temperature increases, the conductivity of electricity decreases, and as the temperature decreases, it increases accordingly. It should be noted that the electrical conductivity of alloys will always be lower than that of any metal that makes up the alloy.
4. Magnetic properties. Obviously magnetic (ferromagnetic) elements include only cobalt, nickel, iron, as well as a number of their alloys. However, when heated to a certain temperature, these substances lose their magnetism. Certain iron alloys at room temperature are not ferromagnetic.
5. Thermal conductivity. This characteristic indicates the ability of heat to transfer to a less heated body from a more heated body without visible movement of its constituent particles. High level thermal conductivity allows metals to be heated and cooled evenly and quickly. Among technical elements Copper has the highest indicator.

Metals occupy a special place in chemistry. The presence of appropriate characteristics allows the use of a particular substance in a certain area.

Chemical properties of metals

1. Corrosion resistance. Corrosion is the destruction of a substance as a result of electrochemical or chemical interaction with environment. The most common example is the rusting of iron. Corrosion resistance is one of the most important natural characteristics of a number of metals. In this regard, substances such as silver, gold, and platinum are called noble. Nickel has high corrosion resistance and other non-ferrous materials are subject to destruction faster and more severely than non-ferrous ones.
2. Oxidability. This characteristic indicates the ability of the element to react with O2 under the influence of oxidizing agents.
3. Solubility. Metals that have unlimited solubility in the liquid state can form solid solutions when solidified. In these solutions, atoms from one component are incorporated into another component only within certain limits.

It should be noted that the physical and chemical properties of metals are one of the main characteristics of these elements.

This lesson is devoted to the study of the topic “ General properties metals Metal connection." During the lesson, the general chemical properties of metals and the features of metallic chemical bonds will be discussed. The teacher will explain the similarity of the chemical and physical properties of metals using a model of them internal structure.

Topic: Chemistry of metals

Lesson: General properties of metals. Metal connection

Metals are characterized by common physical properties: they have a special metallic luster, high thermal and electrical conductivity, and ductility.

Metals also share some common chemical properties. It is important to remember that in chemical reactions metals act as reducing agents: they donate electrons and increase their oxidation state. Let's look at some reactions in which metals participate.

INTERACTION WITH OXYGEN

Many metals can react with oxygen. Usually the products of these reactions are oxides, but there are exceptions, which you will learn about in the next lesson. Let's consider the interaction of magnesium with oxygen.

Magnesium burns in oxygen to form magnesium oxide:

2Mg + O2 = 2MgO

Rice. 1. Combustion of magnesium in oxygen

Magnesium atoms donate their outer electrons to oxygen atoms: two magnesium atoms donate two electrons to two oxygen atoms. In this case, magnesium acts as a reducing agent, and oxygen acts as an oxidizing agent.

Metals react with halogens. The product of this reaction is a metal halide, such as chloride.

Rice. 2. Combustion of potassium in chlorine

Potassium burns in chlorine to form potassium chloride:

2K + Cl 2 = 2KCl

Two potassium atoms donate one electron each to a chlorine molecule. Potassium, increasing the oxidation state, plays the role of a reducing agent, and chlorine, decreasing the oxidation state, plays the role of an oxidizing agent.

Many metals react with sulfur to form sulfides. In these reactions, metals also act as reducing agents, while sulfur will be an oxidizing agent. Sulfur in sulfides is in the oxidation state -2, i.e. it lowers its oxidation number from 0 to -2. For example, when heated, iron reacts with sulfur to form iron (II) sulfide:

Rice. 3. Interaction of iron with sulfur

Metals can also react with hydrogen, nitrogen, and other nonmetals under certain conditions.

Only active metals, such as alkali and alkaline earth metals, react with water without heating. During these reactions, an alkali is formed and hydrogen gas is released. For example, calcium reacts with water to form calcium hydroxide and hydrogen, releasing a large amount of heat:

Ca + 2H 2 O = Ca(OH) 2 + H 2

Less reactive metals, such as iron and zinc, react with water only when heated to form metal oxide and hydrogen. For example:

Zn + H 2 O = ZnO + H 2

In these reactions, the oxidizing agent is the hydrogen atom contained in water.

