Interaction of alkali metals with hydrogen. Alkali metals and their compounds

These are the elements of group I of the periodic system: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr); very soft, ductile, fusible and light, usually silvery white; chemically very active; react violently with water to form alkalis(whence the name).

All alkali metals are extremely active, exhibit reducing properties in all chemical reactions, give up their only valence electron, turning into a positively charged cation, and exhibit a single oxidation state +1.

The reducing ability increases in the series ––Li–Na–K–Rb–Cs.

All alkali metal compounds are ionic in nature.

Almost all salts are soluble in water.

low melting points,

Small values ​​of density,

Soft, cut with a knife

Due to their activity, alkali metals are stored under a layer of kerosene to block the access of air and moisture. Lithium is very light and floats to the surface in kerosene, so it is stored under a layer of petroleum jelly.

Chemical properties of alkali metals

1. Alkali metals actively interact with water:

2Na + 2H 2 O → 2NaOH + H 2

2Li + 2H 2 O → 2LiOH + H 2

2. Reaction of alkali metals with oxygen:

4Li + O 2 → 2Li 2 O (lithium oxide)

2Na + O 2 → Na 2 O 2 (sodium peroxide)

K + O 2 → KO 2 (potassium superoxide)

In air, alkali metals instantly oxidize. Therefore, they are stored under a layer of organic solvents (kerosene, etc.).

3. In the reactions of alkali metals with other non-metals, binary compounds are formed:

2Li + Cl 2 → 2LiCl (halides)

2Na + S → Na 2 S (sulfides)

2Na + H 2 → 2NaH (hydrides)

6Li + N 2 → 2Li 3 N (nitrides)

2Li + 2C → Li 2 C 2 (carbides)

4. Reaction of alkali metals with acids

(rarely carried out, there is a competing reaction with water):

2Na + 2HCl → 2NaCl + H 2

5. Interaction of alkali metals with ammonia

(sodium amide is formed):

2Li + 2NH 3 = 2LiNH 2 + H 2

6. The interaction of alkali metals with alcohols and phenols, which in this case exhibit acidic properties:

2Na + 2C 2 H 5 OH \u003d 2C 2 H 5 ONa + H 2;

2K + 2C 6 H 5 OH = 2C 6 H 5 OK + H 2 ;

7. Qualitative reaction to alkali metal cations - coloring of the flame in the following colors:

Li + - carmine red

Na + - yellow

K + , Rb + and Cs + - violet

Obtaining alkali metals

Lithium, sodium and potassium metal receive electrolysis of molten salts (chlorides), and rubidium and cesium - reduction in vacuum when their chlorides are heated with calcium: 2CsCl + Ca \u003d 2Cs + CaCl 2
On a small scale, vacuum thermal production of sodium and potassium is also used:

2NaCl + CaC 2 \u003d 2Na + CaCl 2 + 2C;
4KCl + 4CaO + Si \u003d 4K + 2CaCl 2 + Ca 2 SiO 4.

Active alkali metals are released in vacuum thermal processes due to their high volatility (their vapors are removed from the reaction zone).

Features of the chemical properties of s-elements of group I and their physiological effect

The electronic configuration of the lithium atom is 1s 2 2s 1 . It has the largest atomic radius in the 2nd period, which facilitates the detachment of the valence electron and the emergence of the Li + ion with a stable inert gas (helium) configuration. Therefore, its compounds are formed with the transfer of an electron from lithium to another atom and the occurrence of an ionic bond with a small amount of covalence. Lithium is a typical metallic element. In substance form, it is an alkali metal. It differs from other members of group I in its small size and the smallest, in comparison with them, activity. In this respect, it resembles the group II element, magnesium, located diagonally from Li. In solutions, the Li + ion is highly solvated; it is surrounded by several tens of water molecules. Lithium, in terms of solvation energy - the addition of solvent molecules, is closer to a proton than to alkali metal cations.

The small size of the Li + ion, the high nuclear charge and only two electrons create conditions for the emergence of a rather significant positive charge field around this particle, therefore, in solutions, a significant number of polar solvent molecules are attracted to it and its coordination number is large, the metal is able to form a significant number of organolithium compounds .

