Special (correctional)
comprehensive boarding school for the blind
and visually impaired children in Perm
Abstract completed
10th grade students
Ponomarev Oleg,
Korshunov Artem
Supervisor:
L.Yu. Zakharova,
chemistry teacher
Perm
Introduction
General characteristics of elements of group I A-group
4 – 10
1.1. History of the discovery and distribution of alkali metals in nature
4 – 5
5 - 6
6 – 8
8 – 9
9 – 10
Biological role of elements of group I A-group. Their use in medicine
11 – 17
Routes of entry of alkali metals into the human body
18 – 21
Practical work
22 – 23
conclusions
24 – 25
Used Books
Introduction
The time has long come when everyone should think about their health and not only their own. We do not very often use the knowledge we acquire at school, for example in chemistry, in everyday life. However, this particular subject can become a source of knowledge about our health. Thanks to chemistry, we learn how the substances of our planet affect the vital processes of the body, and in general human life itself, what is useful to us and in what quantities and, finally, what is harmful and to what extent.
The human body is a complex chemical system that cannot function independently, without connection with the environment. It has been proven that almost all chemical elements are present in a living organism: some are macroelements, while the content of others is negligible, these are microelements. The ways in which elements enter the body are different, and their influence on the body is varied, but each plays its own biological role.
It is impossible to study the meaning of each element within the framework of one work. We have chosen the very first group of chemical elements of D.I. Mendeleev’s periodic table.
Target of this study – study the biological role of alkali metals for the human body.
In this regard, we decided to clarify the following questions for each metal of group IA:
general characteristics and structural features of the atoms of each element, as well as the properties of the substances they form;
presence of the element in the body;
the body's needs for it;
the effect of excess and deficiency of the element on human health;
natural sources;
methods for detecting an element.
1. General characteristics of elements of group I A-group
Period
Group
IN I A-group includes s-elements - alkali metals, which are extremely important for the normal life of animals and people. The macroelements sodium and potassium are of greatest importance for organisms.
3Li
11 Na
19K
37 Rb
55 Cs
87 Fr
1.1. History of discovery and distribution in nature
alkali metals
The name “alkali metals” is due to the fact that the hydroxides of the two main representatives of this group - sodium and potassium - have long been known as alkalis. From these alkalis, subjecting them to electrolysis in a molten state, G. Davy in 1807 for the first time received free potassium and sodium. J. Berzelius proposed to name element No. 11 sodium (from Arabic natrun- soda), and element No. 19, at Gilbert’s suggestion, was named potassium (from the Arabic alkali– alkali).
The remaining metals were isolated by scientists from the compounds later. Lithium was discovered by the Swedish chemist I. Arfvedson in 1817, and at the suggestion of J. Berzelius it was called lithium (from the Greek litos- stone), because Unlike potassium, which until then had only been found in plant ashes, it was found in stone.
Rubidium was isolated in 1861, cesium in 1860. Francium was obtained artificially in 1939. French researcher M. Pere during the decay of actinium, is a radioactive element.
Due to their very easy oxidation, alkali metals occur in nature exclusively in the form of compounds. Some of their natural compounds, in particular sodium and potassium salts, are quite widespread; they are found in many minerals, plants, and natural waters.
Sodium and potassium are common elements: the content of each of them in the earth's crust is approximately 2% by weight. Both metals are found in various minerals and silicate-type burrow rocks.
Sodium chloride NaCl is found in seawater and also forms thick rock salt deposits in many places around the globe. The upper layers of these deposits sometimes contain quite significant amounts of potassium, mainly in the form of chloride KCl or double salts with sodium and magnesium KCl ∙MgCl 2. However, large accumulations of potassium salts of industrial importance are rare. The most important of them are the Solikamsk deposits (sylvinite) in Russia, the Strassfurt deposits in Germany and the Alsatian deposits in France.
Deposits of sodium nitrate NaNO 3 are located in Chile. The water of many lakes contains Na 2 CO 3 soda. Finally, huge quantities of sodium sulfate Na 2 SO 4 are found in the Kara-Bogaz-Gol Bay of the Caspian Sea, where this salt is deposited in a thick layer on the bottom during the winter months.
Lithium, rubidium and cesium are much less common than sodium and potassium. Lithium is the most common, but minerals containing it rarely form large accumulations. Rubidium and cesium are found in small quantities in some lithium minerals.
Francium is found in nature in insignificant quantities (there is hardly 500g of it on the entire globe); it is obtained artificially.
1.2. Structure and properties of alkali metal atoms
The electronic formula of the valence shell of alkali metal atoms is ns 1, i.e. the atoms of these elements have one valence electron in the s sublevel of the outer energy level. Accordingly, the stable oxidation state of alkali metals is +1.
All elements of the IA group are very similar in properties, which is explained by the similar structure of not only the valence electron shell, but also the outer one (with the exception of lithium).
As the radius of an atom in the Li – Na – K – Rb – Cs – Fr group increases, the bond between the valence electron and the nucleus weakens. Accordingly, in this series the ionization energy of alkali metal atoms decreases.
Having one electron in their valence shells, located at a great distance from the nucleus, alkali metal atoms easily give up an electron. This causes low ionization energy. As a result of ionization, E + cations are formed, which have a stable electronic configuration of noble gas atoms.
The table shows some properties of alkali metal atoms.
Characteristic
3 Li
11 Na
1 9K
37 Rb
55 Cs
87 Fr
Valence electrons
2s 1
3s 1
4s 1
5s 1
6s 1
7s 1
Molar mass, g/mol
23,0
39,1
85,5
132,9
Metallic radius of an atom, pm
Crystal radius of an atom, pm
Ionization energy,
kJ/mol
Alkali metals are the most typical representatives of metals: their metallic properties are especially pronounced.
1.3. Alkali metals are simple substances
Silvery-white soft substances (cut with a knife), with a characteristic shine on the freshly cut surface. When exposed to air, the shiny surface of the metal immediately becomes dull due to oxidation.
All of them are light and fusible, and, as a rule, their density increases from Li to Cs, and the melting point, on the contrary, decreases.
Characteristic
Li
Na
K
Rb
Cs
Fr
Density, g/cm 3
0,53
0,97
0,86
1,53
Hardness (diamond = 10)
Electrical conductivity (Hg = 1)
11,2
13,6
Melting point, C
Boiling point, C
1350
Standard electrode potential, V
3,05
2,71
2,92
2,93
2,92
Coordination number
4, 6
4, 6
6, 8
All alkali metals have negative standard redox potentials, large in absolute value. This characterizes them as very strong reducing agents. Only lithium is somewhat inferior to many metals in chemical activity.
