Iodine - description of properties with photos; daily requirement for this substance; description of its deficiency and excess with symptoms; main sources of iodine. What is iodine made from? Processing of natural iodine accumulators
The cat ran and waved its tail. This is not a fairy tale about the chicken Ryaba, but history of the discovery of iodine. It was discovered at a Paris plant that converts sodium nitrate into potassium nitrate. The first became damp in the air, and the second was in short supply.
The transformation took place using the ash remaining from burning algae. The method was invented in 1808, but they did not know what its secret was. The cat that the factory workers were chasing did not know this either. knocked over two vessels - with sulfuric acid and residual production salts.
Purple vapors shot into the air. The owner of the factory, Bernard Kurt, saw this. He conducted several experiments himself, then passed on the information to scientists. The result is that in 1814 the world learned about the existence of a new element. He became iodine.
Chemical and physical properties of iodine
Properties of iodine determined by its location in. The element is included in the 7th group. It contains halogens - the most active non-metals. Iodine, for example, has an easily polarizable electron shell.
That is, it doesn’t cost her any effort to separate in space. This allows cations of other elements to penetrate into the nonmetal atom, whose mass, by the way, is 127. “Guests” in the electron shell change it, making iodine the most covalent of all halogens.
Simply put, an element can form a greater variety of bonds with other atoms. Often iodine is positively polarized. This atom is the most active. What makes it stand out is its color, that same purple.
Iodine atom listed in the periodic table - a natural specimen. This is a stable isotope with atomic mass 127. Other atoms with numbers 125, 129, 131 have also been artificially obtained.
Each of them - radioactive iodine. Isotopes emit beta and gamma rays and are used in medicine. Radioactive iodine is obtained from the fission products of uranium. That is, nuclear reactors serve as laboratories.
Standard iodine is possible Compatible with most non-metals and approximately 40% metals. Noble people, and not only, do not react to the 53rd element. Interaction is also impossible with carbon, oxygen and all inert gases.
Is Yod study, or its compounds can be determined using water. The pure element is almost insoluble in it. Iodites, that is, compounds of a substance with alkali and alkaline earth atoms, are soluble. In its original form, the 53rd element disappears in water only with strong heating.
Iodine solution easy to obtain if you use organic matter. Glycerin, carbon disulfide or carbon tetrachloride are suitable. If the solvent is oxygen-free, it will turn purple. If a liquid has oxygen atoms, iodine will make it .
In its pure form, at room temperature, iodine is purple-black. The luster of the substance is metallic, state of aggregation– . They are dense - almost 5 grams per cubic centimeter.
Crystals are made up of molecules, each of which has 2 atoms. The substance enters the gaseous state at a temperature of 183 degrees. Getting iodine liquid is possible already at 114 Celsius.
Application of iodine
Iodine salts used in the glass industry. We are talking about car headlights and lamps with special effects. The main effect is that iodites serve as filters from oncoming light rays. Drivers know how important it is, sometimes, to neutralize them.
This process is called Polaroid and, in fact, was first used in photographic art. The author of the idea is the Englishman William Talbot. He was an outstanding chemist and physicist of the 19th century.
In the 21st century, digital technologies rule. However, to obtain a negative photo, the iodine variety is still used. In combination with gelatin, it produces an emulsion, which is coated with a glass substrate. Light hits the coating and release begins. More light - more metal. This is how the picture is made.
Iodine application found in metallurgy. Compounds of the element help produce high purity metals. By thermally decomposing iodites, industrialists extract, for example, vanadium and zirconium. These refractory elements are needed for many rocket alloys and nuclear reactor materials.
Can also be found in automotive bearings iodine. Which does it make sense? The element is added to the lubricant. It is recommended for titanium and stainless steel. The processing allows the parts to withstand a load 50 times greater than the standard one. This is despite the fact that there is only 1-2% iodine in the lubricant.
Without the 53rd element, medicine is unthinkable. Iodine in the body controls the functioning of the thyroid gland, is included in the hormones TSH, T3 and T4 produced by it. If there is a deficiency of the element, a goiter develops and cancer is possible.
At the same time, the body cannot produce the substance itself. Iodine comes exclusively from food, dietary supplements and medications. Of the latter, it’s easy to remember “ Iodomarin».
It is prescribed even to infants, especially in areas remote from the seas. In such areas, as a rule, there is a deficiency of the 53rd element, contained mainly in the waters of the oceans and their gifts.
One of the latest developments by doctors is blue iodine. Starch is added to it, which changes the color of the usual solution for external use. Starch also neutralizes the effects of alcohol and other harmful “additives”. Doctors allow this elixir for internal use and for rinsing with iodine. Although a mixture can handle the latter salt, soda, iodine.
