Alkali metals are characterized by the following features. Alkali metals - chemical and biogenic elements
alkali metals.
Alkali metals - elements of the main subgroup of group I of the Periodic system chemical elements D. I. Mendeleev:
lithium Li, sodium Na, potassium K, rubidium Rb, cesium Cs and francium Fr.
These metals are called alkaline because most of their compounds are soluble in water. In Slavic, “leach” means “dissolve”, and this determined the name of this group of metals. When alkali metals are dissolved in water, soluble hydroxides are formed, called alkalis.
The main characteristic of alkali metals: In the Periodic system, they immediately follow the inert gases, so the structural feature of alkali metal atoms is that they contain one electron at a new energy level: their electronic configuration ns1.
The valence electrons of alkali metals can be easily removed, because it is energetically favorable for the atom to donate an electron and acquire the configuration of an inert gas.
Therefore, all alkali metals are characterized by reducing properties. This is confirmed by the low values of their ionization potentials (the ionization potential of the cesium atom is one of the lowest) and electronegativity (EO).
Below is a table of properties of alkali metals:
| Atomic room |
Name, symbol |
Metal radius, nm |
Ionic radius, nm |
Potential ionization, eV |
EO | p, g/cm³ |
t pl, °C |
t bale, °C |
|---|---|---|---|---|---|---|---|---|
| 3 | lithium Li | 0,152 | 0,078 | 5,32 | 0,98 | 0,53 | 181 | 1347 |
| 11 | Sodium Na | 0,190 | 0,098 | 5,14 | 0,93 | 0,97 | 98 | 883 |
| 19 | Potassium K | 0,227 | 0,133 | 4,34 | 0,82 | 0,86 | 64 | 774 |
| 37 | Rubidium Rb | 0,248 | 0,149 | 4,18 | 0,82 | 1,53 | 39 | 688 |
| 55 | Cesium Cs | 0,265 | 0,165 | 3,89 | 0,79 | 1,87 | 28 | 678 |
All metals in this subgroup are silvery white in color.(except for the silvery yellow cesium), they are very soft and can be cut with a scalpel. Lithium, sodium and potassium are lighter than water and float on its surface, reacting with it.
Alkali metals occur naturally in the form of compounds containing singly charged cations.
Many minerals contain metals of the main subgroup of group I. For example, orthoclase, or feldspar, consists of potassium aluminosilicate K2, a similar mineral containing sodium - albite - has the composition Na2. AT sea water contains sodium chloride NaCl, and in the soil - potassium salts - sylvin KCl, sylvinite NaCl. KCl, carnallite KCl. MgCl2 . 6H2O, polyhalite K2SO4. MgSO4. CaSO4 . 2H2O.
Chemical properties of alkali metals
Due to the high chemical activity of alkali metals in relation to water, oxygen, nitrogen, they are stored under a layer of kerosene. To carry out a reaction with an alkali metal, a piece right size carefully cut with a scalpel under a layer of kerosene, in an argon atmosphere thoroughly clean the metal surface from the products of its interaction with air, and only then place the sample in the reaction vessel.
1. Interaction with water. An important property of alkali metals- their high activity in relation to water. Lithium reacts most calmly (without explosion) with water:
When carrying out a similar reaction, sodium burns with a yellow flame and a small explosion occurs. Potassium is even more active: in this case, the explosion is much stronger, and the flame is colored purple.
2. Interaction with oxygen. The combustion products of alkali metals in air have a different composition depending on the activity of the metal.
Only lithium burns in air with the formation of an oxide of the stoichiometric composition:
During the combustion of sodium, peroxide Na2O2 is mainly formed with a small admixture of superoxide NaO2:
The combustion products of potassium, rubidium and cesium contain mainly superoxides: 
To obtain oxides of sodium and potassium, mixtures of hydroxide, peroxide or superoxide are heated with an excess of metal in the absence of oxygen: 
For oxygen compounds of alkali metals, the following regularity is characteristic: as the radius of the alkali metal cation increases, the stability of oxygen compounds containing peroxide ion O22- and superoxide ion O2- increases.