Despite the similarity of properties, sodium and especially lithium differ from other alkali metals. The latter is primarily due to the significant difference in the radii of their atoms and the structure of the electron shells.
Alkali metals are among the most chemically active elements. The chemical activity of alkali metals naturally increases with increasing atomic radius.
Li Na K Rb Cs Fr
Chemical activity increases
The radius of the atom increases
Alkali metals actively interact with almost all non-metals.
When interacting with oxygen lithium forms the oxide Li 2 O, and the remaining alkali metals form peroxides Na 2 O 2 and superoxides KO 2, RbO 2, CsO 2. For example:
4Li (t) + O 2 (g) = 2Li 2 O (t)
2Na (t) + O 2 (g) = Na 2 O 2 (t)
K (t) + O 2 (g) = KO 2 (t)
Alkali metals react actively with halogens, forming EG halides; with sulfur- with the formation of E 2 S sulfides. Alkali metals, with the exception of lithium, do not react directly with nitrogen.
2E(t) + Cl 2 (g) = 2ECl (t)
2E(t) + S (t) = E 2 S (t)
All alkali metals react directly with water, forming EON hydroxides - alkalis and reducing water to hydrogen:
2E (t) + 2H 2 O (l) = 2EON (r) + H 2 (g)
The intensity of interaction with water increases significantly in the Li-Cs series.
The reducing power of alkali metals is so great that they can even reduce hydrogen atoms, turning them into negatively charged H - ions. Thus, when heating alkali metals in a jet hydrogen their hydrides are obtained, for example:
2E(t) + N 2 (g) = 2EN
1.4. Application of alkali metals
Alkali metals and their compounds are widely used in technology.
Lithium is used in nuclear energy. In particular, the 6 Li isotope serves as an industrial source for the production of tritium, and the 7 Li isotope is used as a coolant in uranium reactors. Due to the ability of lithium to easily combine with hydrogen, nitrogen, oxygen, and sulfur, it is used in metallurgy to remove traces of these elements from metals and alloys.
Lithium and its compounds are also used as fuel for rockets. Lubricants containing lithium compounds retain their properties over a wide temperature range. Lithium is used in ceramics, glass and other chemical industries. In general, in terms of importance in modern technology, this metal is one of the most important rare elements.
Cesium and rubidium are used to make solar cells. These devices, which convert radiant energy into electric current energy and are based on the phenomenon of the photoelectric effect, use the ability of cesium and rubidium atoms to split off valence electrons when exposed to radiant energy on the metal.
The most important areas of application of sodium are nuclear energy, metallurgy, and the organic synthesis industry.
In nuclear energy, sodium and its alloy with potassium are used as liquid metal coolants. The alloy of sodium with potassium, containing 77.2% potassium, is in a liquid state over a wide temperature range, has a high heat transfer coefficient and does not interact with most structural materials.
In metallurgy, a number of refractory metals are obtained using the sodium thermal method. In addition, sodium is used as an additive to strengthen lead alloys.
In the organic synthesis industry, sodium is used in the production of many substances. It also serves as a catalyst in the production of some organic polymers.
Potassium is one of the elements required in significant quantities for plant nutrition. Although there is quite a lot of potassium salts in the soil, a lot of it is also carried away with some cultivated plants. Flax, hemp and tobacco carry away especially much potassium. To replenish the loss of potassium from the soil, it is necessary to add potassium fertilizers to the soil.
1.5. Alkali metal compounds
Oxides E 2 ABOUT- solids. They have pronounced basic properties: they interact with water, acids and acid oxides. For example:
E 2 O(t) + H 2 O(l) = 2EON (p)
Peroxides and superoxides E 2 ABOUT 2 and EO 2 alkali metals are strong oxidizing agents. Sodium peroxide and potassium superoxide are used in closed objects (submarines, spacecraft) to absorb carbon dioxide and regenerate oxygen:
2Na 2 O 2 (t) + 2CO 2 (g) = 2Na 2 CO 3 (t) + O 2 (g)
4KO 2 (t) + 2CO 2 (g) = 2K 2 CO 3 (t) + 3O 2 (g)
Sodium peroxide is also used to bleach fabrics, wool, silk, etc.
Alkalis– solid, white, very hygroscopic crystalline substances, relatively fusible and highly soluble in water (with the exception of LiOH). Solid alkalis and their concentrated solutions have a corrosive effect on fabrics, paper and living tissues due to dehydration and alkaline hydrolysis of proteins. Therefore, working with them requires protective precautions. Due to their strong corrosive effect, these alkalis are called caustic (NaOH - caustic soda, caustic, KOH - caustic potassium).
Alkalies dissolve well in water with the release of a large amount of heat, exhibit pronounced properties of strong soluble bases: they interact with acids, acid oxides, salts, amphoteric oxides and hydroxides.
Caustic soda is used in large quantities to purify petroleum products. in the paper and textile industries, for the production of soap and fibers.
Caustic potassium is more expensive and is used less frequently. Its main area of application is the production of liquid soap.
Alkali metal salts– solid crystalline substances of ionic structure. The most important of them are carbonates, sulfates, and chlorides.
Most alkali metal salts are highly soluble in water (with the exception of lithium salts: Li 2 CO 3, LiF, Li 3 PO 4).
With polybasic acids, alkali metals form both medium (E 2 SO 4, E 3 PO 4, E 2 CO 3, E 2 SO 3, etc.) and acidic (ENSO 4, EN 2 PO 4, E 2 NPO 4, ENSO 3, etc.) salts.
Na 2 CO 3 - sodium carbonate, forms crystalline hydrate Na 2 CO 3 ∙10H 2 CO 3, known as crystalline soda, which is used in the production of glass, paper, and soap. This is medium salt.
In everyday life, the more commonly known acidic salt is sodium bicarbonate NaHCO 3; it is used in the food industry (baking soda) and in medicine (baking soda).
K 2 CO 3 - potassium carbonate, technical name - potash, used in the production of liquid soap and for the preparation of refractory glass, and also as a fertilizer.
Na 2 SO 4 ∙10H 2 O – sodium sulfate crystalline hydrate, technical name Glauber’s salt, is used for the production of soda and glass, and also as a laxative.
NaCl - sodium chloride, or table salt, is the most important raw material in the chemical industry and is widely used in everyday life.
2. Biological role of s-elements of group IA. Their use in medicine
Chemical element, E
10 -4 %
0,08%
0,23%
10 -5 %
10 -4 %
Alkali metals in the form of various compounds are part of human and animal tissues.
