Atomic mass of iodine. Iodine: all about the chemical element and its role in human life

Iodine (Jodum), I (in the literature there is also the symbol J) - a chemical element of the VII group of the periodic system of D.I. Mendeleev, belonging to halogens (from the Greek halos - salt and genes - forming), which also include fluorine, chlorine , bromine and astatine.

The ordinal (atomic) number of iodine is 53, the atomic weight (mass) is 126.9.

Of all the elements that exist in nature, iodine is the most mysterious and contradictory in its properties.

The density (specific gravity) of iodine is 4.94 g / cm3, tnl - 113.5 ° С, tKn - 184.35 ° С.

Of the naturally occurring halogens, iodine is the heaviest, unless, of course, you count the radioactive short-lived astatine. Almost all natural iodine consists of atoms of one stable isotope with a mass number of 127. Radioactive 1-125 is formed as a result of spontaneous fission of uranium. Of the artificial isotopes of iodine, the most important are 1-131 and 1-123: they are used in medicine.

The elemental iodine molecule (J2), like other halogens, consists of two atoms. Violet iodine solutions are electrolytes (they conduct an electric current when a potential difference is applied), since in a solution the J2 molecules partially dissociate (decompose) into mobile ions J and J. A noticeable dissociation of J2 is observed at t above 700 ° C, as well as under the action of light. Iodine is the only halogen that is in a solid state under normal conditions, and is a grayish-black plate with a metallic sheen or crystal aggregates with a peculiar (characteristic) odor.

Distinct crystalline structure, the ability to conduct electric current - all these "metallic" properties are characteristic of pure iodine.

However, iodine stands out among other elements, including differing from metals, by the ease of transition to a gaseous state. It is even easier to convert iodine to vapor than to liquid. It is highly volatile and evaporates even at normal room temperature, forming a sharp-smelling purple vapor. With a weak heating of iodine, its so-called sublimation occurs, that is, a transition to a gaseous state bypassing a liquid one, then settling in the form of shiny thin plates; this process serves for the purification of iodine in laboratories and in industry.

Iodine is poorly soluble in water (0.34 g / l at 25 ° C, approximately 1: 5000), but it dissolves well in many organic solvents - carbon disulfide, benzene, alcohol, kerosene, ether, chloroform, as well as in aqueous solutions of iodides ( potassium and sodium), and in the latter the concentration of iodine will be much higher than that which can be obtained by direct dissolution of elemental iodine in water.

The color of iodine solutions in organic matter is not constant. For example, the iodine solution in carbon disulfide is violet, and in alcohol it is brown.

The configuration of the outer electrons of the iodine atom is ns2 np5. In accordance with this, iodine exhibits a variable valence (oxidation state) in the compounds: -1; +1; +3; +5 and +7.

Chemically, iodine is quite active, although to a lesser extent than chlorine and bromine, and even more so fluorine.

With light heating, iodine reacts vigorously with metals, forming colorless iodide salts.

Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide. With some elements - carbon, nitrogen, oxygen, sulfur and selenium - iodine does not combine directly. It is also incompatible with essential oils, ammonia solutions, white sedimentary mercury (an explosive mixture is formed).

Iodine(lat. Iodum), I, a chemical element of the VII group of the periodic table of Mendeleev, belongs to halogens (in the literature there is also the outdated name Iodine and the symbol J); atomic number 53, atomic weight 126.9045; crystals of black-gray color with a metallic sheen. Natural iodine consists of one stable isotope with a mass number of 127. Iodine was discovered in 1811 by the French chemist B. Courtois. Heating the mother brine of seaweed ash with concentrated sulfuric acid, he observed the release of purple vapor (hence the name Iodine - from the Greek iodes, ioeides - similar in color to a violet, purple), which condensed in the form of dark shiny lamellar crystals. In 1813-1814, the French chemist J.L. Gay-Lussac and the English chemist G. Davy proved the elementary nature of iodine.

Distribution of iodine in nature. The average content of iodine in the earth's crust is 4 · 10 -5% by weight. In the mantle and magmas and in the rocks formed from them (granites, basalts, and others), iodine compounds are dispersed; deep-seated iodine minerals are unknown. The history of iodine in the earth's crust is closely related to living matter and biogenic migration. Processes of its concentration are observed in the biosphere, especially by marine organisms (algae, sponges, and others). Eight hypergene minerals of iodine are known to form in the biosphere, but they are very rare. The main reservoir of iodine for the biosphere is the World Ocean (1 liter contains on average 5 · 10 -5 g of iodine). From the ocean, Iodine compounds, dissolved in drops of seawater, enter the atmosphere and are carried by winds to the continents. (Areas remote from the ocean or fenced off from sea winds by mountains are depleted in iodine) Iodine is easily adsorbed by organic matter of soils and sea silts. When these silts are compacted and sedimentary rocks are formed, desorption occurs, part of the iodine compounds pass into groundwater. This is how the iodine-bromine waters used for the extraction of iodine are formed, which are especially characteristic of the regions of oil fields (in some places, 1 liter of these waters contains over 100 mg of iodine).

