Halogens in the periodic table are located to the left of the noble gases. These five toxic non-metallic elements are in group 7 of the periodic table. These include fluorine, chlorine, bromine, iodine and astatine. Although astatine is radioactive and has only short-lived isotopes, it behaves like iodine and is often classified as a halogen. Since the halogen elements have seven valence electrons, they need only one extra electron to form a full octet. This characteristic makes them more reactive than other groups of non-metals.
General characteristics
Halogens form diatomic molecules (of the type X2, where X denotes a halogen atom) - a stable form of the existence of halogens in the form of free elements. The bonds of these diatomic molecules are non-polar, covalent and single. The chemical properties of halogens allow them to easily combine with most elements, so they never occur uncombined in nature. Fluorine is the most active halogen and astatine the least.
All halogens form group I s alts with similarproperties. In these compounds, halogens are present as halide anions with a charge of -1 (for example, Cl-, Br-). The ending -id indicates the presence of halide anions; e.g. Cl- is called "chloride".
In addition, the chemical properties of halogens allow them to act as oxidizing agents - to oxidize metals. Most chemical reactions involving halogens are redox reactions in aqueous solution. Halogens form single bonds with carbon or nitrogen in organic compounds where their oxidation state (CO) is -1. When a halogen atom is replaced by a covalently bonded hydrogen atom in an organic compound, the prefix halo- can be used in a general sense, or the prefixes fluoro-, chloro-, bromine-, iodine- for specific halogens. Halogen elements can be cross-linked to form diatomic molecules with polar covalent single bonds.
Chlorine (Cl2) was the first halogen discovered in 1774, followed by iodine (I2), bromine (Br2), fluorine (F2) and astatine (At, discovered last, in 1940). The name "halogen" comes from the Greek roots hal- ("s alt") and -gen ("to form"). Together, these words mean "s alt-forming", emphasizing the fact that halogens react with metals to form s alts. Halite is the name of rock s alt, a natural mineral composed of sodium chloride (NaCl). And finally, halogens are used in everyday life - fluoride is found in toothpaste, chlorine disinfects drinking water, and iodine promotes the production of hormones.thyroid.
Chemical elements
Fluorine is an element with atomic number 9, denoted by the symbol F. Elemental fluorine was first discovered in 1886 by isolating it from hydrofluoric acid. In its free state, fluorine exists as a diatomic molecule (F2) and is the most common halogen in the earth's crust. Fluorine is the most electronegative element on the periodic table. At room temperature, it is a pale yellow gas. Fluorine also has a relatively small atomic radius. Its CO is -1, except for the elemental diatomic state, in which its oxidation state is zero. Fluorine is extremely reactive and interacts directly with all elements except helium (He), neon (Ne), and argon (Ar). In H2O solution, hydrofluoric acid (HF) is a weak acid. Although fluorine is strongly electronegative, its electronegativity does not determine acidity; HF is a weak acid due to the fact that the fluorine ion is basic (pH> 7). In addition, fluorine produces very powerful oxidizers. For example, fluorine can react with the inert gas xenon to form a strong oxidant xenon difluoride (XeF2). Fluorine has many uses.
Chlorine is an element with atomic number 17 and chemical symbol Cl. Discovered in 1774 by isolating it from hydrochloric acid. In its elemental state, it forms a diatomic molecule Cl2. Chlorine has several COs: -1, +1, 3, 5 and7. At room temperature, it is a light green gas. Since the bond that forms between two chlorine atoms is weak, the Cl2 molecule has a very high ability to enter into compounds. Chlorine reacts with metals to form s alts called chlorides. Chlorine ions are the most common ions found in sea water. Chlorine also has two isotopes: 35Cl and 37Cl. Sodium chloride is the most common of all chlorides.