Sodium and potassium are vital elements that are constantly present in the body and participate in metabolism. Lithium, rubidium and cesium are also constantly contained in the body, but their physiological and biochemical role is poorly understood. They can be classified as trace elements.
In the human body, alkali metals are found in the form of the E + cation.
The similarity of the electronic structure of alkali metal ions, and, consequently, the physicochemical properties of the compounds also determines the similarity of their effect on biological processes. Differences in electronic structure determine their different biological roles. On this basis, it is possible to predict the behavior of alkali metals in living organisms.
Thus, sodium and lithium accumulate in the extracellular fluid, and potassium, rubidium and cesium accumulate in the intracellular fluid. Lithium and sodium are especially close in biological action. For example, they are very similar in their enzyme-activating properties.
The similarity of the properties of sodium and lithium determines their interchangeability in the body. In this regard, with excessive introduction of sodium or lithium ions into the body, they are able to equivalently replace each other. This is the basis for the administration of sodium chloride in cases of lithium salt poisoning. In accordance with Le Chatelier's principle, the balance between sodium and lithium ions in the body shifts towards the elimination of Li + ions, which leads to a decrease in its concentration and the achievement of a therapeutic effect.
Rubidium and cesium are close in physical and chemical properties to potassium ions, so they behave in a similar way in living organisms. In the systems studied, potassium, rubidium and cesium are synergists, and with lithium they are antagonists. The similarity of rubidium and potassium is the basis for the introduction of potassium salts into the body in case of poisoning with rubidium salts.
Sodium and potassium, as a rule, are antagonists, but in some cases the similarity of many physicochemical properties determines their interchange in living organisms. For example, with an increase in the amount of sodium in the body, the excretion of potassium by the kidneys increases, i.e., hypokalemia occurs.
Lithium. The lithium content in the human body is about 70 mg (10 mmol). Lithium is one of the most valuable microelements, or, as they also call it, mini-metals. Lithium was once used to treat gout and eczema. And in 1971 An interesting message appeared in the magazine “Medical News”: in those areas where drinking water contains large amounts of lithium, people are kinder and calmer, there are fewer rude people and brawlers among them, and there are significantly fewer mental illnesses. The psychotropic properties of this metal were revealed. Lithium began to be used for depression, hypochondria, aggressiveness and even drug addiction.
However, lithium can be both “good” and “evil”. There have been cases when, during injection treatment with lithium, a powerful metabolic disorder occurred, and serious consequences of this are inevitable.
Lithium compounds in higher animals are concentrated in the liver, kidneys, spleen, lungs, blood, and milk. The maximum amount of lithium is found in human muscles. The biological role of lithium as a trace element has not yet been fully elucidated.
It has been proven that at the level of cell membranes, lithium ions compete with sodium ions when entering cells. Obviously, the replacement of sodium ions in cells with lithium ions is associated with a greater covalency of lithium compounds, as a result of which they are better soluble in phospholipids.
It has been established that some lithium compounds have a positive effect on patients with manic depression. Absorbed from the gastrointestinal tract, lithium ions accumulate in the blood. When the concentration of lithium ions reaches 0.6 mmol/l and above, there is a decrease in emotional tension and a weakening of manic excitement. However, the content of lithium ions in the blood plasma must be strictly controlled. In cases where the concentration of lithium ions exceeds 1.6 mmol/l, negative phenomena are possible.
It is now known that in addition to psychotropic effects, lithium has properties to prevent sclerosis, heart disease, and to some extent diabetes and hypertension. It “helps” magnesium in its anti-sclerotic protection.
At the end of 1977 The results of studies conducted at the Krakow Hematology Clinic were published. The studies were devoted to the influence of lithium on the hematopoietic system. It turned out that this microelement activates the action of bone marrow cells that have not yet died. The discovery could play an important role in the fight against blood cancer. Research is still ongoing. I would like to believe that their results will bring invaluable help to people.
Sodium. The sodium content in the human body weighing 70 kg is about 60 g (2610 mmol). Of this amount, 44% of sodium is in the extracellular fluid and 9% in the intracellular fluid.
The remaining amount of sodium is found in bone tissue, which is the site of deposition of Na + ion in the body. About 40% of the sodium contained in bone tissue is involved in metabolic processes and due to this, the skeleton is either a donor or acceptor of sodium ions, which helps maintain a constant concentration of sodium ions in the extracellular fluid.
Sodium is the main extracellular ion. The human body contains sodium in the form of its soluble salts, mainly NaCl chloride, Na 3 PO 4 phosphate and NaHCO 3 bicarbonate.
Sodium is distributed throughout the body: in blood serum, cerebrospinal fluid, eye fluid, digestive juices, bile, kidneys, skin, bone tissue, lungs, brain.
Sodium ions play an important role in ensuring the constancy of the internal environment of the human body, participates in maintaining a constant osmotic pressure of the biofluid, and ensures the acid-base balance of the body. Sodium ions are involved in the regulation of ion exchange and affect the functioning of enzymes. Together with potassium, magnesium, calcium, and chlorine ions, sodium ion participates in the transmission of nerve impulses through the membranes of nerve cells and maintains normal excitability of muscle cells.
When the sodium content in the body changes, dysfunctions of the nervous, cardiovascular and other systems, smooth and skeletal muscles occur. Sodium chloride NaCl serves as the main source of hydrochloric acid for gastric juice.
Sodium enters the human body mainly in the form of table salt NaCl. The body's true daily need for sodium is 1g, although the average consumption of this element reaches 4 - 7g.
Continuous excess consumption of NaCI contributes to the appearance of hypertension. In the body of a healthy person, a balance is maintained between the amount of sodium consumed and excreted. About 90% of sodium consumed is excreted in urine, and the rest in sweat and feces.
So, to summarize: sodium ions play an important role:
to ensure osmotic homeostasis
to ensure the acid-base balance of the body
in the regulation of water metabolism
in the work of enzymes
in the transmission of nerve impulses
in the work of muscle cells
Isotonic solutionNaCI (0,9%) for injection, it is administered subcutaneously, intravenously and in enemas for dehydration and intoxication, and is also used for washing wounds, eyes, nasal mucosa, as well as for dissolving various medications.