Heavy alkali metals are characterized by the formation of rather stable ozonides of the EO3 composition. All oxygen compounds have various colors, the intensity of which deepens in the series from Li to Cs:
Alkali metal oxides have all the properties of basic oxides: they react with water, acid oxides and acids: 
Peroxides and superoxides exhibit the properties of strong oxidizing agents:
Peroxides and superoxides interact intensively with water, forming hydroxides:
3. Interaction with other substances. Alkali metals react with many non-metals. When heated, they combine with hydrogen to form hydrides, with halogens, sulfur, nitrogen, phosphorus, carbon and silicon to form, respectively, halides, sulfides, nitrides, phosphides, carbides and silicides: 
When heated, alkali metals are able to react with other metals, forming intermetallic compounds. Alkali metals react actively (with an explosion) with acids.
Alkali metals dissolve in liquid ammonia and its derivatives - amines and amides:
When dissolved in liquid ammonia, an alkali metal loses an electron, which is solvated by ammonia molecules and gives the solution a blue color. The resulting amides are easily decomposed by water with the formation of alkali and ammonia:
Alkali metals interact with organic substances, alcohols (with the formation of alcoholates) and carboxylic acids (with the formation of salts):
4. Qualitative determination of alkali metals. Since the ionization potentials of alkali metals are small, when a metal or its compounds is heated in a flame, an atom is ionized, coloring the flame in a certain color:
Obtaining alkali metals
1. To obtain alkali metals, they mainly use the electrolysis of melts of their halides, most often chlorides, which form natural minerals:
cathode: Li+ + e → Li
anode: 2Cl- - 2e → Cl2
2. Sometimes, to obtain alkali metals, electrolysis of melts of their hydroxides is carried out:
Cathode: Na+ + e → Na
anode: 4OH- - 4e → 2H2O + O2
Since alkali metals are to the left of hydrogen in the electrochemical series of voltages, it is impossible to obtain them electrolytically from salt solutions; in this case, the corresponding alkalis and hydrogen are formed.
Alkali metal compounds. Hydroxides
“Lithium is the lightest metal; it has a specific gravity of 0.59, as a result of which it floats even on oil; melts at about 185°, but does not volatilize in red-hot heat. It resembles sodium in color and, like sodium, has a yellow tint.
D. I. Mendeleev. Fundamentals of chemistry.
When in 1817 the 25-year-old Swedish chemist Johan August Arfvedson (1792-1841) isolated a new “flammable alkali” from the mineral petalite, until now unknown nature”(it was lithium hydroxide), his teacher, the famous Swedish chemist Jens Jacob Berzelius (1779-1848), suggested calling it lithion, from the Greek. lithos - stone.
This alkali, in contrast to the already known sodium and potassium, was first discovered in the "kingdom" of stones. In 1818, the English chemist Humphrey Davy (1778-1829) obtained a new metal from lithion, which he called lithium. The same Greek root is in the words "lithosphere", "lithography" (an impression from a stone mold), etc.
Lithium is the lightest of the solids: its density is only 0.53 g/cm3 (half that of water). Lithium is obtained by electrolysis of a melt of lithium chloride. A rare property of metallic lithium is the reaction with nitrogen under normal conditions to form lithium nitride.
Lithium is increasingly used in the production of lithium-ion batteries. As a result, the world production of lithium in 2012 amounted to 37 thousand tons - five times more than in 2005.
Lithium compounds are used in the glass and ceramic industries. Lithium hydroxide - excess absorber carbon dioxide in cabins spaceships and submarines. Lithium carbonate is used in psychiatry to treat certain disorders. The average human contains less than 1 mg of lithium.
Sodium
“The production of metallic sodium is one of the most important discoveries in chemistry, not only because the concept of simple bodies, but especially because in sodium are visible Chemical properties, only weakly expressed in other well-known metals.
D. I. Mendeleev. Fundamentals of chemistry.
Russian name "sodium" (it is also in Swedish and German) comes from the word "natron": this is how the ancient Egyptians called dry soda, which was used in the mummification process. In the XVIII century, the name "natron" was assigned to the "mineral alkali" - caustic soda. Now soda lime is called a mixture of caustic soda and calcium oxide (in English soda lime), and sodium in English (and in many other languages - sodium). The word "soda" comes from Latin name saltwort plants (sodanum). This is a coastal marine plant whose ashes were used in the manufacture of glass in ancient times. This ash contains sodium carbonate, which is called soda. And now soda is the most important component charge for the production of most glasses, including window glass.
