Alcoholic solution of iodine ... Since childhood, an assistant with scratches, abrasions and cuts that is familiar to all children and their parents. It is a fast and effective means, cauterizing and disinfecting the wound surface. However, the scope of the substance is not limited only to medicine, because the chemical properties of iodine are very diverse. The purpose of our article is to familiarize yourself with them in more detail.
Physical characteristic
A simple substance has the form of dark violet 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 pairs. This is sublimation or sublimation. It is explained by a weak bond between the molecules inside the crystal, which are easily detached 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 indicates that it belongs to non-metals. Let us dwell on this question further.
Place of an element in the periodic system
Iodine is in the fifth period, group VII and, along with fluorine, chlorine, bromine and astatine forms a subgroup of halogens. Due to an increase in the nuclear charge and atomic radius, the representatives of halogens weaken 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, as in other halogens. Below we will familiarize ourselves with the structure of the atom of an element.
Features of the electronic formula
Five energy levels and the last of them almost completely filled with electrons confirm the presence of pronounced signs of nonmetals in the element. Like other halogens, iodine is a strong oxidizing agent, taking away from metals and weaker non-metallic elements - sulfur, carbon, nitrogen - an electron that is missing until the fifth level is completed.
Iodine is a non-metal in the molecules of which there is a common pair of p-electrons that binds atoms together. Their density at the point of overlap is greatest, the common electron cloud does not shift 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 a series of halogens, from fluorine to astatine, the strength of the covalent bond decreases. A decrease in the enthalpy is observed, on which the decay of the element molecules into atoms depends. What are the consequences for the chemical properties of iodine?
Why iodine activity is less than other halogens
The reactivity of non-metals is determined by the force of attraction of foreign electrons to the nucleus of their own atom. The smaller the radius of the atom, the higher the electrostatic 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 having a radius much larger than the previously listed halogens. That is why I 2 particles attract electrons weaker, which leads to a weakening of their non-metallic properties. The internal structure of matter inevitably affects its physical characteristics. We give specific examples.
Sublimation and Solubility
A decrease in the mutual attraction of iodine atoms in its molecule leads, as we said earlier, to weakening 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 upon heating 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 of substance can dissolve. This feature is used in the laboratory to extract iodine from an aqueous solution. Shaking it with a small amount of H 2 S, one can observe the violet staining of hydrogen sulfide due to the transition of halogen molecules into it.
Chemical properties of iodine
Interacting with metals, the element always behaves the same. It attracts valence electrons of a 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 a reducing agent, and iodine, the chemical formula of which is I 2 , will be an oxidizing agent. Therefore, it is this high activity of a simple substance that is the reason for its interaction with many metals.
The interaction of iodine with water when heated is noteworthy. In an alkaline environment, the reaction proceeds with the formation of a mixture of iodide and iodic acid. The latter substance exhibits the properties of a strong acid and, when dehydrated, turns into iodine pentoxide. If the solution is acidified, then the above reaction products interact with each other with the formation of the starting substances - free I 2 molecules and water. This reaction belongs to the redox type; the chemical properties of iodine as a strong oxidizing agent are manifested in it.
Qualitative reaction to starch
In both inorganic and organic chemistry, there is a group of reactions that can be used to identify certain types of simple or complex ions in the reaction products. To detect macromolecules of a complex carbohydrate - starch - a 5% alcohol solution of I 2 is often used. For example, a few drops are dripped onto a slice of raw potato, and the color of the solution turns blue. We observe the same effect when a substance enters any starch-containing product. This reaction, which yields blue iodine, is widely used in organic chemistry to confirm the presence of polymer in the test mixture.
The beneficial properties of the product of the interaction of iodine and starch have been known for a long time. It was used in the absence of antimicrobial medications for the treatment of diarrhea, stomach ulcers in remission, and diseases of the respiratory system. Starch paste, containing about 1 teaspoon of an alcoholic solution of iodine per 200 ml of water, was widely used due to the cheapness of the ingredients and the simplicity of preparation.
However, it must be remembered that blue iodine is contraindicated in the treatment of small children, people suffering from hypersensitivity to iodine-containing drugs, as well as patients with a bazedovy disease.
How non-metals react with each other
Among the elements of the main subgroup of group VII, fluorine reacts with iodine - the most active non-metal with the highest degree of oxidation. The process takes place in the cold and is accompanied by an explosion. It interacts with hydrogen under strong heating, and not completely, the reaction product - HI - begins to decompose into the starting materials. Hydroiodic acid is quite strong and, although its characteristics are similar to perchloric acid, it still exhibits 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 I - ions is in the tissues of the thyroid gland, where they are part of thyroid-stimulating hormones: thyroxine and triiodothyronine. They regulate the growth and development of bone tissue, conduction of nerve impulses, 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 thyroxine secretion in adults is associated with iodine deficiency in water and food. It is accompanied by hair loss, the formation of edema, a decrease in physical activity. An excess of an element in the body is also extremely dangerous, since a Bazedov disease develops, the symptoms of which are excitability of the nervous system, tremor of the extremities, and severe emaciation.
A high content of iodine compounds is found in some representatives of the flora world. Lower plants - brown and red algae - accumulate them in their thallus. Among the higher plants, the record for the accumulation of iodine are cherry, persimmon, dates and beets. A large number of elements contain seafood and sea fish.
The distribution of iodides in nature and methods for producing a pure substance
The bulk of the element is present in living organisms and the Earth's shells - the hydrosphere and lithosphere - in a bound state. There are salts 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 substances from the ash of brown algae: fucus, kelp, sargassum.
On an industrial scale, I 2 is isolated from groundwater in oil production processes. When processing some ores, such as Chilean nitrate, potassium iodates and hypoiodates are found in it, from which pure iodine is subsequently mined. It is sufficient to obtain I 2 from a solution of hydrogen iodide, 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 salt - potassium iodide, as well as alcohol and water, medications such as "Iodine-active" and "Iodomarin" are used for medical reasons in endocrinology.
In areas with a low content of natural compounds, in addition to iodized edible salt, you can use a therapeutic agent such as "Antistrumin." It contains the active substance - potassium iodide - and is recommended as a prophylactic drug used to prevent symptoms of endemic goiter.