"Generating salts" - this is how the name of the elements is translated, the properties of which will be discussed in our article. Being in group VII of the periodic system of chemical elements, they are the most active non-metals. The structural features of atoms determine both the physical properties of halogens and their ability to react with metals, hydrogen and other non-metallic elements. Let's consider them in more detail.
How the position in the periodic system affects the structure of the atom
A distinctive feature of halogens is their pronounced electronegativity - the ability to pick up single negatively charged particles from atoms of less active elements.
In this case, the electron shells of fluorine, chlorine, bromine and iodine are filled with electrons up to an octet and become stable anions: F - , CI - , etc. Metal atoms, when interacting with elements of group VII A, give up their particles, turning into positively charged cations, and in the molecules of the salts formed, for example sodium chloride, magnesium fluoride or calcium iodide, a strong ionic bond occurs. A simple substance - a halogen - is a diatomic molecule, for example, CI 2 or F 2 containing a covalent non-polar bond between atoms.
Change in the properties of substances in the VII A group of chemical elements
With an increase in the charge of the nucleus and bloating of the atom due to the addition of new energy layers, the electronegativity of halogens decreases. Indeed, fluorine is the most active non-metal and always has a negative ion charge, i.e., it, when interacting with atoms of other elements, takes away their electrons. Chlorine in reactions with substances is also electronegative, with the exception of oxides, where its atom has a positive oxidation state. The physical properties of halogens and their state of aggregation also change with increasing nuclear charge. Let us dwell on this issue in more detail.
From gas to crystal
The simple substances fluorine and chlorine are highly toxic gases. In low concentrations, they cause irritation of the mucous membranes of the eyes and upper respiratory tract. Prolonged inhalation of halogen vapor leads to paralysis of the respiratory muscles and suffocation with a fatal outcome. That is why the German army in the First World War used chlorine as a chemical weapon.
With an increase in the charge of the atomic nucleus, the aggregative state of substances changes, and bromine is already a heavy red-brown liquid with a pungent odor. It can cause burns on the skin, and is especially dangerous if it gets into the eyes.
We continue the characterization of halogens and dwell on iodine and astatine. Iodine is presented in the form of gray-violet crystals, their density is 4.94 g / cm 3 . The substance has a low melting point - 113.5 ° and when heated, it immediately turns into a gas, bypassing the liquid phase. This phenomenon in chemistry is called sublimation.
Astatine is a radioactive element, in appearance similar to iodine and, like it, is capable of sublimation. In the laboratory, it is obtained by irradiating bismuth atoms with helium atom nuclei. Astatine is the most rare element in nature.
Special properties of fluorine
Having examined the physical properties of halogens, let us dwell on their ability to react with other substances. Fluorine is interesting in this regard . This is the first element that has been able to form compounds with inert gases, in particular with xenon. Several substances were obtained - xenon fluorides with various degrees of oxidation of the inert element: XeF 2 , XeF 4 , XeF 6 . From this moment, the active development of the chemistry of noble gases began.
Another halogen whose formula is CI 2, chlorine, is the second most active element after fluorine. It interacts with oxygen and forms several oxides in which it has such oxidation states: +3, +5, +7. Like all non-metals, chlorine reacts with metals to form salts - chlorides. Chlorine compounds are quite common in nature and are part of many rocks and minerals.
Prevalence of Non-Metals
Halogens in nature are quite common. During periods of volcanic activity, a large number of gaseous compounds of chlorine, fluorine and iodine enter the Earth's atmosphere. In addition, as we said earlier, chlorides are presented in the form of ore-forming compounds: sylvinite (KCI × NaCI double salt ), carnallite and sodium chloride. We also note that chlorine is approximately 0.05% of the mass of the earth's crust. All elements of this series, with the exception of astatine, are not only part of inanimate nature, but are also essential components of plant, animal and human cells.
What elements are part of cellular organelles
Biochemistry is a science that determines the role of chemicals in metabolic processes in a living cell. It confirms the important biological significance of halogens. As it turned out, chlorine has the greatest distribution among prokaryotes and eukaryotes. It is a necessary macrocell in the cytoplasm and in the intercellular fluid. So, chlorine ions are part of the blood plasma, participate in the transport of substances through the cell membrane, they are also involved in the passage of pulses through the nerve fiber. Atomic fluoride is a component of tooth enamel, providing its hardness and resistance to caries. Considering the physical properties of halogens, we find out their value in cellular metabolism.
The role of elements of group VII A in the metabolism
Bromine and iodine are included in complexes of biologically active compounds: enzymes and hormones. For example, triiodothyronine and thyroxine, produced by the tissues of the thyroid gland and containing iodine ions, regulate the most important metabolic processes in the human body. Their insufficient secretion can cause severe endocrine pathologies such as endemic goiter or bazedovy disease. The main sources of intake of bromine and iodine in the body are dietary salt (sodium chloride), seaweeds, such as kelp (it contains iodine and bromine), and seafood.
Halogen production
A classic example, known even from the school chemistry course, is the laboratory experience of the release of free chlorine from hydrochloric acid by the action of manganese dioxide on it when heated. The reaction must be carried out in a fume hood due to the high toxicity of chlorine gas. If potassium permanganate is used as an oxidizing agent, the process can be carried out without heating the reagents. Fluorine, chlorine, bromine and iodine are widely used in chemistry of organic synthesis, in pharmacology and medicine, therefore, the production of halogens is carried out on an industrial scale by electrolysis. To isolate CI 2 molecules, electrolyzers with concentrated sodium chloride solution are used.
Chlorine is reduced at the anode, it is collected and then liquefied under pressure up to 6 atmospheres and at room temperature. To transport the resulting product using steel cylinders. Fluorine, bromine and iodine are also obtained by electrolysis. But they do not use solutions, but the melts of their salts.
Where and how to use non-metals
Both simple substances and compounds of chlorine, fluorine, bromine and iodine are of great importance in human life. For example, the use of halogens in medicine is due to the bactericidal properties of an alcoholic solution of iodine and bleach. The latter substance can be used in quarantine measures, in water purification and degassing of infected areas. The high oxidizing properties of chlorine allow it to be used as a bleach on fabric and paper.
A simple substance is also used in the industrial production of hydrochloric acid. Fluorine is an indispensable component in the synthesis of fluoroplastics, due to the high chemical activity they oxidize rocket fuel. Bromine is part of many drugs used in neurology to stop convulsive states, with nervous exhaustion and insomnia. All the above examples are a clear confirmation of the importance for humans of the use of halogens in industry and everyday life.