Physical properties of iodine. The density of iodine is 4.94 g / cm 3, melting point 113.5 ° C, boiling point 184.35 ° C. The molecule of liquid and gaseous iodine consists of two atoms (I 2). A noticeable dissociation of I 2 = 2I is observed above 700 ° C, as well as under the action of light. Already at ordinary temperatures, iodine evaporates, forming a sharp-smelling violet vapor. With weak heating, iodine sublimes, settling in the form of shiny thin plates; this process serves for the purification of iodine in laboratories and in industry. Iodine is poorly soluble in water (0.33 g / l at 25 ° C), well - in carbon disulfide and organic solvents (benzene, alcohol and others), as well as in aqueous solutions of iodides.

Chemical properties of iodine. The configuration of the outer electrons of the iodine atom is 5s 2 5p 5. In accordance with this, iodine exhibits a variable valence (oxidation state) in compounds: -1 (in HI, KI), +1 (in HIO, KIO), +3 (in ICl 3), +5 (in HIO 3, KIO 3 ) and +7 (in HIO 4, KIO 4). Chemically, iodine is quite active, although to a lesser extent than chlorine and bromine. Iodine with light heating reacts vigorously with metals, forming iodides (Hg + I 2 = HgI 2). Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide. Iodine does not directly combine with carbon, nitrogen, oxygen. Elemental iodine is an oxidizing agent that is less powerful than chlorine and bromine. Hydrogen sulfide H 2 S, sodium thiosulfate Na 2 S 2 O 3 and other reducing agents reduce it to I - (I 2 + H 2 S = S + 2HI). Chlorine and other strong oxidants in aqueous solutions convert it to IO 3 - (5Cl 2 + I 2 + 6H 2 O = 2HIO 3 H + 10HCl). When dissolved in water, iodine partially reacts with it (I 2 + H 2 O = HI + HIO); iodide and iodate are formed in hot aqueous solutions of alkalis (3I 2 + 6NaOH = 5NaI + NaIO 3 + 3H 2 O). Adsorbed on starch, iodine stains it dark blue; it is used in iodometry and qualitative analysis for the detection of iodine.

Iodine vapors are poisonous and irritate mucous membranes. Iodine has a cauterizing and disinfecting effect on the skin. Iodine stains are washed off with solutions of soda or sodium thiosulfate.

Getting Iodine. The raw material for the industrial production of iodine is oil drilling waters; seaweed, as well as mother liquors of Chilean (sodium) nitrate containing up to 0.4% iodine in the form of sodium iodate. To extract iodine from petroleum waters (usually containing 20-40 mg / l iodine in the form of iodides), they are first acted upon with chlorine (2 NaI + Cl 2 = 2NaCl + I 2) or nitrous acid (2NaI + 2NaNO 2 + 2H 2 SO 4 = 2Na 2 SO 4 + 2NO + I 2 + 2H 2 O). The released iodine is either adsorbed by active carbon or blown out by air. Iodine adsorbed by coal are acted upon by caustic alkali or sodium sulfite (I 2 + Na 2 SO 3 + H 2 O = Na 2 SO 4 + 2HI). From the reaction products, free iodine is isolated by the action of chlorine or sulfuric acid and an oxidizing agent, for example, potassium dichromate (K 2 Cr 2 O 7 + 7H 2 SO 4 + 6NaI = K 2 SO 4 + 3Na 2 SO 4 + Cr 2 (SO 4) S + 3I 2). When blown out with air, iodine is absorbed by a mixture of sulfur oxide (IV) with water vapor (2H 2 O + SO 2 + I 2 = H 2 SO 4 + 2HI) and then the iodine is displaced with chlorine (2HI + Cl 2 = 2HCl + I 2). Crude crystalline iodine is purified by sublimation.

The use of iodine. Iodine and its compounds are used mainly in medicine and analytical chemistry, as well as in organic synthesis and photography.

Iodine in the body. Iodine is a trace element necessary for animals and humans. In the soils and plants of the taiga-forest non-chernozem, dry steppe, desert and mountain biogeochemical zones, iodine is contained in insufficient amounts or is not balanced with some other microelements (Co, Mn, Cu); associated with this is the spread of endemic goiter in these zones. The average content of iodine in soils is about 3 · 10 -4%, in plants about 2 · 10 -5%. There is little iodine in surface drinking waters (from 10 -7 to 10 -9%). In the coastal regions, the amount of iodine in 1 m 3 of air can reach 50 μg, in the continental and mountainous regions it is 1 or even 0.2 μg.