Halite is the main mineral of sodium The first person to see what metallic sodium looks like was G. Davy, who isolated the new metal by electrolysis. He also proposed the name of the new element - sodium.
Sodium is a very active metal; it quickly oxidizes in air, becoming covered with a thick crust of reaction products with oxygen and water vapor. A lecture experience is known: if a small piece of sodium is thrown into water, it will begin to react with it, releasing hydrogen. A lot of heat is released in the reaction, which melts the sodium, and its ball runs along the surface. Water cools the sodium and prevents the hydrogen from flaring up, but if the piece of sodium is large, a fire and even an explosion is possible.
Sodium metal is widely used in various syntheses as a reducing agent and also as a desiccant for non-aqueous liquids. It is present in high-capacity sodium-sulphur batteries. A low-melting alloy of sodium and potassium, liquid at room temperature, works as a coolant that removes excess thermal energy from nuclear reactors. Everyone knows yellow flames in the presence of sodium: this is how the flame of a gas burner is colored if the smallest drop of salty soup gets into it. Sodium vapor glows yellow in economical gas-discharge lamps that illuminate the streets.
For many centuries, salt has been the only means of preservation. food products. Without table salt distant sea voyages, round-the-world expeditions and great geographical discoveries. The history of Russia knows a grand uprising, called the Salt Riot, which began in 1648 and swept across the country. One of the reasons for the uprising is the increase in the tax on salt.
Once upon a time, hundreds of thousands of tons of sodium were produced per year: it was used to produce tetraethyl lead, which increases the octane number of gasoline. The ban on leaded gasoline in many countries has led to a decline in sodium production. Now the world production of sodium is about 100 thousand tons per year.
The mineral halite (sodium chloride) forms huge deposits of rock salt. Only in Russia, its reserves amount to tens of billions of tons. Halite usually contains up to 8% other salts, mainly magnesium and calcium. More than 280 million tons of sodium chloride are mined annually, this is one of the largest productions. Once upon a time, sodium nitrate was mined in large quantities in Chile, hence its name - Chilean nitrate.
Other sodium salts, of which many are currently known, are also used. One of the most famous is sodium sulfate. If this salt contains water, it is called Glauber's. Huge amounts of it are formed during the evaporation of water in the Kara-Bogaz-Gol Bay of the Caspian Sea (Turkmenistan), as well as in some salt lakes. Currently, sodium sulfate solutions are used as a heat accumulator in devices that store solar energy, in the production of glass, paper, fabrics.
Salt Sodium is a vital element. Sodium ions are found mainly in the extracellular fluid and are involved in the mechanism of muscle contractions (a lack of sodium causes convulsions), in maintaining water-salt balance (sodium ions retain water in the body) and acid-base balance (maintaining a constant blood pH value). Produced from sodium chloride in the stomach hydrochloric acid, without which it is impossible to digest food. The content of sodium in the body of an average person is about 100 g. Sodium enters the body mainly in the form of table salt, its daily dose is 3-6 g. A single dose of more than 30 g is life-threatening.
Potassium
In Arabic, al-qili is ash, and also something calcined. They also began to call the product obtained from the ashes of plants, i.e. potassium carbonate. In sunflower ash, potassium is more than 30%. Without the Arabic article, this word in Russian turned into "potassium". In addition to Russian and Latin (kalium), this term has been preserved in many European languages: German, Dutch, Danish, Norwegian, Swedish (with the Latin ending -um), Greek (κάλιο), as well as a number of Slavic languages: Serbian (Kalijum), Macedonian (Kalium), Slovenian (Kalij).
Potassium is one of the most abundant elements in earth's crust. Its main minerals are sylvin (potassium chloride), sylvinite (mixed potassium and sodium chloride) and carnallite (mixed potassium and magnesium chloride). Silvin, as well as potassium nitrate (potash, it is also Indian nitrate) are used in large quantities as potash fertilizers. Together with nitrogen and phosphorus, potassium is one of the three most important elements for plant nutrition.