Hypertonic solutionsNaCI (3-5-10%) used externally in the form of compresses and lotions in the treatment of purulent wounds. The use of such compresses promotes, by the law of osmosis, the separation of pus from wounds and plasmolysis of bacteria (antimicrobial effect). A 2-5% NaCI solution is prescribed orally for gastric lavage in case of AgNO 3 poisoning, which is converted into slightly soluble and non-toxic silver chloride:
Ag + + CI - = AgCI (t)
Drinking soda(sodium bicarbonate, bicarbonate of soda) NaHCO 3 is used for various diseases accompanied by high acidity - acidosis (diabetes, etc.). The mechanism for reducing acidity is the interaction of NaHCO 3 with acidic products. In this case, sodium salts of organic acids are formed, which are largely excreted in the urine, and carbon dioxide, which leaves the body with exhaled air:
NaHCO3 (p) + RCOOH (p) → RCOONa(p) + H 2 O(l) + CO 2 (g)
NaHCO 3 is also used for increased acidity of gastric juice, gastric and duodenal ulcers. When taking NaHCO 3, a neutralization reaction of excess hydrochloric acid occurs:
NaHCO 3 (s) + HCl (s) = NaCl (s) + H 2 O (l) + CO 2 (g)
It should be borne in mind that the use of baking soda should be careful, because... may cause a number of side effects.
Solutions of baking soda are used as rinses and washes for inflammatory diseases of the eyes and mucous membranes of the upper respiratory tract. The action of NaHCO 3 as an antiseptic is based on the fact that, as a result of hydrolysis, an aqueous soda solution exhibits slightly alkaline properties:
NaHCO 3 + H 2 O ↔ NaOH + H 2 CO 3
When microbial cells are exposed to alkalis, precipitation of cellular proteins occurs and, as a result, the death of microorganisms.
Glauber's salt(sodium sulfate) Na 2 SO 4 ∙10H 2 O is used as a laxative. This salt is slowly absorbed from the intestine, which leads to the maintenance of increased osmotic pressure in the intestinal cavity for a long time. As a result of osmosis, water accumulates in the intestines, its contents become liquefied, intestinal contractions intensify, and feces are eliminated faster.
Borax(sodium tetraborate) Na 2 B 4 O 7 ∙10H 2 O is used externally as an antiseptic for rinsing, douching, and lubricating. the antiseptic effect of borax is similar to the effect of baking soda and is associated with the alkaline reaction of the aqueous solution of this salt, as well as with the formation of boric acid:
Na 2 B 4 O 7 + 7H 2 O ↔ 4H 3 BO 3 + 2NaOH
Sodium hydroxide in the form of a 10% NaOH solution, it is included in the composition of silane, used in orthopedic practice for casting fire-resistant models in the manufacture of solid prostheses from a cobalt-chrome alloy.
Radioactive isotope 24 Na is used as a tracer to determine the speed of blood flow, and it is also used to treat some forms of leukemia.
Potassium. The potassium content in the human body weighing 70 kg is approximately 160 g (4090 mmol). Potassium is the main intracellular cation, accounting for 2/3 of the total active cellular cations. In most cases, potassium is an antagonist to sodium.
Of the total amount of potassium contained in the body, 98% is found inside cells and only about 2% is in extracellular fluid. Potassium is distributed throughout the body. Its topography: liver, kidneys, heart, bone tissue, muscles, blood, brain, etc.
Potassium ions K+ play an important role in physiological processes:
muscle contraction
in the normal functioning of the heart
participates in the transmission of nerve impulses
in exchange reactions
activates the work of a number of enzymes located inside the cell
regulates acid-base balance
It has protective properties against the unwanted effects of excess sodium and normalizes blood pressure. In the body of people who eat a lot of potassium-rich vegetables - vegetarians - the amount of potassium and sodium are in balance. These people most often have lower blood pressure than their meat-loving fellow citizens.
Has an antisclerotic effect
Potassium has the ability to enhance urine formation
An adult usually consumes 2–3 g of potassium per day with food. The concentration of potassium ions in the extracellular fluid, including plasma, is normally 3.5 - 5.5 mmol/l, and the concentration of intracellular potassium is 115 - 125 mmol/l.
Rubidium and cesium. According to their content in the human body, rubidium and cesium are classified as microelements. They are constantly contained in the body, but their biological role has not yet been clarified.
Rubidium and cesium are found in all studied organs of mammals and humans. Entering the body with food, they are quickly absorbed from the gastrointestinal tract into the blood. The average level of rubidium in the blood is 2.3-2.7 mg/l, and its concentration in erythrocytes is almost three times higher than in plasma. Rubidium and cesium are distributed very evenly in organs and tissues, and rubidium mainly accumulates in the muscles, and cesium enters the intestine and is reabsorbed in its descending sections.
The role of rubidium and cesium in some physiological processes is known. Currently, the stimulating effect of these elements on circulatory functions and the effectiveness of the use of their salts for hypotension of various origins have been established. In the laboratory of I.P. Pavlov, S.S. Botkin found that cesium and rubidium chlorides cause an increase in blood pressure for a long time and that this effect is associated mainly with increased cardiovascular activity and constriction of peripheral vessels.
Being a complete analogue of potassium, rubidium also accumulates in intracellular fluid and can replace an equivalent amount of potassium in various processes. Synergism (chemical) is the simultaneous combined effect of two (or more) factors, characterized by the fact that such a combined effect significantly exceeds the effect of each individual component. A potassium synergist, rubidium activates many of the same enzymes as potassium.
Radioactive isotopes 137 Cs and 87 Rb are used in radiotherapy of malignant tumors, as well as in the study of potassium metabolism. Due to their rapid breakdown, they can even be introduced into the body without fear of long-term harmful effects.
Franc. It is a radioactive chemical element obtained artificially. There is evidence that francium is capable of selectively accumulating in tumors at the earliest stages of their development. These observations may be useful in diagnosing cancer.
Thus, Of the IA group elements, Li, Rb, Cs are physiologically active, and Na and K are vital. The similarity of the physicochemical properties of Li and Na, due to the similarity of the electronic structure of their atoms, is also manifested in the biological action of cations (accumulation in extracellular fluid, interchangeability). The similar nature of the biological action of cations of elements of long periods - K +, Rb +, Cs + (accumulation in intracellular fluid, interchangeability) is also due to the similarity of their electronic structure and physicochemical properties. This is the basis for the use of sodium and potassium preparations for poisoning with lithium and rubidium salts.
3. Routes of entry of alkali metals
into the human body
The ways in which chemical elements enter the human body are varied; they are presented in the diagram:
Human
In the process of evolution from inorganic to bioorganic substances, the basis for the use of certain chemical elements in the creation of biological systems is natural selection.
The table shows data on the content of group I A elements - alkali metals - in the earth's crust, sea water, plant and animal organisms and in the human body (mass fraction in %).