The absorption of iodine by plants depends on the content of its compounds in the soil and on the type of plants. Some organisms (the so-called Iodine concentrators), for example, algae - fucus, kelp, phyllophora, accumulate up to 1% Iodine, some sponges - up to 8.5% (in the skeletal substance spongin). Iodine-concentrating algae are used for its industrial production. Iodine enters the animal organism with food, water, air. The main source of iodine is plant foods and feed. Absorption of iodine occurs in the anterior sections of the small intestine. The human body accumulates from 20 to 50 mg of iodine, including about 10-25 mg in the muscles, and 6-15 mg in the thyroid gland. With the help of radioactive iodine (131 I and 125 I), it was shown that in the thyroid gland iodine accumulates in the mitochondria of epithelial cells and is part of the diiodo- and monoiodotyrosines formed in them, which are condensed into the hormone tetraiodothyronine (thyroxine). Iodine is excreted from the body mainly through the kidneys (up to 70-80%), milk, salivary and sweat glands, partly with bile.

In various biogeochemical provinces, the content of iodine in the daily diet varies (for humans from 20 to 240 μg, for sheep from 20 to 400 μg). The animal's need for iodine depends on its physiological state, season, temperature, adaptation of the body to the iodine content in the environment. The daily requirement for iodine in humans and animals is about 3 μg per 1 kg of body weight (increases during pregnancy, increased growth, cooling). The introduction of iodine into the body increases basal metabolism, enhances oxidative processes, tones up muscles, and stimulates sexual function.

Due to the greater or lesser lack of iodine in food and water, iodination of table salt is used, which usually contains 10-25 g of potassium iodide per ton of salt. The use of fertilizers containing iodine can double and triple its content in crops.

Iodine in medicine. Preparations containing iodine have antibacterial and antifungal properties, they also have anti-inflammatory and distracting effects; they are used externally for disinfecting wounds, preparing the operating field. When taken orally, iodine preparations affect the metabolism, enhance the function of the thyroid gland. Small doses of iodine (microiodine) inhibit the function of the thyroid gland, acting on the formation of thyroid-stimulating hormone in the anterior lobes of the pituitary gland. Since iodine affects protein and fat (lipid) metabolism, it has found application in the treatment of atherosclerosis, as it lowers blood cholesterol; also increases the fibrinolytic activity of the blood. For diagnostic purposes, radiopaque substances containing iodine are used.

With prolonged use of iodine preparations and with increased sensitivity to them, iodism may appear - runny nose, urticaria, Quincke's edema, salivation and lacrimation, acne-like rash (iododerma), etc. Iodine preparations should not be taken with pulmonary tuberculosis, pregnancy, kidney disease, chronic pyoderma, hemorrhagic diathesis, urticaria.

Radioactive iodine. Artificially radioactive isotopes of iodine - 125 I, 131 I, 132 I and others are widely used in biology and especially in medicine to determine the functional state of the thyroid gland and treat a number of its diseases. The use of radioactive iodine in diagnostics is associated with the ability of iodine to selectively accumulate in the thyroid gland; use for medicinal purposes is based on the ability of β-radiation of radioisotopes of iodine to destroy the secretory cells of the gland. When the environment is polluted by the products of nuclear fission, radioactive isotopes of iodine are quickly included in the biological cycle, eventually getting into milk and, consequently, into the human body. Particularly dangerous is their penetration into the body of children, whose thyroid gland is 10 times smaller than that of adults, and, moreover, has a greater radiosensitivity. In order to reduce the deposition of radioactive isotopes of iodine in the thyroid gland, it is recommended to use preparations of stable iodine (100-200 mg per dose). Radioactive iodine is rapidly and completely absorbed in the gastrointestinal tract and is selectively deposited in the thyroid gland. Its absorption depends on the functional state of the gland. Relatively high concentrations of radioisotopes of iodine are also found in the salivary and mammary glands and the mucous membrane of the gastrointestinal tract. Radioactive iodine not absorbed by the thyroid gland is almost completely and relatively quickly excreted in the urine.

DEFINITION

Iodine located in the fifth period of the VII group of the main (A) subgroup of the Periodic table.

Refers to elements p-families. Non-metal. Designation - I. Serial number - 53. Relative atomic mass - 126.905 amu.

The electronic structure of the iodine atom

The iodine atom consists of a positively charged nucleus (+53), inside which there are 53 protons and 74 neutrons, and around, in five orbits, 53 electrons move.

Fig. 1. Schematic structure of the iodine atom.

The orbital distribution of electrons is as follows:

53Te) 2) 8) 18) 18) 7;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 5 .

The external energy level of the iodine atom contains 7 electrons, which are valence. The energy diagram of the ground state takes the following form:

The valence electrons of the iodine atom can be characterized by a set of four quantum numbers: n(main quantum), l(orbital), m l(magnetic) and s(spin):

Sublevel

Examples of problem solving

EXAMPLE 1

Iodine or iodine is familiar to everyone. Having cut our finger, we reach for a bottle of iodine, more precisely, with its alcohol solution ...
Nevertheless, this element is highly unique and each of us, regardless of education and profession, has to rediscover it for ourselves more than once. The history of this element is also peculiar.