Sylvin is one of the main potassium minerals (along with sylvinite and carnallite). The element's English name is potassium, as is Russian name potassium carbonate (potash), borrowed from the languages of the Germanic group; in English, German and Dutch ash is ash, pot is a pot, i.e. potash is “ash from a pot”. Previously, potassium carbonate was obtained by evaporating the extract from the ash in vats; it was used to make soap. Potassium soap, unlike sodium soap, is liquid. From the Arabic name for ash came the name of alkali in many European languages: English. and goll. alkali, German Alkali, French and ital. alcali etc. The same root is present in the word "alkaloids" i.e. "like alkalis").
Potassium was the first element discovered by G. Davy (he also received lithium, barium, calcium, strontium, magnesium and boron for the first time). Davy electrolyzed a wet lump of potassium hydroxide. At the same time, according to Davy, “small balls with a strong metallic sheen appeared on its surface, outwardly no different from mercury. Some of them, immediately after their formation, burned out with an explosion and with the appearance of a bright flame, while others did not burn out, but only dimmed, and their surface was covered with a white film. Potassium is a very active metal. His small piece, brought into the water, explodes.
Potassium is an important bioelement, the human body contains from 160 to 250 g of potassium, more than sodium. Potassium ions are involved in the passage of nerve impulses. Fruits and vegetables contain a lot of potassium.
Potassium hydroxide is used to make soap. It serves as an electrolyte in alkaline batteries - iron-nickel, nickel-metal hydride. Previously, potassium nitrate (potassium nitrate) was consumed in large quantities for the production of black powder; now it is used as a fertilizer.
Natural potassium contains 0.0117% of the long-lived radionuclide 40K with a half-life of 1.26 billion years. This explains the fact that potassium-40 "survived" to our time from the moment of its synthesis in nuclear reactions in stars. However, since the formation of the Earth 4.5 billion years ago, the content of 40K on the planet has decreased by 12.5 times due to its decay! A human body weighing 70 kg contains approximately 20 mg 40K, or 3 x 1020 atoms, of which more than 5000 atoms decay every second! It is possible that such "internal" irradiation (enhanced by the decay of carbon-14) was one of the causes of mutations in the course of the evolution of wildlife. World production of potassium metal is small: about 200 tons per year.
rubidium and cesium
Rubidium and cesium are the first chemical elements discovered using spectral analysis. This method was developed by German scientists and friends - the physicist Gustav Robert Kirchhoff (1824-1887) and the chemist Robert Wilhelm Bunsen (1811-1899), who worked at the University of Heidelberg. With this extremely sensitive method, they analyzed all the substances they came across in the hope of finding something new. And in the early 1860s. discovered two new elements. This happened when they analyzed the dry residue obtained by evaporating water from the mineral springs of the Bad Dürkheim resort, 30 km from Heidelberg. In the spectrum of this substance, in addition to the lines of sodium, potassium and lithium already known to them, Kirchhoff and Bunsen noticed two weak blue lines. They realized that these lines belong to an unknown chemical element that is present in water in very small quantities. According to the light of the spectral lines, a new element
Continuing their research, Kirchhoff and Bunsen discovered in the aluminosilicate mineral lepido (lithium mica) sent to them from Saxony, another element, in the spectrum of which dark red lines stood out. It was called rubidium: from lat. rubidus - red. The same element was found in mineral water, from where the chemist Bunsen managed to isolate it. It is worth mentioning that 44 tons had to be processed to obtain a few grams of rubidium salt. mineral water and over 180 kg of lepidolite.
Cesium crystals can be stored in a sealed ampoule. And as in late XIX century, in no less titanic work on the isolation of radium salt, radioactivity served as a "compass" for Marie Curie, a spectroscope was a similar "compass" for Kirchhoff and Bunsen.
