Alcohol solution of iodine … Since childhood, a well-known helper for scratches, abrasions and cuts to all children and their parents. It is a fast and effective agent that cauterizes and disinfects the wound surface. However, the scope of the substance is not limited to medicine, because the chemical properties of iodine are very diverse. The purpose of our article is to get to know them in more detail.
Physical characteristics
A simple substance looks like dark purple crystals. When heated, due to the peculiarities of the internal structure of the crystal lattice, namely the presence of molecules in its nodes, the compound does not melt, but immediately forms vapors. This is sublimation or sublimation. It is explained by a weak bond between the molecules inside the crystal, which are easily separated from each other - a gaseous phase of the substance is formed. The number of iodine in the periodic table is 53. And its position among other chemical elements indicatesbelonging to non-metals. Let's dwell on this issue further.
Place of an element in the Periodic Table
Iodine is in the fifth period, group VII and, along with fluorine, chlorine, bromine and astatine forms a subgroup of halogens. Due to the increase in the nuclear charge and atomic radius, the representatives of halogens have a weakening of non-metallic properties, therefore iodine is less active than chlorine or bromine, and its electronegativity is also lower. The atomic mass of iodine is 126, 9045. A simple substance is represented by diatomic molecules, like other halogens. Below we will get acquainted with the structure of the atom of the element.
Features of the electronic formula
Five energy levels and the last of them almost completely filled with electrons confirm that the element has pronounced signs of non-metals. Like other halogens, iodine is a strong oxidizing agent, taking away from metals and weaker non-metallic elements - sulfur, carbon, nitrogen - the electron missing before the completion of the fifth level.
Iodine is a non-metal whose molecules contain a common pair of p-electrons that binds atoms together. Their density at the place of overlap is the highest, the common electron cloud does not move to any of the atoms and is located in the center of the molecule. A non-polar covalent bond is formed, and the molecule itself has a linear shape. In the halogen series, from fluorine to astatine, the strength of the covalent bond decreases. There is a decrease in the enthalpy value, on which the decay of element molecules into atoms depends. What implications does this have for the chemical properties of iodine?
Why is iodine less active than other halogens
The reactivity of non-metals is determined by the force of attraction to the nucleus of their own atom of foreign electrons. The smaller the radius of an atom, the higher the electrostatic attraction forces of its negatively charged particles of other atoms. The higher the number of the period in which the element is located, the more energy levels it will have. Iodine is in the fifth period, and it has more energy layers than bromine, chlorine and fluorine. That is why the iodine molecule contains atoms that have a radius much larger than that of the previously listed halogens. That is why I2 particles attract electrons weaker, which leads to a weakening of their non-metallic properties. The internal structure of a substance inevitably affects its physical characteristics. Here are some specific examples.
Sublimation and solubility
Reducing the mutual attraction of iodine atoms in its molecule leads, as we said earlier, to a weakening of the strength of the covalent non-polar bond. There is a decrease in the resistance of the compound to high temperature and an increase in the thermal dissociation of its molecules. A distinctive feature of halogen: the transition of a substance when heated from a solid state immediately to a gaseous state, i.e. sublimation is the main physical characteristic of iodine. Its solubility in organic solvents, such as carbon disulfide, benzene, ethanol, is higher than in water. So, in 100 g of water at 20 ° C, only 0.02 g can dissolvesubstances. This feature is used in the laboratory to extract iodine from an aqueous solution. Shaking it with a small amount of H2S, you can observe the purple color of hydrogen sulfide due to the transition of halogen molecules into it.
Chemical properties of iodine
When interacting with metals, the element always behaves in the same way. It attracts the valence electrons of the metal atom, which are located either on the last energy layer (s-elements, such as sodium, calcium, lithium, etc.), or on the penultimate layer containing, for example, d-electrons. These include iron, manganese, copper and others. In these reactions, the metal will be the reducing agent, and iodine, whose chemical formula is I2, will be the oxidizing agent. Therefore, it is this high activity of a simple substance that is the reason for its interaction with many metals.