Bromine is a chemical element with atomic number 35 and symbol Br. It was first discovered in 1826. In its elemental form, bromine is a diatomic molecule Br2. At room temperature, it is a reddish-brown liquid. Its CO is -1, +1, 3, 4 and 5. Bromine is more active than iodine, but less active than chlorine. In addition, bromine has two isotopes: 79Br and 81Br. Bromine occurs as bromide s alts dissolved in sea water. In recent years, the production of bromide in the world has increased significantly due to its availability and long life. Like other halogens, bromine is an oxidizing agent and is highly toxic.
Iodine is a chemical element with atomic number 53 and symbol I. Iodine has oxidation states: -1, +1, +5 and +7. Exists as a diatomic molecule, I2. At room temperature it is a purple solid. Iodine has one stable isotope, 127I. First discovered in 1811with seaweed and sulfuric acid. Currently, iodine ions can be isolated in sea water. Although iodine is not very soluble in water, its solubility can be increased by using separate iodides. Iodine plays an important role in the body, participating in the production of thyroid hormones.
Astatine is a radioactive element with atomic number 85 and symbol At. Its possible oxidation states are -1, +1, 3, 5, and 7. The only halogen that is not a diatomic molecule. Under normal conditions, it is a black metallic solid. Astatine is a very rare element, so little is known about it. In addition, astatine has a very short half-life, no longer than a few hours. Received in 1940 as a result of synthesis. It is believed that astatine is similar to iodine. Features metallic properties.
The table below shows the structure of halogen atoms, the structure of the outer layer of electrons.
| Halogen | Electron configuration |
| Fluorine | 1s2 2s2 2p5 |
| Chlorine | 3s2 3p5 |
| Bromine | 3d10 4s2 4p5 |
| Iodine | 4d10 5s2 5p5 |
| Astatine | 4f14 5d106s2 6p5 |
Similar structure of the outer layer of electrons determines that the physical and chemical properties of halogens are similar. However, when comparing these elements, differences are also observed.
Periodic properties in the halogen group
Physical properties of simple substances halogens change with increasing element number. For better understanding and greater clarity, we offer you several tables.
The melting and boiling points of the group increase as the size of the molecule increases (F <Cl
Table 1. Halogens. Physical properties: melting and boiling points
| Halogen | Melting T (˚C) | Boiling point (˚C) |
| Fluorine | -220 | -188 |
| Chlorine | -101 | -35 |
| Bromine | -7.2 | 58.8 |
| Iodine | 114 | 184 |
| Astatine | 302 | 337 |
Atomic radius increases
The size of the nucleus increases (F < Cl < Br < I < At), as the number of protons and neutrons increases. In addition, more and more energy levels are added with each period. This results in a larger orbital, and therefore an increase in the radius of the atom.
Table 2. Halogens. Physical properties: atomic radii
| Halogen | Covalent radius (pm) | Ionic (X-) radius (pm) |
| Fluorine | 71 | 133 |
| Chlorine | 99 | 181 |
| Bromine | 114 | 196 |
| Iodine | 133 | 220 |
| Astatine | 150 |
Ionization energy decreases
If the outer valence electrons are not near the nucleus, then it will not take much energy to remove them from it. Thus, the energy needed to push the outer electron out is not as high at the bottom of the element group, as there are more energy levels. In addition, the high ionization energy causes the element to exhibit non-metallic qualities. Iodine and astatine display exhibit metallic properties because the ionization energy is reduced (At < I < Br < Cl < F).
Table 3. Halogens. Physical properties: ionization energy
| Halogen | Ionization energy (kJ/mol) |
| fluorine | 1681 |
| chlorine | 1251 |
| bromine | 1140 |
| iodine | 1008 |
| astatine | 890±40 |
Electronegativity decreases
The number of valence electrons in an atom increases with increasing energy levels at progressively lower levels. The electrons are progressively further away from the nucleus; Thus, the nucleus and electrons are not both attracted to each other. An increase in shielding is observed. Therefore, Electronegativity decreases with increasing period (At < I < Br < Cl < F).
