Halogens are a group of chemical elements that comprise group 17 of the periodic table, including fluorine, chlorine, bromine, iodine, and astatine. They possess unique properties, such as high reactivity, low melting and boiling points, and are known for their ability to form stable compounds with other elements. Their molecular structures are characterized by having seven valence electrons, making them highly electronegative. Halogens are widely used in various applications, such as the production of chemicals, medicines, cleaning agents, disinfectants, and the semiconductor industry. In this article, we will explore more about the properties, structures, and uses of halogens.
Chemical characteristics of halogens: main properties highlighted.
Halogens are a group of chemical elements that include fluorine, chlorine, bromine, iodine, and astatine. They have unique chemical characteristics that distinguish them from other elements in the periodic table.
One of the main properties of halogens is their high reactivity. They tend to form compounds easily, primarily through the formation of covalent bonds. This reactivity is due to their high electronegativity, which makes them capable of attracting electrons from other atoms.
Another striking characteristic of halogens is their color. Fluorine and chlorine are greenish-yellow gases, bromine is a dark red liquid, iodine is a violet solid, and astatine is a black solid. This peculiar coloration is one way to identify halogens.
Furthermore, halogens are known for their toxicity. Fluorine, for example, is highly poisonous in its pure form and can cause serious harm if ingested. Chlorine, on the other hand, is used as a disinfectant in swimming pools and water treatment systems due to its antimicrobial properties.
In short, halogens are chemical elements with unique properties, such as high reactivity, characteristic coloration, and toxicity. They play an important role in various chemical processes and have a variety of uses in different industries.
Main halogen chemical agents used in industrial processes and water treatment.
Halogens are chemical elements in group 17 of the periodic table, known for their reactive properties and versatility in various industrial and water treatment processes. The main halogenated chemical agents used are chlorine, fluorine, bromine, and iodine.
O chlorine Chlorine is one of the most widely used halogens in industry, used in the manufacture of chemicals, water purification, and the bleaching of paper and textiles. Furthermore, chlorine is essential in the water disinfection process, eliminating microorganisms and ensuring safety for human consumption.
O fluorine It also plays an important role in industrial processes, being used in the production of chemical compounds, in the manufacture of glass and in dentistry, through water fluoridation and the use of fluoride toothpastes to prevent cavities.
O bromine It is primarily used in the production of chemicals such as flame retardants, pesticides, and medicines. Bromine is also used in the treatment of swimming pool and spa water, acting as an effective disinfectant and oxidizer.
O iodine It is used in the pharmaceutical industry, dye manufacturing, and chemical production. Furthermore, iodine is used in water treatment to eliminate bacteria, viruses, and parasites, ensuring the quality of water for human consumption.
In summary, halogenated chemical agents play a fundamental role in industrial and water treatment processes, contributing to the health and safety of the population and to the development of various productive activities.
Identifying halogens: simple techniques for recognizing chemical elements in the halogen family.
Halogens are a group of chemical elements comprising fluorine, chlorine, bromine, iodine, and astatine. They possess unique properties, such as high reactivity and electron affinity. To identify halogens, there are a few simple techniques that can be used.
One of the most common ways to identify halogens is through the flame test. When heating a compound containing a halogen, the flame will emit a characteristic color, which varies depending on the element present. For example, fluorine produces a pale yellow flame, while chlorine emits a deep green color.
Another technique for identifying halogens is the bromine water test. When bromine water is added to an unknown substance, a specific color change will occur if halogens are present. Bromine, for example, forms an orange solution when in contact with water.
Furthermore, halogens can also be identified through specific chemical tests, such as precipitation reactions. For example, adding silver nitrate to a solution containing a halogen will form a precipitate characteristic of each element in the halogen family.
In summary, simple techniques for identifying halogens include the flame test, the bromine water test, and specific chemical tests. These strategies are useful for recognizing the chemical elements of the halogen family and can be applied in laboratories and chemistry studies.
Why are halogens highly reactive and oxidizing on the periodic table?