Metals located in the voltage series to the right of hydrogen do not react with water.

You already know that metals in the voltage series to the left of hydrogen react with acids. In these reactions, metals donate electrons and act as a reducing agent. The oxidizing agent is hydrogen cations formed in acid solutions. For example, zinc reacts with hydrochloric acid:

Zn + 2HCl = ZnCl 2 + H 2

Otherwise, reactions of metals with nitric and concentrated sulfuric acids occur. In these reactions, practically no hydrogen is released. We'll talk about these interactions in future lessons.

A metal can react with a salt solution if it is more active than the metal contained in the salt. For example, iron replaces copper from copper(II) sulfate:

Fe + CuSO 4 = FeSO 4 + Cu

Iron is a reducing agent, copper cations are an oxidizing agent.

Let's try to explain why metals have common physical and chemical properties. To do this, consider a model of the internal structure of a metal.

Metal atoms have relatively large radii and a small number of outer electrons. These electrons are weakly attracted to the nucleus, so in chemical reactions metals act as reducing agents, donating electrons from the outer energy level.

At the nodes of the crystal lattice of metals there are not only neutral atoms, but also metal cations, because outer electrons move freely throughout the crystal lattice. In this case, atoms, giving up electrons, become cations, and cations, accepting electrons, turn into electrically neutral atoms.

Rice. 4. Model of the internal structure of metal

A chemical bond that is formed as a result of the attraction of metal cations to freely moving electrons is called metal.

The electrical and thermal conductivity of metals is explained by the presence of free electrons, which can be carriers electric current and carriers of heat. The plasticity of the metal is explained by the fact that the chemical bond does not break under mechanical stress, because a chemical bond is established not between specific atoms and cations, but between all metal cations with all free electrons in the metal crystal.

1. Mikityuk A.D. Collection of problems and exercises in chemistry. 8-11 grades / A.D. Mikityuk. - M.: Publishing house. "Exam", 2009.

2. Orzhekovsky P.A. Chemistry: 9th grade: textbook. for general education establishment / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. - M.: AST: Astrel, 2007. (§23)

3. Orzhekovsky P.A. Chemistry: 9th grade: general education. establishment / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013. (§6)

4. Rudzitis G.E. Chemistry: inorganic. chemistry. Organ. chemistry: textbook. for 9th grade. / G.E. Rudzitis, F.G. Feldman. - M.: Education, OJSC “Moscow Textbooks”, 2009.

5. Khomchenko I.D. Collection of problems and exercises in chemistry for high school. - M.: RIA “New Wave”: Publisher Umerenkov, 2008.

6. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed. V.A. Volodin, Ved. scientific ed. I. Leenson. - M.: Avanta+, 2003.

Additional web resources

1. A unified collection of digital educational resources (video experiences on the topic) ().

2. Electronic version of the journal “Chemistry and Life” ().

Homework

p.41 Nos. A1, A2 from the Textbook of Orzhekovsky P.A. “Chemistry: 9th grade” (M.: Astrel, 2013).

