Chemical element iodine - formula, structure and properties

Iodine
(the trivial (common) name is
iodine
; from the Greek ἰώδης - “violet (violet)”) is a chemical element with atomic number 53. Belongs to the 17th group of the periodic table of chemical elements (according to the outdated short form of the periodic system, it belongs to the main subgroup VII of group, or group VIIA), is in the fifth period of the table.
The atomic mass of the element is 126.90447 a. e.m.. Denoted by the symbol I
(from the Latin Iodum).
A chemically active non-metal, belongs to the group of halogens. The simple substance iodine
under normal conditions is black-gray crystals with a violet metallic luster; it easily forms violet vapors with a pungent odor. Elemental iodine is highly toxic. The molecule of a simple substance is diatomic (formula I2).

Content

• 1 Name and designation
• 2 History
• 3 Being in nature
• 4 Physical properties 4.1 Isotopes

Isotopes of the element

Only one natural isotope of the element is known - iodine-127. Isotopes are two or more forms of an element. They differ from each other by their mass number. The number written to the right of the element's name is the mass number. It represents the number of protons plus neutrons in the nucleus of an element's atom. The number of protons defines an element, but the number of neutrons in an atom of any one element can vary. Each variation is an isotope.

Approximately 30 radioactive isotopes of iodine have been produced artificially. These are isotopes that break apart and release some form of radiation. They are formed when very small particles burn atoms. These particles stick to atoms and make them radioactive.

Application of isotopes

A number of iodine isotopes have commercial uses. For medical purposes, they are introduced into the patient's body through the mouth and then pass through the body in the bloodstream. When they travel, they emit radiation. This radiation is detected using X-ray film. A medical professional can tell how well the body is functioning by observing the radiation pattern. Iodine isotopes are also used for the following purposes:

• Iodine-123 - in studies of the brain, kidneys and thyroid gland.
• Iodine-125 - to study the pancreas, blood flow, liver, mineral absorption in the bones and protein loss in the body.
• And iodine-131 is used in studies of the liver, kidneys, blood flow, lungs, brain, and pancreas.

The most common isotope is iodine-131. When ingested, it tends to go directly to the thyroid gland and is then used to produce thyroid hormones.

Name and designation

The name of the element was proposed by Gay-Lussac and comes from ancient Greek. ἰο-ειδής (lit. "violet-like"), which refers to the color of the steam observed by French chemist Bernard Courtois when heating a mother brine of seaweed ash with concentrated sulfuric acid. In medicine and biology, this element and simple substance is usually called iodine
, for example, "iodine solution", in accordance with the old version of the name that existed in chemical nomenclature until the mid-20th century.

In modern chemical nomenclature, the name iodine

.
The same situation exists in some other languages, for example, in German: the commonly used Jod and the terminologically correct Iod. Coinciding with the element's name change in the 1950s, the element symbol J
was replaced by
I
.

Metabolism

Iodine absorption occurs in the upper parts of the small intestine, where it enters in the form of organic and inorganic compounds - iodides, iodinated amino acids, and fatty acids. Most of the absorbed iodine binds to a specific carrier protein, and in this form is distributed to organs and tissues.

At the same time, it enters the liver, kidneys, ovaries in women, and the prostate gland in men. A certain amount of the microelement is absorbed by the skin and its appendages, hair and nails.

But the main consumer of I is, of course, the thyroid gland. The functional tissue of this gland consists of many tiny vesicles, follicles. The inside of the follicles is lined with thyrocyte cells and filled with colloid. This viscous substance contains thyroglobulin proteins, which come here from thyrocytes.

The amino acid L-tyrosine is involved in the formation of thyroglobulins. Thyroglobulins are the raw materials for the formation of triiodothyronine and thyroxine.

Iodine first moves from the blood into thyrocytes, and then into the colloid. Here, with the participation of iron and the specific enzyme thyroid peroxidase, sequential iodination occurs, the addition of I atoms to the thyroglobulin molecule.

1 molecule joins - monoiodothyronine is formed, 2 - diiodothyronine. True, these substances are not active. But with the further addition of iodine, triiodothyronine or T3 and thyroxine or T4 are formed.

These substances already have hormonal activity. True, this activity, like their content, is not the same. The content of T4 is several times higher than T3. But T3 is more active than T4. It has been established that T3 is formed from T4 during deiodination, the elimination of an iodine molecule. Thyroid hormones, thyroxine and triiodothyronine, are released into the blood.