Table 4. Halogens. Physical properties: electronegativity
| Halogen | Electronegativity |
| fluorine | 4.0 |
| chlorine | 3.0 |
| bromine | 2.8 |
| iodine | 2.5 |
| astatine | 2.2 |
Electron affinity decreases
As the size of an atom increases with increasing period, electron affinity tends to decrease (B < I < Br < F < Cl). An exception is fluorine, whose affinity is less than that of chlorine. This can be explained by the smaller size of fluorine compared to chlorine.
Table 5. Electron affinity of halogens
| Halogen | Electron affinity (kJ/mol) |
| fluorine | -328.0 |
| chlorine | -349.0 |
| bromine | -324.6 |
| iodine | -295.2 |
| astatine | -270.1 |
Reactivity of elements decreases
The reactivity of halogens decreases with increasing period (At <I
Inorganic chemistry. Hydrogen + halogens
A halide is formed when a halogen reacts with another, less electronegative element to form a binary compound. Hydrogen reacts with halogens to form HX halides:
- hydrogen fluoride HF;
- hydrogen chloride HCl;
- hydrogen bromide HBr;
- hydroiodine HI.
Hydrogen halides easily dissolve in water to form hydrohalic (hydrofluoric, hydrochloric, hydrobromic, hydroiodic) acids. The properties of these acids are given below.
Acids are formed by the following reaction: HX (aq) + H2O (l) → Х- (aq) + H 3O+ (aq).
All hydrogen halides form strong acids except HF.
The acidity of hydrohalic acids increases: HF <HCl <HBr <HI.
Hydrofluoric acid can engrave glass and some inorganic fluorides for a long time.
It may seem counterintuitive that HF is the weakest hydrohalic acid, as fluorine has the highestelectronegativity. However, the H-F bond is very strong, resulting in a very weak acid. A strong bond is determined by a short bond length and a high dissociation energy. Of all the hydrogen halides, HF has the shortest bond length and the largest bond dissociation energy.
Halogen oxoacids
Halogen oxoacids are acids with hydrogen, oxygen and halogen atoms. Their acidity can be determined using structure analysis. Halogen oxoacids are listed below:
- Hypochlorous acid HOCl.
- Chloric acid HClO2.
- Chloric acid HClO3.
- Perchloric acid HClO4.
- Hypochlorous acid HOBr.
- Bromomic acid HBrO3.
- Bromoic acid HBrO4.
- Hyiodic acid HOI.
- Iodonic acid HIO3.
- Methaiodic acid HIO4, H5IO6.
In each of these acids, a proton is bonded to an oxygen atom, so comparing proton bond lengths is useless here. Electronegativity plays a dominant role here. Acid activity increases with the number of oxygen atoms bound to the central atom.
Appearance and state of matter
The main physical properties of halogens can be summarized in the following table.
| State of matter (at room temperature) | Halogen | Appearance |
| hard | iodine | purple |
| astatine | black | |
| liquid | bromine | red-brown |
| gaseous | fluorine | pale tan |
| chlorine | pale green |
Appearance explanation
The color of halogens is the result of the absorption of visible light by molecules, which causes the excitation of electrons. Fluorine absorbs violet light and therefore appears light yellow. Iodine, on the other hand, absorbs yellow light and appears purple (yellow and purple are complementary colors). The color of halogens becomes darker as the period increases.
In closed containers, liquid bromine and solid iodine are in equilibrium with their vapors, which can be observed as a colored gas.
Although the color of astatine is unknown, it is assumed that it must be darker than iodine (i.e. black) in accordance with the observed pattern.
Now, if you are asked: "Characterize the physical properties of halogens", you will have something to say.
The oxidation state of halogens in compounds
Oxidation state is often used instead of "halogen valency". As a rule, the oxidation state is -1. But if a halogen is bonded to oxygen or another halogen, it can take on other states:CO oxygen -2 has priority. In the case of two different halogen atoms bonded together, the more electronegative atom prevails and takes CO -1.