Sodium begins the 3rd period, so it has only 1e at the external level - , occupying the 3s orbital. The radius of the Na atom is the largest in the 3rd period. These two features determine the nature of the element. Its electronic configuration is 1s 2 2s 2 2p 6 3s 1 . The only oxidation state of sodium is +1. Its electronegativity is very low, therefore sodium is present in compounds only in the form of a positively charged ion and gives the chemical bond an ionic character. The size of the Na + ion is much larger than Li +, and its solvation is not so great. However, it does not exist in free form in solution.

The physiological significance of K + and Na + ions is associated with their different adsorbability on the surface of the components that make up the earth's crust. Sodium compounds are only slightly adsorbed, while potassium compounds are strongly retained by clay and other substances. Cell membranes, being the cell-environment interface, are permeable to K + ions, as a result of which the intracellular concentration of K + is much higher than that of Na + ions. At the same time, the concentration of Na + in the blood plasma exceeds the content of potassium in it. This circumstance is associated with the emergence of the membrane potential of cells. Ions K + and Na + - one of the main components of the liquid phase of the body. Their ratio with Ca 2+ ions is strictly defined, and its violation leads to pathology. The introduction of Na + ions into the body does not have a noticeable harmful effect. An increase in the content of K + ions is harmful, but under normal conditions, an increase in its concentration never reaches dangerous values. The effect of Rb + , Cs + , Li + ions has not yet been sufficiently studied.

Of the various lesions associated with the use of alkali metal compounds, burns with hydroxide solutions are most common. The action of alkalis is associated with the dissolution of skin proteins in them and the formation of alkaline albuminates. Alkali is released again as a result of their hydrolysis and acts on the deeper layers of the body, causing the appearance of ulcers. Nails under the influence of alkalis become dull and brittle. Eye damage, even with very dilute alkali solutions, is accompanied not only by superficial destruction, but by violations of deeper parts of the eye (iris) and leads to blindness. During the hydrolysis of alkali metal amides, alkali and ammonia are simultaneously formed, causing fibrinous-type tracheobronchitis and pneumonia.

Potassium was obtained by G. Davy almost simultaneously with sodium in 1807 during the electrolysis of wet potassium hydroxide. From the name of this compound - "caustic potash" and the element got its name. The properties of potassium differ markedly from the properties of sodium, due to the difference in the radii of their atoms and ions. In potassium compounds, the bond is more ionic, and in the form of the K + ion, it has a lesser polarizing effect than sodium, due to its large size. The natural mixture consists of three isotopes 39 K, 40 K, 41 K. One of them is 40 K ‑ is radioactive and a certain proportion of the radioactivity of minerals and soil is associated with the presence of this isotope. Its half-life is long - 1.32 billion years. Determining the presence of potassium in a sample is quite easy: vapors of the metal and its compounds turn the flame purple-red. The spectrum of the element is quite simple and proves the presence of 1e - on the 4s orbital. The study of it served as one of the grounds for finding general patterns in the structure of the spectra.

In 1861 Robert Bunsen discovered a new element while studying the salt of mineral springs by spectral analysis. Its presence was proved by dark red lines in the spectrum, which other elements did not give. By the color of these lines, the element was named rubidium (rubidus-dark red). In 1863, R. Bunsen obtained this metal in its pure form by reducing rubidium tartrate (tartar salt) with soot. A feature of the element is the slight excitability of its atoms. Electron emission from it appears under the action of red rays of the visible spectrum. This is due to a small difference in the energies of the atomic 4d and 5s orbitals. Of all the alkaline elements with stable isotopes, rubidium (like cesium) has one of the largest atomic radii and a low ionization potential. Such parameters determine the nature of the element: high electropositivity, extreme chemical activity, low melting point (39 0 C) and low resistance to external influences.

