Post subject metals to chemistry. Metals: general characteristics of metals and alloys

Metals (from Latin metallum - mine, mine) are a group of elements in the form of simple substances with characteristic metallic properties, such as high thermal and electrical conductivity, positive temperature coefficient of resistance, high plasticity and metallic luster.

Of the 118 chemical elements discovered at the moment (of which not all are officially recognized), metals include:

6 elements in the group of alkali metals,
6 in the group of alkaline earth metals,
38 in the group of transition metals,
11 in the group of light metals,
7 in the group of semi-metals,
14 in the group lanthanides + lanthanum,
14 in the actinide group (physical properties have not been studied for all elements) + actinium,
outside of certain groups beryllium and magnesium.

Thus, 96 elements out of all discovered may belong to metals.

In astrophysics, the term "metal" can have a different meaning and mean all chemical elements heavier than helium

Characteristic properties of metals

Metallic luster (typical not only for metals: non-metals iodine and carbon in the form of graphite also have it)
Good electrical conductivity
Possibility of easy machining
High density (usually metals are heavier than non-metals)
High melting point (exceptions: mercury, gallium and alkali metals)
High thermal conductivity
In reactions, they are most often reducing agents.

Physical properties of metals

All metals (except for mercury and, conventionally, france) under normal conditions are in solid state, however, have different hardness. Below is the Mohs hardness of some metals.

Melting points pure metals range from −39 ° C (mercury) to 3410 ° C (tungsten). Most metals (excluding alkali) have a high melting point, but some "normal" metals such as tin and lead can be melted on a conventional electric or gas stove.

Depending on the density, metals are divided into light (density 0.53 ÷ 5 g / cm³) and heavy (5 ÷ 22.5 g / cm³). The lightest metal is lithium (density 0.53 g / cm³). It is impossible to name the heaviest metal at present, since the densities of osmium and iridium - the two heaviest metals - are almost equal (about 22.6 g / cm³ - exactly twice the density of lead), and it is extremely difficult to calculate their exact density: this requires completely purify metals, because any impurities reduce their density.

Most metals plastic, that is, the metal wire can be bent without breaking. This is due to the displacement of the layers of metal atoms without breaking the bond between them. The most ductile are gold, silver and copper. Foil with a thickness of 0.003 mm can be made of gold, which is used for gilding products. However, not all metals are ductile. Zinc or tin wire crunches when bent; manganese and bismuth do not bend at all during deformation, but break immediately. Plasticity also depends on the purity of the metal; so, very pure chromium is very ductile, but, contaminated with even minor impurities, it becomes brittle and harder. Some metals such as gold, silver, lead, aluminum, osmium can grow together, but this can take decades.

All metals are good conduct an electric current; this is due to the presence in their crystal lattices of mobile electrons moving under the action of an electric field. Silver, copper and aluminum have the highest electrical conductivity; for this reason, the last two metals are most commonly used as wire material. Sodium also has a very high electrical conductivity; in experimental equipment, attempts are known to use sodium current conductors in the form of thin-walled stainless steel tubes filled with sodium. Due to the low specific gravity of sodium, with equal resistance, sodium "wires" are much lighter than copper ones and even somewhat lighter than aluminum ones.

The high thermal conductivity of metals also depends on the mobility of free electrons. Therefore, the series of thermal conductivities is similar to the series of electrical conductivities, and the best conductor of heat, like electricity, is silver. Sodium also finds use as a good heat conductor; it is widely known, for example, the use of sodium in the valves of automobile engines to improve their cooling.

Colour most metals have approximately the same - light gray with a bluish tint. Gold, copper and cesium are respectively yellow, red and light yellow.

Chemical properties of metals

At the external electronic level, most metals have a small number of electrons (1-3), therefore, in most reactions they act as reducing agents (that is, they "give up" their electrons)

Reactions with simple substances

All metals react with oxygen, except for gold and platinum. The reaction with silver occurs at high temperatures, but silver (II) oxide is practically not formed, since it is thermally unstable. Depending on the metal, the output may contain oxides, peroxides, superoxides:

lithium oxide

sodium peroxide

potassium superoxide

To obtain oxide from peroxide, the peroxide is reduced with a metal:

With medium and low-activity metals, the reaction occurs when heated:

Only the most active metals react with nitrogen, only lithium interacts at room temperature, forming nitrides:

When heated:

All metals react with sulfur, except for gold and platinum:

Iron reacts with sulfur when heated to form sulfide:

Only the most active metals react with hydrogen, that is, metals of groups IA and IIA, except for Be. Reactions are carried out by heating, and hydrides are formed. In reactions, the metal acts as a reducing agent, the oxidation state of hydrogen is −1:

Only the most active metals react with carbon. In this case, acetylenides or methanides are formed. Acetylenides, when interacting with water, give acetylene, methanides - methane.

If in the periodic table of elements of D.I. Mendeleev we draw a diagonal from beryllium to astatine, then on the left below the diagonal there will be metal elements (these also include elements of side subgroups, highlighted in blue), and on the top right - nonmetal elements (highlighted yellow). Elements located near the diagonal - semimetals or metalloids (B, Si, Ge, Sb, etc.), have a dual character (highlighted in pink).

As you can see from the figure, the vast majority of elements are metals.

By their chemical nature, metals are chemical elements whose atoms donate electrons from an external or pre-external energy level, thus forming positively charged ions.

Almost all metals have relatively large radii and a small number of electrons (from 1 to 3) at the external energy level. Metals are characterized by low values of electronegativity and reducing properties.

The most typical metals are located at the beginning of the periods (starting from the second), further from left to right, the metallic properties weaken. In the group from top to bottom, metallic properties are enhanced, because the radius of the atoms increases (due to an increase in the number of energy levels). This leads to a decrease in the electronegativity (the ability to attract electrons) of elements and an increase in the reducing properties (the ability to donate electrons to other atoms in chemical reactions).

Typical metals are s-elements (elements of the IA-group from Li to Fr. elements of the PA-group from Mg to Ra). The general electronic formula of their atoms is ns 1-2. They are characterized by the oxidation states + I and + II, respectively.

A small number of electrons (1-2) at the outer energy level of typical metal atoms suggests a slight loss of these electrons and the manifestation of strong reducing properties, which reflect low values of electronegativity. Hence, the chemical properties and methods of obtaining typical metals are limited.

A characteristic feature of typical metals is the tendency of their atoms to form cations and ionic chemical bonds with nonmetal atoms. Compounds of typical metals with non-metals are ionic crystals "metal cation anion of non-metal", for example K + Br -, Ca 2+ O 2-. Cations of typical metals are also included in compounds with complex anions - hydroxides and salts, for example, Mg 2+ (OH -) 2, (Li +) 2CO 3 2-.

Metals of A-groups forming a diagonal of amphotericity in Periodic table Be-Al-Ge-Sb-Po, as well as adjacent metals (Ga, In, Tl, Sn, Pb, Bi) do not exhibit typically metallic properties. The general electronic formula of their atoms ns 2 np 0-4 assumes a greater variety of oxidation states, a greater ability to retain its own electrons, a gradual decrease in their reductive ability and the appearance of oxidative capacity, especially in high degrees oxidation (typical examples are compounds Tl III, Pb IV, Bi v). A similar chemical behavior is typical for most (d-elements, i.e., elements of B-groups of the Periodic Table ( typical examples- amphoteric elements Cr and Zn).

This manifestation of the duality (amphotericity) of properties, both metallic (basic) and non-metallic, is due to the nature of the chemical bond. In the solid state, compounds of atypical metals with non-metals contain predominantly covalent bonds (but less strong than bonds between non-metals). In solution, these bonds are easily broken, and the compounds dissociate into ions (in whole or in part). For example, gallium metal consists of Ga 2 molecules, in the solid state aluminum and mercury (II) chlorides AlCl 3 and HgCl 2 contain strongly covalent bonds, but in a solution of AlCl 3 it dissociates almost completely, and HgCl 2 - to a very small extent (and then on ions НgСl + and Сl -).