First acquaintance with iodine

Iodine was discovered in 1811 by the French chemist-technologist Bernard Courtois (1777-1838), the son of the famous saltpeter. During the years of the French Revolution, he had already helped his father "to extract from the bowels of the earth the main element of the weapon to defeat tyrants," and later took up saltpeter on his own.
At that time, saltpeter was obtained in the so-called saltpeter, or piles. These were heaps of plant and animal waste mixed with construction waste, limestone, marl. The ammonia formed during rotting was oxidized by microorganisms, first into nitrous HN02, and then into nitric HNO 3 acid, which reacted with calcium carbonate, converting it into nitrate Ca (N0 3) 2. It was removed from the mixture with hot water, and then potash was added. There was a reaction of Ca (N0 3) a + K 2 CO 3 → 2KN0 3 + CaCO ↓.
The potassium nitrate solution was decanted from the precipitate and evaporated. The obtained crystals of potassium nitrate were purified by additional recrystallization.
Courtois was not a simple artisan. After working for three years in a pharmacy, he received permission to attend lectures in chemistry and study in the laboratory of the Ecole Polytechnique in Paris at the famous Furcroix. He applied his knowledge to the study of seaweed ash, from which soda was then extracted. Courtois noticed that the copper boiler, in which the ash solutions were evaporated, collapsed too quickly. In the mother liquor, after evaporation and precipitation of crystalline sodium and potassium sulfates, their sulfides and, apparently, something else remained. By adding concentrated sulfuric acid to the solution, Courtois discovered the release of violet vapors. It is possible that something similar was observed by colleagues and contemporaries of Courtois, but it was he who was the first to move from observations to research, from research to conclusions.

These are the conclusions (citing an article written by Courtois): “The mother liquor solution obtained from algae contains a fairly large amount of an unusual and curious substance. It is easy to distinguish it. To do this, it is enough to add sulfuric acid to the mother liquor and heat it in a retort connected to a receiver. The new substance ... precipitates as a black powder that turns into a gorgeous purple vapor when heated. These vapors condense in the form of brilliant crystalline plates having a luster similar to the luster of crystalline lead sulfide ... The amazing color of the vapors of the new substance allows it to be distinguished from all hitherto known substances, and it has other remarkable properties, which gives its discovery the greatest interest " ...
In 1813, the first scientific publication about this substance appeared; chemists from different countries began to study it, including such luminaries of science as Joseph Gay-Lussac and Humphrey Davy. A year later, these scientists established the elementary nature of the substance discovered by Courtois, and Gay-Lussac called the new element iodine - from the Greek - dark blue, purple.
Second acquaintance: properties are common and unusual.