Rubidium and cesium are typical alkali metals. This was confirmed when the chemist Bunsen, by reducing the salt of rubidium, obtained this element in the form of a metal. More active cesium was obtained in pure form only in 1881 by the Swedish chemist Carl Theodor Setterberg (1853-1941) by electrolysis of molten cesium cyanide. Cesium is one of the most fusible metals. In its pure form, it has a golden color. But it is not easy to obtain pure cesium: in air it instantly ignites spontaneously. Pure rubidium melts at only 39.3 °C, cesium - 10 degrees lower, and on a very hot summer day, samples of these metals in ampoules become liquid.
The world production of metallic rubidium is small - about 3 tons per year. In medicine, rubidium-87 is used: its atoms are absorbed by blood cells, and by emitting fast electrons from them, with the help of special equipment, you can see "bottlenecks" in the blood vessels. Rubidium is used in solar cells.
Gustav Kirchhoff (left) and Robert Bunsen discovered rubidium using a spectroscope. In the spectrum of lepidolite, they found dark red lines and gave the name to the new element - rubidium. The body of a middle-aged person contains approximately 0.7 g of rubidium, and cesium - only 0.04 mg.
Electronic transitions in cesium atoms are used in extremely accurate "atomic clocks". All over the world there are now more than 70 such most accurate clocks - time standards: the error is less than a second in 100 million years. A cesium clock has a unit of time - a second.
It was proposed to use cesium ions to accelerate the rocket using an electric jet engine. In it, ions are accelerated in a strong electrostatic field and ejected through a nozzle.
Electric rocket engines with low thrust are capable of operating for a long time and flying over long distances.
France
This element was discovered (according to its radioactivity) in 1939 by Marguerite Perey (1909-1975), an employee of the Radium Institute in Paris, and she named it in honor of her homeland in 1946.
Francium is a neighbor of cesium in the Periodic Table of the Elements. D. I. Mendeleev called the then undiscovered element - ekacesium. This last and heaviest alkali metal is strikingly different from all others in its group. Firstly, no one has ever seen and will not see even the smallest piece of France. Secondly, francium does not have such physical properties as density, melting point and boiling point. So the term "heaviest metal" can only be attributed to its atoms, but not to a simple substance. And all because francium is an artificially obtained highly radioactive element, its longest-lived isotope 223 Fr has a half-life of only 22 minutes. And in order to study the physical properties of a substance, you need to have it in the form of at least the smallest piece. But for France it is impossible.
Marguerite Perey is the first woman elected (in 1962) to the French Academy of Sciences. Francium is obtained artificially. And as it fuses, its atoms rapidly decay. Moreover, the more accumulated atoms, the more of them decays per unit time. So, in order to simply keep the number of francium atoms constant, they must be synthesized at a rate no less than the rate of their decay. During the synthesis of francium in Dubna by irradiating uranium with a powerful beam of protons, about a million atoms of this element were produced every second. At this rate of synthesis, the rate of decay of the sample becomes equal to the rate of its formation when the number of its atoms is equal to two billion. This is a completely negligible amount of substance, it is not even visible under a microscope.
In addition, these atoms are not assembled into a piece of metal, but are distributed over the surface of the uranium target. So it is not surprising that in everything the globe at any moment there will be no more than two or three tens of grams of francium scattered singly in radioactive rocks.
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
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, which is relatively weakly bound to the nucleus. Each alkali metal starts a new period in the periodic table. The alkali metal is able to donate its outer electron more easily than any other element of this period. The cut of an alkali metal in an inert medium has a bright silvery sheen. Alkali metals are characterized by low density, good electrical conductivity and melt at a relatively low temperatures(Table 2).
Due to their high activity, alkali metals do not exist in pure form, but occur in nature only in the form of compounds (excluding francium), for example, with oxygen (clays and silicates) or with halogens (sodium chloride). Chlorides are raw materials for obtaining alkali metals in a free state. Sea water contains ALKALINE METALS 3% NaCl and trace amounts of other salts. It is clear that the lakes inland seas, as well as underground salt deposits and brines contain alkali metal halides in higher concentrations than sea water. For example, the salt content in the waters of the Great Salt Lake (Utah, USA) is 13.827.7%, and in the Dead Sea (Israel) up to 31%, depending on the area of the water surface, which varies with the season. It can be assumed that the insignificant content of KCl in sea water compared to NaCl is explained by the assimilation of the K+ ion by marine plants.