General physical properties of metals

Due to the presence of free electrons ("electron gas") in the crystal lattice, all metals exhibit the following characteristic general properties:

1) Plastic- the ability to easily change shape, be drawn into wire, rolled into thin sheets.

2) Metallic luster and opacity. This is due to the interaction of free electrons with light incident on the metal.

3) Electrical conductivity... It is explained by the directional movement of free electrons from the negative to the positive pole under the influence of a small potential difference. When heated, the electrical conductivity decreases, because with an increase in temperature, the vibrations of atoms and ions in the nodes of the crystal lattice intensify, which complicates the directional movement of the "electron gas".

4) Thermal conductivity. It is caused by the high mobility of free electrons, due to which there is a rapid equalization of temperature over the mass of the metal. Bismuth and mercury have the highest thermal conductivity.

5) Hardness. The hardest is chrome (cuts glass); the softest - alkali metals - potassium, sodium, rubidium and cesium - are cut with a knife.

6) Density. It is the less, the less atomic mass metal and larger radius of the atom. The lightest is lithium (ρ = 0.53 g / cm3); the heaviest is osmium (ρ = 22.6 g / cm3). Metals with a density of less than 5 g / cm3 are considered "light metals".

7) Melting and boiling points. The lowest-melting metal is mercury (melting point = -39 ° C), the most refractory metal is tungsten (melting point = 3390 ° C). Metals with t ° pl. above 1000 ° C are considered refractory, below - low melting.

General chemical properties of metals

Strong reducing agents: Me 0 - nē → Me n +

A number of stresses characterize the comparative activity of metals in redox reactions in aqueous solutions.

I. Reactions of metals with non-metals

1) With oxygen:
2Mg + O 2 → 2MgO

2) With gray:
Hg + S → HgS

3) With halogens:
Ni + Cl 2 - t ° → NiCl 2

4) With nitrogen:
3Ca + N 2 - t ° → Ca 3 N 2

5) With phosphorus:
3Ca + 2P - t ° → Ca 3 P 2

6) With hydrogen (only alkali and alkaline earth metals react):
2Li + H 2 → 2LiH

Ca + H 2 → CaH 2

II. Reactions of metals with acids

1) Metals in the electrochemical series of voltages up to H reduce non-oxidizing acids to hydrogen:

Mg + 2HCl → MgCl 2 + H 2

2Al + 6HCl → 2AlCl 3 + 3H 2

6Na + 2H 3 PO 4 → 2Na 3 PO 4 + 3H 2

2) With oxidizing acids:

With the interaction of nitric acid of any concentration and concentrated sulfuric with metals hydrogen is never released!

Zn + 2H 2 SO 4 (К) → ZnSO 4 + SO 2 + 2H 2 O

4Zn + 5H 2 SO 4 (К) → 4ZnSO 4 + H 2 S + 4H 2 O

3Zn + 4H 2 SO 4 (К) → 3ZnSO 4 + S + 4H 2 O

2H 2 SO 4 (k) + Cu → Cu SO 4 + SO 2 + 2H 2 O

10HNO 3 + 4Mg → 4Mg (NO 3) 2 + NH 4 NO 3 + 3H 2 O

4HNO 3 (c) + Cu → Cu (NO 3) 2 + 2NO 2 + 2H 2 O

III. Interaction of metals with water

1) Active (alkali and alkaline earth metals) form a soluble base (alkali) and hydrogen:

2Na + 2H 2 O → 2NaOH + H 2

Ca + 2H 2 O → Ca (OH) 2 + H 2

2) Metals of medium activity are oxidized by water when heated to oxide:

Zn + H 2 O - t ° → ZnO + H 2

3) Inactive (Au, Ag, Pt) - do not react.

IV. Displacement of less active metals from solutions of their salts by more active metals:

Cu + HgCl 2 → Hg + CuCl 2

Fe + CuSO 4 → Cu + FeSO 4

In industry, not pure metals are often used, but their mixtures - alloys, in which the beneficial properties of one metal are complemented by the beneficial properties of another. So, copper has a low hardness and is of little use for the manufacture of machine parts, while copper-zinc alloys ( brass) are already quite solid and are widely used in mechanical engineering. Aluminum has high ductility and sufficient lightness (low density), but too soft. On its basis, an alloy with magnesium, copper and manganese is prepared - duralumin (duralumin), which, without losing useful properties aluminum, acquires high hardness and becomes suitable in aircraft construction. Alloys of iron with carbon (and additives of other metals) are widely known cast iron and steel.

Free metals are reducing agents. but reactivity some metals are small due to the fact that they are covered surface oxide film, in varying degrees, resistant to the action of chemicals such as water, solutions of acids and alkalis.

For example, lead is always covered with an oxide film, for its transition into solution requires not only the action of a reagent (for example, dilute nitric acid), but also heating. The oxide film on aluminum prevents it from reacting with water, but is destroyed by acids and alkalis. Loose oxide film (rust), formed on the surface of iron in humid air, does not interfere with further oxidation of iron.

Under the influence concentrated acids on metals are formed steady oxide film. This phenomenon is called passivation... So, in concentrated sulfuric acid metals such as Be, Bi, Co, Fe, Mg and Nb are passivated (and then do not react with acid), and metals A1, Be, Bi, Co, Cr, Fe, Nb, Ni, Pb in concentrated nitric acid , Th and U.

When interacting with oxidants in acidic solutions, most metals are converted into cations, the charge of which is determined by the stable oxidation state of a given element in compounds (Na +, Ca 2+, A1 3+, Fe 2+ and Fe 3+)

The reducing activity of metals in an acidic solution is transmitted by a series of voltages. Most of the metals are converted into a solution with hydrochloric and dilute sulfuric acids, but Cu, Ag and Hg - only sulfuric (concentrated) and nitric acids, and Pt and Au - "aqua regia".

Corrosion of metals

An undesirable chemical property of metals is their, i.e., active destruction (oxidation) upon contact with water and under the influence of oxygen dissolved in it (oxygen corrosion). For example, corrosion of iron products in water is widely known, as a result of which rust is formed and the products are crumbled into powder.

Corrosion of metals occurs in water also due to the presence of dissolved gases CO 2 and SO 2; an acidic environment is created, and H + cations are displaced by active metals in the form of hydrogen H 2 ( hydrogen corrosion).

The place of contact of two dissimilar metals ( contact corrosion). A galvanic pair arises between one metal, such as Fe, and another metal, such as Sn or Cu, placed in water. The flow of electrons goes from the more active metal, which is to the left in the series of voltages (Fe), to the less active metal (Sn, Cu), and the more active metal is destroyed (corroded).

It is because of this that the tinned surface of cans (tin-coated iron) rusts when stored in a humid atmosphere and carelessly handling them (iron quickly collapses after the appearance of at least a small scratch that allows iron to come into contact with moisture). On the contrary, the galvanized surface of an iron bucket does not rust for a long time, because even in the presence of scratches, it is not iron that corrodes, but zinc (a more active metal than iron).

Corrosion resistance for a given metal is enhanced when it is coated with a more active metal or when they are fused; thus, plating iron with chromium or making an iron-chromium alloy eliminates the corrosion of iron. Chromium-plated iron and steel containing chromium ( stainless steel), have high corrosion resistance.

electrometallurgy, i.e., obtaining metals by electrolysis of melts (for the most active metals) or salt solutions;

pyrometallurgy, i.e., the reduction of metals from ores at high temperatures (for example, the production of iron in domain process);

hydrometallurgy, i.e., the separation of metals from solutions of their salts with more active metals (for example, obtaining copper from a CuSO 4 solution by the action of zinc, iron or aluminum).