Iodine is a chemical element of group VII the periodic system. The atomic number is 53. The atomic mass is 126.9044. Halogen. Of the naturally occurring halogens, it is the heaviest, unless, of course, you count the radioactive short-lived astatine. Almost all natural iodine consists of atoms of a single isotope with a mass number of 127. Radioactive iodine - 125 is formed as a result of the spontaneous fission of uranium. Of the artificial isotopes of iodine, the most important are iodine - 131 and iodine - 133; they are used in medicine.
The elemental iodine molecule, like other halogens, consists of two atoms. Iodine, the only halogen species, is solid under normal conditions. The beautiful dark blue crystals of iodine are most similar to graphite. Distinct crystalline structure, the ability to conduct electric current - all these "metallic" properties are characteristic of pure iodine.
But, unlike graphite and most metals, iodine very easily turns into a gaseous state. It is even easier to convert iodine to vapor than to liquid.
To melt iodine, a rather low temperature is needed: + 113.5 ° C, but, in addition, it is necessary that the partial pressure of iodine vapor above the melting crystals is at least one atmosphere. In other words, iodine can be melted in a narrow-necked flask, but not in an open laboratory dish. In this case, iodine vapors do not accumulate, and when heated, iodine will sublime - it will go into a gaseous state, bypassing the liquid one, which usually happens when this substance is heated. By the way, the boiling point of iodine is not much higher than the melting point, it is only 184.35 ° C.
But not only by the simplicity of conversion to a gaseous state iodine is released among other elements... Very peculiar, for example, its interaction with water.
Elemental iodine does not dissolve in water: at 25 ° C only 0.3395 g / l. Nevertheless, you can get a much more concentrated aqueous solution of element No. 53, using the same simple technique that doctors use when they need to keep the iodine tincture longer (3- or 5% solution of iodine in alcohol): so that the iodine tincture does not fizzle out , a little potassium iodide KI is added to it. The same substance helps to obtain iodine-rich aqueous solutions: iodine is mixed with a not too dilute solution of iodine ralium.
KI molecules are capable of attaching elemental iodine molecules. If one molecule enters the reaction on each side, a red-brown potassium triiodide is formed. Potassium iodide can also attach a larger number of iodine molecules, as a result, compounds of various compositions are obtained up to K19. These substances are called polyiodides. Polyiodides are unstable, and their solution always contains elemental iodine, and in a much higher concentration than that which can be obtained by direct dissolution of iodine.
In many organic solvents - carbon disulfide, kerosene, alcohol, benzene, ether, chloroform - iodine dissolves easily. The color of non-aqueous solutions of iodine is not constant. For example, its solution in carbon disulfide is violet, and in alcohol it is brown. How can this be explained?
Obviously, violet solutions contain iodine in the form of 12 molecules. If a solution of a different color is obtained, it is logical to assume the existence of iodine compounds with a solvent in it. However, not all chemists share this view. Some of them believe that the differences in the color of iodine solutions are explained by the existence of various kinds of forces connecting the molecules of the solvent and the solute.
Violet iodine solutions conduct electricity, since in solution molecules 12 partially dissociate into ions 1+ and I-. This assumption does not contradict the ideas about the possible valences of iodine. Its main valences are: 1 "(such compounds are called iodides), 5+ (iodates) and 7+ (periodates). But iodine compounds are also known, in which it exhibits valencies 1+ and 3+, playing the role of a monovalent or trivalent metal There is a compound of iodine with oxygen, in which element No. 53 is octavalent, - U4.
But most often iodine, as befits a halogen (there are seven electrons on the outer shell of an atom), exhibits a valence of 1 “. Like other halogens, it is quite active - it reacts directly with most metals (even noble silver is resistant to the action of iodine only at temperatures up to 50 ° C), but is inferior to chlorine and bromine, not to mention fluorine. Some elements - carbon, nitrogen, oxygen, sulfur, selenium - do not directly react with iodine.

third acquaintance:

It turns out that there is less iodine on Earth than lutetium
Iodine is a rather rare element. Its clarke (content in the earth's crust in weight percent) is only 4-10 ~ 5%. It is less than the most difficult to obtain elements of the lanthanide family - thulium and lutetium.
Iodine has one feature that makes it akin to "rare earths" - extreme absent-mindedness in nature. Not the most common element, iodine is present literally everywhere. Even in seemingly super-pure crystals of rock crystal, micro-admixtures of iodine are found. In transparent calcites, the content of element No. 53 reaches 5-10 ~ 6%. Iodine is present in the soil, in sea and river water, in plant cells and in the organisms of Animals. But minerals rich in iodine are very few. The most famous of them is Ca (IO 5) 2 lautarite. But there are no industrial deposits of lautarite on Earth.
To obtain iodine, it is necessary to concentrate natural solutions containing this element, for example, the water of salt lakes or associated oil waters, or to process natural concentrators of iodine - seaweed. A ton of dried seaweed (kelp) contains up to 5 kg of iodine, while a ton of sea water contains only 20-30 mg.
Like most vital elements, iodine is circulating in nature. Since many iodine compounds are readily soluble in water, iodine is leached out of igneous rocks and carried to seas and oceans. Seawater evaporates and raises masses of elemental iodine into the air. Precisely elementary: compounds of element No. 53 in the presence of carbon dioxide are easily oxidized by oxygen up to 12.
The winds that carry air masses from the ocean to the mainland also carry iodine, which, together with atmospheric precipitation, falls to the ground, gets into the soil, groundwater, and living organisms. The latter concentrate iodine, but, dying, return it to the soil, from where it is again washed out by natural waters, enters the ocean, evaporates, and everything starts anew. This is just a general scheme, in which all the particulars and chemical transformations that are inevitable at different stages of this eternal rotation are omitted.
And the cycle of iodine has been studied very well, and this is not surprising: the role of trace amounts of this element in the life of plants, animals, humans is too great ...