The table shows that the greater the abundance of an element in the earth’s crust, the more it is in the human body.
Li
Na
K
Rb
Cs
Earth's crust
6,5∙10 -3
0,03
accurate data
No
The soil
3∙10 -3
0,63
1,36
5∙10 -3
Sea water
1,5∙10 -5
1,06
0,038
2∙10 -5
Plants
1∙10 -5
0,02
5∙10 -4
Animals
10 -4
0,27
10 -5
Human
10 -4
0,08
0,23
10 -5
10 -4
The alkali metals most necessary for the human body are sodium and potassium. Almost all elements enter the human body mainly through food.
Lithium sources.
Lithium is found in some mineral waters, as well as sea and rock salt. It is also found in plants, but its concentration, like any microelements, depends not only on the type and part of the plant, but also on the time of year and even day, on collection conditions and weather, as well as on the area where this plant grows.
In our country, lithium was studied by employees of the Institute of Geochemistry named after Acad. V.I. Vernadsky in Moscow. It was found that the above-ground parts of plants are richer in lithium than the roots. Most lithium is found in plants of the rose family, cloves, and nightshades, which include tomatoes and potatoes. Although within one family the difference in its content can be enormous - several dozen times. This depends on the geographic location and lithium content in the soil.
Sources of sodium.
Sodium is present in various dietary supplements in the form of monosodium glutamate (flavor), sodium saccharin (sweetener), sodium nitrate (preservative), sodium ascorbate (antioxidant) and sodium bicarbonate (baking soda), as well as in some medications (antacids). However, most of the sodium in the diet comes from salt.
NaCl levels are relatively low in all foods that have not been specially processed. However, salt has been used as a preservative and flavoring for several centuries. It is also used as a dye, filler and to control the fermentation process (for example, when baking bread). For this reason, it is added to foods such as ham, sausages, bacon and other meat products, smoked fish and meats, canned vegetables, most butters, margarine, cheese, unsweetened foods, snack foods, and the cereals we eat at home. breakfast.
The recommended sodium intake is 1.5 grams in a day. Excess salt in the diet is associated with an increased likelihood of stomach cancer and is harmful to the kidneys, especially if they have any problems with the urinary system. Excess salt is one of the leading lifestyle factors that leads to hypertension. If hypertension is asymptomatic, it increases the risk of cardiovascular disease and stroke. Current guidelines for the prevention of hypertension have shown that the most effective diet for the prevention and treatment of high blood pressure should be low in sodium and fat and include large amounts of low-fat dairy products (a source of calcium) and fruits and vegetables (a source of potassium). Thus, it is important to change the diet as a whole, rather than focusing on any one component of the diet. Other important positive factors include physical activity and normal body weight.
People with kidney disease and very young children cannot tolerate large amounts of sodium because their kidneys cannot eliminate it. For this reason, you should not add salt to the food of young children.
By law, food labels must list sodium content, but some manufacturers ignore this rule and list the amount of salt.
We remember: “ Table salt can be annoying our health!»
Sources of potassium.
The best source of potassium is plant foods. These are watermelons, melons, oranges, tangerines, bananas, dried fruits (figs, apricots, rose hips). Berries rich in potassium include lingonberries, strawberries, black and red currants. There is a lot of potassium in vegetables (especially potatoes), legumes, wholemeal products, and rice.
The body's reaction to potassium deficiency.
With a lack of potassium in the body, muscle weakness, intestinal lethargy, and cardiac dysfunction are observed.
“I haven’t gotten up yet, I’m already tired” - this is how the doctor figuratively and clearly characterizes potassium deficiency in the body. A low potassium content in the body usually leads to asthenia (mental and physical exhaustion, fatigue), impaired renal function and depletion of the adrenal cortex. There is a risk of disruption of metabolic processes and conductivity in the myocardium.
Potassium deficiency reduces performance, slows down wound healing, and leads to impaired neuromuscular conduction. Dry skin, dullness and weakness of hair are noted (this is a matter of serious concern, especially for women and girls).
Sudden death may occur with increasing stress. There is poor transmission of nerve impulses. Diuretics (diuretics) reduce potassium absorption. When preparing food, it is necessary to pay attention to the fact that potassium compounds are water-soluble. This circumstance requires you to wash products containing it before chopping them and cook them in a small amount of water.
By the way, traditional medicine believes that the passionate desire to drink alcohol is associated with a lack of potassium in the body.
For potassium depletion use potassium chloride KCl 4 - 5 times a day, 1 g.
The body's reaction to excess potassium.
With an excess of potassium in the body, the main functions of the heart are inhibited: a decrease in the excitability of the heart muscle, a slowdown in the heart rate, deterioration of conductivity, and a weakening of the force of heart contractions. In high concentrations, potassium ions cause cardiac arrest in diastole (the contraction phase of the ventricles of the heart). The toxic dose of potassium is 6 g. The lethal dose is 14 g. Potassium salts can be toxic to the body due to the anion associated with the potassium ion, for example, KCN (potassium cyanide).
To regulate the content of these nutrients, you can take into account the data presented in the following table.
4. Practical part
Experience 1.Flame coloring with compounds.
One of the methods for qualitative detection of alkali metal compounds is based on their ability to color the burner flame.
Solutions of alkali metal salts must be poured into test tubes. Wash the iron wire in hydrochloric acid and then ignite it in a burner flame.
Then you need to moisten the wire with a solution of the salt being tested and add it to the flame.
Salts containing lithium cations, as well as lithium color the flames red color, sodium cations and metal sodium- V yellow, potassium cations and metal potassium color the flames violet color. For better observation, you can view the color through blue glass.
Thus, Li +, Na + and K + ions were discovered in solutions of salts LiCl, NaCl, Na 2 CO 3, Na 2 SO 4, NaNO 3, KCl, KNO 3, K 2 CO 3.
Experience 2.Interaction of alkali metals with water.
Add a piece of metal, thoroughly cleaned of the oxide film, into a glass of water. After dissolving the metal, the solution medium was examined using phenolphthalein.
Carry out this experiment with pieces of lithium, sodium and potassium. The reaction with potassium was most active; it was accompanied by the combustion of potassium, violet sparks and gas evolution were observed. Sodium reacted with water, producing yellow sparks, while lithium reacted most calmly.
The resulting solutions with phenolphthalein turned crimson, indicating the presence of alkali in the solution.
2Li + 2H 2 O = 2LiOH + H 2
2Na + 2H 2 O = 2NaOH + H 2
2K + 2H 2 O = 2KOH + H 2
Experience 3. Hydrolysis of sodium and potassium salts.