In the free form, alkali metals are obtained by electrolysis of melts of salts such as NaCl, CaCl2, CaF2 or hydroxides (NaOH), since there is no more active metal capable of displacing the alkali metal from the halide. During the electrolysis of halides, it is necessary to isolate the metal released at the cathode, since at the same time gaseous halogen is released at the anode, which actively reacts with the released metal.
See also ALKALI PRODUCTION
Since alkali metals have only one electron on the outer layer, each of them is the most active in its period, so Li is the most active metal in the first period of eight elements, Na, respectively, in the second, and K is the most active metal of the third period, containing 18 elements (first transition period). In the alkali metal subgroup (IA), the ability to donate an electron increases from top to bottom.
Chemical properties. All alkali metals actively react with oxygen, forming oxides or peroxides, differing from each other in this: Li turns into Li2O, and other alkali metals into a mixture of M2O2 and MO2, while Rb and Cs ignite. All alkali metals form with hydrogen salt-like, thermally stable at high temperatures, hydrides of composition M + H, which are active reducing agents; hydrides are decomposed by water with the formation of alkalis and hydrogen and the release of heat, causing ignition of the gas, and the rate of this reaction for lithium is higher than for Na and K.
See also HYDROGEN; OXYGEN.
In liquid ammonia, alkali metals dissolve to form blue solutions, and (unlike the reaction with water) can be isolated again by evaporating ammonia or adding an appropriate salt (for example, NaCl from its ammonia solution). When reacting with gaseous ammonia, the reaction proceeds similarly to the reaction with water:
Alkali metal amides exhibit basic properties similar to hydroxides. Most alkali metal compounds, except for some lithium compounds, are highly soluble in water. In terms of atomic size and charge density, lithium is close to magnesium, so the properties of the compounds of these elements are similar. In terms of solubility and thermal stability, lithium carbonate is similar to magnesium and beryllium carbonates of subgroup IIA elements; these carbonates decompose at relatively low temperatures due to the stronger binding of MO. Lithium salts are better soluble in organic solvents (alcohols, ethers, petroleum solvents) than other alkali metal salts. Lithium (like magnesium) reacts directly with nitrogen to form Li3N (magnesium forms Mg3N2), while sodium and other alkali metals can only form nitrides under harsh conditions. The metals of subgroup IA react with carbon, but the most easy reaction is with lithium (apparently due to its small radius) and the least easy with cesium. Conversely, active alkali metals directly react with CO, forming carbonyls (for example, K(CO)x), while less active Li and Na only under certain conditions.
Application. Alkali metals are used both in industry and in chemical laboratories, for example, for syntheses. Lithium is used to produce hard light alloys, which differ, however, in brittleness. Large quantities sodium are consumed to obtain an Na4Pb alloy, from which tetraethyl lead Pb(C2H5)4 is obtained, an antiknock gasoline fuel. Lithium, sodium and calcium are used as components of soft bearing alloys. The only and therefore mobile electron on the outer layer makes alkali metals excellent conductors of heat and electricity. Alloys of potassium and sodium, which remain liquid over a wide temperature range, are used as a heat exchange fluid in some types of nuclear reactors and due to high temperatures in nuclear reactor used to produce steam. Sodium metal in the form of supply busbars is used in electrochemical technology to transmit high power currents. Lithium hydride LiH is a convenient source of hydrogen released as a result of the reaction of the hydride with water. Lithium aluminum hydride LiAlH4 and lithium hydride are used as reducing agents in organic and inorganic synthesis. Due to the small ionic radius and correspondingly high charge density, lithium is active in reactions with water, therefore lithium compounds are highly hygroscopic, and lithium chloride LiCl is used to dry the air during the operation of devices. Alkali metal hydroxides are strong bases, highly soluble in water; they are used to create an alkaline environment. Sodium hydroxide, as the cheapest alkali, is widely used (in the USA alone, more than 2.26 million tons of it are consumed per year).
