1. Metals react with non-metals.
2Me+ n Hal 2 → 2 MeHal n
4Li + O2 = 2Li2O
Alkali metals, with the exception of lithium, form peroxides:
2Na + O 2 \u003d Na 2 O 2
2. Metals standing up to hydrogen react with acids (except nitric and sulfuric conc.) with the release of hydrogen
Me + HCl → salt + H2
2 Al + 6 HCl → 2 AlCl3 + 3 H2
Pb + 2 HCl → PbCl2↓ + H2
3. Active metals react with water to form alkali and release hydrogen.
2Me+ 2n H 2 O → 2Me(OH) n + n H2
The product of metal oxidation is its hydroxide - Me (OH) n (where n is the oxidation state of the metal).
For example:
Ca + 2H 2 O → Ca (OH) 2 + H 2
4. Intermediate activity metals react with water when heated to form metal oxide and hydrogen.
2Me + nH 2 O → Me 2 O n + nH 2
The oxidation product in such reactions is metal oxide Me 2 O n (where n is the oxidation state of the metal).
3Fe + 4H 2 O → Fe 2 O 3 FeO + 4H 2
5. Metals standing after hydrogen do not react with water and acid solutions (except for nitric and sulfuric conc.)
6. More active metals displace less active ones from solutions of their salts.
CuSO 4 + Zn \u003d ZnSO 4 + Cu
CuSO 4 + Fe \u003d FeSO 4 + Cu
Active metals - zinc and iron replaced copper in sulfate and formed salts. Zinc and iron are oxidized, and copper is restored.
7. Halogens react with water and alkali solution.
Fluorine, unlike other halogens, oxidizes water:
2H 2 O+2F 2 = 4HF + O 2 .
in the cold: Cl2 + 2KOH = KClO + KCl + H2OCl2 + 2KOH = KClO + KCl + H2O chloride and hypochlorite are formed
heating: 3Cl2+6KOH−→KClO3+5KCl+3H2O3Cl2+6KOH→t,∘CKClO3+5KCl+3H2O forms loride and chlorate
8 Active halogens (except fluorine) displace less active halogens from solutions of their salts.
9. Halogens do not react with oxygen.
10. Amphoteric metals (Al, Be, Zn) react with solutions of alkalis and acids.
3Zn+4H2SO4= 3 ZnSO4+S+4H2O
11. Magnesium reacts with carbon dioxide and silicon oxide.
2Mg + CO2 = C + 2MgO
SiO2+2Mg=Si+2MgO
12. Alkali metals (except lithium) form peroxides with oxygen.
2Na + O 2 \u003d Na 2 O 2
3. Classification of inorganic compounds
Simple substances - substances whose molecules consist of atoms of the same type (atoms of the same element). In chemical reactions, they cannot decompose to form other substances.
Complex Substances (or chemical compounds) - substances whose molecules consist of atoms of different types (atoms of various chemical elements). In chemical reactions, they decompose to form several other substances.
Simple substances are divided into two large groups: metals and non-metals.
Metals - a group of elements with characteristic metallic properties: solids (with the exception of mercury) have a metallic luster, are good conductors of heat and electricity, malleable (iron (Fe), copper (Cu), aluminum (Al), mercury (Hg), gold (Au), silver (Ag), etc.).
non-metals - a group of elements: solid, liquid (bromine) and gaseous substances that do not have a metallic sheen, are insulators, brittle.
And complex substances, in turn, are divided into four groups, or classes: oxides, bases, acids and salts.
oxides - these are complex substances, the composition of the molecules of which includes atoms of oxygen and some other substance.
Foundations - These are complex substances in which metal atoms are connected to one or more hydroxyl groups.
From the point of view of the theory of electrolytic dissociation, bases are complex substances, the dissociation of which in an aqueous solution produces metal cations (or NH4 +) and hydroxide - anions OH-.
acids - these are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms.
salt - These are complex substances whose molecules consist of metal atoms and acid residues. Salt is a product of partial or complete replacement of hydrogen atoms of an acid by a metal.