Treatment with iodine is allowed not only in its stable, but also in its radioactive forms. So the 131st isotope is used to restore the functions of the thyroid gland. The procedures are strictly regulated, since an excess of radioactive iodine can cause cancer.
Iodine extraction
How much iodine mined per year? About 30,000 tons. World reserves of the element are estimated at almost 15,000,000 tons. Most of them are hidden in iodine compounds. It is rarely found in its pure form.
The method of isolating substances from natural reservoirs – algae – is still relevant. A ton of dried kelp contains 5 kilograms iodine.
Everyone is familiar with iodine or iodine. Having cut our finger, we reach for a bottle of iodine, or rather its alcohol solution...
Nevertheless, this element is highly unique and each of us, regardless of education and profession, has to rediscover it 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 maker. During the years of the Great French Revolution, he already helped his father “extract from the bowels of the earth the main element of weapons to defeat tyrants,” and later took up the production of saltpeter on his own.
At that time, saltpeter was obtained in so-called saltpeter containers, or burts. These were heaps made up of plant and animal waste mixed with construction waste, limestone, and marl. The ammonia formed during decay was oxidized by microorganisms first into nitrogenous HN02, and then into nitric acid HNO3, which reacted with calcium carbonate, converting it into nitrate Ca(N03)2. It was removed from the mixture hot water, and then potash was added. The reaction was Ca (N0 3) a + K 2 C0 3 → 2KN0 3 + CaCO ↓.
The potassium nitrate solution was poured from the sediment and evaporated. The resulting crystals of potassium nitrate were purified by additional recrystallization.
Courtois was not a simple artisan. After working in a pharmacy for three years, he received permission to attend lectures on chemistry and study in the laboratory of the Ecole Polytechnique in Paris with the famous Fourcroy. 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 was being destroyed too quickly. After evaporation and precipitation of crystalline sodium and potassium sulfates, their sulfides and, apparently, something else remained in the mother solution. By adding concentrated sulfuric acid to the solution, Courtois discovered the release of violet vapors. It is possible that something similar was observed by Courtois’ colleagues and contemporaries, but it was he who was the first to move from observations to research, from research to conclusions.
These are the conclusions (we quote an article written by Courtois): “The mother liquor of algae-derived lye contains a fairly large amount of an unusual and curious substance. It's easy to highlight. To do this, just add sulfuric acid to the mother solution and heat it in a retort connected to the receiver. The new substance... precipitates in the form of a black powder, which, when heated, turns into a magnificent vapor purple. These vapors condense in the form of shiny crystalline plates, having a luster similar to that of crystalline lead sulfide... Amazing coloring the vapors of the new substance make it possible to distinguish it from all hitherto known substances, and other remarkable properties are observed in it, 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 Humphry Davy. A year later, these scientists established the elemental nature of the substance discovered by Courtois, and Gay-Lussac named the new element iodine - from the Greek - dark blue, violet.
Second acquaintance: ordinary and unusual properties.
Iodine is a chemical element of group VIIperiodic table. Atomic number - 53. Atomic mass - 126.9044. Halogen. Of the halogens found in nature, 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 is the only halogen that exists in a solid state under normal conditions. Beautiful dark blue iodine crystals are most similar to graphite. Distinct crystalline structure, ability to conduct electricity- all these “metallic” properties are characteristic of pure iodine.
But, unlike graphite and most metals, iodine very easily goes into a gaseous state. It is even easier to convert iodine into vapor than into liquid.
To melt iodine, you need quite low temperature: + 113.5° C, but, in addition, it is necessary that the partial pressure of iodine vapor above the melting crystals be 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 vapor does not accumulate, and when heated, the iodine will sublimate - it will go into a gaseous state, bypassing the liquid state, which usually happens when this substance is heated. By the way, the boiling point of iodine is not much more temperature melting, it is equal to only 184.35 ° C.
But not only the ease of transfer to a gaseous state iodine stands out among other elements. For example, its interaction with water is very peculiar.
Elemental iodine does not dissolve well in water: at 25°C only 0.3395 g/l. Nevertheless, you can obtain a much more concentrated aqueous solution of element No. 53 by using the same simple technique that doctors use when they need to preserve iodine tincture (3- or 5% solution of iodine in alcohol) longer: so that the iodine tincture does not fizzle out , add a little potassium iodide KI to it. The same substance also helps to obtain iodine-rich aqueous solutions: iodine is mixed with a not too diluted solution of ralium iodide.
KI molecules are capable of attaching molecules of elemental iodine. If one molecule reacts on each side, red-brown potassium triiodide is formed. Potassium iodide can add a larger number of iodine molecules, resulting in compounds of various compositions 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 what 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 purple, and in alcohol it is brown. How can we explain this?