The nature of the salt solution environment is studied using acid-base indicators.
Universal indicator papers dipped into solutions of alkali metal salts formed by weak acids Na 2 CO 3 and K 2 CO 3 turned blue, which indicates an alkaline reaction of the solutions. hydrolysis occurred in solutions - the interaction of salts with water molecules:
Na 2 CO 3 ↔ 2Na + + CO 3 2-
CO 3 2- + H 2 O ↔ HCO 3 - + OH -
Na 2 CO 3 + H 2 O ↔ NaHCO 3 + NaOH
Solutions of salts of strong acids NaNO 3, KNO 3, NaCl, KCl, LiCl showed a neutral environment (the color of the indicator paper did not change), which means that hydrolysis of these salts does not occur
conclusions
Why is it so important to know the content of chemical elements in the body?
Chemical elements are not synthesized, unlike many organic substances, in the body, but come from outside with food, air, through the skin and mucous membranes. Therefore, the determination of chemical elements allows you to find out about:
how much does your body correspond to the ideal (by the way, about 20% of people do not have any deviations and, thus, live in harmony with nature);
Are you eating right, does your diet provide the necessary set of nutrients;
Do bad habits harm the body?
how safe is the environment in which you live; the food you eat; Your workplace;
do your stomach, intestines, liver, kidneys, skin function well, regulating the processes of absorption and excretion of nutrients;
Do you have any chronic diseases or a predisposition to them?
Are you being treated correctly?
What diseases are most closely related to elemental imbalance?
First of all, this is:
decreased immunity;
diseases of the skin, hair, nails;
scoliosis, osteoporosis, osteochondrosis;
hypertension;
allergies, including bronchial asthma;
diabetes, obesity;
diseases of the cardiovascular system;
blood diseases (anemia);
intestinal dysbiosis, chronic gastritis, colitis;
infertility, decreased potency in men;
impaired growth and development in children.
Many years of experience of doctors shows that more than 80% of the population have a more or less pronounced imbalance of microelements. Therefore, if you have any , you should pay attention to this!
Many scientists believe that not only are all chemical elements present in a living organism, but each of them performs a specific biological function.
We have clarified the biological role of only one group of chemical elements. Alkali metals are extremely important for human health, like most others. It is very important for human health to maintain the optimal concentration of each element: both a deficiency of an element and its excess are harmful.
The stability of the chemical composition of the body is one of the most important and mandatory conditions for its normal functioning. .
There is an erroneous, although widespread, opinion about the possibility of correcting an imbalance in the elemental composition of the human body by enriching the diet with certain products containing the necessary mineral elements. However, it should be taken into account that the presence of necessary macro- and microelements in food and water (which is especially obvious for residents of rural areas) depends to a large extent on the so-called “local biogeochemical cycle” of elements, which determines the content of macro- and microelements in food plants and animals.
A deficiency or excess of certain elements in the human body, as a rule, is a consequence of a deficiency or excess of these elements passing through the food chain: from soil to plants and animals to humans. When a deficiency of any element develops, nutritional correction is not enough, even if products from other regions are used for this purpose, the soils of which are enriched with the necessary microelement.
Only an individual selection of special mineral and other preparations aimed at normalizing the microelement balance of the body will provide real and effective help in the development of a pathological condition.
In conclusion, we present the commandments of traditional and scientific medicine that everyone should know:
Everything is connected to everything.
Everything has to go somewhere.
Nature knows best.
Nothing comes for free.
Used Books
1. Gabrielyan O.S. Chemistry, 9th grade, Textbook for educational institutions. - M. “Bustard”, 2001
2. Glinka N.L. General chemistry, Textbook for universities. - L. “Chemistry”, 1983
3. General chemistry. Chemistry of biogenic elements. Textbook for honey. specialist. call. Yu.A. Ershov and others - M. “Higher School”, 1993
4. Sychev A.P., Fadeev G.N. Chemistry of metals. Tutorial. – M. “Enlightenment”, 1984
5. MHTML. Do c ument. integrated lesson “Alkali metals”. Festival "Open Lesson", 2003
6.
7.
Alkali metals are a group of inorganic substances, simple elements of the periodic table. They all have a similar atomic structure and, accordingly, similar properties. The group includes potassium, sodium, lithium, cesium, rubidium, francium and the theoretically described but not yet synthesized element ununennium. The first five substances exist in nature, francium is an artificially created, radioactive element. Alkali metals got their name from their ability to form alkalis in reaction with water.
All elements of the group are chemically active, therefore they are found on Earth only in the composition of various minerals, for example, rock, potassium, table salt, borax, feldspar, sea water, underground brines, Chilean nitrate. Francium often accompanies uranium ores; rubidium and cesium - minerals with sodium and potassium.
Properties
All representatives of the group are soft metals; they can be cut with a knife or bent by hand. Externally - shiny, white (except for cesium). Cesium has a golden sheen. Lightweight: sodium and potassium are lighter than water, lithium floats even in kerosene. Classic metals with good electrical and thermal conductivity. They burn and give the flame a characteristic color, which is one of the analytical ways to determine the type of metal. Low-melting, the most “refractory” is lithium (+180.5 °C). Cesium melts right in your hands at a temperature of +28.4 °C.
The activity in the group increases as the atomic mass increases: Li →Cs. They have reducing properties, including in reaction with hydrogen. They exhibit a valence of -1. React violently with water (all except lithium - explosively); with acids and oxygen. They interact with non-metals, alcohols, aqueous ammonia and its derivatives, carboxylic acids, and many metals.
Potassium and sodium are biogenic elements, participate in the water-salt and acid-base balance of the human body, and are necessary for normal blood circulation and the functioning of many enzymes. Potassium is important for plants.
Our body also contains rubidium. It was found in blood, bones, brain, lungs. It has an anti-inflammatory, anti-allergic effect, slows down the reactions of the nervous system, strengthens the immune system, and has a positive effect on blood composition.
Precautionary measures
Alkali metals are very dangerous and can ignite and explode simply from contact with water or air. Many reactions occur violently, so it is allowed to work with them only after careful instructions, using all precautions, wearing a protective mask and safety glasses.
Solutions of potassium, sodium and lithium in water are strong alkalis (potassium, sodium, lithium hydroxides); contact with skin results in deep, painful burns. Contact of alkalis, even low concentrations, in the eyes can lead to blindness. Reactions with acids, ammonia, and alcohols result in the release of flammable and explosive hydrogen.
Alkali metals are stored under a layer of kerosene or petroleum jelly in sealed containers. Manipulations with pure reagents are carried out in an argon atmosphere.