For example, in iodine chloride (ICl) chlorine has CO -1, and iodine +1. Chlorine is more electronegative than iodine, so its CO is -1.
In bromic acid (HBrO4) oxygen has CO -8 (-2 x 4 atoms=-8). Hydrogen has an overall oxidation state of +1. Adding these values gives CO -7. Since the final CO of the compound must be zero, the CO of bromine is +7.
The third exception to the rule is the oxidation state of halogen in elemental form (X2), where its CO is zero.
| Halogen | CO in compounds |
| fluorine | -1 |
| chlorine | -1, +1, +3, +5, +7 |
| bromine | -1, +1, +3, +4, +5 |
| iodine | -1, +1, +5, +7 |
| astatine | -1, +1, +3, +5, +7 |
Why is the SD of fluorine always -1?
Electronegativity increases with period. Therefore, fluorine has the highest electronegativity of all the elements, as evidenced by its position in the periodic table. Its electronic configuration is 1s2 2s2 2p5. If fluorine gains one more electron, the outermost p-orbitals are completely filled and make up a full octet. Because fluorine hashigh electronegativity, it can easily take an electron from a neighboring atom. Fluorine in this case is isoelectronic to the inert gas (with eight valence electrons), all of its outer orbitals are filled. In this state, fluorine is much more stable.
Production and use of halogens
In nature, halogens are in the state of anions, so free halogens are obtained by oxidation by electrolysis or with the help of oxidizing agents. For example, chlorine is produced by the hydrolysis of a s alt solution. The use of halogens and their compounds is diverse.
- Fluorine. Although fluorine is highly reactive, it is used in many industrial applications. For example, it is a key component of polytetrafluoroethylene (Teflon) and some other fluoropolymers. Chlorofluorocarbons are organic chemicals that were previously used as refrigerants and propellants in aerosols. Their use has ceased due to their possible impact on the environment. They have been replaced by hydrochlorofluorocarbons. Fluoride is added to toothpaste (SnF2) and drinking water (NaF) to prevent tooth decay. This halogen is found in the clay used to make certain types of ceramics (LiF), used in nuclear power (UF6), to produce the antibiotic fluoroquinolone, aluminum (Na3 AlF6), for high voltage insulation (SF6).
- Chlorine has also found a variety of uses. It is used to disinfect drinking water and swimming pools. Sodium hypochlorite (NaClO)is the main component of bleaches. Hydrochloric acid is widely used in industry and laboratories. Chlorine is present in polyvinyl chloride (PVC) and other polymers that are used to insulate wires, pipes, and electronics. In addition, chlorine has proven useful in the pharmaceutical industry. Medicines containing chlorine are used to treat infections, allergies, and diabetes. The neutral form of hydrochloride is a component of many drugs. Chlorine is also used to sterilize hospital equipment and disinfect. In agriculture, chlorine is an ingredient in many commercial pesticides: DDT (dichlorodiphenyltrichloroethane) was used as an agricultural insecticide, but its use has been discontinued.
- Bromine, due to its incombustibility, is used to suppress combustion. It is also found in methyl bromide, a pesticide used to preserve crops and suppress bacteria. However, the excessive use of methyl bromide has been phased out due to its effect on the ozone layer. Bromine is used in the production of gasoline, photographic film, fire extinguishers, medicines for the treatment of pneumonia and Alzheimer's disease.
- Iodine plays an important role in the proper functioning of the thyroid gland. If the body does not get enough iodine, the thyroid gland enlarges. To prevent goiter, this halogen is added to table s alt. Iodine is also used as an antiseptic. Iodine is found in solutions used forcleaning open wounds, as well as in disinfectant sprays. In addition, silver iodide is essential in photography.
- Astatine is a radioactive and rare earth halogen, so it is not yet used anywhere. However, it is believed that this element may help iodine in the regulation of thyroid hormones.