Obviously, violet solutions contain iodine in the form of molecules 12. If the result is a solution of a different color, it is logical to assume the existence of iodine compounds with the solvent in it. However, not all chemists share this point of view. Some of them believe that the differences in the color of iodine solutions are explained by the existence of various types of forces connecting the molecules of the solvent and the dissolved substance.
Violet solutions of iodine conduct electricity, since in solution the molecules 12 partially dissociate into 1+ and I- ions. This assumption does not contradict the ideas about the possible valences of iodine. Its main valencies are: 1" (such compounds are called iodides), 5+ (iodates) and 7+ (periodates). But iodine compounds are also known in which it exhibits valencies of 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 - IO4.
But most often, iodine, as befits a halogen (there are seven electrons on the outer shell of the 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 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 react directly with iodine.
third meeting:
It turns out that there is less iodine on Earth than lutetium
Iodine is a fairly rare element. His Clark (contents in earth's crust in weight percent) - 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 similar to “rare earths” - extreme dispersion in nature. Although far from being the most abundant element, iodine is present literally everywhere. Even in seemingly ultra-pure rock crystals, micro-impurities of iodine are found. In transparent calcites, the content of element No. 53 reaches 5-10~6%. Iodine is found in soil, sea and river water, plant cells and animal organisms. But there are very few minerals rich in iodine. The most famous of them is lautarite Ca(IO 5) 2. But industrial deposits There is no lautarite on Earth.
To obtain iodine, it is necessary to concentrate natural solutions containing this element, for example, water from salt lakes or associated oil waters, or to process natural iodine concentrators - 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 cycles in nature. Since many iodine compounds are highly soluble in water, iodine is leached from igneous rocks and carried into the seas and oceans. Sea water, evaporating, lifts masses of elemental iodine into the air. Precisely elementary: compounds of element No. 53 in the presence carbon dioxide easily oxidized by oxygen to 12.
The winds that carry air masses From the ocean to the mainland, iodine is also transferred, which, together with precipitation, falls to the ground, enters the soil, groundwater, and living organisms. The latter concentrate iodine, but, dying, return it to the soil, from where it is washed out again natural waters, falls into the ocean, evaporates, and everything starts again. It's just general scheme, in which all the details and chemical transformations that are inevitable at different stages of this eternal rotation are omitted.
And the iodine cycle has been studied very well, and this is not surprising: the role of microquantities of this element in the life of plants, animals, and humans is too great...
Iodine fourth introduction: 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 microelements; we will limit ourselves to its role in human life.
Back in 1854, the Frenchman Chatain, an excellent analytical chemist, discovered that the prevalence of goiter is directly dependent on the iodine content in the air, soil, and food consumed by people. Colleagues protested Chaten's conclusions; Moreover, the French Academy of Sciences recognized them as harmful. As for the origin of the disease, it was then believed that it could be caused by 42 causes - iodine deficiency did not appear on this list.
Almost half a century passed before the authority of the German scientists Baumann and Oswald forced French scientists to admit the mistake. Experiments by Bauman and Oswald showed that the thyroid gland contains a surprising amount of iodine and produces iodine-containing hormones. Lack of iodine initially leads to only a slight enlargement of the thyroid gland, but as it progresses, this disease - endemic goiter - affects many systems of the body. As a result, metabolism is disrupted and growth slows down. In some cases, endemic goiter can lead to deafness, cretinism... This disease is more common in mountainous areas and in places far from the sea.
The widespread spread of the disease can be judged even from works of art. One of the best female portraits by Rubens, “The Straw Hat”. U beautiful woman depicted in the portrait, swelling of the neck is noticeable (a doctor would immediately say: the thyroid gland is enlarged). Andromeda from the painting “Perseus and Andromeda” has the same symptoms. Signs of iodine deficiency are also visible in some people depicted in portraits and paintings by Rembrandt, Dürer, Van Dyck...
In our country, most of the regions of which are remote from the sea, the fight against endemic goiter is constantly carried out - primarily by means of prevention. The simplest and most reliable remedy is the addition of microdoses of Iodide to table salt.
It is interesting to note that history medicinal use Yoda goes back centuries. The healing properties of substances containing iodine were known 3 thousand years before this element was discovered. Chinese Code 1567 BC e. recommends seaweed for the treatment of goiter...
The antiseptic properties of iodine in surgery were first used by the French physician Buape. Oddly enough, the simplest dosage forms of iodine - aqueous and alcoholic solutions - did not find use 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 preparing the surgical field with iodine tincture is erroneously attributed to the German doctor Grossikh. Meanwhile, back in 1904, four years before Grossikh, the 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 surgery .