The discovery of cesium, like rubidium, is associated with spectral analysis. In 1860, R. Bunsen discovered two bright blue lines in the spectrum that did not belong to any element known at that time. Hence the name "caesius" (caesius), which means sky blue. It is the last element of the alkali metal subgroup still found in measurable amounts. The largest atomic radius and the smallest first ionization potentials determine the nature and behavior of this element. It has a pronounced electropositivity and pronounced metallic qualities. The desire to donate the outer 6s-electron leads to the fact that all its reactions proceed extremely violently. A small difference in the energies of the atomic 5d and 6s orbitals is responsible for the slight excitability of the atoms. Electronic emission in cesium is observed under the action of invisible infrared rays (thermal). This feature of the atomic structure determines the good electrical conductivity of the current. All this makes cesium indispensable in electronic devices. Recently, more and more attention has been paid to cesium plasma as a fuel of the future and in connection with the solution of the problem of thermonuclear fusion.

In air, lithium actively reacts not only with oxygen, but also with nitrogen and is covered with a film consisting of Li 3 N (up to 75%) and Li 2 O. The remaining alkali metals form peroxides (Na 2 O 2) and superoxides (K 2 O 4 or KO 2).

The following substances react with water:

Li 3 N + 3 H 2 O \u003d 3 LiOH + NH 3;

Na 2 O 2 + 2 H 2 O \u003d 2 NaOH + H 2 O 2;

K 2 O 4 + 2 H 2 O \u003d 2 KOH + H 2 O 2 + O 2.

For air regeneration in submarines and spaceships, in insulating gas masks and breathing apparatus of combat swimmers (submarine saboteurs), a mixture of "oxon" was used:

Na 2 O 2 + CO 2 \u003d Na 2 CO 3 + 0.5 O 2;

K 2 O 4 + CO 2 \u003d K 2 CO 3 + 1.5 O 2.

This is currently the standard filling of regenerating cartridges for insulating gas masks for firefighters.
Alkali metals react when heated with hydrogen to form hydrides:

Lithium hydride is used as a strong reducing agent.

Hydroxides alkali metals corrode glass and porcelain dishes, they can not be heated in quartz dishes:

SiO 2 + 2NaOH \u003d Na 2 SiO 3 + H 2 O.

Sodium and potassium hydroxides do not split off water when heated up to their boiling point (more than 1300 0 C). Some sodium compounds are called soda:

a) soda ash, anhydrous soda, laundry soda or just soda - sodium carbonate Na 2 CO 3;
b) crystalline soda - sodium carbonate crystal hydrate Na 2 CO 3. 10H2O;
c) bicarbonate or drinking - sodium bicarbonate NaHCO 3;
d) sodium hydroxide NaOH is called caustic soda or caustic.

Alkali metals - francium, cesium, rubidium, potassium, sodium, lithium - are so called because they form alkalis when interacting with water. Because of their high reactivity, these elements should be stored under mineral oil or kerosene. The most active of all these substances is francium (possesses radioactivity).

Alkali metals are soft, silvery substances. Their freshly cut surface has a characteristic luster. Alkali metals boil and melt at low temperatures, have high thermal and electrical conductivity. They also have a low density.

Chemical properties of alkali metals

Substances are strong reducing agents, exhibit in compounds the oxidation state (single) +1. With an increase in the atomic mass of alkali metals, the reducing ability also increases. Almost all compounds are soluble in water, all of them are ionic in nature.

When heated moderately, alkali metals ignite in air. In combination with hydrogen, substances form salt-like hydrides. Combustion products are usually peroxides.

Alkali metal oxides are yellow solids (oxides of rubidium and potassium), white and lithium), and orange (cesium oxide) colors. These oxides are capable of reacting with water, acids, oxygen, acid and amphoteric oxides. These basic properties are inherent in all of them and are pronounced.

Alkali metal peroxides are yellowish-white powders. They are able to react with carbon dioxide and carbon monoxide, acids, non-metals, water.

Alkali metal hydroxides are white, water-soluble solids. In these compounds, the basic properties of alkalis are manifested (quite clearly). From lithium to francium, the strength of the bases and the degree of solubility in water increase. Hydroxides are considered fairly strong electrolytes. They react with salts, and oxides, individual non-metals. With the exception of the compound with lithium, all the others exhibit thermal stability. When calcined, it decomposes into water and oxide. These compounds are obtained by electrolysis of chloride aqueous solutions, a number of exchange reactions. Hydroxides are also obtained by the interaction of elements (or oxides) with water.