In the blood plasma they are bound by another carrier, thyroxine-binding globulin, and in this form are distributed to organs and tissues. Having fulfilled their function, they are partially destroyed and partially removed unchanged. Free iodine, and iodine as part of thyroid hormones, leaves our body mainly in urine, and to a lesser extent in feces.

A certain amount of I is excreted in saliva and sweat. It is noteworthy that the excretion of iodine in the urine (ioduria) can be used to judge the presence of iodine in the body. The more iodine enters the body, the more it is excreted in the urine, and vice versa.

Therefore, low ioduria indicates a lack of I. And for the same reason, determination of iodine in urine is used to identify iodine deficiency conditions.

Being in nature

Iodine.
Iodine is a rare element. Its clarke is only 400 mg/t. However, it is extremely scattered in nature and, being far from the most common element, is present almost everywhere. Iodine is found in the form of iodides in sea water (20-30 mg per ton of sea water). Present in living organisms, most of all in algae (2.5 g per ton of dried seaweed, kelp). 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 of 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 most famous of the iodine minerals is lautarite Ca(IO3)2. Some other iodine minerals are iodide bromite Ag(Br, Cl, I), embolite Ag(Cl, Br), myersite CuI·4AgI.

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, lye from potassium and saltpeter industries, which greatly increases the cost of producing iodine from such raw materials.

Receiving and finding

This element is produced commercially from iodine-containing brines. Natural brines or brines extracted from oil wells containing up to 150 mg per liter (0.02 oz per gallon) are found in Java, California and northern Italy. The world's leading producers include Chile, Japan, China, Russia and Azerbaijan.

Impurities such as clay, sand and oil are removed by filtration and the solution is passed through a stream of sulfur dioxide and then through several containers containing bundles of copper wire. The resulting copper iodide is removed by filtration, washed with water, dried and finely ground. The product is heated with potassium carbonate to produce potassium iodide, which is then oxidized to the free element with dichromate and sulfuric acid.

Physical properties

Liquid iodine at the bottom of a beaker
Natural iodine consists of only one isotope - iodine-127 (see Isotopes of iodine). The configuration of the outer electron layer is 5s2p5. In compounds it exhibits oxidation states −1, 0, +1, +3, +5 and +7 (valences I, III, V and VII).

The radius of the neutral iodine atom is 0.136 nm, the ionic radii of I−, I5+ and I7+ are, respectively, 0.206; 0.058-0.109; 0.056-0.067 nm. The energies of sequential ionization of a neutral iodine atom are equal, respectively: 10.45; 19.10; 33 eV. Electron affinity −3.08 eV. According to the Pauling scale, the electronegativity of iodine is 2.66, iodine is a non-metal.

Under normal conditions, iodine is a solid substance, black-gray or dark purple crystals with a weak metallic luster and a specific odor.

The vapors have a characteristic purple color, just like solutions in non-polar organic solvents, for example, benzene - in contrast to the brown solution in polar ethyl alcohol. Slightly soluble in water (0.28 g/l), better soluble in aqueous solutions of alkali metal iodides to form triiodides (for example, potassium triiodide KI3).

When heated at atmospheric pressure, iodine sublimates (sublimates), turning into violet vapor; When cooled at atmospheric pressure, iodine vapor crystallizes, bypassing the liquid state. This is used in practice to purify iodine from non-volatile impurities.

Liquid iodine can be obtained by heating it under pressure.

Isotopes

There are 37 known isotopes of iodine with mass numbers from 108 to 144. Of these, only 127I is stable, the half-life of the remaining iodine isotopes ranges from 103 μs to 1.57⋅107 years;
individual isotopes are used for therapeutic and diagnostic purposes. The radioactive nuclide 131I decays with the emission of β-particles (the most probable maximum energies are 0.248, 0.334 and 0.606 MeV), as well as with the emission of γ-quanta with energies from 0.08 to 0.723 MeV.

basic information

Iodine is an essential element necessary for life. It is best known for its role in the production of thyroid hormones in humans, as well as in all vertebrates. Iodine deficiency can lead to serious health problems, including goiter (enlarged thyroid gland), mental retardation and cretinism.