Native metals are sometimes found in nature (typical examples are Ag, Au, Pt, Hg), but more often metals are in the form of compounds ( metal ores). By prevalence in earth crust metals are different: from the most common - Al, Na, Ca, Fe, Mg, K, Ti) to the rarest ones - Bi, In, Ag, Au, Pt, Re.

Metals are chemical elements that have the property of high electrical conductivity. Metal atoms can donate a certain amount of their electrons located at the external or pre-external energy levels, while creating ions (positively charged particles).

As of today, 114 chemical elements are known. Of these, 96 are metals. Without metals, life on Earth would be impossible, since they in their pure form or their compounds are the most important component of the organic and mineral environment, actively participating in the vital processes of all living organisms.

Molecules of all metals, with a few exceptions, have large radii and a small number of electrons located at the external energy level. The number of such electrons can be from one to three. The exceptions are lead, the number of electrons at the outer level of which is 4; bismuth with 5 electrons; polonium with 6 electrons; germanium, antimony and tin.

Also characteristic feature All elements of this group are small values of electronegativity and the possibility of recovery.

Periodic table divides all elements into metals and non-metals very conditionally. To find out whether a substance belongs to metals, you need to draw the astatine-boron diagonal. On the right, in the main subgroups, non-metals will be located, and on the left - metals (with the exception of inert gases). All elements that are in close proximity to this line are called metalloids, which means that they have both metallic and non-metallic properties. Such elements are boron, silicon, arsenic, germanium, tellurium, antimony and polonium.

Metals are also divided into transitional and non-transitional. This classification is based on the location of the element in the periodicity table. Transition metals are classified as secondary subgroups, and intransitive metals are referred to as the main ones. Metal molecules of the main subgroups have s and p sublevels filled with electrons; and molecules of side subgroups are d- and f-levels.

According to their chemical properties, all metals are distinguished by an easy return of valence electrons, forming positive ions. Therefore, all metals in a free state belong to reducing agents.

This restorative ability is different for each element, and it is determined by the location of the metal in the electrochemical voltage series. This series gives a characteristic of the chemical activity of metals that they exhibit when redox reactions occur in an aqueous medium, and has the following form:

Li K Rb Cs Ca Na Mg Al Mn Zn Cr Cr Fe Ni Sn Pb Cu Hg Ag Pt Ag Pt Au

The very first in the row are metals with maximum reducing properties and minimum oxidizing capabilities. In descending order, the reducing properties of the elements decrease and the oxidizing properties increase.

Alkali metals can be easily oxidized by oxygen in the air. They also react with simple substances, while copper and iron will only react when heated, and platinum and gold will not oxidize at all. Some metals create an oxide film on the surface, and there will be no further oxidation process.

Look around for a second ... How many metal things can you see? Usually, when we think of metals, we think of substances that are shiny and durable. However, they are also found in our food and in our bodies. Let's get to know complete list metals, known to science, find out their basic properties and find out why they are so special.

Elements that easily lose electrons that are shiny (reflective), malleable (can be molded into other shapes), and are considered good conductors of heat and electricity are called metals. They are critical to our way of life, as they are not only part of structures and technologies, but are also essential for the production of almost all items. There is even metal in human body... Looking at the label of a multivitamin formula, you will see dozens of listed compounds.

You may not have known that elements such as sodium, calcium, magnesium and zinc are essential for life, and if they are absent from our bodies, our health could be in serious danger. For example, calcium is essential for healthy bones, and magnesium is essential for metabolism. Zinc enhances the function of the immune system, and iron helps blood cells carry oxygen throughout the body. However, the metals in our bodies differ from the metal in a spoon or steel bridge in that they have lost electrons. They are called cations.

Metals also have antibiotic properties, which is why railings and handles in public places are often made from these elements. Many instruments are known to be made of silver to prevent bacteria from growing. Artificial joints are made from titanium alloys, which simultaneously prevent infection and make the recipients stronger.

Metals on the periodic table

All elements in Dmitry Mendeleev are divided into two large groups: metals and non-metals. The first is the most numerous. Most of the elements are metals (blue). Non-metals in the table are shown against a yellow background. There is also a group of elements that are classified as metalloids (red). All metals are grouped on the left side of the table. Note that hydrogen is grouped with metals in the upper left corner. Despite this, it is considered non-metallic. However, some scientists theorize that there may be metallic hydrogen in the core of the planet Jupiter.

Metal bonding

Many of the wonderful and beneficial qualities of an element have to do with how its atoms connect to one another. In this case, certain connections arise. The metallic interaction of atoms leads to the creation of metallic structures. Any sample of this item in Everyday life, from car to coins in your pocket, includes a metal connection.

During this process, the metal atoms share their outer electrons evenly with each other. Electrons flowing between positively charged ions transfer heat and electricity easily, making these elements such good conductors of heat and electricity. Copper wires are used for power supply.

Metal reactions

Reactivity refers to the tendency of an element to react with chemicals in its environment. It can be different. Certain metals, such as potassium and sodium (in columns 1 and 2 of the periodic table), react readily with many different chemicals and are rarely found in their pure, elemental form. Both usually exist only in compounds (associated with one or more other elements) or as ions (a charged version of their elemental form).

On the other hand, there are other metals, they are also called jewelry. Gold, silver and platinum are not very reactive and are usually found in their pure form. lose electrons more easily than non-metals, but not as easily as reactive metals such as sodium. Platinum is relatively unreactive and highly resistant to reactions with oxygen.

Element properties

When you studied the alphabet in primary school, you've found that all letters have their own unique set of properties. For example, some had straight lines, some had curves, and others had both types of lines. The same can be said for elements. Each of them has a unique set of physical and chemical properties. Physical properties are qualities inherent in certain substances. Shiny or not, how well it conducts heat and electricity, at what temperature it melts, how much density it has.

Chemical properties include those qualities that are observed when reacting to exposure to oxygen if they burn (how difficult it will be for them to keep their electrons during a chemical reaction). Different elements can share properties in common. For example, iron and copper are both elements that conduct electricity. However, they do not have the same properties. For example, when iron is exposed to humid air, it rusts, but when copper is exposed to the same conditions, it takes on a specific green coating. This is why the Statue of Liberty is green, not rusty. It's made of copper, not iron.)

Organization of elements: metals and non-metals

The fact that the elements have some common and unique properties, allows you to sort them into a nice, tidy chart called the periodic table. It organizes the elements based on their atomic number and properties. So, in the periodic table, we find elements grouped together that have common properties. Iron and copper are close to each other, both are metals. Iron is denoted by "Fe" and copper is denoted by "Cu".

Most of the elements in the periodic table - and they tend to be found on the left side of the table. They are grouped together because they have specific physical and chemical properties. For example, metals are dense, shiny, they are good conductors of heat and electricity, and they easily lose electrons in chemical reactions. In contrast, non-metals have opposite properties. They are not dense, do not conduct heat and electricity, and tend to receive electrons, not give them away. When we look at the periodic table, we can see that most of the non-metals are grouped to the right. These are elements such as helium, carbon, nitrogen and oxygen.

What are Heavy Metals?

The list of metals is quite numerous. Some of them can accumulate in the body and do not harm it, such as natural strontium (formula Sr), which is an analogue of calcium, as it is deposited productively in bone tissue. Which ones are called heavy and why? Consider four examples: lead, copper, mercury, and arsenic.

Where are these elements located and how do they affect the environment and human health? Heavy metals are naturally occurring metallic compounds that have a very high density compared to other metals - at least five times the density of water. They are toxic to humans. Even small doses can have serious consequences.