Iodine fourth acquaintance: the biological functions of iodine

They are not limited to iodine tincture. We will not talk in detail about the role of iodine in plant life - it is one of the most important trace elements, we will limit ourselves to its role in human life.
Back in 1854, the Frenchman Chaten, an excellent chemical analyst, discovered that the prevalence of goiter is directly dependent on the iodine content in the air, soil, food consumed by people. Colleagues challenged the findings of Chaten; moreover, the French Academy of Sciences recognized them as harmful. As for the origin of the disease, then it was believed that 42 reasons could cause it - the lack of iodine did not appear on this list.
Almost half a century passed before the authority of the German scientists Baumann and Oswald forced the French scientists to admit their mistake. The experiments of Baumann and Oswald showed that the thyroid gland contains an amazing amount of iodine and produces iodine-containing hormones. Lack of iodine initially leads to only a slight increase in the thyroid gland, but as it progresses, this disease - endemic goiter - affects many body systems. As a result, metabolism is disturbed, growth slows down. In some cases, endemic goiter can lead to deafness, to cretinism ... This disease is more common in mountainous regions and in places far from the sea.
The widespread occurrence of the disease can be judged even by the works of painting. One of the best female portraits of Rubens "Straw Hat". The beautiful woman depicted in the portrait has a noticeable swelling of the neck (the doctor would immediately say: the thyroid gland is enlarged). Andromeda in Perseus and Andromeda has the same symptoms. Signs of iodine deficiency are also seen in some people depicted in portraits and paintings by Rembrandt, Durer, Van Dyck ...
In our country, most of whose regions are far from the sea, the fight against endemic goiter is carried out constantly - primarily by means of prophylaxis. The simplest and most reliable remedy is the addition of microdoses of iodides to table salt.
It is interesting to note that the history of the therapeutic use of iodine goes back centuries. The healing properties of substances containing iodine were known 3 thousand years before this element was discovered. Chinese Code 1567 BC NS. recommends seaweeds for the treatment of goiter ...
The antiseptic properties of iodine in surgery were first used by the French physician Bouapet. Oddly enough, the simplest dosage forms of iodine - aqueous and alcoholic solutions - have not been used in surgery for a very long time, although back in 1865-1866. the great Russian surgeon N.I. Pirogov used iodine tincture in the treatment of wounds.
The priority of preparation of the operating field with the help of iodine tincture is erroneously attributed to the German doctor Grossich. Meanwhile, back in 1904, four years before Grossich, Russian military doctor N.P. Filonchikov, in his article "Aqueous solutions of iodine as an antiseptic liquid in surgery" drew the attention of surgeons to the enormous advantages of aqueous and alcoholic solutions of iodine precisely in preparation for the operation. ...
Needless to say, these simple drugs have not lost their significance to this day. Interestingly, sometimes iodine tincture is prescribed as an internal one: a few drops per cup of milk. This can be beneficial in atherosclerosis, but it must be remembered that iodine is useful only in small doses, and in large doses it is toxic.

Iodine fifth acquaintance - purely utilitarian

Not only doctors are interested in iodine. Geologists and botanists, chemists and metallurgists need it.
Like other halogens, iodine forms numerous organoiodine compounds, which are included in the composition of some dyes.
Iodine compounds are used in photography and the film industry for the preparation of special photographic emulsions and photographic plates.
Iodine is used as a catalyst in the production of synthetic rubbers.
Obtaining ultrapure materials - silicon, titanium, hafnium, zirconium - is also not complete without this element. The iodide method for obtaining pure metals is used quite often.
iodine preparations are used as a dry lubricant for rubbing surfaces made of steel and titanium.