Lithium. The lightest metal, has two stable isotopes with atomic masses 6 and 7; the heavy isotope is more common, its content is 92.6% of all lithium atoms. Lithium was discovered by A. Arfvedson in 1817 and isolated by R. Bunsen and A. Mathisen in 1855. It is used in the production thermonuclear weapons (H-bomb), to increase the hardness of alloys and in pharmaceuticals. Lithium salts are used to increase the hardness and chemical resistance of glass, in the technology of alkaline batteries, to bind oxygen during welding.
Sodium. Known since antiquity, it was isolated by H. Davy in 1807. It is a soft metal, its compounds such as alkali (sodium hydroxide NaOH) are widely used, baking soda(sodium bicarbonate NaHCO3) and soda ash (sodium carbonate Na2CO3). Metal is also used in the form of vapors in dim gas-discharge lamps for street lighting.
Potassium. Known since antiquity, it was also identified by H. Davy in 1807. Potassium salts are well known: potassium nitrate (potassium nitrate KNO3), potash (potassium carbonate K2CO3), caustic potash (potassium hydroxide KOH), etc. Potassium metal also finds various applications in technologies of heat exchange alloys.
Rubidium was discovered by spectroscopy by R. Bunsen in 1861; contains 27.85% radioactive rubidium Rb-87. Rubidium, like other metals of subgroup IA, is highly reactive and must be stored under a layer of oil or kerosene to avoid oxidation by atmospheric oxygen. Rubidium finds a variety of applications, including photovoltaic technology, radio vacuum devices and pharmaceuticals.
Cesium. Cesium compounds are widely distributed in nature, usually in small quantities together with compounds of other alkali metals. The mineral pollucite silicate contains 34% cesium oxide Cs2O. The element was discovered by R. Bunsen by spectroscopy in 1860. The main application of cesium is the production of photocells and electronic tubes, one of the radioactive isotopes of cesium, Cs-137, is used in radiation therapy and scientific research.
France. The last member of the alkali metal family, francium, is so radioactive that it does not exist in the earth's crust in more than trace amounts. Information about francium and its compounds is based on the study of its insignificant amount, artificially obtained (at a high-energy accelerator) during the a-decay of actinium-227. The longest-lived isotope 22387Fr decays in 21 min into 22388Ra and b-particles. According to a rough estimate, the metallic radius of francium is 2.7 . Francium has most of the properties of other alkali metals and is highly electron-donating. It forms soluble salts and hydroxide. Francium exhibits oxidation state I in all compounds.
Collier Encyclopedia. - Open society. 2000 .
Alkali metals are the common name for the elements of the 1st group of the periodic table of chemical elements. Its composition is lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), and the hypothetical element ununenium (Uue). The name of the group comes from the name of soluble sodium and potassium hydroxides, which have the reaction and taste of alkali. Consider common features structures of atoms of elements, properties, production and use of simple substances.
Outdated and new group numbering
According to the outdated numbering system, alkali metals, occupying the leftmost vertical column of the periodic table, belong to I-A group. In 1989, the International Chemical Union (IUPAC) proposed a different option (long-period) as the main one. Alkali metals according to new classification and continuous numbering refer to the 1st group. The representative of the 2nd period, lithium, opens this set, and the radioactive element of the 7th period, francium, completes it. All metals of the 1st group have one s-electron in the outer shell of atoms, which they easily give up (recover).
The structure of alkali metal atoms
The elements of the 1st group are characterized by the presence of a second energy level, which repeats the structure of the previous inert gas. Lithium has 2 electrons on the penultimate layer, the rest have 8 electrons each. AT chemical reactions atoms easily donate an external s-electron, acquiring an energetically favorable configuration of a noble gas. Elements of the 1st group have small values of ionization energy and electronegativity (EO). They easily form singly charged positive ions. In the transition from lithium to francium, the number of protons and electrons, the radius of the atom, increases. Rubidium, cesium and francium donate an outer electron more easily than the elements that precede them in the group. Consequently, in the group from top to bottom, the restorative capacity increases.