Metal atoms relatively easily give up valence electrons and become positively charged ions. Therefore, metals are reducing agents. Metals react with simple substances: Ca + C12 - CaC12. Active metals react with water: 2Na + 2H20 = 2NaOH + H2f. Metals standing in the series of standard electrode potentials up to hydrogen interact with dilute solutions of acids (except for HN03) with the release of hydrogen: Zn + 2HC1 = ZnCl2 + H2f. Metals react with aqueous solutions of salts of less active metals: Ni + CuS04 = NiS04 + Cu J. Metals react with oxidizing acids: C. Methods for producing metals Modern metallurgy produces more than 75 metals and numerous alloys based on them. Depending on the methods of obtaining metals, pyrohydro- and electrometallurgy are distinguished. GG) Pyrometallurgy covers methods of obtaining metals from ores using reduction reactions carried out at high temperatures. Coal, active metals, carbon monoxide (II), hydrogen, and methane are used as reducing agents. Cu20 + C - 2Cu + CO, t° Cu20 + CO - 2Cu + C02, t° Cr203 + 2A1 - 2Cg + A1203, (aluminothermy) t° TiCl2 + 2Mg - Ti + 2MgCl2, (magnesiumthermy) t° W03 + 3H2 = W+3H20. (hydrogenothermy) |C Hydrometallurgy is the production of metals from solutions of their salts. For example, when copper ore containing copper oxide (I) is treated with dilute sulfuric acid, copper goes into solution in the form of sulfate: CuO + H2S04 = CuS04 + H20. Copper is then removed from the solution either by electrolysis or by displacement using iron powder: CuS04 + Fe = FeS04 + Cu. [h] Electrometallurgy is methods for producing metals from their molten oxides or salts using electrolysis: electrolysis 2NaCl - 2Na + Cl2. Questions and tasks for independent solution 1. Indicate the position of metals in the periodic table of D.I. Mendeleev. 2. Show the physical and chemical properties of metals. 3. Explain the reason for the common properties of metals. 4. Show the change in the chemical activity of metals of the main subgroups of groups I and II of the periodic table. 5. How do the metallic properties of elements of periods II and III change? Name the most refractory and the most fusible metals. 7. Indicate which metals are found in nature in a native state and which are found only in the form of compounds. How can this be explained? 8. What is the nature of alloys? How the composition of an alloy affects its properties. Show with specific examples. Indicate the most important methods for obtaining metals from ores. 10l Name the types of pyrometallurgy. What reducing agents are used in each specific method? Why? 11. Name the metals that are obtained using hydrometallurgy. What is the essence and what are the advantages of this method over others? 12. Give examples of the production of metals using electrometallurgy. In what case is this method used? 13. What are modern methods obtaining metals of high purity? 14. What is “electrode potential”? Which metal has the highest and which has the lowest electrode potential in an aqueous solution? 15. Describe a number of standard electrode potentials? 16. Is it possible to displace metallic iron from an aqueous solution of its sulfate using metallic zinc, nickel, and sodium? Why? 17. What is the principle of operation of galvanic cells? What metals can be used in them? 18. What processes are classified as corrosion? What types of corrosion do you know? 19. What is called electrochemical corrosion? What methods of protection against it do you know? 20. How does its contact with other metals affect the corrosion of iron? Which metal will be destroyed first on a damaged surface of tinned, galvanized and nickel-plated iron? 21. What process is called electrolysis? Write reactions that reflect the processes occurring at the cathode and anode during the electrolysis of molten sodium chloride, aqueous solutions of sodium chloride, copper sulfate, sodium sulfate, sulfuric acid. 22. What role does the electrode material play during electrolysis processes? Give examples of electrolysis processes occurring with soluble and insoluble electrodes. 23. Alloy used for preparation copper coins, contains 95% copper. Determine the second metal included in the alloy if, when processing a one-kopeck coin with an excess of hydrochloric acid, 62.2 ml of hydrogen (n.u.) was released. aluminum. 24. A sample of metal carbide weighing 6 g was burned in oxygen. In this case, 2.24 liters of carbon monoxide (IV) (no.) was formed. Determine what metal was included in the carbide. 25. Show what products will be released during the electrolysis of an aqueous solution of nickel sulfate if the process proceeds: a) with coal; b) with nickel electrodes? 26. During electrolysis of an aqueous solution copper sulfate 2.8 liters of gas (n.o.) were released at the anode. What gas is this? What and in what quantity was released at the cathode? 27. Draw up a diagram of the electrolysis of an aqueous solution of potassium nitrate flowing on the electrodes. What is the amount of electricity passed if 280 ml of gas (n.o.) is released at the anode? What and in what quantity was released at the cathode?