Powerful iodine incandescent lamps are being manufactured. The glass bulb of such a lamp is filled not with an inert gas, but with the vapor of the hearth, which themselves emit light at a high temperature.
Iodine and its compounds are used in laboratory practice for analysis and in chemotronic devices, the action of which is based on the redox reactions of iodine ...
A lot of work of geologists, chemists and technologists is spent on the search for iodine raw materials and the development of methods for the extraction of iodine. Until the 60s of the last century, algae were the only source of inventive production of iodine. In 1868, iodine began to be obtained from wastes of saltpeter production, which contain iodate and sodium iodide. Free raw materials and an easy way to obtain iodine from saltpeter mother liquors ensured widespread use of Chilean iodine. During the First World War, the supply of Chilean nitrate and iodine ceased, and soon the lack of iodine began to affect the general state of the pharmaceutical industry in Europe. The search began for cost-effective methods of producing iodine. In our country, already during the years of Soviet power, iodine began to be obtained from the underground and oil waters of the Kuban, where it was discovered by the Russian chemist A. L. Potylitsin back in 1882. Later, similar waters were discovered in Turkmenistan and Azerbaijan.
But the content of iodine in groundwater and associated waters of oil production is very small. This was the main difficulty in creating economically viable industrial methods for producing iodine. It was necessary to find a "chemical bait" that would form a fairly strong compound with iodine and concentrate it. Initially, starch turned out to be such a "bait", then copper and silver salts, which bound iodine into insoluble compounds. We tried kerosene - iodine dissolves well in it. But all these methods turned out to be expensive and sometimes flammable.
In 1930, the Soviet engineer V.P.Denisovich developed the Coal method for extracting iodine from oil waters, and this method was for a long time the basis of Soviet iodine production. A kilogram of coal accumulated up to 40 g of iodine per month ...
Other methods have been tried. Already in recent decades, it was found that iodine is selectively sorbed by high-molecular-weight ion-exchange resins. In the iodine industry of the world, the ion exchange method is still used to a limited extent. There have been attempts to apply it in our country, but the low iodine content and insufficient selectivity of ion exchangers for iodine have not yet allowed this, of course, a promising method to radically transform the iodine industry.
Geotechnological methods of iodine extraction are also promising. They will make it possible to extract iodine from the associated waters of oil and gas fields without pumping these waters to the surface. Special reagents introduced through the well will concentrate iodine underground, and not a weak solution will go to the surface, but a concentrate. Then, obviously, the production of iodine and its consumption by industry will sharply increase - the complex of properties inherent in this element is very attractive to it.
JOD AND MAN. The human body not only does not need large amounts of iodine, but with surprising constancy maintains a constant concentration (10 ~ 5-10 ~ 6%) of iodine in the blood, the so-called iodine mirror of blood. Of the total amount of iodine in the body, which is about 25 mg, more than half is in the thyroid gland. Almost all of the iodine contained in this gland is part of various derivatives of tyrosine, the thyroid hormone, and only a small part of it, about 1%, is in the form of inorganic iodine I1-.
Large doses of elemental iodine are dangerous: a dose of 2-3 g is fatal. At the same time, much larger doses are allowed in the form of iodide.
If a significant amount of inorganic iodine salts is introduced into the body with food, its concentration in the blood will increase 1000 times, but after 24 hours the iodine mirror of the blood will return to normal. The level of the iodine mirror strictly obeys the laws of internal exchange and practically does not depend on the experimental conditions.
In medical practice, organoiodine compounds are used for X-ray diagnostics. The rather heavy nuclei of iodine atoms scatter X-rays. With the introduction of such a diagnostic agent into the body, extremely clear X-ray images of individual areas of tissues and organs are obtained.
UNDER AND SPACE RAYS. Academician V. I. Vernadsky believed that cosmic rays play an important role in the formation of iodine in the earth's crust, which cause nuclear reactions in the earth's crust, that is, the transformation of some elements into others. Thanks to these transformations, very small amounts of new atoms, including iodine atoms, can be formed in rocks.
IODE _ LUBRICANT. Only 0.6% iodine added to hydrocarbon oils significantly reduces the friction work in stainless steel and titanium bearings. This makes it possible to increase the load on the rubbing parts by more than 50 times.
IODINE AND GLASS. Iodine is used to make special polaroid glass. Crystals of iodine salts are introduced into glass (or plastic), which are distributed in a strictly regular way. The vibrations of the light beam cannot pass through them in all directions. It turns out a kind of filter, called a polaroid, which removes the oncoming blinding stream of light. This glass is used in cars. By combining several polaroids or by rotating polaroid glasses, extremely colorful effects can be achieved - a phenomenon used in cinema and theater.
DO YOU KNOW THAT:

• the content of iodine in human blood depends on the season: from September to January, the concentration of iodine in the blood decreases, from February a new rise begins, and in May - June the iodine mirror reaches its highest level. These oscillations have a relatively small amplitude, and their causes are still a mystery;
• eggs, milk, fish contain a lot of iodine from food products; there is a lot of iodine in seaweed, which is marketed in the form of canned food, dragees and other products;
• the first iodine plant in Russia was built in 1915 in Yekaterinoslav (now Dnepropetrovsk); received iodine from the ashes of the Black Sea algae phyllophora; during the First World War, 200 kg of iodine were produced at this plant;
• if a thundercloud is "sown" with silver iodide or lead iodide, then instead of hail, a finely dispersed snow croup is formed in the cloud: a cloud sown with such salts is poured by Rain and does not harm crops.

Iodine was discovered in 1811 by a Parisian manufacturer of saltpeter named Courtois in soda made from the ashes of coastal plants. In 1813 Gay-Lussac investigated a new substance and gave it the name for the violet color of the vapor - iodine. It is derived from the Greek word for dark blue, violet. Then, when it was found to be similar to chlorine, Davy suggested calling the element iodine (analogous to chlorine); this name is still accepted in England and the USA.

Receiving:

The main source of iodine production in the USSR is underground drilling waters, which contain up to 10 - 50 mg / l of iodine. Iodine compounds are also present in seawater, but in such small quantities that it is very difficult to isolate them directly from the water. However, there are some algae that accumulate iodine in their tissues. The ash of these algae serves as a raw material for the production of iodine. Iodine is also found in the form of potassium salts - KIO 3 iodate and KIO 4 periodate, accompanying deposits of sodium nitrate (saltpeter) in Chile and Bolivia.
Iodine can be obtained similarly to chlorine by oxidizing HI with various oxidizing agents. In industry, it is usually obtained from iodides by acting on their solutions with chlorine. Thus, the production of iodine is based on the oxidation of its ions, and chlorine is used as an oxidizing agent.

Physical properties:

Iodine at room temperature is dark violet crystals with a faint luster. When heated under atmospheric pressure, it sublimes (sublimes), turning into a violet vapor; when cooled, iodine vapors crystallize, bypassing the liquid state. This is used in practice for the purification of iodine from non-volatile impurities. Slightly soluble in water, well in many organic solvents.