Halogens are a group of highly reactive and oxidizing chemical elements in the periodic table. This is due to their electron configuration, specifically the presence of one less electron in their valence shell. Halogens include fluorine, chlorine, bromine, iodine, and astatine, and all exhibit this distinctive characteristic.
With only one electron missing from their valence shell, halogens are constantly seeking electrons to achieve stability. This makes them highly reactive, as they are ready to react with other elements to gain or share electrons. This tendency to gain electrons makes them excellent oxidizers, capable of ripping electrons from other elements in chemical reactions.
Furthermore, halogens possess high electronegativity, meaning they have a strong attraction to electrons. This makes them even more likely to form ionic or covalent bonds with other elements, resulting in stable chemical compounds. This ability to form a variety of compounds makes them extremely versatile in terms of their applications in industry and scientific research.
In summary, halogens are highly reactive and oxidizing due to their electron configuration, electronegativity, and tendency to gain electrons to achieve stability. These unique characteristics make them essential elements in modern chemistry and a variety of industrial and scientific applications.
Halogens: properties, structures and uses
Os halogens Halogens are non-metallic elements belonging to Group VIIA or 17 of the periodic table. They have high electronegativity and high electron affinity, which significantly affects the ionic nature of their bonds with metals. The word 'halogens' is of Greek origin and means "salt-forming."
But what are these halogens? Fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the ephemeral, radioactive element acetate (At). They are so reactive that they react with each other to form diatomic molecules: F 2 Cl 2 Br 2 , The 2 and At 2 . These molecules are characterized by having similar structural properties (linear molecules), although with different physical states.
In the image above, three halogens are shown. From left to right: chlorine, bromine, and iodine. Neither fluorine nor astatine can be stored in glass containers, as the latter cannot withstand their corrosive properties. Note how the organoleptic properties of the halogens change as you move down the group to the element iodine.
Fluorine is a yellowish gas; chlorine is also a yellow-green gas; bromine is a dark reddish liquid; iodine is a black solid with violet eyes; and astatic is a dark, shiny metallic solid.
Halogens are capable of reacting with almost all elements in the periodic table, even some noble gases (such as xenon and krypton). When they do so, they can oxidize atoms in their most positive oxidation states, transforming them into powerful oxidizing agents.
Similarly, they impart specific properties to molecules when they bind or replace some of their atoms. These types of compounds are called halides. In fact, halides are the main natural source of halogens, and many of them are dissolved in the sea or are part of minerals; such as fluorite (CaF 2 ).
Halogens and halides have a wide variety of uses; from industrial or technological, to simply enhancing the flavor of certain foods, as does rock salt (sodium chloride).
Physical and chemical properties
Atomic weights
Fluorine (F) 18,99 g/mol; Chlorine (Cl) 35,45 g/mol; Bromine (Br) 79,90 g/mol; Iodine (I) 126,9 g/mol and Astatine (At) 210 g/mol,
Physical State
Gaseous gas; Cl gas; liquid Br; solid and solid Eu.
Cor
F, pale yellow-brown; Cl, pale green; Br, reddish-brown; I, violet; and At, metallic black * * (assumed)
Melting points
F -219,6º C; Cl -101,5º C; Br -7,3 ° C; I 113,7º C and 302º C.
Boiling points
F -118,12°C; Cl -34,04 ° C; Br 58,8°C; I 184,3º C and? At 337º C.
Density at 25°C
F- 0,0017 g/cm 3 ; Cl 0,0032 g / cm 3 ; Br- 3,102 g / cm 3 ; I- 4,93 g/cm 3 and At- 6,2-6,5 g/cm 3
Water solubility
0,091 mmol Cl/cm 3 ; Br- 0,21 mmol/cm 3 and I- 0,0013 mmol/cm 3 .
Ionization energy
F-1.681 kJ/mol; Cl-1.251 kJ/mol; Br-1.140 kJ/mol; I-1.008 kJ/mol and At-890 kJ/mol.
Electronegativity
F-4.0; Cl-3,0; Br-2,8; I-2.5 and At-2.2.
Halogens have seven valence electrons, hence their great desire to gain an electron. Furthermore, halogens have high electronegativity due to their small atomic radii and the strong attraction the nucleus exerts on the valence electrons.