Needless to say, these simple drugs have not lost their significance to this day. It’s interesting that sometimes iodine tincture is also prescribed internally: a few drops per cup of milk. This can be beneficial for atherosclerosis, but you need to remember that iodine is useful only in small doses, and in large doses it is toxic.
Yod fifth acquaintance - purely utilitarian
Not only doctors are interested in iodine. It is needed by geologists and botanists, chemists and metallurgists.
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 artificial rubbers.
The production of ultrapure materials - silicon, titanium, hafnium, zirconium - is also not complete without this element. The iodide method for producing pure metals is used quite often.
Iodine preparations are used as a dry lubricant for rubbing surfaces made of steel and titanium.
High-power incandescent iodine lamps are manufactured. The glass bulb of such a lamp is filled not with an inert gas, but with hearth vapors, which themselves emit light when high temperature.
Iodine and its compounds are used in laboratory practice for analysis and in chemotron devices, the action of which is based on the redox reactions of iodine...
A lot of work of geologists, chemists and technologists goes into searching for iodine raw materials and developing methods for extracting iodine. Until the 60s of the last century, algae were the only source of industrial iodine production. In 1868, iodine began to be obtained from saltpeter production waste, which contains iodate and sodium iodide. Free raw materials and a simple method for obtaining iodine from saltpeter mother solutions ensured widespread distribution of Chilean iodine. First world war The supply of Chilean saltpeter and iodine stopped, and soon the lack of iodine began to affect the general state of the pharmaceutical industry in Europe. The search began for cost-effective ways to obtain iodine. In our country, already during the years of Soviet power, iodine began to be obtained from 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 iodine content in groundwater and associated waters from oil production is very low. 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, this “bait” turned out to be starch, 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, Soviet engineer V.P. Denisovich developed the Coal method for extracting iodine from oil waters, and this method was the basis of Soviet iodine production for quite a long time. Up to 40 g of iodine accumulated in a kilogram of coal per month...
Other methods have also been tried. Already in recent decades it has been discovered that iodine is selectively sorbed by high-molecular ion-exchange resins. In the world's iodine industry, the ion exchange method is still used to a limited extent. There have been attempts to use it in our country, but the low iodine content and insufficient selectivity of ion exchangers for iodine have not yet allowed this, undoubtedly promising method, to radically transform the iodine industry.
Geotechnological methods for extracting iodine are also promising. They will make it possible to extract iodine from associated waters of oil and gas fields without pumping these waters to the surface. Special reagents introduced through a well will concentrate iodine underground, and not a weak solution, but a concentrate will flow to the surface. Then, obviously, the production of iodine and its consumption by industry will increase sharply - the complex of properties inherent in this element is very attractive to it.
IOD AND MAN. The human body not only does not need large quantities of iodine, but with amazing constancy maintains a constant concentration (10~5-10~6%) of iodine in the blood, the so-called iodine mirror of the blood. From total number Of iodine in the body, amounting to about 25 mg, more than half is found in the thyroid gland. Almost all 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 lethal. At the same time, in the form of iodide, much larger doses can be taken orally.
If you introduce a significant amount of inorganic iodine salts into the body with food, its concentration in the blood will increase 1000 times, but after 24 hours the iodine level in the blood will return to normal. The level of the iodine mirror strictly obeys the laws of internal metabolism and practically does not depend on the experimental conditions.
In medical practice, organoiodine compounds are used for x-ray diagnostics. Sufficiently heavy nuclei of iodine atoms scatter X-rays. When such a diagnostic agent is introduced into the body, exceptionally clear X-ray images of individual sections of tissues and organs are obtained.
UNDER AND COSMIC RAYS. Academician V.I. Vernadsky believed that cosmic rays play a large 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 into rocks ah, very small amounts of new atoms can be formed, including iodine atoms.
IODINE _ LUBRICANT. Just 0.6% iodine added to hydrocarbon oils greatly reduces the work of friction in bearings made of stainless steel and titanium. This allows you to increase the load on 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 strictly regularly. Vibrations of the light beam cannot pass through them in all directions. The result is a kind of filter, called a Polaroid, which diverts the oncoming blinding stream of light. This type of glass is used in cars. By combining several polaroids or rotating polaroid glasses, exceptionally colorful effects can be achieved - this phenomenon is used in film technology and in the theater.