Lead. It is a heavy metal that is toxic to humans, especially children. Poisoning with this substance can lead to neurological problems. Although it was once very attractive due to its flexibility, high density and ability to absorb harmful radiation, lead has been phased out in many ways. This soft, silvery metal found on Earth is dangerous to humans and builds up in the body over time. The worst thing is that you can't get rid of it. It sits there, accumulates and gradually poisons the body. Lead is toxic to the nervous system and can cause serious brain damage in children. It was widely used in the 1800s to create makeup and was used as one of the ingredients in hair dye up until 1978. Today, lead is used mainly in large batteries as shields for x-rays or isolation for radioactive material.
Copper. It is a reddish brown heavy metal that has many uses. Copper is still one of the best conductors for electricity and heat, and many electrical wires are made of this metal and covered with plastic. Coins, mostly small change, are also made from this element of the periodic table. Acute copper poisoning is rare, but like lead, it can build up in tissues, eventually leading to toxicity. People who are exposed to large amounts of copper or copper dust are also at risk.
Mercury. This metal is toxic in any form and can even be absorbed by the skin. Its uniqueness lies in the fact that it is liquid at room temperature, it is sometimes called "fast silver". It can be seen in a thermometer because as a liquid it absorbs heat, changing volume with even the slightest difference in temperature. This allows the mercury to rise or fall in the glass tube. Because this substance is a potent neurotoxin, many companies are switching to dyed red.
Arsenic. From the time of the Roman Empire until the Victorian era, arsenic was considered the "king of poisons" as well as the "poison of kings". The story is riddled with countless examples of both royalty and common people committing murder for personal gain using arsenic compounds that had no smell, color or taste. Despite all negative influences, this metalloid also has its own uses, even in medicine. For example, arsenic trioxide is a very effective drug used to treat people with acute promyelocytic leukemia.

What is Precious Metal?

Precious metal is a metal that can be rare or difficult to mine, and is also economically very valuable. What is the list of precious metals? There are three of them:

Platinum. Despite its infusibility, it is used in jewelry, electronics, automobiles, chemical processes and even in medicine.
Gold. This precious metal is used to make jewelry and gold coins. However, it has many other uses. It is used in medicine, manufacturing and laboratory equipment.
Silver. This silver-white noble metal is very malleable. in its pure form it is quite heavy, it is lighter than lead, but heavier than copper.

Metals: types and properties

Most of the elements can be viewed as metals. They are grouped in the middle on the left side of the table. Metals are alkali, alkaline earth, transition, lanthanides and actinides.

They all have several properties in common, these are:

solid at room temperature (excluding mercury);
usually shiny;
with a high melting point;
good conductor of heat and electricity;
with a low ability to ionize;
with low electronegativity;
pliable (able to take a given shape);
plastic (can be pulled into a wire);
high density;
a substance that loses electrons in reactions.

List of metals known to science

lithium;
beryllium;
sodium;
magnesium;
aluminum;
potassium;
calcium;
scandium;
titanium;
vanadium;
chromium;
manganese;
iron;
cobalt;
nickel;
copper;
zinc;
gallium;
rubidium;
strontium;
yttrium;
zirconium;
niobium;
molybdenum;
technetium;
ruthenium;
rhodium;
palladium;
silver;
cadmium;
indium;
copernicium;
cesium;
barium;
tin;
iron;
bismuth;
lead;
Mercury;
tungsten;
gold;
platinum;
osmium;
hafnium;
germanium;
iridium;
niobium;
rhenium;
antimony;
thallium;
tantalum;
francium;
livermore.

In total, about 105 chemical elements are known, most of which are metals. The latter are a very common element in nature, which is found both in pure form and in all kinds of compounds.

Metals lie in the bowels of the earth, they can be found in various bodies of water, in the bodies of animals and humans, in plants and even in the atmosphere. In the periodic table, they are located from lithium (metal with the formula Li) and ending with livermorium (Lv). She continues to replenish the table with new elements, and mainly metals.

General information about metals

You know that most of the chemical elements are classified as metals - 92 out of 114 known elements.

Metals are chemical elements, the atoms of which donate electrons of the outer (and some of the pre-outer) electron layer, turning into positive ions.

This property of metal atoms, as you know, is determined by the fact that they have relatively large radii and a small number of electrons (mainly from 1 to 3) on the outer layer.

The only exceptions are 6 metals: germanium, tin, lead atoms on the outer layer have 4 electrons, antimony and bismuth atoms -5, polonium atoms - 6.

Metal atoms are characterized by small values of electronegativity (from 0.7 to 1.9) and exclusively reductive properties, that is, the ability to donate electrons.

You already know that in the Periodic Table of Chemical Alements of D.I. Mendeleev, metals are below the boron-astatine diagonal, and I am also above it in side subgroups. In the periods and clay subgroups, the regularities known to you in the change of the metallic, and therefore the reducing properties of the atoms of the elements, operate.

Chemical elements located near the boron-statat diagonal have dual properties: in some of their compounds they behave like metals, in others they exhibit the properties of a non-metal.

In side subgroups, the reducing properties of metals with an increase in the serial number most often decrease. Compare the activity of the metals of the I group of the secondary subgroup known to you: Cu, Ag, Au; II group of a side subgroup - and you will see for yourself.

This can be explained by the fact that the strength of the bond of valence electrons with the nucleus of the atoms of these metals in to a greater extent the magnitude of the nuclear charge affects, not the radius of the atom. The magnitude of the nuclear charge increases significantly, the attraction of electrons to the nucleus increases. At the same time, the radius of the atom increases, but not as significantly as for metals of the main subgroups.

Simple substances formed by chemical elements - metals, n complex metal-containing substances play crucial role in the mineral and organic "life" of the Earth. It is enough to remember that the atoms (nones) of the metal elements are part of compounds that determine the metabolism in the human body, animals, plants. For example, 76 elements have been found in human blood, and only 14 of them are not metals. In the human body, some metal elements (calcium, potassium, sodium, magnesium) are present in a large number, that is, they are macronutrients. And metals such as chromium, manganese, iron, cobalt, copper, zinc, molybdenum are present in small quantities, that is, these are trace elements. If a person weighs 70 kg, then his body contains (in grams): calcium - 1700, potassium - 250, sodium - 70, magnesium - 42, iron - 5. zinc - 3. All metals are extremely important, health problems arise and with their lack, and with an excess.

For example, sodium ions regulate the water content in the body, the transmission of nerve impulses. Its deficiency leads to headaches, weakness, poor memory, loss of appetite, and excess leads to increased blood pressure, hypertension, heart disease. Nutritionists recommend that you consume no more than 5 grams (1 teaspoon) of sodium chloride (NaCl) per adult per day. The effect of metals on the state of animals and plants can be found in Table 16.

Simple substances - metals

The development of the production of metals (simple substances) and alloys was associated with the emergence of civilization ("Bronze Age", Iron Age).

The scientific and technological revolution that began about 100 years ago, which affected both industry and the social sphere, is also closely related to the production of metals. On the basis of tungsten, molybdenum, titanium and other metals, they began to create corrosion-resistant, superhard, refractory alloys, the use of which greatly expanded the possibilities of mechanical engineering. In nuclear and space technology, tungsten and rhenium alloys are used to make parts that operate at temperatures up to 3000 ºС. in medicine, surgical instruments are used from tantalum and platinum alloys, unique ceramics based on titanium and zirconium oxides.

And, of course, we must not forget that most alloys use the well-known metal iron (Fig. 37), and the basis of many light alloys is made up of relatively "young" metals: aluminum and magnesium.

Supernovae have become composite materials, representing, for example, a polymer or ceramics, which inside (like concrete with iron rods) are reinforced with metal fibers, which can be from tungsten, molybdenum, steel and other metals and alloys - it all depends on the goal that is necessary to achieve it material properties.

You already have an idea of the nature of the chemical bond in metal crystals. Let us recall, using the example of one of them - sodium, how it is formed.
Figure 38 shows a diagram of the crystal lattice of sodium metal. In it, each sodium atom is surrounded by eight neighboring ones. Sodium atoms, like all metals, have many free valence orbitals and few valence electrons.