As a pure element, it is a shiny purple-black non-metal that is solid under standard conditions. It easily changes from a solid to a gaseous state, bypassing the liquid form, and emits a purple vapor. Although it is technically a non-metal, it does have some metallic qualities. The main characteristics of the element are:

• Name: Iodine.
• Symbol: I.
• Atomic number: 53.
• Atomic mass: 126.90447 a. eat.
• Melting point: 113.5 °C.
• Boiling point: 184.0 °C.
• Electronic formula of iodine (Electronic configuration): 1s22s22p63s23p63d104s24p64d105s25p5.
• Atomic structure: number of protons - 53, electrons - 53, neutrons - 74.
• Valence variable: -1, +1, (+3), (+4), +5, +7.
• Classification: halogen.
• Crystal structure: rhombic.
• Density at 20°C: 4.93 g/cm3.
• Color: black-gray.

Chemical properties

Iodine belongs to the group of halogens.

Electronic formula (Electronic configuration) of iodine: 1s22s22p63s23p63d104s24p64d105s25p5.

Forms a number of acids: hydroiodic (HI), iodic (HIO), iodous (HIO2), iodic (HIO3), iodic (HIO4).

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

• A fairly well-known qualitative reaction to iodine is its interaction with starch, in which a blue color is observed as a result of the formation of an inclusion compound. This reaction was discovered in 1814 by Jean-Jacques Colin and Henri-François Gaultier de Claubry.
• When slightly heated, iodine reacts energetically with metals, forming iodides:

Hg + I2 → HgI2

• Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide:

H2 + I2 → 2HI

• Iodine is an oxidizing agent, less powerful than fluorine, chlorine and bromine. Hydrogen sulfide H2S, Na2S2O3 and other reducing agents reduce it to the I− ion:

I2 + H2S → S + 2HI I2 + 2Na2S2O3 → 2NaI + Na2S4O6
The last reaction is also used in analytical chemistry for the determination of iodine.

• When dissolved in water, iodine partially reacts with it (According to Kuzmenko’s “Principles of Chemistry”: the reaction does not occur even when heated, the text needs checking)

I2 + H2O → HI + HIO, p K
c=15.99

• Reaction of formation of triiodine nitride:

3I2 + 5NH3 → 3NH4I + NH3 ⋅ NI3↓
Triiodine nitride in the dry crystalline state decomposes to release violet iodine vapor, which is demonstrated as a spectacular chemical reaction.

• Alkali metal iodides are very prone to attach (dissolve) halogen molecules in solutions to form polyiodides (periodides) - potassium triiodide, potassium dichloroiodate I:

KI + I2 → KI3

Sources of income

UP TO 60% of iodine comes to us in animal products, up to 30% in plant products, and the rest in water. We receive a certain amount of microelement in the inhaled air. The generally recognized leaders in content I are fish and seafood.

Content of I in 100 g of products:

During heat treatment, products lose up to 50% or more of the iodine they contain. To minimize the loss of microelements, products should be cooked whole or cut into large pieces over low heat, in a small volume of water, for a short time, and in a container covered with a lid.

Another artificial food source of iodine is iodized salt. This is table salt, sodium chloride, with the addition of iodine compounds - sodium and potassium iodides and iodates. The use of iodized salt is recommended for people living in endemic iodine-deficient areas.

Some facts should be taken into account. Iodized salt gives foods a specific bitter taste, and when heated, the amount of iodine decreases. For these reasons, it should not be used for boiling, cooking, or canning foods. Add it to food immediately before consumption. The shelf life of this salt, compared to regular salt without iodine, is short and is 6 months. It should be stored in a place protected from light.

Application

In medicine

5% alcohol solution of iodine
“Iodine solution” is referenced here. A separate article is needed on this topic.

Main article: Lugol's solution

A 5 percent alcohol solution of iodine is used to disinfect the skin around an injury (torn, cut or other wound), but not for oral administration if there is iodine deficiency in the body. Products of the addition of iodine to starch and other IUDs (the so-called “ Blue iodine”

"—Iodinol, Yox, Betadine, etc.) are milder antiseptics.

If there are a large number of intramuscular injections, the patient is given an iodine mesh in their place - a mesh is drawn with iodine on the area where the injections are made (for example, on the buttocks). This is necessary so that the “bumps” formed at the sites of intramuscular injections quickly dissolve.

It is widely advertised in alternative (unofficial) medicine, but its use without a doctor’s prescription is generally poorly justified and is often accompanied by various advertising claims.

It is used less and less as an antiseptic; along with an alcohol solution of iodine, brilliant green, fucorcin, pyoctanin, hydrogen peroxide solutions, etc. are used.

In X-ray and tomographic studies, iodine-containing contrast agents are widely used.