DO YOU KNOW THAT:
- The iodine content in human blood depends on the time of year: from September to January the iodine concentration in the blood decreases, from February a new rise begins, and in May - June the iodine level reaches highest level. These oscillations have a relatively small amplitude, and their causes still remain a mystery;
- Food products contain a lot of iodine: eggs, milk, fish; there is a lot of iodine in seaweed, which goes on sale in the form of canned food, dragees and other products;
- the first iodine plant in Russia was built in 1915 in Yekaterinoslav (now Dnepropetrovsk); obtained iodine from the ash of the Black Sea algae Phyllophora; during the First World War, 200 kg of iodine was produced at this plant;
- if a thundercloud is “seeded” with silver iodide or lead iodide, then instead of hail, fine snow pellets are formed in the cloud: a cloud seeded with such salts sheds Rain and does not harm the crops.
Iodine(lat. Iodum), I, a chemical element of group VII of the periodic system of Mendeleev, belongs to the halogens (the outdated name Iodine and the symbol J are also found in the literature); atomic number 53, atomic mass 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. By heating the mother brine of seaweed ash with concentrated sulfuric acid, he observed the release of violet vapor (hence the name Iodine - from the Greek iodes, ioides - violet-like in color, violet), which condensed into dark shiny plate-like crystals. In 1813-1814, the French chemist J. L. Gay-Lussac and the English chemist G. Davy proved the elemental nature of iodine.
Distribution of iodine in nature. The average iodine content in the earth's crust is 4·10 -5% by mass. Iodine compounds are scattered in the mantle and magmas and in the rocks formed from them (granites, basalts and others); deep minerals of Iodine are unknown. The history of iodine in the earth's crust is closely related to living matter and biogenic migration. In the biosphere, processes of its concentration are observed, especially by marine organisms (algae, sponges and others). Eight supergene iodine minerals 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 sea water enter the atmosphere and are carried by winds to the continents. (Locations remote from the ocean or fenced off from sea winds mountains, depleted in iodine) Iodine is easily adsorbed by organic matter in soils and marine silts. When these silts are compacted and sedimentary rocks form, desorption occurs, and some of the iodine compounds pass into The groundwater. This is how iodine-bromine waters used for the extraction of iodine are formed, especially characteristic of oil field areas (in some places, 1 liter of these waters contains over 100 mg of iodine).
Physical properties of Iodine. Iodine density 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 influence of light. Already at ordinary temperatures, iodine evaporates, forming a sharp-smelling purple vapor. When heated slightly, iodine sublimes, settling in the form of shiny thin plates; this process serves to purify iodine in laboratories and industry. Iodine is poorly soluble in water (0.33 g/l at 25 °C), well soluble 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 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 reacts vigorously with metals when slightly heated, forming iodides (Hg + I 2 = HgI 2). Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide. Iodine does not combine directly with carbon, nitrogen, or oxygen. Elemental Iodine is an oxidizing agent, 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 oxidizing agents in aqueous solutions convert it into 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); in hot aqueous solutions of alkalis, iodide and iodate are formed (3I 2 + 6NaOH = 5NaI + NaIO 3 + 3H 2 O). When adsorbed on starch, iodine turns 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.
Obtaining Iodine. The raw material for the industrial production of iodine is oil drilling water; seaweed, as well as mother solutions of Chilean (sodium) nitrate containing up to 0.4% Iodine in the form of sodium iodate. To extract iodine from oil waters (usually containing 20-40 mg/l Iodine in the form of iodides), they are first treated 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 with air. Iodine adsorbed by coal is treated with caustic alkali or sodium sulfite (I 2 + Na 2 SO 3 + H 2 O = Na 2 SO 4 + 2HI). Free Iodine is isolated from the reaction products 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 Iodine is replaced with chlorine (2HI + Cl 2 = 2HCl + I 2). Crude crystalline iodine is purified by sublimation.
Application of Iodine. Iodine and its compounds are used mainly in medicine and in analytical chemistry, as well as in organic synthesis and photography.
Iodine in the body. Iodine is a microelement essential for animals and humans. In soils and plants of taiga-forest non-chernozem, dry steppe, desert and mountain biogeochemical zones, iodine is contained in insufficient quantities or is not balanced with some other microelements (Co, Mn, Cu); This is associated with the spread of endemic goiter in these areas. The average iodine content in soils is about 3·10 -4%, in plants about 2·10 -5%. In superficial drinking water There is little iodine (from 10 -7 to 10 -9%). In coastal areas, the amount of iodine in 1 m 3 of air can reach 50 mcg, in continental and mountainous areas it is 1 or even 0.2 mcg.