The only valence electron of the sodium atom Zs 1 can occupy any of the nine free orbitals, because they are not very different in energy level. When atoms approach each other, when a crystal lattice is formed, the valence orbitals of neighboring atoms overlap, due to which electrons freely move from one orbital to another, making a bond between all atoms of the metal crystal.

This type of chemical bond is called a metallic bond. A metal bond is formed by elements whose atoms on the outer layer have few valence electrons in comparison with a large number of outer energetically close orbitals. Their valence electrons are weakly held in the atom. The electrons that make the connection are socialized and move throughout the entire crystal lattice of the neutral metal as a whole.

Substances with a metal bond are inherent in metallic crystal lattices, which are usually depicted schematically by teak, as shown in the figure, the nodes are cations and metal atoms. The socialized electrons electrostatically attract metal cations located at the edge of their crystal lattice, ensuring its stability and strength (the socialized electrons are depicted as black small balls).

A metallic bond is a bond in metals and alloys between metal atoms-ions located in the crystal lattice ullah, which is carried out by shared valence electrons.

Some metals crystallize in two or more crystalline forms. This property of substances - to exist in several crystalline modifications - is called polymorphism. Polymorphism for simple substances is known to you as allotropy.

Tin has two crystalline modifications:
alpha is stable below 13.2 ºС with density р - 5.74 g / cm3. This is gray tin. It has crystal lattice type almaav (atomic):
betta is stable above 13.2 ºС with a density p - 6.55 g / cm3. This is white tin.

White tin is a very soft metal. When cooled below 13.2 ºС, it disintegrates into a gray powder, since at the transition | 1 "n, its specific volume significantly increases. This phenomenon is called the tin plague. Of course, the special type of chemical bond and the type of crystal lattice of metals should determine and explain their physical properties.

What are they? These are metallic luster, plasticity, high electrical conductivity and thermal conductivity, an increase in electrical resistance with increasing temperature, as well as such practically significant properties as density, melting and boiling points, hardness, and magnetic properties.

Let's try to explain the reasons that determine the basic physical properties of metals. Why are metals ductile?

Mechanical action on a crystal with a metal crystal lattice causes a displacement of the layers of ion-atoms relative to each other, since electrons move throughout the crystal, bond breakage does not occur, therefore, high plasticity is characteristic of metals.

A similar effect on a solid with connected bonds (atomic crystal lattice) leads to rupture covalent bonds... The breaking of bonds in the ionic lattice leads to mutual repulsion of like charged ions (Fig. 40). Therefore, substances with atomic and ionic crystal lattices are fragile.

The most plastic metals are Au, Af, Cu, Sn, Pb, Zn. They are easily drawn into wire, amenable to forging, pressing, rolling into sheets - For example, gold foil with a thickness of 0.008 nm can be made from gold, and a thread 1 km long can be drawn from 0.5 g of this metal.

Even mercury, which, as you know, is liquid at room temperature, becomes malleable at low temperatures, like lead. Only Bi and Mn do not have plasticity, they are brittle.

Why do metals have a characteristic luster and are also opaque?

The electrons that fill the interatomic space reflect light rays (rather than transmit them, like glass), with most metals equally scattering all rays of the visible part of the spectrum. Therefore, they have a silvery white or grey colour... Strontium, gold and copper absorb to a greater extent short waves (close to purple) and reflect long waves of the light spectrum, therefore they have light yellow, yellow and copper colors, respectively.

Although in practice, you know, metal does not always seem like a light body to us. First, its surface can oxidize and lose its luster. Therefore, native copper looks like a greenish stone. And secondly, even pure metal may not shine. Very thin sheets of silver and gold have a completely unexpected appearance - they have a bluish-green color. And fine metal powders appear dark gray, even black.

Silver, aluminum, palladium have the highest reflectivity. They are used in the manufacture of mirrors, including spotlights.

Why do metals have high electrical and thermal conductivity?

Chaotically moving electrons in a metal under the influence of an applied electric voltage acquire directional motion, that is, conduct an electric current. With an increase in the temperature of the meta-aphid, the amplitudes of the vibrations of atoms and ions located in the nodes of the crystal lattice increase. This makes it difficult for electrons to move, the electrical conductivity of the metal drops. At low temperatures, the vibrational motion, on the contrary, is greatly reduced and the electrical conductivity of metals increases sharply. Near absolute zero, there is practically no resistance in metals, and in most metals, superconductivity appears.

It should be noted that non-metals with electrical conductivity (for example, graphite), on the contrary, do not conduct electric current at low temperatures due to the absence of free electrons. And only with an increase in temperature and the destruction of some covalent bonds, their electrical conductivity begins to increase.

Silver, copper, and also gold, aluminum have the highest electrical conductivity, the lowest - manganese, lead, mercury.

Most often, with the same regularity as electrical conductivity, the thermal conductivity of metals changes.

They are due to the high mobility of free electrons, which, colliding with vibrating ions and atoms, exchange energy with them. Therefore, the temperature is equalized throughout the piece of metal.

The mechanical strength, density, and melting point of metals are very different. Moreover, with an increase in the number of eekgrons. binding ion-atoms, and with a decrease in the interatomic distance in crystals, the indices of these properties increase.

So, alkali metals, whose atoms have one valence electron, are soft (cut with a knife), with a low density (lithium is the lightest metal with p - 0.53 g / cm3) and melt at low temperatures (for example, the melting point of cesium is 29 "C) The only metal that is liquid under normal conditions is mercury, which has a melting point of 38.9 "C.

Calcium, which has two electrons on the outer energy level of atoms, is much harder and melts at a higher temperature (842 ° C).

Even more arched is the crystal lattice formed by scandium atoms, which have three valence electrons.

But the most daunting crystal lattices, high densities and melting points are observed in metals of the side subgroups V, VI, VII, MP groups. This is because. that for metals of side subgroups with unsaved valence electrons on the d-sublevel, the formation of very strong covalent bonds between atoms, in addition to the metal one, carried out by the electrons of the outer layer from the s-orbitals, is characteristic.

Remember that the heaviest metal is osmium (a component of superhard and wear-resistant alloys), the most refractory metal is tungsten (used to make lamp filaments), the hardest metal is Cr Cr (scratches glass). They are part of the materials from which metal-cutting tools, brake pads of heavy machines, etc. are made.

Metals differ in relation to magnetic fields... But for this feature, they are divided into three groups:

Ferromagnetic Capable of being magnetized under the influence of even weak magnetic fields (iron - alpha form, cobalt, nickel, gadolinium);

Paramagnetic show a weak ability to magnetize (aluminum, chromium, titanium, almost all lanthanides);

Diamagnetic ones are not attracted to the magnet, even slightly repelled from it (tin, stranded, bismuth).

Recall that when considering the electronic structure of metals, we subdivided metals into metals of the main subgroups (k- and p-elements) and metals of secondary subgroups.

In technology, it is customary to classify metals according to various physical properties:

a) density - lungs (p< 5 г/см3) и тяжелые (все остальные);
b) melting temperature - fusible and refractory.

Classification of metals by chemical properties

Metals with low chemical activity are called noble metals (silver, gold, platinum and its analogue - osmium, iridium, ruthenium, palladium, rhodium).
Alkali (metals of group I of the main subgroup), alkaline earth (calcium, strontium, barium, radium), as well as rare earth metals (scandium, yttrium, lanthanum and lanthanides, actinium and actinides) are distinguished by the proximity of chemical properties.

General chemical properties of metals

Metal atoms relatively easily donate valence electrons and pass into positively charged nones, that is, they are oxidized. This, as you know, is the main common property of both atoms and simple substances, metals.

Metals in chemical reactions are always a reducing agent. The reducing ability of atoms of simple substances - metals, formed by chemical elements of one period or one main subgroup of DI Mendeleev's Periodic Table, changes naturally.