Care should be taken to dispose of residues from experiments with alkali metals. All metal residues must first be neutralized.
Application
Alkali metals are s-elements. In the outer electron layer, each of them has one electron (ns1). The radii of atoms from top to bottom in the subgroup increase, the ionization energy decreases, and the reduction activity, as well as the ability to donate valence electrons from the outer layer, increases.
The metals in question are very active, so they are not found in nature in a free state. They can be found in the form of compounds in minerals (table salt NaCl, sylvinite NaCl∙KCl, Glauber's salt NaSO4∙10H2O and others) or as ions in sea water.
Physical properties of alkali metals
All alkali metals under normal conditions are silvery-white crystalline substances with high thermal and electrical conductivity. They have body-centered cubic packing (BCCP). The densities, boiling and melting points of group I metals are relatively low. From top to bottom in the subgroup, densities increase and melting temperatures decrease.
Preparation of alkali metals
Alkali metals are usually obtained by electrolysis of molten salts (usually chlorides) or alkalis. During the electrolysis of NaCl melt, for example, pure sodium is released at the cathode, and chlorine gas is released at the anode: 2NaCl(melt)=2Na+Cl2.
Chemical properties of alkali metals
In terms of chemical properties, lithium, sodium, potassium, rubidium, cesium and francium are the most active metals and one of the most powerful reducing agents. In reactions, they easily give up electrons from the outer layer, turning into positively charged ions. In compounds formed by alkali metals, ionic bonding predominates.
When alkali metals interact with oxygen, peroxides are formed as the main product, and oxides as a by-product:
4Na+O2=2Na2O (sodium oxide).
With halogens they give halides, with sulfur - sulfides, with hydrogen - hydrides:
2Na+Cl2=2NaCl (sodium chloride),
2Na+S=Na2S (sodium sulfide),
2Na+H2=2NaH (sodium hydride).
Sodium hydride is an unstable compound. It decomposes with water, yielding alkali and free hydrogen:
NaH+H2O=NaOH+H2.
Free hydrogen is also formed when alkali metals themselves react with water:
2Na+2H2O=2NaOH+H2.
These metals also react with dilute acids, displacing hydrogen from them:
2Na+2HCl=2NaCl+H2.
Alkali metals react with organic halides using the Wurtz reaction.
Alkali metals- these are the elements of the 1st group of the periodic table of chemical elements (according to the outdated classification - elements of the main subgroup of group I): lithium Li, sodium Na, potassium K, rubidium Rb, cesium Cs, France Fr, and despondent Uue. When alkali metals dissolve in water, soluble hydroxides are formed, called alkalis.
Chemical properties of alkali metals
Due to the high chemical activity of alkali metals towards water, oxygen, and sometimes even nitrogen (Li, Cs), they are stored under a layer of kerosene. To carry out a reaction with an alkali metal, a piece of the required size is carefully cut off with a scalpel under a layer of kerosene, the metal surface is thoroughly cleaned in an argon atmosphere from the products of its interaction with air, and only then the sample is placed in the reaction vessel.
1. Interaction with water. An important property of alkali metals is their high activity towards water. Lithium reacts most calmly (without explosion) with water:
When a similar reaction is carried out, 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 different compositions depending on the activity of the metal.
· Only lithium burns in air to form an oxide of stoichiometric composition:
· When burning sodium mainly Na 2 O 2 peroxide is formed with a small admixture of NaO 2 superoxide:
· In combustion products potassium, rubidium And cesium contains mainly superoxides:
To obtain sodium and potassium oxides, mixtures of hydroxide, peroxide or superoxide with an excess of metal are heated in the absence of oxygen:
The following pattern is characteristic of oxygen compounds of alkali metals: as the radius of the alkali metal cation increases, the stability of oxygen compounds containing peroxide ion O 2 2− and superoxide ion O 2− increases.
Heavy alkali metals are characterized by the formation of fairly stable ozonides composition of EO 3. All oxygen compounds have different 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, acidic 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 nonmetals. 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 capable of reacting with other metals, forming intermetallic compounds. Alkali metals react actively (explosively) 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 to form alkali and ammonia:
Alkali metals interact with organic substances, alcohols (to form alcoholates) and carboxylic acids (to form salts):
4. Qualitative determination of alkali metals. Since the ionization potentials of alkali metals are small, when the metal or its compounds are heated in a flame, the atom is ionized, coloring the flame a certain color:
Flame coloring with alkali metals
and their connections
Alkaline earth metals.
Alkaline earth metals- chemical elements of group II of the periodic table of elements: beryllium, magnesium, calcium, strontium, barium and radium.
Physical properties
All alkaline earth metals are gray substances that are solid at room temperature. Unlike alkali metals, they are significantly harder and generally cannot be cut with a knife (with the exception of strontium). The density of alkaline earth metals with atomic number increases, although growth is clearly observed only starting with calcium, which has the lowest density among them (ρ = 1.55 g/cm³), the heaviest is radium, the density of which is approximately equal to the density of iron.
Chemical properties
Alkaline earth metals have an outer energy level electronic configuration ns², and are s-elements, along with the alkali metals. Having two valence electrons, alkaline earth metals easily give them up, and in all compounds they have an oxidation state of +2 (very rarely +1).
The chemical activity of alkaline earth metals increases with increasing atomic number. Beryllium in its compact form does not react with oxygen or halogens, even at red heat temperatures (up to 600 °C; reactions with oxygen and other chalcogens require an even higher temperature, fluorine is an exception). Magnesium is protected by an oxide film at room temperature and higher temperatures (up to 650 °C) and does not oxidize further. Calcium oxidizes slowly and deeply at room temperature (in the presence of water vapor), and burns with slight heating in oxygen, but is stable in dry air at room temperature. Strontium, barium and radium quickly oxidize in air, giving a mixture of oxides and nitrides, so they, like alkali metals (and calcium), are stored under a layer of kerosene.