The first material that people learned to use for their needs is stone. However, later, when a person became aware of the properties of metals, the stone moved far back. It is these substances and their alloys that have become the most important and main material in the hands of people. Household items, tools of labor were made from them, premises were built. Therefore, in this article we will consider what metals are, the general characteristics, properties and use of which are so relevant to this day. Indeed, literally immediately after the Stone Age, a whole galaxy of metal ones followed: copper, bronze and iron.
Metals: general characteristics
What unites all representatives of these simple substances? Of course, this is the structure of their crystal lattice, types of chemical bonds and features of the electronic structure of the atom. After all, hence the characteristic physical properties that underlie the use of these materials by humans.
First of all, consider metals as chemical elements of the periodic system. In it, they are located quite freely, occupying 95 cells out of 115 known today. There are several features of their location in the general system:
- They form the main subgroups of groups I and II, as well as III, starting with aluminum.
- All side subgroups consist only of metals.
- They are located below the conditional diagonal from boron to astatine.
Based on such data, it is easy to see that non-metals are collected in the upper right part of the system, and the rest of the space belongs to the elements we are considering.
All of them have several features of the electronic structure of the atom:
The general characteristics of metals and non-metals makes it possible to identify patterns in their structure. So, the crystal lattice of the first is metallic, special. Its nodes contain several types of particles at once:
- ions;
- atoms;
- electrons.
A common cloud accumulates inside, called electron gas, which explains all the physical properties of these substances. The type of chemical bond in metals is of the same name with them.
Physical properties
There are a number of parameters that unite all metals. Their general characteristics in terms of physical properties are as follows.
The listed parameters are the general characteristics of metals, that is, everything that unites them into one large family. However, it should be understood that there are exceptions to every rule. Moreover, there are too many elements of this kind. Therefore, within the family itself there are also divisions into various groups, which we will consider below and for which we will indicate the characteristic features.
Chemical properties
From the point of view of the science of chemistry, all metals are reducing agents. And, very strong. The fewer electrons in the outer level and the larger the atomic radius, the stronger the metal according to the specified parameter.
As a result, metals are able to react with:
This is just a general overview of chemical properties. After all, for each group of elements they are purely individual.
alkaline earth metals
The general characteristics of alkaline earth metals are as follows:
Thus, alkaline earth metals are common elements of the s-family, exhibiting high chemical activity and are strong reducing agents and important participants in biological processes in the body.
alkali metals
The general characteristic begins with their name. They received it for the ability to dissolve in water, forming alkalis - caustic hydroxides. Reactions with water are very violent, sometimes flammable. These substances are not found in free form in nature, since their chemical activity is too high. They react with air, water vapor, non-metals, acids, oxides and salts, that is, with almost everything.
This is due to their electronic structure. At the outer level, there is only one electron, which they easily give away. These are the strongest reducing agents, which is why it took quite a long time to obtain them in their pure form. This was first done by Humphrey Davy already in the 18th century by electrolysis of sodium hydroxide. Now all representatives of this group are mined using this method.
The general characteristic of alkali metals is also that they constitute the first group of the main subgroup of the periodic system. All of them are important elements that form many valuable natural compounds used by man.
General characteristics of metals of d- and f-families
This group of elements includes all those whose oxidation state can vary. This means that, depending on the conditions, the metal can act as both an oxidizing agent and a reducing agent. Such elements have a great ability to enter into reactions. Among them are a large number of amphoteric substances.
The common name for all these atoms is transition elements. They received it for the fact that, in terms of their properties, they really stand, as it were, in the middle, between typical metals of the s-family and non-metals of the p-family.
The general characteristic of transition metals implies the designation of their similar properties. They are the following:
- a large number of electrons in the outer level;
- large atomic radius;
- several degrees of oxidation (from +3 to +7);
- are on the d- or f-sublevel;
- form 4-6 large periods of the system.
As simple substances, the metals of this group are very strong, ductile and malleable, therefore they are of great industrial importance.
