Here the reader will find information about 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, location 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 stricter classification method, these are all elements of the seventh group, the main subgroup.
Halogens are elements capable of reacting with almost all substances of a simple type, with the exception of a certain amount of non-metals. All of them are energy oxidizing agents, therefore, in natural conditions, as a rule, they are in a mixed form with other substances. The indicator of chemical activity of halogens decreases with increasing their serial numbering.
The following elements are considered halogens: fluorine, chlorine, bromine, iodine, astatine and artificially created tennessine.
As mentioned earlier, all halogens are oxidizing agents with pronounced properties, and besides, they are all non-metals. The outer energy level has seven electrons. Interaction with metals leads to the formation of ionic bonds and s alts. Almost all halogens, with the exception of fluorine, can act as a reducing agent, reaching the highest oxidation state of +7, but this requires that they interact with elements that have a high degree of electronegativity.
Features of etymology
In 1841, the Swedish chemist J. Berzelius proposed to introduce the term halogens, referring to them the then known F, Br, I. However, before the introduction of this term in relation to the entire group of such elements, in 1811., the German scientist I. Schweigger called chlorine the same word, the term itself was translated from Greek as “s alt”.
Atomic structure and oxidation states
The electron configuration of the outer atomic shell of halogens is as follows: astatine - 6s26p5, iodine - 5s 25p5, bromine 4s24p5, chlorine – 3s 23p5, fluorine 2s22p5.
Halogens are elements that have seven electrons on the electron shell of the outer type, which allows them to "easily" attach an electron that is not enough to complete the shell. Typically, the oxidation state appears as -1. Cl, Br, I and At, reacting with elements having a higher degree, begin to show a positive oxidation state: +1, +3, +5, +7. Fluorine has a constant oxidation state of -1.
Distribution
In view of itshighly reactive halogens are usually found as compounds. The distribution level in the earth's crust decreases in accordance with the increase in atomic radius from F to I. Astatine in the earth's crust is measured in grams, and tennessine is artificially created.
Halogens occur naturally most commonly 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 oceanic waters and naturally occurring brines. F is a poorly soluble representative of halogens and is most often found in sedimentary rocks, and its main source is calcium fluoride.
Physical quality characteristics
Halogens can be very different from each other, and they have the following physical properties:
- Fluorine (F2) is a light yellow gas with 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 (Cl2) is a gas that does not compress at normal temperature, even under pressure, has a suffocating, pungent odor and a green-yellow color. It begins to melt at -101 °С, and boil at -34 °С.
- Bromine (Br2) is a volatile and heavy liquid with a brown color and a sharp, fetid odor. Melts at -7°C and boils at 58°C.
- Iodine (I2) - This solid type substance has a dark gray color, and it has a metallic luster, the smell is quite sharp. The melting process starts atreaching 113.5 °С, and boils at 184.885 °С.
- A rare halogen is astatine (At2), which is a solid and has a black-blue color with a metallic sheen. The melting point corresponds to 244 ° C, and boiling begins after reaching 309 ° C.
Chemical nature of halogens
Halogens are elements with very high oxidizing 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 of the representatives of metals, getting into the atmosphere of fluorine, are subject to self-ignition, while releasing heat in huge quantities.
Without exposing fluorine to heat, it can react with a large number of non-metals, such as H2, C, P, S, Si. The type of reactions in this case is exothermic and may be accompanied by an explosion. When heated, F forces the remaining halogens to oxidize, and when exposed to radiation, this element is able to completely react with heavy gases of an inert nature.
When interacting 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 activity level 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 substances of a complex type. Able to displace Br and I as a result of heating from the 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 bromine 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. Can dissolve in H2O and partially react with it.
The halogen element iodine forms a simple substance I2 and is able to react with H2O, dissolves in iodide solutions, forming while complex anions. I differs from most halogens in that it does not react with most representatives of non-metals and slowly reacts with metals, while it must be heated. It reacts with hydrogen only when subjected to strong heating, and the reaction is endothermic.
Rare halogen astatine (At) is less reactive than iodine, but can react with metals. Dissociation produces both anions and cations.
Applications
Halogen compounds are widely used by man in a wide variety of fields. natural cryolite(Na3AlF6) is used to obtain Al. Bromine and iodine are often used as simple substances by pharmaceutical and chemical companies. Halogens are often used in the manufacture of machine parts. Headlights are one of those things. 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 to detect both you and other motorists. Xenon is considered one of the best composite materials for creating headlights. Halogen, however, is not much inferior in quality to this inert gas.
A good halogen is fluorine, an additive widely used in toothpaste. It helps prevent the occurrence of dental disease - caries.
The halogen element such as chlorine (Cl) finds its use in the production of HCl, often used in the synthesis of organic substances such as plastics, rubber, synthetic fibers, dyes and solvents, etc. As well as compounds chlorine is used as bleach for linen, cotton, paper, and as a bacteria-fighting agent in drinking water.
Attention! Toxic
Due to their very high reactivity, halogens are rightfully called poisonous. The ability to enter into reactions is most pronounced in fluorine. Halogens have pronounced asphyxiant properties and are capable of damaging tissues upon interaction.
Fluorine in vapors and aerosols is considered one of the most potentiallydangerous forms of halogens that are harmful to surrounding living beings. 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 can see, halogens are a very important part of the periodic table of Mendeleev, they have many properties, differ in physical and chemical qualities, atomic structure, oxidation state and ability to react with metals and non-metals. In industry, they are used in a variety of ways, ranging from additives in personal care products to the synthesis of organic chemicals or bleaches. Although xenon is one of the best ways to maintain and create light in a car headlight, halogen is still almost as good as xenon and is also widely used and has its advantages.
Now you know what a halogen is. A scanword with any questions about these substances is no longer a hindrance for you.