The absorption of iodine by plants depends on the content of its compounds in the soil and on the type of plant. Some organisms (so-called iodine concentrators), for example, seaweed - fucus, kelp, phyllophora, accumulate up to 1% Iodine, some sponges - up to 8.5% (in the skeletal substance spongin). Algae that concentrate iodine are used for its industrial production. IN animal organism Iodine comes with food, water, and air. The main source of iodine is plant products and feed. Iodine absorption 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. Using 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 condense into the hormone tetraiodothyronine (thyroxine). Iodine is excreted from the body mainly through the kidneys (up to 70-80%), mammary, salivary and sweat glands, partly with bile.
In different biogeochemical provinces, the iodine content in the daily diet varies (for humans from 20 to 240 mcg, for sheep from 20 to 400 mcg). An animal's need for iodine depends on its physiological state, time of year, temperature, and the body's adaptation to the iodine content in the environment. The daily need for Iodine in humans and animals is about 3 mcg per 1 kg of body weight (increases during pregnancy, increased growth, and cooling). The introduction of Iodine into the body increases basal metabolism, enhances oxidative processes, tones muscles, and stimulates sexual function.
Due to a greater or lesser deficiency of Iodine in food and water, iodization of table salt is used, usually containing 10-25 g of potassium iodide per 1 ton of salt. The use of fertilizers containing iodine can double or triple its content in crops.
Iodine in medicine. Preparations containing iodine have antibacterial and antifungal properties, they also have an anti-inflammatory and distracting effect; They are used externally to disinfect wounds and prepare the surgical field. When taken orally, Iodine preparations affect metabolism and enhance thyroid function. Small doses of Iodine (microiodine) inhibit the function of the thyroid gland, affecting the formation of thyroid-stimulating hormone in the anterior pituitary gland. Since iodine affects protein and fat (lipid) metabolism, it has found application in the treatment of atherosclerosis, as it reduces cholesterol in the blood; also increases the fibrinolytic activity of the blood. For diagnostic purposes, radiopaque agents 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 in case of pulmonary tuberculosis, pregnancy, kidney disease, chronic pyoderma, hemorrhagic diathesis, urticaria.
Iodine is radioactive. 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 in medicinal purposes based on the ability of β-radiation of iodine radioisotopes to destroy the secretory cells of the gland. When the environment is contaminated with nuclear fission products, radioactive isotopes of iodine quickly enter the biological cycle, ultimately ending up in milk and, consequently, in the human body. Their penetration into the body of children, whose thyroid gland is 10 times smaller than that of adults and also has greater radiosensitivity, is especially dangerous. In order to reduce the deposition of radioactive isotopes of iodine in the thyroid gland, it is recommended to use stable iodine preparations (100-200 mg per dose). Radioactive iodine is quickly and completely absorbed from the gastrointestinal tract and 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.
IOD, iodine (Latin Iodum), I, a chemical element of group VII of the short form (group 17 of the long form) of the periodic table, belongs to the halogens; atomic number 53, atomic mass 126.90447. One stable isotope, 127 I, is found in nature. Radioactive isotopes with mass numbers of 108-144 have been artificially obtained.
Historical reference. Iodine was first isolated in 1811 by the French chemist B. Courtois by reacting concentrated H 2 SO 4 on seaweed ash. The Latin name of the element comes from the Greek ιώδης - violet and is associated with the color of iodine vapor.
Prevalence in nature. The iodine content in the earth's crust is 4·10 -5% by mass. In nature, iodine is mainly found in sea water and algae, as well as in oil drilling waters; is part of minerals - natural iodides and iodates, for example lautarite Ca(IO 3) 2.
Properties. The configuration of the outer electron shell of the iodine atom is 5s 2 5p 5. In compounds, iodine exhibits oxidation states -1, +1, +3, +5, +7; Pauling electronegativity 2.66; atomic radius 140 pm; the radius of I ions is 206 pm, I 5+ 109 pm. In gaseous, liquid and solid states iodine exists in the form of diatomic molecules I 2 . Noticeable dissociation (about 3%) of I 2 molecules into atoms begins at temperatures above 800 ° C, as well as under the influence of light. I 2 molecules are diamagnetic.
Iodine is a black crystalline substance with a violet metallic sheen; rhombic crystal lattice; t melting point 113.7 °C, boiling point 184.3 °C, density of solid iodine 4940 kg/m3. Iodine is poorly soluble in water (0.33 g/dm3 at 25 °C); the solubility of iodine in water increases with increasing temperature, as well as with the addition of potassium iodide KI due to the formation of the KI 3 complex. Iodine is highly soluble in many organic solvents (benzene, hexane, alcohols, carbon tetrachloride, etc.). Solid iodine easily sublimes to form violet vapors that have a sharp, specific odor.