Reactivity
Halogens are highly reactive, which would explain their toxicity. Furthermore, they are oxidizing agents.
The decreasing order of reactivity is: F > Cl > Br > I > At.
State in nature
Due to their high reactivity, halogen atoms are not free in nature; but they are forming aggregates or as diatomic molecules linked by covalent bonds.
Molecular structures
Halogens do not exist in nature as elementary atoms, but as diatomic molecules. However, they all have in common a linear molecular structure, the only differences being the length of their bonds and intermolecular interactions.
The linear molecules XX (X 2 ) are characterized by being unstable, because both atoms strongly attract the electron pair to them. Because their outer electrons undergo a very high effective nuclear charge, Zef. The higher the Zef, the shorter the bond distance XX.
As you move down the group, Zef becomes weaker and the stability of these molecules increases. Thus, the decreasing order of reactivity is: F 2 > Cl 2 > Br 2 > I 2 However, it is incongruent to compare astatine with fluoride, since there are not enough stable isotopes known due to their radioactivity.
Intermolecular interactions
On the other hand, their molecules lack a dipole moment, being nonpolar. This fact accounts for their weak intermolecular interactions, whose only latent force is London dispersion, which is proportional to the atomic mass and molecular area.
In this way, the small molecule of F 2 does not have enough mass or electrons to form a solid. Unlike I 2 , the iodine molecule, which remains a solid that emits purple vapors.
Bromine represents an intermediate example between the two extremes: Br molecules 2 interact enough to be in a liquid state.
Astatic probably, due to its increasing metallic character, does not appear as At 2, but as atoms forming metallic bonds.
Regarding the colors (yellow-greenish-yellow-red-purple-black), the most appropriate explanation is based on molecular orbital theory (MOT). The energy distance between the last complete molecular orbital and the next highest energy (of the link) is bridged by the absorption of a photon with increasingly longer wavelengths.
Halides
Halogens react to form halides, either inorganic or organic. The best known are the hydrogen halides: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI).
All of them, when dissolved in water, produce acidic solutions—so acidic that HF can degrade any glass container. Furthermore, they are considered starting materials for the synthesis of extremely strong acids.
There are also so-called metal halides, which have chemical formulas that depend on the metal's valence. For example, alkali metal halides have the formula MX, and these include: NaCl, sodium chloride; KBr, potassium bromide; CsF, cesium fluoride; and LiI, lithium iodide.
Halides of alkaline earth metals, transition metals, or p-block metals have the formula MX n , being the positive charge of the metal. Thus, some examples are: FeCl 3 , ferric trichloride; MgBr 2 , magnesium bromide; AlF 3 , aluminum trifluoride; and Cul 2 , cupric iodide.
However, halogens can also form bonds with carbon atoms, thus interfering in the complex world of organic chemistry and biochemistry. These compounds are called organic halides and have the general chemical formula RX, where X is any halogen.
Uses
Chlorine
in the industry
-Bromine and chlorine are used in the textile industry to bleach and treat wool, preventing shrinkage when wet.
It is used as a waste disinfectant and for purifying drinking water and swimming pools. Chlorine-derived compounds are also used in laundries and the paper industry.
-It is used in the manufacture of special batteries and chlorinated hydrocarbons. It is also used in the processing of meat, vegetables, fish, and fruits. Chlorine also acts as a bactericidal agent.
It is used to clean and brighten leather and bleach cellulose. Previously, nitrogen trichloride was used as a bleach and flour conditioner.
-Posphene gas (COCl 2 ) is used in numerous industrial synthesis processes, as well as in the manufacture of military gases. Phosphene is highly toxic and was responsible for numerous deaths during World War I, where the gas was used.
-This gas is also found in insecticides and fumigants.
NaCl is a very abundant salt used to season food and preserve meat and poultry. It is also used in oral and intravenous rehydration fluids.
Medicine
-The halogen atoms that bind to drugs make them more lipophilic. This allows the drugs to more easily cross cell membranes, dissolving in the lipids that form them.