Oxides and hydroxides of alkaline earth metals tend to increase their basic properties with increasing atomic number: Be(OH) 2 is an amphoteric, water-insoluble hydroxide, but soluble in acids (and also exhibits acidic properties in the presence of strong alkalis), Mg(OH) 2 - weak base, insoluble in water, Ca(OH) 2 - strong but slightly soluble base in water, Sr(OH) 2 - more soluble in water than calcium hydroxide, strong base (alkali) at high temperatures close to the boiling point water (100 °C), Ba(OH) 2 is a strong base (alkali), not inferior in strength to KOH or NaOH, and Ra(OH) 2 is one of the strongest alkalis, a very corrosive substance
Being in nature
All alkaline earth metals are found (in varying quantities) in nature. Due to their high chemical activity, all of them are not found in a free state. The most common alkaline earth metal is calcium, the amount of which is 3.38% (by weight of the earth’s crust). It is slightly inferior to magnesium, the amount of which is 2.35% (of the mass of the earth’s crust). Barium and strontium are also common in nature, accounting for 0.05 and 0.034% of the mass of the earth's crust, respectively. Beryllium is a rare element, the amount of which is 6·10−4% of the mass of the earth's crust. As for radium, which is radioactive, it is the rarest of all alkaline earth metals, but it is always found in small quantities in uranium ores. In particular, it can be isolated from there chemically. Its content is 1·10−10% (of the mass of the earth’s crust)
Aluminum.
Aluminum- an element of the main subgroup of the third group of the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 13. Denoted by the symbol Al(lat. Aluminum). Belongs to the group of light metals. The most common metal and the third most abundant chemical element in the earth's crust (after oxygen and silicon).
Simple substance aluminum- a lightweight, paramagnetic metal of silver-white color, easy to form, cast, and machine. Aluminum has high thermal and electrical conductivity and resistance to corrosion due to the rapid formation of strong oxide films that protect the surface from further interaction.
Aluminum was first obtained by the Danish physicist Hans Oersted in 1825 by the action of potassium amalgam on aluminum chloride followed by distillation of mercury. The modern production method was developed independently by the American Charles Hall and the Frenchman Paul Héroux in 1886. It consists of dissolving aluminum oxide Al 2 O 3 in a melt of cryolite Na 3 AlF 6 followed by electrolysis using consumable coke or graphite electrodes. This production method requires a lot of electricity, and therefore became popular only in the 20th century.
To produce 1000 kg of crude aluminum, 1920 kg of alumina, 65 kg of cryolite, 35 kg of aluminum fluoride, 600 kg of anode mass and 17 thousand kWh of DC electricity are required
ALKALI METALS
SUBGROUP IA. ALKALI METALS
LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CESIUM, FRANCE
The electronic structure of alkali metals is characterized by the presence of one electron in the outer electron shell, which is relatively weakly bound to the nucleus. Each alkali metal begins a new period in the periodic table. The alkali metal is able to give up its outer electron more easily than any other element of this period. A cut of an alkali metal in an inert environment has a bright silvery sheen. Alkali metals are characterized by low density, good electrical conductivity, and melt at relatively low temperatures (Table 2).
Due to their high activity, alkali metals do not exist in pure form, but are found 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 the production of alkali metals in a free state. Sea water contains ALKALI METALS 3% NaCl and trace amounts of other salts. It is obvious that lakes and inland seas, as well as underground salt deposits and brines, contain alkali metal halides in higher concentrations than seawater. 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 changes with the time of year. It can be assumed that the insignificant content of KCl in seawater compared to NaCl is explained by the assimilation of the K+ ion by marine plants.
In their free form, alkali metals are obtained by electrolysis of molten 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 a 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 in their 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 in the third period, containing 18 elements (first transition period). In the alkali metal (IA) subgroup, 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, and Rb and Cs ignite. All alkali metals form with hydrogen salt-like hydrides of composition M+H, thermally stable at high temperatures, which are active reducing agents; hydrides decompose with water to form alkalis and hydrogen and release 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, forming blue solutions, and (unlike reaction with water) can be released again by evaporating the ammonia or adding an appropriate salt (for example, NaCl from its ammonia solution). When reacting with ammonia gas, the reaction proceeds similar to the reaction with water:
Alkali metal amides exhibit basic properties similar to hydroxides. Most alkali metal compounds, except 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 compounds of these elements are similar. In 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 stronger MO bonds. Lithium salts are more soluble in organic solvents (alcohols, ethers, petroleum solvents) than salts of other alkali metals. 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. Metals of subgroup IA react with carbon, but the interaction occurs most easily with lithium (obviously due to its small radius) and least easily with cesium. Conversely, active alkali metals react directly with CO, forming carbonyls (for example, K(CO)x), and 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, however, are brittle. Large quantities of sodium are consumed to produce the Na4Pb alloy, from which tetraethyl lead Pb(C2H5)4, an antiknock agent for gasoline fuel, is obtained. Lithium, sodium and calcium are used as components of soft bearing alloys. The single and therefore mobile electron in 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 the high temperatures in a nuclear reactor, are used to produce steam. Metallic sodium 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 when the hydride reacts with water. Lithium aluminum hydride LiAlH4 and lithium hydride are used as reducing agents in organic and inorganic synthesis. Due to its 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 air when operating 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 (more than 2.26 million tons are consumed per year in the USA alone).
Lithium. The lightest metal, it 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. Mathiesen in 1855. It is used in the production of thermonuclear weapons (hydrogen bombs), to increase the hardness of alloys and in pharmaceuticals. Lithium salts are used to increase the hardness and chemical resistance of glass, in alkaline battery technology, and 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), baking soda (sodium bicarbonate NaHCO3) and soda ash (sodium carbonate Na2CO3) are widely used. Metal is also used in the form of vapors in dim gas-discharge lamps for street lighting.
Potassium. Known since ancient times, it was also isolated by H. Davy in 1807. Potassium salts are well known: potassium nitrate (potassium nitrate KNO3), potash (potassium carbonate K2CO3), caustic potassium (potassium hydroxide KOH), etc. Potassium metal also finds various uses in technologies of heat transfer 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 chemically highly reactive and must be stored under a layer of oil or kerosene to avoid oxidation by atmospheric oxygen. Rubidium has a variety of uses, including solar cell technology, radiovacuum devices, and pharmaceuticals.
Cesium. Cesium compounds are widespread 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 using spectroscopy in 1860. The main use of cesium is the production of solar cells and electron tubes; one of the radioactive isotopes of cesium, Cs-137, is used in radiation therapy and scientific research.
Franc. The last member of the alkali metal family, francium, is so radioactive that it is not found in more than trace quantities in the earth's crust. Information about francium and its compounds is based on the study of an insignificant amount of it, artificially obtained (in a high-energy accelerator) during the a-decay of actinium-227. The longest-lived isotope 22387Fr decays in 21 minutes into 22388Ra and b-particles. As a rough estimate, the metallic radius of francium is 2.7. Francium has most of the properties characteristic of other alkali metals and is characterized by high electron-donating activity. It forms soluble salts and hydroxide. In all compounds, francium exhibits oxidation state I.
Collier's Encyclopedia. - Open Society. 2000 .