Here the reader will find information on halogens, chemical elements of the periodic table of D. I. Mendeleev. The content of the article will allow you to get acquainted with their chemical and physical properties, being in nature, methods of application, etc.
General information
Halogens are all elements of the chemical table of D. I. Mendeleev, which are in the seventeenth group. According to a more strict classification method, these are all elements of the seventh group, the main subgroup.
Halogens are elements capable of reacting with almost all simple substances, with the exception of a certain amount of non-metals. All of them are energetic oxidizing agents, therefore, under natural conditions, as a rule, they are in mixed form with other substances. The indicator of the chemical activity of halogens decreases with an increase in their serial numbering.
The following elements are considered halogens: fluorine, chlorine, bromine, iodine, astatine and artificially created tennesin.
As mentioned earlier, all halogens are oxidizing agents with pronounced properties, and besides, they are all non-metals. 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 the highest oxidative degree of +7, however, for this it is necessary that they interact with elements having a high degree of electronegativity.
Features of etymology
In 1841, the Swedish chemical scientist J. Berzelius proposed introducing the term halogens, referring to them at that time as F, Br, I. However, before the introduction of this term in relation to the entire group of such elements, in 1811, the German scientist And Schweiger was called chlorine by the same word, the term itself was translated from the Greek language as "malt."
Atomic structure and oxidative degrees
The electron configuration of the outer atomic shell of the halogens is as follows: astatine - 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 the outer shell of an external type, which allows them to "attach little electron" with little effort, which is not enough to complete the shell. Typically, the oxidation state appears as -1. Cl, Br, I, and At, reacting with elements with a higher degree, begin to show a positive oxidative degree: +1, +3, +5, +7. Fluorine has a constant oxidative state of -1.
Spread
Due to their high degree of reactivity, halogens are usually in the form of compounds. The level of distribution in the earth’s crust decreases in accordance with the increase in the atomic radius from F to I. Astatine in the earth’s crust is measured in grams at all, and tennessin is created artificially.
Halogens are found in nature most often in halide compounds, and iodine can also take the form of potassium or sodium iodate. Due to their solubility in water, they are present in ocean waters and brines of natural origin. F is a sparingly soluble representative of halogens and is most often found in sedimentary rocks, and its main source is calcium fluoride.
Physical quality characteristics
Halogens can differ greatly among themselves, and they have the following physical properties:
- Fluorine (F2) is a light yellow gas, has a pungent and irritating odor, and is not compressed under normal temperature conditions. The melting point is -220 ° C, and the boiling point is -188 ° C.
- Chlorine (Cl 2 ) is a gas that does not shrink at ordinary temperature, even when under pressure, has a suffocating, pungent odor and a greenish-yellow color. It begins to melt at -101 ° , and boils at -34 ° .
- Bromine (Br 2 ) is a volatile and heavy liquid with a brownish-brown color and a pungent fetid odor. It melts at -7 ° C, and boils at 58 ° C.
- Iodine (I 2 ) - this solid type substance has a dark gray color, and is characterized by a metallic luster, the smell is quite sharp. The melting process begins when it reaches 113.5 ° C, and boils at 184.885 ° C.
- A rare halogen is astatine (At 2 ), which is a solid substance and has a black and blue color with a metallic sheen. The melting point corresponds to the mark of 244 ° C, and boiling begins after reaching 309 ° C.
The chemical nature of halogens
Halogens are elements with a 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 types of metals, not excluding any known. Most representatives of metals, getting into the atmosphere of fluorine, are self-igniting, while releasing heat in huge quantities.
Without subjecting the fluorine to heat, it can react with a large number of non-metals, for example H2, C, P, S, Si. The type of reaction in this case is exothermic and may be accompanied by an explosion. When heated, F forces the remaining halogens to oxidize, and when irradiated, this element is able to completely react with heavy gases of an inert nature.
Entering into interaction with substances of a 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. Its level of 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, when heated or in good light, chlorine creates a violent reaction accompanied by an explosion.
In addition and substitution reactions, Cl can react with a large number of compounds of a complex type. It is able to displace Br and I as a result of heating from compounds created by them with metal or hydrogen, and can also react with alkaline substances.
Bromine is chemically less active than chlorine or fluorine, but still shows itself very brightly. This is due to the fact that Br is most often 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. It can be dissolved in H 2 O and partially react with it.
The halogen-element iodine forms a simple substance I 2 and is able to react with H 2 O, dissolves in iodides of solutions, forming complex anions. It differs from most halogens in that it does not react with most non-metals and slowly reacts with metals, and it must be heated. It reacts with hydrogen only when subjected to strong heating, and the reaction is endothermic.
Rare halogen astatine (At) exhibits reactivity less than iodine, but can react with metals. As a result of dissociation, both anions and cations arise.
Areas of use
Halogen compounds are widely used by man in a wide variety of fields of activity. Natural cryolite (Na 3 AlF 6 ) is used to produce Al. Bromine and iodine are often used by pharmaceutical and chemical companies as simple substances. In the manufacture of spare parts for machines, halogens are often used. Headlights are one such detail. It is very important to choose the right material for this component of the car, as the headlights illuminate the road at night and are a way of detecting both you and other motorists. One of the best components for creating headlights is xenon. However, halogen is not much inferior in quality to this inert gas.
Good halogen is fluoride, an additive widely used in the manufacture of toothpastes. It helps to prevent dental caries.
A halogen element such as chlorine (Cl) finds its application in the production of HCl, and is often used in the synthesis of organic substances such as plastic, rubber, synthetic fibers, dyes and solvents, etc. Also, chlorine compounds are used as bleaches flax and cotton material, paper and as a means to combat bacteria in drinking water.
Attention! Toxic!
Due to the very high reactivity, halogens are rightly called poisonous. The most pronounced ability to enter into reactions is expressed in fluorine. Halogens have pronounced asphyxiating properties and are capable of damaging tissues during interaction.
Fluoride 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 when a large concentration is reached.
To summarize
As we see, halogens are a very important part of the periodic table, they have many properties, differ in physical and chemical properties, atomic structure, oxidation state and ability to react with metals and nonmetals. In industry, they are used in a variety of ways, from additives to personal care products to synthetic substances of organic chemistry 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 inferior to it and is also widely used and has its own advantages.
Now you know what halogen is. A scanword with any questions about these substances is no longer an obstacle for you.