Iodine-131, like some radioactive isotopes of iodine (125I, 132I), are used in medicine for the diagnosis and treatment of thyroid diseases. The isotope is widely used in the treatment of diffuse toxic goiter (Graves disease) and some tumors. According to radiation safety standards NRB-99/2009 adopted in Russia, discharge from the clinic of a patient treated with iodine-131 is permitted when the total activity of this nuclide in the patient’s body decreases to a level of 0.4 GBq.

In criminology

In forensic science, iodine vapor is used to detect fingerprints on paper surfaces, such as banknotes.

In technology: metal refining

Sources of light

Iodine is used in light sources:

• halogen lamps - as a component of the gas filler of the bulb to deposit the evaporated tungsten filament back onto it.
• metal halide arc lamps - halides of a number of metals are used as the discharge gas medium, the use of various mixtures of which makes it possible to obtain lamps with a wide variety of spectral characteristics.

Battery production

Iodine is used as a component of the positive electrode (oxidizer) in lithium-ion batteries for automobiles.

Laser fusion

Some organiodine compounds are used for the production of ultra-powerful gas lasers using excited iodine atoms (research in the field of laser thermonuclear fusion).

Radioelectronic industry]

In recent years, the demand for iodine from manufacturers of liquid crystal displays has sharply increased.

Dynamics of iodine consumption

World consumption of iodine in 2005 amounted to 25.8 thousand tons

Daily requirement

The iodine requirement is from 2 to 4 mcg per 1 kg of body weight. By age category, this indicator looks like this:

The need for iodine increases in: stressful situations (physical activity, illness), taking medications that suppress thyroid function. Among these drugs:

• some nonsteroidal anti-inflammatory drugs
• glucocorticoids
• interferons
• beta blockers
• heparin
• lithium salts
• specific drugs prescribed for hyperthyroidism, excessive thyroid function: Thiamazole (Mercazolil), Propylthiouracil.

In this case, the need for a microelement can reach 400 mcg. In any case, the daily intake of I should not exceed the toxic threshold of 500 mcg.

Biological role

Iodine is a trace element and is present in all living organisms. Its content in plants depends on the presence of its compounds in soil and water. Some seaweeds (seaweed, kelp, fucus and others) accumulate up to 1% iodine. Aquatic plants of the duckweed family are rich in iodine. Iodine is included in the skeletal protein of sponges and the skeletal proteins of marine polychaete worms.

Iodine and the thyroid gland

In animals and humans, iodine is part of the so-called thyroid hormones produced by the thyroid gland - thyroxine and triiodothyronine, which have a multifaceted effect on the growth, development and metabolism of the body.

The human body (body weight 70 kg) contains 12-20 mg of iodine. A person’s daily need for iodine is determined by age, physiological state and body weight. For a middle-aged person of normal build (normosthenic), the daily dose of iodine is 0.15 mg.

The absence or deficiency of iodine in the diet (which is typical in some areas) leads to diseases (endemic goiter, cretinism, hypothyroidism). In this regard, potassium iodide, sodium iodide or potassium iodate (iodized salt) are added to table salt sold in areas with a natural geochemical deficiency of iodine.

Lack of iodine leads to diseases of the thyroid gland (for example, Graves' disease, cretinism). Also, with a slight lack of iodine, fatigue, headache, depressed mood, natural laziness, nervousness and irritability are noted; memory and intelligence weakens. Over time, arrhythmia appears, blood pressure rises, and the level of hemoglobin in the blood drops.

Excess iodine in food is usually easily tolerated by the body, but in some cases in people with hypersensitivity, this excess can also lead to thyroid disorders.

Toxicity

Iodine is toxic. Lethal dose (LD50) - 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, fever, vomiting, diarrhea, brown coating on the tongue, heart pain and increased heart rate appear. After a day, blood appears in the urine. After 2 days, renal failure and myocarditis appear. Without treatment, death occurs.

The maximum permissible concentration of iodine in water is 0.125 mg/dm³, in air 1 mg/m³.

Radioactive iodine-131 (radiiodine), which is a beta and gamma emitter, is especially dangerous for the human body, since radioactive isotopes are not biochemically different from stable ones. Therefore, almost all radioactive iodine, like regular iodine, is concentrated in the thyroid gland, which leads to its irradiation and dysfunction. The main sources of air pollution with radioactive iodine are nuclear power plants and pharmaceutical production. At the same time, this property of radioiodine allows it to be used to combat thyroid tumors and diagnose its diseases (see above).

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.

• Thyroiditis