Almost all salts of the described metals (with the exception of individual lithium salts) are well soluble in water. Formed by weak acids, salt solutions have a medium reaction (alkaline) due to hydrolysis, while salts formed by strong acids do not hydrolyze. Common salts are stone silicate glue (soluble glass), Bertolet salt, potassium permanganate, drinking soda, soda ash and others.

All alkali metal compounds have the ability to change the color of the flame. This is used in chemical analysis. So, the flame is colored with lithium ions, purple with potassium ions, yellow with sodium, whitish-pink with rubidium, violet-red with cesium.

Due to the fact that all alkaline elements are the strongest reducing agents, they can be obtained by electrolysis of molten salts.

Application of alkali metals

Elements are used in various fields of human activity. For example, cesium is used in solar cells. Lithium is used as a catalyst in bearing alloys. Sodium is present in gas discharge lamps, nuclear reactors as a coolant. Rubidium is used in research activities.

Chemistry studies the properties of metals and non-metals. Did you know that there are alkaline and non-alkaline metals? And we not only know, but we will also give you a list for successful preparation in the subject of chemistry. So, the list of alkali metals is already given in the periodic table of Mendeleev. There, all the metals of the main subgroup in the first group are alkaline.

These are lithium, potassium, sodium, cesium, rubidium and francium. Only these metals are called alkaline. And they are called so because if they interact with water, then alkalis are formed as a result.

There is another type of metal - it is alkaline earth. If you want a list of only alkali metals, then there are only 6 metals. If all metals, the hydroxides of which have alkaline properties, then four more elements will enter - calcium, strontium, barium and radium.

It is difficult to find all alkali metals in their pure form in nature - after all, they easily enter into compounds. In particular, these metals are found in the form of these compounds.

Properties of alkali metals

Alkali metals are excellent conductors of heat and are good conductors of electricity.

Alkali metals have a low melting point

The density of metals increases with increasing number, but it becomes easier to melt them if the metals are at the bottom of the group.

Obtaining alkali metals

Usually alkali metals are obtained by electrolysis, however, two alkaline earth metals, strontium and barium, are obtained using the aluminothermic method.

Chemical properties

As we said, these metals are very active, they are also excellent reducing agents. They are found in the form of compounds in which the ionic bond will be the main one.

As a rule, they always form stable compounds. The main reactions and additional properties of alkali metals are given in the table:

So, now, using the list and table, as well as the periodic system of Mendeleev, you can tell a lot about alkali metals.

You can see what alkali metals look like. There is also a list and given bond reactions with water, sulfur, acids, salts and halogens.

ALKALI METALS

Alkali metals include elements of the first group, the main subgroup: lithium, sodium, potassium, rubidium, cesium, francium.

Being innature

Na-2.64% (by mass), K-2.5% (by mass), Li, Rb, Cs - much less, Fr - artificially obtained element

Li

Li 2 O Al 2 O 3 4SiO 2 - spodumene

Na

NaCl - table salt (rock salt), halite

Na 2 SO 4 10H 2 O - Glauber's salt (mirabilite)

NaNO 3 - Chilean saltpeter

Na 3 AlF 6 - cryolite
Na 2 B 4 O 7 10H 2 O - borax

K

KCl NaCl - sylvinite

KCl MgCl 2 6H 2 O - carnallite

K 2 O Al 2 O 3 6SiO 2 - feldspar (orthoclase)

Properties of alkali metals

As the atomic number increases, the atomic radius increases, the ability to donate valence electrons increases, and the reduction activity increases:

Physical properties

Low melting points, low densities, soft, cut with a knife.

Chemical properties

Typical metals, very strong reducing agents. In compounds, they exhibit a single oxidation state +1. The reducing power increases with increasing atomic mass. All compounds are ionic in nature, almost all are soluble in water. Hydroxides R–OH are alkalis, their strength increases with an increase in the atomic mass of the metal.

They ignite in air with moderate heating. With hydrogen they form salt-like hydrides. Combustion products are most often peroxides.