The reducing activity of a metal in chemical reactions that take place in aqueous solutions reflects its position in the electrochemical series of metal voltages.

1. The more to the left the metal is in this row, the more powerful a reducing agent it is.
2. Each metal is capable of displacing (reducing) and saline in solution those metals that are in the series of voltages after it (to the right).
3. Metals located in the series of voltages to the left of hydrogen are capable of displacing it from acids in solution.
4. Metals, which are the strongest reducing agents (alkaline and alkaline earth), in any aqueous solution interact primarily with water.

The reducing activity of a metal, determined by the electrochemical series, does not always correspond to its position in the Periodic Table. This is because. That when determining the position of a metal in a series of voltages, not only the energy of electron detachment from individual atoms is taken into account, but also the energy spent on the destruction of the crystal lattice, as well as the energy released during the hydration of ions.

For example, lithium is more active in aqueous solutions than sodium (although, according to its position in the Periodic Table, Na is a more active metal). The point is that the hydration energy of Li + ions is much higher than the hydration energy of Na + ions. therefore, the first process is energetically more beneficial.
Having considered the general provisions characterizing the reducing properties of metals, we turn to specific chemical reactions.

Interaction with simple non-metallic substances

1. With oxygen, most metals form oxides - basic and amphoteric. Acidic transition metal oxides such as chromium oxide or manganese oxide are not formed by direct oxidation of the metal with oxygen. They are obtained indirectly.

Alkali metals Na, K actively react with atmospheric oxygen, forming peroxides.

Sodium oxide is obtained indirectly by calcining peroxides with the corresponding metals:

Lithium and alkaline earth metals interact with atmospheric oxygen to form basic oxides.

Metals other than gold and platinum metals, which are generally not oxidized by atmospheric oxygen, interact with it less actively or when heated.

2. With halogens, metals form salts of hydrohalic acids.

3. With hydrogen, the most active metals form hydrides - ionic saline substances in which hydrogen has an oxidation state of -1, for example:
calcium hydride.

Many transition metals form hydrides with hydrogen special type- there is a kind of dissolution or introduction of hydrogen into the crystal lattice of metals between atoms and ions, while the metal retains its appearance, but increases in volume. The absorbed hydrogen is in the metal, apparently in atomic form. There are also intermediate metal hydrides.

4. With sulfur, metals form salts - sulfides.

5. Metals react with nitrogen a little more difficult, since the chemical bond in the nitrogen molecule T ^ r is very strong, and nitrides are formed. At ordinary temperatures, only lithium interacts with nitrogen.

Interaction with complex substances

1.With water. Under normal conditions, alkali and alkaline earth metals displace hydrogen from water and form soluble alkali bases.

Other metals, which stand in the series of voltages before hydrogen, can also displace hydrogen from water under certain conditions. But aluminum reacts violently with water only if the oxide film is removed from its surface.

Magnesium interacts with water only when boiling, while hydrogen is also evolved. If burning magnesium is added to water, then combustion continues, as the reaction proceeds: hydrogen burns. Iron interacts with water only when it is hot.

2. Metals in the series of voltages up to hydrogen interact with acids in solution. This produces salt and hydrogen. But lead (and some other metals), despite its position in the series of voltages (to the left of hydrogen), is almost insoluble in dilute sulfuric acid, since the resulting lead sulfate PbSO is insoluble and creates a protective film on the metal surface.

3. With salts of less active metals in solution. As a result of this reaction, a salt of a more active metal is formed and a less active metal is liberated in a free form.

It must be remembered that the reaction takes place in cases where the resulting salt is soluble. The displacement of metals from their compounds by other metals was first studied in detail by N.N. Beketov, a prominent Russian physicochemist. He arranged the metals according to their chemical activity in the "negative row", which became the prototype of a number of metal voltages.

4.C organic matter... Interaction with organic acids is similar to reactions with mineral acids. Alcohols, on the other hand, can exhibit weak acidic properties when interacting with alkali metals.

Metals are involved in reactions with haloalkanes, which are used to obtain lower cycloalkanes and for syntheses, during which the carbon skeleton of the molecule becomes more complex (reaction of A. Würz):

5. Metals, hydroxides of which are amphoteric, interact with alkalis in solution.

6. Metals can form chemical compounds with each other, which have received a common name - intermetallic compounds. They most often do not show the oxidation states of atoms, which are characteristic of compounds of metals with non-metals.

Intermetallic compounds usually do not have a constant composition, the chemical bond in them is mainly metallic. The formation of these compounds is more typical for metals of side subgroups.

Metal oxides and hydroxides

The oxides formed by typical metals are classified as salt-forming, with basic properties. As you know, hydroxides correspond to them. which are bases, which are soluble in water in the case of alkali and alkaline earth metals, are strong electrolytes and are called alkalis.

Oxides and hydroxides of some metals are amphoteric, that is, they can exhibit both basic and acidic properties, depending on the substances with which they interact.

For example:

Many metals of side subgroups, which have a variable oxidation state in the compounds, can form several oxides and hydroxides, the nature of which depends on the oxidation state of the metal.

For example, chromium in compounds exhibits three oxidation states: +2, +3, +6, therefore it forms three series of oxides and hydroxides, and with an increase in the oxidation state, the acidic character is enhanced and the basic one is weakened.

Corrosion of metals

When metals interact with substances environment Their surfaces are formed by compounds with completely different properties than the metals themselves. In an ordinary vein, we often use the words "rust", "rusting", seeing a brownish-red bloom on items made of iron and its alloys. Rusting is a common case of corrosion.

Corrosion is a process of spontaneous destruction of metals and not) aliyahsm of the environment (from Lat. - corrosion).

However, almost all metals undergo destruction, and as a result, many of their properties deteriorate (or are completely lost): strength, plasticity, gloss decrease, electrical conductivity decreases, and friction between moving parts of mnins also increases, the dimensions of parts change, etc.

Corrosion of metals is continuous and local.

Nerven is not as dangerous as the second, its manifestations can be taken into account when designing structures and devices. Local corrosion is much more dangerous, although metal losses here can be small. One of the most dangerous of its types is point. They consist in the formation of through lesions, that is, point cavities - pits, while the strength of individual sections decreases, the reliability of structures, apparatus, structures decreases.

Corrosion of metals causes great economic harm. Humanity suffers huge material losses in the re-euntat of the destruction of pipelines, machine parts, ships, bridges, and various equipment.

Corrosion leads to a decrease in the reliability of the operation of metal structures - Given the possible destruction, it is necessary to overestimate the strength of some products (for example, aircraft parts, turbine blades), which means an increase in metal consumption, and this requires additional economic costs.

Corrosion leads to production downtime due to the replacement of out-of-order equipment, to the loss of raw materials and products as a result of the destruction of halo, oil and water pipelines. It is impossible not to take into account the damage to nature, and therefore to human health, caused as a result of the leakage of oil products and other chemical substances... Corrosion can lead to contamination) of the product, and therefore to a decrease in its quality. The cost of reimbursing losses due to corrosion is enormous. They account for about 30% of the annual production of metals worldwide.

From all that has been said, it follows that a very important problem is to find ways to protect metals and alloys from corrosion.

They are very diverse. But for their choice, it is necessary to know and take into account the chemical essence of corrosion processes.

But the chemical nature of corrosion is an oxidation-reduction process. Several types of corrosion are distinguished depending on the environment in which it flows.

The most common types of corrosion: chemical and electrochemical.

I. Chemical corrosion occurs in a non-conductive environment. This type of corrosion manifests itself in the case of the interaction of metals with dry gases or liquids - non-electrolytes (gasoline, kerosene, etc.). Parts and assemblies of engines, gas turbines, and rocket launchers are subject to such destruction. Chemical corrosion is often observed during the processing of metals at high temperatures.