Chemical properties:

Free iodine is extremely reactive. It interacts with almost all simple substances. The reactions of the combination of iodine with metals proceed especially quickly and with the release of a large amount of heat.
It reacts with hydrogen only with sufficiently strong heating and not completely, since the reverse reaction begins - the decomposition of hydrogen iodide:
H 2 + I 2 = 2HI - 53.1 kJ
It dissolves in iodide solutions, forming unstable complexes. Disproportionates with alkalis, forming iodides and hypoiodites. It is oxidized with nitric acid to iodic acid.
If hydrogen sulfide water (an aqueous solution of H 2 S) is added to a yellowish aqueous solution of iodine, then the liquid becomes discolored and becomes cloudy from the released sulfur:
H 2 S + I 2 = S + 2HI

In compounds, it exhibits oxidation states -1, +1, +3, +5, +7.

The most important connections:

Hydrogen iodide, gas, very similar in its properties to hydrogen chloride, but differs in more pronounced reducing properties. We are very soluble in water (425: 1), a concentrated solution of hydrogen iodide fumes due to the release of HI, which forms a mist with water vapor.
In aqueous solution, it is one of the strongest acids.
Even at room temperature, hydrogen iodide is gradually oxidized by atmospheric oxygen, and under the influence of light, the reaction is greatly accelerated:
4HI + O 2 = 2I 2 + 2H 2 O
The reducing properties of hydrogen iodide are noticeably manifested when interacting with concentrated sulfuric acid, which is reduced to free sulfur or even to H 2 S. Therefore, HI cannot be obtained by the action of sulfuric acid on iodides. Usually hydrogen iodide is obtained by the action of water on compounds of iodine with phosphorus - PI 3. The latter undergoes complete hydrolysis, forming phosphorous acid and hydrogen iodide:
PI 3 + 3H 2 O = H 3 PO 3 + 3HI
A solution of hydrogen iodide (up to 50% concentration) can also be obtained by passing H 2 S into an aqueous suspension of iodine.
Iodides, hydroiodic acid salts. Potassium iodide is used in medicine - in particular, for diseases of the endocrine system, photoreagents.
Hypoxic acid - HOI is an amphoteric compound, in which the basic properties slightly prevail over acidic ones. Can be obtained in solution by the interaction of iodine with water
I 2 + H 2 O = HI + HOI
Iodic acid - HIO 3 can be obtained by oxidizing iodine water with chlorine:
I 2 + 5Cl 2 + 6H 2 O = 2HIO 3 + 10HCl
Colorless crystals, quite stable at room temperature. Strong acid, vigorous oxidizing agent. Salts - iodates, strong oxidants in acidic environments.
Iodine (V) oxide, iodic anhydride, can be obtained by gently heating HIO 3 to 200 ° C, powder. When heated above 300 ° C, it decomposes into iodine and oxygen, exhibits oxidizing properties, in particular, it is used to absorb CO in analysis:
5CO + I 2 O 5 = I 2 + 5CO 2
Iodic acid - HIO 4 and its salts (periodates) are well studied. The acid itself can be obtained by the action of HClO 4 on iodine: 2HIO 4 + I 2 = 2HIO 4 + Cl 2
or by electrolysis of a solution of HIO 3: HIO 3 + H 2 O = H 2 (cathode) + HIO 4 (anode)
Iodic acid is released from the solution in the form of colorless crystals with the composition HIO 4 2H 2 O. This hydrate should be considered as a pentabasic acid H 5 IO 6(orthoiodic), since in it all five hydrogen atoms can be replaced by metals with the formation of salts (for example, Ag 5 IO 6). Iodic acid is a weak but stronger oxidizing agent than HClO 4.
Iodine (VII) oxide I 2 O 7 was not obtained.
Iodine fluorides, IF 5, IF 7- liquids, hydrolyzed by water, fluorinating agents.
Iodine chlorides, ICl, ICl 3- krist. substances dissolve in chloride solutions with the formation of complexes - and -, iodinating agents.

Application:

Iodine is widely used in the chemical industry (iodide refining of Zr and Ti), for the synthesis of semiconductor materials.
Iodine and its compounds are used in analytical chemistry (iodometry) In medicine, in the form of the so-called iodine tincture (10% solution of iodine in ethyl alcohol), an antiseptic and hemostatic agent. Iodine compounds for the prevention (iodization of products) and treatment of thyroid diseases, radioactive isotopes are also used there 125 I, 131 I, 132 I.
World production (excluding the USSR) - about 10 thousand tons / year (1976).
MPC is about 1 mg / m 3.

See also:
P.A. Wallet. The ubiquitous iodine. "Chemistry" (appendix to the gas. "September 1"), No. 20, 2005