Chlorine diffuses into neurons of the central nervous system through ion channels linked to GABA neurotransmitter receptors, producing a sedative effect. This is the mechanism of action of several anxiolytics.
HCl is present in the stomach, where it acts by creating a reducing environment that favors food processing. Furthermore, HCl activates pepsin, an enzyme that initiates protein hydrolysis, a stage prior to intestinal absorption of protein material.
Others
-Hydrochloric acid (HCl) is used in cleaning toilets, in teaching and research laboratories, and in many industries.
PVC (polyvinyl chloride) is a vinyl chloride polymer used in clothing, flooring, electrical cables, flexible pipes, tubing, inflatable structures, and roof tiles. Chlorine is also used as an intermediate in the production of other plastic materials.
– Chlorine is used in the extraction of bromine.
Methyl chloride has an anesthetic function. It is also used in the preparation of certain silicone polymers and in the extraction of fats, oils, and resins.
– Chloroform (CHCl 3 ) is a solvent used in many laboratories, especially in organic chemistry and biochemistry laboratories, from teaching to research.
-And finally, regarding chlorine, trichloroethylene is used to degrease metal parts.
bromo
Bromine is used in gold mining and oil and gas drilling. It is also used as a combustion retardant in the plastics and gas industries. Bromine isolates fire from oxygen, causing it to go out.
It is an intermediate in the manufacture of hydraulic fluids, cooling and dehumidifying agents, and hair styling preparations. Potassium bromide is used in the manufacture of photographic plates and paper.
Potassium bromide is also used as an anticonvulsant, but due to the potential for salt to cause neurological dysfunction, its use has been reduced. Another common use is as a tablet for solid-state infrared spectroscopy sample measurements.
Bromine compounds are present in medications used to treat pneumonia. Bromine compounds are also present in medications used in trials for the treatment of Alzheimer's disease.
Bromine is used to reduce mercury contamination in coal-fired power plants. It is also used in the textile industry to create dyes of different colors.
-Methylbromine has been used as a pesticide for soil and housing fumigation, but its harmful effect on ozone has limited its use.
-Halogen lamps are incandescent and the addition of small amounts of bromine and iodine allows a reduction in the size of the lamps.
Iodine
-Iodine is involved in the functioning of the thyroid gland, a hormone that regulates the body's metabolism. The thyroid gland secretes the hormones T3 and T4, which exert their action on target organs. For example, the hormonal action on the heart muscle causes an increase in blood pressure and heart rate.
-In addition, iodine is used to identify the presence of starch. Silver iodide is a reagent used in photo development.
Fluorine
Some fluoride compounds are added to toothpastes to prevent cavities. Fluoride derivatives are present in various anesthetics. The pharmaceutical industry incorporates fluoride into medications to study potential improvements in their effects on the body.
Hydrofluoric acid is used to etch glass. It is also used in the production of halons (extinguishing gases, such as freon). A fluorine compound is used in the electrolysis of aluminum to achieve its purification.
Anti-reflective coatings contain a fluorine compound. This is used in the manufacture of plasma displays, flat-panel displays, and microelectromechanical systems. Fluorine is also present in the clay used in some ceramics.
astato
It is thought that astado could contribute to iodine in regulating the functioning of the thyroid gland. In addition, its radioactive isotope ( 210 At) has been used in cancer studies in mice.
References
- Encyclopedia of Occupational Health and Safety. Halogens and their compounds. [PDF]. Taken from:
- Employment.gob.es
- Chemistry LibreTexts. Group 17: General Properties of Halogens. Retrieved from: chem.libretexts.org
- Wikipedia (2018). Halogen Retrieved from: en.wikipedia.org
- Jim Clark (May 2015). Atomic and physical properties of the elements in group 7 (the halogens). Retrieved from: chemguide.co.uk
- Whitten, KW, Davis, RE, Peck, ML, and Stanley, GG Chemistry (2003), 8th ed. Cengage Learning
- Halogen Elements Taken from: elements.org.es
- Brown Laurel. (April 24, 2017). Halogen Characteristics. Sciencing. Retrieved from: sciencing.com