Most metals are oxidized by atmospheric oxygen, forming oxide films on the surface. If this film is strong, dense, well bonded to the metal, then it protects the metal from further destruction. In iron, it is loose, porous, easily separates from the surface and therefore is not able to protect the metal from further destruction.

II. Electrochemical corrosion occurs in a conductive environment (in an electrolyte) with the appearance inside the system electric current... As a rule, metals and alloys are heterogeneous and contain inclusions of various impurities. When they come into contact with electrolytes, some parts of the surface begin to play the role of an anode (give up electrons), while others play the role of a cathode (receive electrons).

In one case, gas evolution (Ng) will be observed. In the other, the formation of rust.

So, electrochemical corrosion is a reaction that occurs in environments that conduct current (as opposed to chemical corrosion). The process occurs when two metals come into contact or on the surface of a metal containing inclusions that are less active conductors (this can also be a non-metal).

At the anode (more active metal), metal atoms are oxidized with the formation of cations (dissolution).

At the cathode (less active conductor), there is a reduction of hydrogen ions or oxygen molecules with the formation of H2 or OH- hydroxide ions, respectively.

Hydrogen cations and dissolved oxygen are the most important oxidizing agents causing electrochemical corrosion.

The corrosion rate is higher, the more different metals (metal and impurities) differ in their activity (for metals - the farther from each other they are located in the series of stresses). Corrosion increases significantly with increasing temperature.

Can serve as an electrolyte sea water, river water, condensed moisture and, of course, well-known to all electrolytes - solutions of salts, acids, alkalis.

You obviously remember that in winter, industrial salt is used to remove snow and ice from sidewalks (sodium chloride, sometimes calcium chloride, etc.) - The resulting solutions drain into the sewer pipelines, thereby creating a favorable environment for electrochemical corrosion of underground utilities.

Corrosion protection methods

Already during the design of metal structures, their manufacture provides for measures of protection against corrosion.

1. Grinding the surfaces of the product so that moisture does not linger on them.
2. The use of alloyed alloys containing special additives: chromium, nickel, which at high temperatures on the metal surface form a stable oxide layer. Well-known alloyed steels - stainless steel, which make household items (scabbard forks, spoons), machine parts, tools.
3. Application of protective coatings.

Let's consider their types.

Non-metallic - non-oxidizing oils, special varnishes, paints. True, they are short-lived, but cheap.

Chemical - artificially created surface films: oxide, citric, silicide, polymer, etc. For example, all small arms In the details of many precision instruments, burnishing is the process of obtaining the thinnest film of iron oxides on the surface of a steel product. The resulting artificial oxide film is very durable and gives the product a beautiful black and blue tint. Polymer coatings are made from polyethylene, polyvinyl chloride, and polyamide resins. They are applied in two ways: the heated product is placed in a polymer powder, which melts and is welded to the metal, or the metal surface is treated with a polymer solution in a low-yield solvent, which quickly evaporates, and the polymer film remains on the product.

Metallic - these are coatings with other metals, on the surface of which, under the action of oxidants, stable protective films are formed.

The application of chromium on the surface - chrome plating, nickel - nickel plating, zinc - zinc plating, tin - tin plating, etc. The coating can also be a chemically passive metal - gold, silver, copper.

4. Electrochemical methods of protection.

Protective (anodic) - a piece of more active metal (protector) is attached to the protected metal structure, which serves as an anode and is destroyed in the presence of an electrolyte. Magnesium, aluminum, zinc are used as a protector for the protection of ship hulls, pipelines, cables and other stylish products;

Cathodic - the metal structure is connected to the cathode of an external current source, which excludes the possibility of its anodic destruction

5. Special treatment of the electrolyte or the environment in which the protected metal structure is located.

Damask craftsmen are known for descaling and
rust used solutions of sulfuric acid with the addition of brewer's yeast, flour, starch. These fetch and were among the first inhibitors. They did not allow the acid to act on the weapon metal, as a result, only scale and rust dissolved. Ural armourers used pickling soups for these purposes - solutions of sulfuric acid with the addition of flour bran.

Examples of the use of modern inhibitors: hydrochloric acid during transportation and storage is perfectly "tamed" by butylamine derivatives. a sulphuric acid- nitric acid; volatile diethylamine is injected into various containers. Note that inhibitors act only on the metal, making it passive with respect to the medium, for example, to an acid solution. Science knows more than 5 thousand corrosion inhibitors.

Removal of oxygen dissolved in water (deaeration). This process is used in the preparation of water entering boiler plants.

Methods for obtaining metals

The significant chemical activity of metals (interaction with atmospheric oxygen, other non-metals, water, salt solutions, acids) leads to the fact that in the earth's crust they are found mainly in the form of compounds: oxides, sulfides, sulfates, chlorides, carbonates, etc.

In a free form, there are metals located in a series of voltages to the right of hydrogen, although much more often copper and mercury can be found in nature in the form of compounds.

Minerals and rocks containing metals and their compounds, from which the separation of pure metals is technically possible and economically feasible, are called ores.

Obtaining metals from ores is the task of metallurgy.
Metallurgy is also the science of industrial methods of obtaining metals from ores. and industry.
Any metallurgical process is the process of reducing metal ions using various reducing agents.

To implement this process, it is necessary to take into account the activity of the metal, select a reducing agent, consider the technological feasibility, economic and environmental factors. Accordingly, there are following ways obtaining metals: pyrometallurgical. hydrometallurgical, electrometallurgical.

Pyrometallurgy - reduction of metals from ores at high temperatures using carbon, carbon oxide (P). hydrogen, metals - aluminum, magnesium.

For example, tin is reduced from cassiterite, while copper is reduced from cuprite by calcining with coal (coke). Sulfide ores are preliminarily subjected to roasting under the access of air, and then the resulting oxide is reduced with coal. Metals are also isolated from carbonate ores by pumping a coal, since carbonates decompose when heated, turning into oxides, and the latter are reduced by coal.

Hydrometallurgy is the recovery of metals from their salts in solution. The process takes place in 2 stages:

1) the natural compound is dissolved in a suitable reagent to form a salt solution of this metal;
2) this metal is displaced from the obtained rakhtvory more active or reduced by electrolysis. For example, to obtain copper for ores containing copper oxide CuO, it is treated with dilute sulfuric kiglot.

Then, copper is removed from the salt solution either by electrolysis, or the sulfate is displaced with iron. In this way, silver, zinc, molybdenum, gold, uranium are obtained.

Electrometallurgy is the reduction of metals in the course of electrolysis of solutions or melts of their compounds.

Electrolysis

If electrodes are lowered into a solution or molten electrolyte and a constant electric current is passed, then the ions will move in a directional way: cations - to the cathode (negatively charged electrode), anions - to the anode (positively charged electrode).

At the cathode, cations accept electrons and are reduced at the anode, anions donate electrons and are oxidized. This process is called electrolysis.
Electrolysis is an oxidative-reduction process that takes place during the course of an electric current passing through an electrolyte or electrolyte solution.

The simplest example of such processes is the electrolysis of molten salts. Consider the process of electrolysis of sodium chloride melt. The process of thermal dissociation takes place in the melt. Under the action of an electrical current, cations move to the cathode and receive electrons from it.
Metallic sodium is formed at the cathode, and chlorine gas at the anode.

The main thing that you must remember: in the process of electrolysis due to electrical energy, a chemical reaction is carried out, which cannot go spontaneously.

The situation is more complicated in the case of electrolysis of electrolyte solutions.

In a salt solution, in addition to metal ions and an acidic residue, water molecules are present. Therefore, when considering the processes on the electrodes, it is necessary to take into account their participation in electrolysis.

For the determination of electrolysis products aqueous solutions electrolytes, the following rules apply.