The easy oxidizability of alkali metals leads to the fact that the elements of the 1st group exist in nature in the form of compounds of their singly charged cations. The content in the earth's crust of sodium - 2.0%, potassium - 1.1%. Other elements in it are in small quantities, for example, francium reserves - 340 g. Sodium chloride is dissolved in sea water, brine of salt lakes and estuaries, forms deposits of rock or common salt. Along with halite, sylvinite NaCl occurs. KCl and sylvin KCl. Feldspar is formed by potassium aluminosilicate K 2 . Sodium carbonate is dissolved in the water of a number of lakes, and the reserves of the element's sulfate are concentrated in the waters of the Caspian Sea (Kara-Bogaz-Gol). There are deposits of sodium nitrate in Chile (Chilean saltpeter). There are a limited number of naturally occurring lithium compounds. Rubidium and cesium are found as impurities in compounds of elements of the 1st group, and francium is found in the composition of uranium ores.
Alkali metal discovery sequence
The British chemist and physicist G. Davy in 1807 carried out the electrolysis of alkali melts, for the first time obtaining sodium and potassium in a free form. In 1817, the Swedish scientist Johann Arfvedson discovered the element lithium in minerals, and in 1825 G. Davy isolated the pure metal. Rubidium was first discovered in 1861 by R. Bunsen and G. Kirchhoff. German researchers analyzed the composition of aluminosilicates and obtained a red line in the spectrum corresponding to a new element. In 1939, an employee of the Paris Institute of Radioactivity, Marguerite Pere, established the existence of an isotope of francium. She also named the element in honor of her homeland. Ununennium (eca-francium) is the provisional name for a new type of atom with atomic number 119. The chemical symbol Uue is temporarily used. Researchers since 1985 have been trying to synthesize a new element, which will be the first in the 8th period, the seventh in the 1st group.
Physical properties of alkali metals
Almost all alkali metals are silvery white and have a metallic luster when freshly cut (cesium is golden yellow). In air, the luster fades, a gray film appears, on lithium it is greenish-black. This metal has the highest hardness among its neighbors in the group, but is inferior to talc, the softest mineral that opens the Mohs scale. Sodium and potassium are easily bent, they can be cut. Rubidium, cesium and francium in their pure form represent a pasty mass. The melting of alkali metals occurs at a relatively low temperature. For lithium, it reaches 180.54 °C. Sodium melts at 97.86°C, potassium at 63.51°C, rubidium at 39.32°C, and cesium at 28.44°C. The density of alkali metals is less than their related substances. Lithium floats in kerosene, rises to the surface of the water, potassium and sodium also float in it.
Crystal state
Crystallization of alkali metals occurs in the cubic syngony (body-centered). The atoms in its composition have a conduction band, to the free levels of which electrons can pass. It is these active particles that carry out a special chemical bond - a metallic one. The commonality of the structure of energy levels and the nature of crystal lattices explain the similarity of the elements of the 1st group. In the transition from lithium to cesium, the masses of the elements' atoms increase, which leads to a regular increase in density, as well as to a change in other properties.
Chemical properties of alkali metals
The only external electron in alkali metal atoms is weakly attracted to the nucleus, so they are characterized by low ionization energy, negative or close to zero electron affinity. Elements of the 1st group, having reducing activity, are practically incapable of oxidizing. In the group from top to bottom, activity in chemical reactions increases:
Production and use of alkali metals
Metals belonging to the 1st group are produced in industry by electrolysis of melts of their halides and other natural compounds. When decomposed under the action electric current positive ions at the cathode gain electrons and are reduced to the free metal. The anion is oxidized at the opposite electrode.
During the electrolysis of hydroxide melts, OH particles are oxidized at the anode, oxygen is released and water is obtained. Another method is the thermal reduction of alkali metals from the melts of their salts with calcium. Simple substances and compounds of elements of the 1st group have practical value. Lithium serves as a raw material in nuclear power engineering and is used in rocket technology. In metallurgy, it is used to remove residuals of hydrogen, nitrogen, oxygen, and sulfur. Hydroxide supplement electrolyte in alkaline batteries.
Sodium is necessary for nuclear energy, metallurgy, and organic synthesis. Cesium and rubidium are used in the manufacture of solar cells. Hydroxides and salts, especially chlorides, nitrates, sulfates, carbonates of alkali metals, are widely used. Cations have biological activity, sodium and potassium ions are especially important for the human body.