Halogens are ... Halogen compounds

Here the reader will find information on halogens, chemical elements of the periodic table of DI Mendeleyev. The content of the article will allow you to get acquainted with their chemical and physical properties, finding in nature, methods of application, etc.

General information

Halogens are all elements of the chemical table of DI Mendeleyev, located in the seventeenth group. By a more rigorous method of classification, these are all elements of the seventh group, the main subgroup.

Halogens are elements capable of reacting with practically all substances of a simple type except for a certain number of nonmetals. All of them are energy oxidants, therefore, in natural conditions, as a rule, they are in a mixed form with other substances. The index of chemical activity of halogens decreases with increasing their ordinal numbering.

Halogens are the following elements: fluorine, chlorine, bromine, iodine, astatine and artificially created tennesses.

As stated earlier, all halogens are oxidants with pronounced properties, besides all of them are nonmetals. The external energy level has seven electrons. Interaction with metals leads to the formation of ionic bonds and salts. Almost all halogens, with the exception of fluorine, can manifest themselves as a reducing agent, reaching a higher oxidative degree of +7, but for this it is necessary that they interact with elements having a greater degree of electronegativity.

Features of etymology

In 1841 the Swedish chemist J. Berzelius proposed to introduce the term halogens, referring to them known at that time F, Br, I. However, before the introduction of this term with respect to the whole group of such elements, in 1811, German scientist AND Schweiger called the same word chlorine, the term was translated from the Greek language as "salt".

Atomic structure and oxidizing powers

The configuration of the electrons of the outer atomic shell of halogens has the following form: astat - 6s ² 6p ⁵ , iodine - 5s ² 5p ⁵ , bromine 4s ² 4p ⁵ , chlorine - 3s ² 3p ⁵ , fluorine 2s ² 2p ⁵ .

Halogens are elements that have seven electrons on an electron shell of an external type, which allows them to "effortlessly" attach an electron that is not sufficient to complete the shell. Usually the oxidation state is expressed as -1. Cl, Br, I and At reacting with elements having a higher degree, begin to show a positive oxidative degree: +1, +3, +5, +7. Fluorine has a constant oxidation degree -1.

Spread

In view of their high degree of reactivity, halogens are usually in the form of compounds. The level of propagation in the earth's crust decreases in accordance with the increase in the atomic radius from F to I. The astat in the earth's crust is measured in grams altogether, and tennesses are created artificially.

Halogens are found in nature most often in halide compounds, and iodine can also take the form of potassium iodate or sodium. Due to their solubility in water, they are present in oceanic waters and brines of natural origin. F is an insoluble representative of halogens and is most often found in sedimentary rocks, and its main source is calcium fluoride.

Physical qualitative characteristics

Halogens between themselves can be very different, and they have the following physical properties:

1. Fluorine (F2) is a gas of light yellow color, has a sharp and irritating odor, and also does not undergo compression under normal temperature conditions. The melting point is -220 ° C, and the boiling point -188 ° C.
2. Chlorine (Cl ₂ ) is a gas that does not contract at ordinary temperatures, even when exposed to pressure, has an asphyxiating, pungent smell and a greenish-yellow color. Melting starts at -101 ° C, and boils at -34 ° C.
3. Bromine (Br ₂ ) is a volatile and heavy liquid with a brownish-brown color and a sharp fetid odor. It melts at -7 ° C, and boils at 58 ° C.
4. Iodine (I ₂ ) - this solid substance has a dark gray color, and it has a metallic luster, the smell is quite sharp. The melting process begins at a temperature of 113.5 ° C, and boils at 184.885 ° C.
5. A rare halogen is an astat (At ₂ ), which is a solid and has a black and blue color with a metallic luster. The melting point corresponds to a mark of 244 ° C, and the boiling begins after reaching 309 ° C.