Side subgroups of the periodic system
The general characteristics of the metals of the secondary subgroups completely coincide with those of the transitional ones. And this is not surprising, because, in fact, it is exactly the same thing. It's just that the side subgroups of the system are formed precisely by representatives of the d- and f-families, that is, transition metals. Therefore, we can say that these concepts are synonyms.
The most active and important of them are the first row of 10 representatives from scandium to zinc. All of them are of great industrial importance and are often used by man, especially for smelting.
Alloys
The general characteristics of metals and alloys makes it possible to understand where and how it is possible to use these substances. Such compounds have undergone great transformations in the last decades, because more and more new additives are being discovered and synthesized to improve their quality.
The most famous alloys today are:
- brass;
- duralumin;
- cast iron;
- steel;
- bronze;
- will win;
- nichrome and others.
What is an alloy? This is a mixture of metals obtained by smelting the latter in special furnace devices. This is done in order to obtain a product that is superior in properties to the pure substances that form it.
Comparison of properties of metals and non-metals
If we talk about general properties, then the characteristics of metals and non-metals will differ in one very significant point: for the latter, similar features cannot be distinguished, since they differ greatly in their manifested properties, both physical and chemical.
Therefore, it is impossible to create such a characteristic for non-metals. It is only possible to separately consider the representatives of each group and describe their properties.
CHEMICAL PROPERTIES OF METALS
According to their chemical properties, metals are divided into:1 ) Active (alkali and alkaline earth metals, Mg, Al, Zn, etc.)
2) Metalsaverage activity (Fe, Cr, Mn, etc.);
3 ) Inactive (Cu, Ag)
4) noble metals – Au, Pt, Pd, etc.
In reactions - only reducing agents. Metal atoms easily donate electrons from the outer (and some of them from the pre-outer) electron layer, turning into positive ions. Possible oxidation states Me Lower 0,+1,+2,+3 Higher +4,+5,+6,+7,+8
1. INTERACTION WITH NON-METALS
1. WITH HYDROGEN
Metals of groups IA and IIA react when heated, except for beryllium. Solid unstable substances hydrides are formed, other metals do not react.
2K + H₂ = 2KH (potassium hydride)
Ca + H₂ = CaH₂
2. WITH OXYGEN
All metals react except gold and platinum. The reaction with silver occurs at high temperatures, but silver(II) oxide is practically not formed, since it is thermally unstable. Alkali metals under normal conditions form oxides, peroxides, superoxides (lithium - oxide, sodium - peroxide, potassium, cesium, rubidium - superoxide
4Li + O2 = 2Li2O (oxide)
2Na + O2 = Na2O2 (peroxide)
K+O2=KO2 (superoxide)
The remaining metals of the main subgroups under normal conditions form oxides with an oxidation state equal to the group number 2Сa + O2 = 2СaO
2Сa+O2=2СaO
The metals of the secondary subgroups form oxides under normal conditions and when heated, oxides of various degrees of oxidation, and iron iron scale Fe3O4 (Fe⁺²O∙Fe2⁺³O3)
3Fe + 2O2 = Fe3O4
4Cu + O₂ = 2Cu₂⁺¹O (red) 2Cu + O₂ = 2Cu⁺²O (black);
2Zn + O₂ = ZnO 4Cr + 3O2 = 2Cr2O3
3. WITH HALOGENS
halides (fluorides, chlorides, bromides, iodides). Alkaline under normal conditions with F, Cl, Br ignite:
2Na + Cl2 = 2NaCl (chloride)
Alkaline earth and aluminum react under normal conditions:
FROMa+Cl2=FROMaCl2
2Al+3Cl2 = 2AlCl3
Metals of secondary subgroups at elevated temperatures
Cu + Cl₂ = Cu⁺²Cl₂ Zn + Cl₂ = ZnCl₂
2Fe + ЗС12 = 2Fe⁺³Cl3 iron chloride (+3) 2Cr + 3Br2 = 2Cr⁺³Br3
2Cu + I₂ = 2Cu⁺¹I(there is no copper iodide (+2)!)