Noteworthy is the interaction of iodine with water when heated. In an alkaline medium, the reaction proceeds with the formation of a mixture of iodide and iodic acids. The latter substance exhibits the properties of a strong acid and, upon dehydration, turns into iodine pentoxide. If the solution is acidified, then the above reaction products interact with each other to form the initial substances - free molecules I2 and water. This reaction belongs to the redox type, it exhibits the chemical properties of iodine as a strong oxidizing agent.
Qualitative starch reaction
Both in inorganic and organic chemistry there is a group of reactions, with the help ofwhich can be identified in the interaction products certain types of simple or complex ions. To detect macromolecules of a complex carbohydrate - starch - a 5% alcohol solution of I2 is often used. For example, a few drops of it are dripped onto a slice of a raw potato, and the color of the solution becomes blue. We observe the same effect when a substance enters any starch-containing product. This reaction, which produces blue iodine, is widely used in organic chemistry to confirm the presence of a polymer in a test mixture.
The beneficial properties of the product of the interaction of iodine and starch have long been known. It was used in the absence of antimicrobial drugs for the treatment of diarrhea, gastric ulcers in remission, diseases of the respiratory system. Starch paste, containing about 1 teaspoon of an iodine alcohol solution per 200 ml of water, was widely used due to the cheapness of the ingredients and ease of preparation.
However, it must be remembered that blue iodine is contraindicated in the treatment of young children, people suffering from hypersensitivity to iodine-containing drugs, as well as patients with Graves' disease.
How non-metals react with each other
Among the elements of the main subgroup of group VII, iodine reacts with fluorine, the most active non-metal with the highest degree of oxidation. The process takes place in the cold and is accompanied by an explosion. With hydrogen, I2 interacts with strong heating, and not completely, the reaction product - HI - begins to decompose into the starting substances. Hydroiodic acid is quite strong and although similar in characteristics to hydrochloric acid, it still shows more pronounced signs of a reducing agent. As you can see, the chemical properties of iodine are due to its belonging to active non-metals, however, the element is inferior in oxidizing ability to bromine, chlorine and, of course, fluorine.
The role of the element in living organisms
The highest content of ions I- is located in the tissues of the thyroid gland, where they are part of the thyroid-stimulating hormones: thyroxine and triiodothyronine. They regulate the growth and development of bone tissue, the conduction of nerve impulses, and the metabolic rate. Especially dangerous is the lack of iodine-containing hormones in childhood, since mental retardation and the appearance of symptoms of a disease such as cretinism are possible.
Insufficient secretion of thyroxin in adults is associated with iodine deficiency in water and food. It is accompanied by hair loss, the formation of edema, and a decrease in physical activity. An excess of an element in the body is also extremely dangerous, as Graves' disease develops, the symptoms of which are excitability of the nervous system, tremor of the limbs, and severe weight loss.
The high content of iodine compounds is found in some representatives of the world of flora. Lower plants - brown and red algae - accumulate them in their thallus. Among higher plants, sour cherries, persimmons, dates and beets are the record holders for the accumulation of iodine. Seafood and sea fish contain a large amount of the element.
Distribution of iodides in nature and methods for obtaining a pure substance
The bulk of the element is present in living organisms and the shells of the Earth - the hydrosphere and lithosphere - in a bound state. There are s alts of the element in sea water, but their concentration is insignificant, therefore it is unprofitable to extract pure iodine from it. It is much more efficient to obtain a substance from the ashes of brown algae: fucus, kelp, sargassum.
On an industrial scale, I2 is isolated from groundwater in oil extraction processes. During the processing of some ores, such as Chilean s altpeter, potassium iodates and hypoiodates are found in it, from which pure iodine is subsequently extracted. It is quite cost-effective to obtain I2 from a solution of hydrogen iodine by oxidizing it with chlorine. The resulting compound is an important raw material for the pharmaceutical industry.
In addition to the already mentioned 5% alcohol solution of iodine, which contains not only a simple substance, but also a s alt - potassium iodide, as well as alcohol and water, in endocrinology, for medical reasons, drugs such as "Iodine-active" and " Iodomarin".
In areas with a low content of natural compounds, in addition to iodized table s alt, you can use a remedy such as Antistrumine. It contains the active ingredient - potassium iodide - and is recommended as a prophylactic drug used to prevent the symptoms of endemic goiter.