Iodine is the least reactive halogen. Iodine does not directly interact with noble gases, oxygen, sulfur, nitrogen, and carbon. When heated, iodine reacts with metals (metal iodides are formed, for example aluminum iodide AlI 3), phosphorus (phosphorus iodide ΡΙ 3), hydrogen (hydrogen iodide HI), and other halogens (interhalogen compounds). Iodine is a less strong oxidizing agent than chlorine and bromine. Iodine is more characterized by reducing properties. Thus, chlorine oxidizes iodine to iodic acid HIO 3: I 2 + 5Сl 2 + 6H 2 O = 2НIO 3 + 10НCl.
For iodine, a number of oxygen-containing acids are known, corresponding various degrees oxidation of iodine: iodine HIO (oxidation state of iodine +1; salts are hypoiodites, for example potassium hypoiodite KIO), iodine HIO 3 (+5; iodates, for example potassium iodate KIO 3), periodic, or metaiodic, HIO 4 and orthoperiodic, or orthoiodine , H 5 IO 6 (+7; salts - metaperiodates, for example potassium metaperiodate KIO 4 ; orthoperiodates, for example potassium dihydroorthoperiodate Κ 3 Η 2 ΙO 6 ; common name for salts of acids containing iodine in the oxidation state +7 - periodates). Oxygen-containing acids and their salts have oxidizing properties. HIO - weak acid; HIO and hypoiodites exist only in aqueous solutions. Solutions of HIO are prepared by the interaction of iodine with water, solutions of hypoiodites by the interaction of iodine with alkali solutions. HIO 3 is a colorless crystalline substance with a melting point of 110 °C, highly soluble in water; when heated to 300 °C, it splits off water to form acid oxide I 2 O 5 . HIO 3 is obtained by oxidation of iodine with fuming nitric acid: 3I 2 + 10HNO 3 = 6HIO 3 + 10NO + 2H 2 O. Iodates are soluble in water crystalline substances; obtained by reacting iodine with hot alkali solutions. When heated above 400 °C, iodates decompose, for example: 4KIO 3 = KI + 3KIO 4. H 5 IO 6 is a colorless crystalline substance, melting point 128 °C. Heating H 5 IO 6 to 100 ° C in a vacuum leads to the formation of HIO 4 (Η 5 ΙO 6 = HIO 4 + 2H 2 O), which decomposes at a higher temperature: 2HIO 4 = 2HIO 3 + O 2. In aqueous solutions, H 5 IO 6 exhibits the properties of a weak polybasic acid. H 5 IO 6 is obtained by an exchange reaction, for example, Ba 3 (H 2 IO 6) 2 + 3H 2 SO 4 = 2H 5 IO 6 + 3BaSO 4, followed by evaporation of the filtrate. Periodates are crystalline substances, resistant to heat, soluble in water; obtained by electrochemical oxidation of iodates.
The dissolution of iodine in water is a complex chemical process, including not only dissolution, but also disproportionation (I 2 + H 2 O = HI + HIO) and decomposition of HIO (ЗHIO = 2HI + HIO 3). The rate of disproportionation of HIO is high, especially in alkaline compounds (3I 2 + 6NaOH = NaIO 3 + 5NaI + 3H 2 O). Since the equilibrium constant of the reaction I 2 + H 2 O = HI + HIO is small (K = 2∙10 - 13), iodine in an aqueous solution is present in the form of I 2, and iodine water does not decompose when stored in the dark and has a neutral reaction.
Biological role. Iodine is a trace element. The daily human need for iodine is about 0.2 mg. The main physiological significance of iodine is determined by its participation in the function of the thyroid gland. The iodine entering it is involved in the biosynthesis of thyroid hormones. Lack of iodine intake leads to the development of endemic goiter; excess iodine in the body is observed in some liver diseases.
Receipt. In industry, iodine is isolated from drilling waters and seaweed ash. To extract iodine, drilling water containing iodides is treated with acidification with chlorine; the released iodine is blown out with water vapor. To purify iodine, sulfur dioxide SO 2 (I 2 + SO 2 + 2H 2 O = 2HI + H 2 SO 4) is passed through the reaction mixture and the resulting HI is oxidized to I 2 (for example, with chlorine: 2HI + Cl 2 = 2HCl + I 2 ). Iodates formed by burning algae are reduced with sulfur dioxide (2NaIO 3 + 5SO 2 + 4H 2 O = 2NaHSO 4 + 3H 2 SO 4 + I 2); the released iodine is purified by sublimation. In the laboratory, iodine is obtained by oxidation of iodides in an acidic environment (for example, using manganese dioxide: 2KI + MnO 2 + 2H 2 SO 4 = I 2 + MnSO 4 + 2H 2 O + K 2 SO 4); the resulting iodine is extracted or separated by steam distillation.
World iodine production is 15-16 thousand tons/year (2004).