The chemical nature of halogens

Halogens are elements with very high oxidative activity, which weakens in the direction from F to At. Fluorine, being the most active representative of halogens, can react with all kinds of metals, not excluding any known. Most of the representatives of metals, getting into the atmosphere of fluorine, undergo self-ignition, while releasing heat in huge quantities.

Without fluorine exposure to heating, it can react with a large number of non-metals, for example H2, C, P, S, Si. The type of reactions in this case is exothermic and can be accompanied by an explosion. When heated, F forces the remaining halogens to oxidize, and when subjected to irradiation, this element is able to react with heavy gases of an inert nature.

Interacting with substances of complex type, fluorine causes high energy reactions, for example, by oxidizing water, it can cause an explosion.

Chlorine can also be reactive, especially in the free state. The level of its activity is less than that of fluorine, but it is able to react with almost all simple substances, but nitrogen, oxygen and noble gases do not react with it. Interacting with hydrogen, with heating or good lighting, chlorine creates a violent reaction accompanied by an explosion.

In addition and substitution reactions, Cl can react with a large number of substances of a complex type. Is able to displace Br and I as a result of heating from the compounds created by them with a metal or hydrogen, and can also react with alkaline substances.

Bromine is chemically less active than chlorine or fluorine, but still very brightly manifests itself. This is due to the fact that more often bromine Br is used as a liquid, because in this state the initial degree of concentration under other identical conditions is higher than that of Cl. Widely used in chemistry, especially organic. Can dissolve in H ₂ O and react with it partially.

The halogen element iodine forms a simple substance I ₂ and is able to react with H ₂ O, dissolves in iodide solutions, forming complex anions. From the majority of halogens, I differs in that it does not react with most nonmetallic agents and reacts slowly to metals, while it needs to be heated. With hydrogen reacts, only undergoing strong heating, and the reaction is endothermic.

Rare halogen astat (At) shows less reactivity than iodine, but can react with metals. As a result of dissociation, both anions and cations arise.

Areas of use

The compounds of halogens are widely used by man in a wide variety of fields of activity. Natural cryolite (Na ₃ AlF ₆ ) is used to prepare Al. Bromine and iodine are often used as simple substances by pharmaceutical and chemical companies. In the production of spare parts for cars, halogens are often used. Headlights are one of these details. Qualitatively choose the material for this component of the machine is very important, since the lights illuminate the road at night and are a way to detect both you and other motorists. One of the best composite materials for the creation of headlights is xenon. Halogen is nevertheless inferior in quality to this inert gas.

A good halogen is fluorine, an additive widely used in the production of toothpastes. It helps prevent the occurrence of a dental disease - caries.

Such an element-halogen as chlorine (Cl), finds its application in the production of HCl, is often used in the synthesis of organic substances such as plastic, rubber, synthetic fibers, dyes and solvents, etc. As well as chlorine compounds are used as bleaching agents Linen and cotton material, paper and as a means for fighting bacteria in drinking water.

Attention! Toxic!

In view of the very high reactivity, halogens are rightly called poisonous. Most clearly, the ability to join the reaction is expressed in fluorine. Halogens have pronounced asphyxiating properties and are capable of affecting tissues during interaction.

Fluorine in vapors and aerosols is considered one of the most potentially dangerous forms of halogens, harmful to surrounding living things. This is due to the fact that it is poorly perceived by the sense of smell and is felt only after reaching a high concentration.

Summing up

As we see, halogens are a very important part of Mendeleev's periodic table; they have many properties, differ in physical and chemical properties, atomic structure, degree of oxidation and ability to react with metals and non-metals. In industry, they are used in a variety of ways, from additives to personal care products to the synthesis of organic chemicals or bleaches. Despite the fact that one of the best ways to maintain and create light in the headlight of a car is xenon, halogen nevertheless is practically not inferior to it and is also widely used and has its advantages.

Now you know what halogen is. Skanvord with any questions about these substances for you is no longer a hindrance.