4. INTERACTION WITH SULFUR
when heated even with alkali metals, with mercury under normal conditions. All metals react except gold and platinum
Withgray – sulfides: 2K + S = K2S 2Li+S = Li2S (sulfide)
FROMa+S=FROMaS(sulfide) 2Al+3S = Al2S3 Cu + S = Cu⁺²S (black)
Zn + S = ZnS 2Cr + 3S = Cr2⁺³S3 Fe + S = Fe⁺²S
5. INTERACTION WITH PHOSPHORUS AND NITROGEN
leaks when heated (exception: lithium with nitrogen under normal conditions) :
with phosphorus - phosphides: 3Ca + 2 P=Ca3P2,
With nitrogen - nitrides 6Li + N2 = 3Li2N (lithium nitride) (n.o.) 3Mg + N2 = Mg3N2 (magnesium nitride) 2Al + N2 = 2A1N 2Cr + N2 = 2CrN 3Fe + N2 = Fe₃⁺²N₂¯³
6. INTERACTION WITH CARBON AND SILICON
flows when heated:
Carbides are formed with carbon. Only the most active metals react with carbon. From alkali metals, carbides form lithium and sodium, potassium, rubidium, cesium do not interact with carbon:
2Li + 2C = Li2C2, Ca + 2C = CaC2
Metals - d-elements form compounds of non-stoichiometric composition such as solid solutions with carbon: WC, ZnC, TiC - are used to obtain superhard steels.
with silicon - silicides: 4Cs + Si = Cs4Si,
7. INTERACTION OF METALS WITH WATER:
Metals that reach hydrogen in the electrochemical series of voltages react with water. Alkali and alkaline earth metals react with water without heating, forming soluble hydroxides (alkalis) and hydrogen, aluminum (after the destruction of the oxide film - amalgation), magnesium when heated, form insoluble bases and hydrogen .
2Na + 2HOH = 2NaOH + H2
FROMa + 2HOH = Ca(OH)2 + H2
2Al + 6H2O = 2Al(OH)3 + ZH2
The remaining metals react with water only in a hot state, forming oxides (iron - iron scale)
Zn + H2O = ZnO + H2 3Fe + 4HOH = Fe3O4 + 4H2 2Cr + 3H₂O = Cr₂O₃ + 3H₂
8 WITH OXYGEN AND WATER
In air, iron and chromium easily oxidize in the presence of moisture (rusting)
4Fe + 3O2 + 6H2O = 4Fe(OH)3
4Cr + 3O2 + 6H2O = 4Cr(OH)3
9. INTERACTION OF METALS WITH OXIDES
Metals (Al, Mg, Ca), reduce non-metals or less active metals from their oxides at high temperature → non-metal or low-active metal and oxide (calciumthermy, magnesiumthermy, aluminothermy)
2Al + Cr2O3 = 2Cr + Al2O3 3Са + Cr₂O₃ = 3СаО + 2Cr (800 °C) 8Al + 3Fe3O4 = 4Al2O3 + 9Fe (thermite) 2Mg + CO2 = 2MgO + С Mg + N2O = MgO + N2 Zn + CO2 = ZnO + CO 2Cu + 2NO = 2CuO + N2 3Zn + SO2 = ZnS + 2ZnO
10. WITH OXIDES
Metals iron and chromium react with oxides, reducing the degree of oxidation
Cr + Cr2⁺³O3 = 3Cr⁺²O Fe+ Fe2⁺³O3 = 3Fe⁺²O
11. INTERACTION OF METALS WITH ALKALI
Only those metals interact with alkalis, the oxides and hydroxides of which have amphoteric properties ((Zn, Al, Cr (III), Fe (III), etc. MELT → metal salt + hydrogen.
2NaOH + Zn → Na2ZnO2 + H2 (sodium zincate)
2Al + 2(NaOH H2O) = 2NaAlO2 + 3H2
SOLUTION → complex metal salt + hydrogen.