Application. Iodine and its compounds are used in medicine; Iodine preparations capable of releasing elemental iodine have antibacterial, antifungal and anti-inflammatory properties. Iodine is used in transport chemical reactions for the production of high-purity Ti, Zr and other metals, as well as silicon; for filling iodine incandescent lamps, which are characterized by high luminous efficiency, small size and long service life. Radioactive isotopes 125 I (T 1/2 59.4 days), 131 I (T 1 /2 8.04 days), 132 Ι (T 1 /2 2.28 hours) are used in biology and medicine to determine the functional state of the thyroid gland and treatment of its diseases.
Iodine is toxic; its vapors irritate mucous membranes and cause dermatitis.
Lit.: Greenwood N.N., Earnshaw A. Chemistry of the elements. 2nd ed. Oxf.; Boston, 1997; Drozdov A.A., Mazo G.N., Zlomanov V.P., Spiridonov F.M. Inorganic chemistry. M., 2004. T. 2.
(first electron)
(according to Pauling)
| I | 53 |
| 126,90447 | |
| 5s 2 5p 5 | |
| Iodine | |
Iodine, iodine(from ancient Greek ιώδης, iodes - “violet”) - an element of the main subgroup of the seventh group, the fifth period of the periodic system chemical elements D.I. Mendeleev, with atomic number 53. Denoted by the symbol I (lat. Iodum). A chemically active non-metal, belongs to the group of halogens. The simple substance iodine (CAS number: 7553-56-2) under normal conditions is crystals black-gray with a violet metallic sheen, easily forms violet vapors with a pungent odor. The molecule of the substance is diatomic (formula I 2).
In medicine and biology, this substance is usually called iodine(for example, “iodine solution”), in the periodic table and chemical literature the name is used iodine.
Story
Iodine was discovered in 1811 by Courtois in seaweed ash, and in 1815 Gay-Lussac began to consider it as a chemical element.
Element symbol J was replaced by I relatively recently, in the 50s of the XX century.
Being in nature
IN large quantities found in the form of iodides in sea water. It is also known in nature in free form, as a mineral, but such finds are rare - in the thermal springs of Vesuvius and on the island. Vulcano (Italy). Reserves of natural iodides are estimated at 15 million tons, 99% of reserves are located in Chile and Japan. Currently, intensive iodine mining is carried out in these countries, for example, the Chilean Atacama Minerals produces over 720 tons of iodine per year.
The raw material for the industrial production of iodine in Russia is oil drilling water, while in foreign countries that do not have oil fields, seaweed is used, as well as mother liquors of Chilean (sodium) nitrate, which makes the production of iodine from such raw materials much more expensive.
Physical properties
The vapors have a characteristic purple color, just like solutions in non-polar organic solvents such as benzene - in contrast to the brown solution in a polar alcohol. Iodine at room temperature appears as dark purple crystals with a faint luster. When heated at atmospheric pressure it sublimates (sublimates), turning into violet vapor; When cooled, iodine vapor crystallizes, bypassing the liquid state. This is used in practice to purify iodine from non-volatile impurities.
Chemical properties
Chemically, iodine is quite active, although to a lesser extent than chlorine and bromine.
- When slightly heated, iodine reacts energetically with metals, forming iodides:
- Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide:
- Elemental iodine is an oxidizing agent, less powerful than chlorine and bromine. Hydrogen sulfide H 2 S, Na 2 S 2 O 3 and other reducing agents reduce it to the I - ion:
- When dissolved in water, iodine partially reacts with it:
Application
Medicine
It is widely used in alternative (unofficial) medicine, but its use without a doctor’s prescription is generally poorly justified, and is often accompanied by various advertising statements.
see also
Battery production
Iodine is used as the positive electrode (oxidizing agent) in lithium-iodine batteries for electric vehicles.
Laser fusion
Some organoiodine compounds are used to produce high-power gas lasers using excited iodine atoms (laser fusion research and industry).
Radioelectronics industry
In recent years, the demand for iodine from manufacturers of liquid crystal displays has sharply increased.
Dynamics of iodine consumption
Toxicity
Iodine is a toxic substance. Lethal dose 2-3 g. Causes damage to the kidneys and cardiovascular system. When inhaling iodine vapor, a headache, cough, runny nose appears, and possibly pulmonary edema. Contact with the mucous membrane of the eyes causes lacrimation, eye pain and redness. If ingested, general weakness, headache, vomiting, diarrhea, brown coating on the tongue, heart pain and increased heart rate appear. After a day, the kidneys become inflamed and blood appears in the urine. If left untreated, the kidneys may fail within 2-3 days and myocarditis may occur. Without treatment, death occurs.