The reducing ability increases in the series Li–Na–K–Rb–Cs

1. Actively interact with water:

2Li + 2H 2 O → 2LiOH + H 2

2. Reaction with acids:

2Na + 2HCl → 2NaCl + H 2

3. Reaction with oxygen:

4Li + O 2 → 2Li 2 O (lithium oxide)

2Na + O 2 → Na 2 O 2 (sodium peroxide)

K + O 2 → KO 2 (potassium superoxide)

In air, alkali metals instantly oxidize. Therefore, they are stored under a layer of organic solvents (kerosene, etc.).

4. In reactions with other non-metals, binary compounds are formed:

2Li + Cl 2 → 2LiCl (halides)

2Na + S → Na 2 S (sulfides)

2Na + H 2 → 2NaH (hydrides)

6Li + N 2 → 2Li 3 N (nitrides)

2Li + 2C → Li 2 C 2 (carbides)

5. A qualitative reaction to alkali metal cations is the coloring of the flame in the following colors:

Li + - carmine red

Na + - yellow

K + , Rb + and Cs + - violet

Receipt

Because alkali metals are the strongest reducing agents, they can be restored from compounds only by electrolysis of molten salts:
2NaCl=2Na+Cl 2

Application of alkali metals

Lithium - bearing alloys, catalyst

Sodium - gas discharge lamps, coolant in nuclear reactors

Rubidium - research work

Cesium - photocells

Alkali metal oxides, peroxides and superoxides

Receipt

Oxidation of the metal produces only lithium oxide

4Li + O 2 → 2Li 2 O

(in other cases, peroxides or superoxides are obtained).

All oxides (except Li 2 O) are obtained by heating a mixture of peroxide (or superoxide) with an excess of metal:

Na 2 O 2 + 2Na → 2Na 2 O

KO 2 + 3K → 2K 2 O

Chem. elements (alkaline elements) that make up Ch. subgroup 1 group periodic. systems of elements, as well as simple substances corresponding to them - metals. Shch. m. include lithium Li (at. number 3), sodium Na (11), potassium K (19), rubidium Rb (37), tse ... Physical Encyclopedia

ALKALI METALS- ALKALI METALS, monovalent metals that make up the first group of the periodic table: lithium, SODIUM, RUBIDIUM, CAESIUM and FRANCE. These are soft, silvery-white metals that quickly oxidize in air and react violently with water when ... ... Scientific and technical encyclopedic dictionary

alkali metals- ALKALI METALS: lithium Li, sodium Na, potassium K, rubidium Rb, cesium Cs, francium Fr. Soft metals, easy to cut (except Li), Rb, Cs and Fr almost pasty under ordinary conditions; Li is the lightest of all metals, Na and K are lighter than water. Chemically very... Illustrated Encyclopedic Dictionary

ALKALI METALS- chemical elements Li, Na, K, Rb, Cs, Fr. Name from alkali hydroxides of alkali metals ... Big Encyclopedic Dictionary

ALKALI METALS- elements of group I of the periodic system: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr); very soft, ductile, fusible and light, usually silvery white; chemically very active; react violently with... Russian encyclopedia of labor protection

alkali metals- Group, incl. Li, Na, K, Rb, Cs, Fr. Topics metallurgy in general EN alkali metals … Technical Translator's Handbook

ALKALI METALS- SUB-GROUP IA. ALKALI METALS LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CESIUM, FRANCE The electronic structure of alkali metals is characterized by the presence of one electron on the outer electron shell, relatively weakly bound to the nucleus. From each ... ... Collier Encyclopedia

alkali metals- Alkali metals Alkali metals. Metals of the first group of the Periodic system, namely: lithium, sodium, potassium, rubidium, cesium and francium. They form strictly alkaline hydroxides, hence their name. (Source: "Metals and Alloys. Handbook." Under ... ... Glossary of metallurgical terms

alkali metals Encyclopedic Dictionary of Metallurgy

ALKALI METALS- chemical elements Li, Na, K, Rb, Cs, Fr. So named because their hydroxides are the strongest alkalis. Chemically, alkali metals are the most active metals. Their activity increases from Li to Fr... Metallurgical Dictionary

Books

• A set of tables. Chemistry. Metals (12 tables) , . Educational album of 12 sheets. Art. 5-8683-012 Alkali metals. Chemistry of alkali metals. Elements II A - groups. Hardness of water. Aluminum. The use of aluminium. Iron. Types of corrosion. Methods…