1. The process at the cathode does not depend on the material of the cathode on which it is made, but on the position of the metal (electrolyte cation) in the electrochemical series of voltages, while if:

1.1. The electrolyte cation is located in the series of voltages at the beginning of the series (along Al inclusive), then the process of water reduction occurs at the cathode (hydrogen is released). Metal cations are not reduced; they remain in solution.
1.2. The electrolyte cation is in a series of voltages between aluminum and hydrogen, then both metal nones and water molecules are reduced at the cathode.
1.3. The electrolyte cation is in the series of voltages after hydrogen, then metal cations are reduced at the cathode.
1.4. The solution contains cations of different metals, then the downloaded metal cation is reduced, standing in a series of voltages

These rules are reflected in diagram 10.

2. The process at the anode depends on the material of the anode and on the nature of the annon (Scheme 11).

2.1. If the anode dissolves (iron, zinc. Copper, silver and all metals that are oxidized during electrolysis), then the anode metal is oxidized, despite the nature of the anion. 2.2. If the anode does not dissolve (it is called inert - graphite, gold, platinum), then:
a) during the electrolysis of solutions of salts of anoxic acids (pro-methorides), an anion is oxidized at the anode;
b) during the electrolysis of solutions of salts of oxygen-containing acid and fluorides, the process of water oxidation takes place at the anode. Anions are not oxidized, they remain in solution;

Electrolysis of melts and solutions of substances is widely used in industry:

1. For the production of metals (aluminum, magnesium, sodium, cadmium are obtained only by electrolysis).
2. For the production of hydrogen, halogens, alkalis.
3. For the purification of metals - refining (purification of copper, nickel, lead is carried out by the electrochemical method).
4. To protect metals from corrosion - applying protective coatings in the form of a thin layer of another metal resistant to corrosion (chrome, nickel, copper, silver, gold) - electroplating.
5. Obtaining metal copies, plates - electroplating.

Practical task

1. How are the structure of metals related to their arrangement in the main and secondary subgroups of the periodic table of chemical elements of DI Mendeleev?
2. Why do alkali and alkaline earth metals have a single oxidation state in compounds: (+1) and (+2), respectively, and metals of side subgroups, as a rule, exhibit different oxidation states in compounds?
3. What oxidation states can manganese exhibit? What oxides to hydrocents correspond to manganese in these oxidation states? What is their nature?
4. Compare the electronic structure of the atoms of the elements of group VII: manganese and chlorine. Explain the difference in their chemical properties and the presence of different oxidation states of atoms for both elements.
5. Why does the position of metals in the electrochemical series of voltages not always correspond to their position in the Periodic Table of DI Mendeleev?
9. Make the equations for the reactions of sodium and magnesium with acetic acid. In which case and why will the reaction rate be higher?
11. What methods of obtaining metals do you know? What is the essence of all methods?
14. What is corrosion? What types of corrosion do you know? Which one represents a physicochemical process?
15. Can the following processes be considered as corrosion: a) oxidation of iron during electric welding, b) interaction of zinc with hydrochloric acid when obtaining etched acid for soldering? Give a reasoned answer.
17. The manganese product is in water and comes into contact with the copper product. Will both of them remain unchanged?
18. Will the iron structure be protected from electrochemical corrosion in water if a plate of another metal is stepped on it: a) magnesium, b) lead, c) nickel?
19. For what purpose is the surface of tanks for storing petroleum products (gasoline, kerosene) painted with silver - a mixture of aluminum powder with one of the vegetable oils?
20. On the surface of the acidified soil of the garden uchetkl there are iron pipes with inserted brass taps. What will corrode: yiyang faucet pipe? Where is the destruction most pronounced?
21. What is the difference between electrolysis of melts and electrolysis of aqueous solutions?
22 *. What metals can be obtained by electrolysis of their salt melts and cannot be obtained by electrolysis of aqueous solutions of these substances?
23 *. Make the equations for the electrolysis of barium chloride in: a) melt, b) solution
28. To a solution containing 27 g of copper (II) chloride was added 1-4 g of iron filings. What mass of copper was released as a result of this reaction?
Answer: 12.8 g.
29. What mass of zinc sulfate can be obtained by reacting excess zinc with 500 ml of a 20% sulfuric acid solution with a density of 1.14 g / ml?
Answer: 187.3 g.
31. When processing 8 g of a mixture of magnesium and magnesium oxide with hydrochloric acid, 5.6 liters of hydrogen (n, u.) Were released. What is mass fraction(in%) JUNE in the original mixture?
Answer: 75%.
34. Determine the mass fraction (in percent) of carbon in steel (an alloy of iron with carbon), if during the combustion of its sample weighing 10 g in a stream of oxygen, 0.28 liters of carbon oxide (IV) (standard) were collected.
Answer: 1.5%.
35. A 0.5 g sample of sodium was placed in water. Neither the neutralization of the resulting solution consumed 29.2 g of 1.5% hydrochloric acid. What is the mass fraction (percentage) of sodium in the sample?
Answer: 55.2%.
36. An alloy of copper and aluminum was treated with an excess of sodium hydroxide solution, while a gas with a volume of 1.344 L (standard unit) was evolved. The residue after the reaction was dissolved in nitric acid, then the solution was evaporated and calcined to constant weight, which turned out to be equal to 0.4 g. alloy composition? Answer: 1.08 g Al 0.32 g Cu or 77.14% Al 22.86% Cu.
37. What mass of cast iron containing 94% iron can be obtained from 1 ton of red iron ore (Fe2O3) containing 20% of impurities?
Answer: 595.74 kg.

Metals in nature

If you carefully studied chemistry in previous classes, then you know that the periodic table has more than ninety types of metals and about sixty of them can be found in natural environment.

Naturally occurring metals can be roughly divided into the following groups:

Metals that can be found in nature in free form;
metals found as compounds;
metals that can be found in mixed form, that is, they can be both in free form and in the form of compounds.

Unlike other chemical elements, metals are quite often found in nature in the form of simple substances. They usually have a native state. Such metals, which are presented in the form of simple substances, include gold, silver, copper, platinum, mercury and others.

But not all metals found in the natural environment are present in their native state. Some metals can be found in the form of compounds and are called minerals.

In addition, chemical elements such as silver, mercury and copper can be found both in the native state and in the state of having the appearance of compounds.

All those minerals from which metals can be obtained in the future are called ores. In nature, there is an ore, which includes iron. This compound is called iron ore. And if the composition contains copper, but accordingly, such a compound is called copper ore.

Of course, the most common metals in nature are metals that actively interact with oxygen and sulfur. They are called metal oxides and sulfides.

Aluminum is such a common element that forms metal. Aluminum is found in clay and is also found in gemstones such as sapphire and ruby.

The second most popular and widespread metal is iron. It, as a rule, occurs in nature in the form of compounds, and in its native form it can only be found in the composition of meteorite stones.

The next most common in the natural environment, or rather in the earth's crust, are metals such as magnesium, calcium, sodium, potassium.

Holding coins in your hand, you probably noticed that they give off a characteristic smell. But it turns out that this is not the smell of metal, but the smell that comes from the compounds, which is formed when the metal comes into contact with human sweat.

Did you know that Switzerland has established the production of gold bars in the form of a chocolate bar, which can be broken into slices and used as a gift or means of payment? The company produces such chocolate bars from gold, silver, platinum and palladium. If such a tile is broken into slices, then each of them weighs only one gram.

And yet, a rather interesting property is possessed by such a metal alloy as nitinol. It is unique in that it has a memory effect and, when heated, a deformed product made of this alloy is able to return to its original form. Such peculiar materials with the so-called memory are used for the manufacture of bushings. They have the property of shrinking at low temperatures, and at room temperature these sleeves are straightened and this connection is even more reliable than welding. And this phenomenon occurs due to the fact that these alloys have a thermoelastic structure.

Have you ever wondered why it is customary to add an alloy of silver or copper to gold jewelry? It turns out that this is because gold in its pure form is very soft and easy to scratch even with a fingernail.