2NaOH + Zn0 + 2H2O = Na2 + H2 (sodium tetrahydroxozincate) 2Al + 2NaOH + 6H2O = 2Na + 3H2
12. INTERACTION WITH ACIDS (EXCEPT HNO3 and H2SO4 (conc.)
Metals standing in the electrochemical series of voltages of metals to the left of hydrogen displace it from dilute acids → salt and hydrogen
Remember! Nitric acid never releases hydrogen when interacting with metals.
Mg + 2HC1 = MgCl2 + H2
Al + 2HC1 = Al⁺³Cl₃ + H2
13. REACTIONS WITH SALT
Active metals displace less active metals from salts. Recovery from solutions:
CuSO4 + Zn = ZnSO4 + Cu
FeSO4 + Cu =REACTIONSNO
Mg + CuCl2(pp) = MgCl2 +FROMu
Recovery of metals from melts of their salts
3Na+ AlCl₃ = 3NaCl + Al
TiCl2 + 2Mg = MgCl2 + Ti
Group B metals react with salts, lowering their oxidation state.
2Fe⁺³Cl3 + Fe = 3Fe⁺²Cl2
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.
To chemical - oxidizability, solubility and corrosion resistance.
To mechanical - strength, hardness, elasticity, viscosity, plasticity.
To technological - hardenability, fluidity, malleability, weldability, machinability.
1. Physical and chemical properties.
Color. Metals are opaque, i.e. do not let light through, and in this reflected light, each metal has its own special shade - color.
Of the technical metals, only copper (red) and its alloys are colored. The color of other metals ranges from steel gray to silvery 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.
According to the specific gravity, light metals and heavy metals are distinguished. Of the technical metals, magnesium is the lightest (specific gravity 1.74), the heaviest is tungsten (specific gravity 19.3). The specific gravity of metals depends to some extent on the way they are produced and processed.
Fusibility. The ability to change from a solid to a liquid state when heated is the most important property of metals. When heated, all metals pass from a solid state to a liquid state, and when a molten metal is cooled, from a liquid state to a solid state. The melting point of technical alloys has not one specific melting point, but a range of temperatures, sometimes quite significant.
Electrical conductivity. Conductivity is 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 the temperature decreases, it increases. When approaching absolute zero (-273 0 С), the electrical conductivity of metals ranges from +232 0 (tin) to 3370 0 (tungsten) indefinitely. Most increases (resistance drops to near 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 hotter place to a less heated place without visible movement of the 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 rises, the thermal conductivity decreases, and as the temperature decreases, it increases.
Heat capacity. Heat capacity is the amount of heat required to raise the temperature of a body by 10.
The specific heat capacity of a substance is the amount of heat in kilograms - calories, which must be reported to 1 kg of a substance in order to raise its temperature by 1 0.
The specific heat capacity of metals in comparison with other substances is small, which makes it relatively easy to heat them to high temperatures.
Expansion when heated. The ratio of the increment in the length of the 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 corrosion resistance (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 the action of external forces without collapsing.
Hardness. Hardness is the ability of a body to resist the penetration of another, more solid body into it.
Elasticity. The elasticity of a metal is its property to restore its shape after the termination 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 (shock) external forces. Viscosity is the opposite property of brittleness.
Plastic. Plasticity is the property of a metal to be deformed without destruction under the action of external forces and to retain a new shape after the cessation of the forces. Plasticity is a property that is the opposite of elasticity.
In table. 1 shows the properties of technical metals.
Table 1.
Properties of technical metals.
| metal name | Specific gravity (density) g \ cm 3 | Melting point 0 С | Brinell hardness | Tensile strength (tensile strength) kg \ mm 2 | Relative extension % | Relative contraction of the cross section % |
| Aluminum Tungsten Iron Cobalt Magnesium Manganese Copper Nickel Tin Lead Chromium Zinc | 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 Fragile 22 40-50 2-4 1,8 Fragile 11,3-15 | 40 - 21-55 3 15 Fragile 60 40 40 50 Fragile 5-20 | 85 - 68-55 - 20 Fragile 75 70 74 100 Fragile - |
3. Significance of the properties of metals.
Mechanical properties. The first requirement for any product is sufficient strength.
Metals have a higher strength compared to other materials, so the 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. For the manufacture of other cutting tools, tool steels and alloys are used.
For the manufacture of springs and springs, special steels and alloys with high elasticity are used.
Ductile metals are used in cases where parts are subjected to shock loading during operation.
The plasticity of metals makes it possible to process them by pressure (forging, rolling).
physical properties. In aircraft, auto and carriage building, the weight of parts is often the most important characteristic, so aluminum and especially magnesium alloys are indispensable here. Specific strength (the ratio of tensile strength to specific gravity) for some alloys, such as aluminum, is higher than for mild steel.
Fusibility used to obtain castings by pouring molten metal into molds. Low-melting metals (such as 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 printing matrices, in devices that serve 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 - for incandescent lamps, electric heaters.
Magnetic properties metals play a primary role in electrical engineering (dynamos, motors, transformers), for communication devices (telephone and telegraph sets) and are used in many other types of machines and devices.
Thermal conductivity metals makes it possible to produce their physical properties. Thermal conductivity is also used in the production of 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, radio tubes. The expansion of metals must be taken into account when constructing long structures such as bridges. It should also be borne in mind that two parts made of metals with different coefficients of expansion and fastened together can bend and even break when heated.
Chemical properties. Corrosion resistance is especially important for products operating in highly oxidizing environments (grate grates, parts of chemical machines and devices). To achieve high corrosion resistance, special stainless, acid-resistant and heat-resistant steels are produced, and protective coatings are also used.
Metals differ greatly in their chemical activity. The chemical activity of a metal can be roughly judged by its position in.
The most active metals are located at the beginning of this row (on the left), the most inactive - at the end (on the right).
Reactions with simple substances. Metals react with non-metals to form binary compounds. The reaction conditions, and sometimes their products, vary greatly for different metals.
So, for example, alkali metals actively react with oxygen (including in the composition of air) at room temperature with the formation of oxides and peroxides.
4Li + O 2 = 2Li 2 O;
2Na + O 2 \u003d Na 2 O 2
Intermediate activity metals react with oxygen when heated. In this case, oxides are formed:
2Mg + O 2 \u003d t 2MgO.
Inactive metals (for example, gold, platinum) do not react with oxygen and therefore practically do not change their brilliance in air.
Most metals, when heated with sulfur powder, form the corresponding sulfides:
Reactions with complex substances. Compounds of all classes react with metals - oxides (including water), acids, bases and salts.
Active metals react violently with water at room temperature:
2Li + 2H 2 O \u003d 2LiOH + H 2;
Ba + 2H 2 O \u003d Ba (OH) 2 + H 2.
The surface of metals such as magnesium and aluminium, for example, is protected by a dense film of the corresponding oxide. This prevents the reaction with water. However, if this film is removed or its integrity is violated, then these metals also actively react. For example, powdered magnesium reacts with hot water:
Mg + 2H 2 O \u003d 100 ° C Mg (OH) 2 + H 2.
At elevated temperatures, less active metals also react with water: Zn, Fe, Mil, etc. In this case, the corresponding oxides are formed. For example, when water vapor is passed over hot iron shavings, the following reaction occurs:
3Fe + 4H 2 O \u003d t Fe 3 O 4 + 4H 2.
Metals in the activity series up to hydrogen react with acids (except HNO 3) to form salts and hydrogen. Active metals (K, Na, Ca, Mg) react with acid solutions very violently (at high speed):
Ca + 2HCl \u003d CaCl 2 + H 2;
2Al + 3H 2 SO 4 \u003d Al 2 (SO 4) 3 + 3H 2.
Inactive metals are often practically insoluble in acids. This is due to the formation of an insoluble salt film on their surface. For example, lead, which is in the activity series up to hydrogen, practically does not dissolve in dilute sulfuric and hydrochloric acids due to the formation of a film of insoluble salts (PbSO 4 and PbCl 2) on its surface.
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