A message on the topic of halogen compounds. Halogens and their compounds. Biological significance of halogens and their compounds

Symbol

element

Ordinal

Number

Structure

external

electronic

layer

2s 2 2p 5

3s 2 3p 5

4s 2 4p 5

5 s 2 5 p 5

6 s 2 6 p 5

Relative electro

negativity (EO)

4,0

3,0

2,8

2,5

~2,2

Atomic radius, nm

0,064

0,099

0,114

0,133

–

Degrees

oxidation

1, +1, +3,
+5, +7

–

State of aggregation

Pale green
gas

Green-yellow.
gas

Buraya
liquid

Dark violet
crystals

Black
crystals

t °pl.(°С)

219

101

114

227

t °boiling (°С)

183

185

317

ρ (g/cm3)

1,51

1,57

3,14

4,93

–

Solubility in water

(g/100g water)

reacts
with water

2,5: 1
by volume

3,5

0,02

–

Name

Atomic structure diagram

Electronic formula

Fluorine

F +9) 2) 7

… 2s 2 2p 5

Chlorine

Cl +17) 2) 8) 7

… 3s 2 3p 5

Bromine

Br +35) 2) 8) 18) 7

…4s 2 4p 5

Iodine

I +53) 2) 8) 18) 18) 7

…5s 2 5p 5

1. Interaction with metals

Mg + Cl 2 → MgCl 2

2.Reactions with non-metals

H 2 + Cl 2 → 2HCl

3. Interaction with alkalis in the cold

2NaOH + Cl 2 → NaCl + NaClO + H 2 O

4. Interaction with alkalis when heated

6NaOH + 3Cl 2 → 5NaCl + NaClO 3 + 3H 2 O

5. Displacement of less active halogens from halides

2KBr + Cl 2 → 2KCl + Br 2

6. With water

H 2 O + Cl 2 ↔ HCl + HClO (chlorine water)

Fluorine

is widely used as a fluorinating agent in the production of various fluorides (SF 6, BF 3, WF 6 and others), including compounds of the noble gases xenon (Xe) and krypton (Kr). Uranium hexafluoride UF 6 is used to separate uranium (U) isotopes. Fluorine is used in the production of Teflon, other fluoroplastics, fluorine rubber, fluorine-containing organic matter and materials that are widely used in technology, especially in cases where resistance to aggressive environments is required, high temperature and so on.

Chlorine

used in the production of chlorine-containing organic compounds (60-75%), inorganic substances(10-20%), for bleaching cellulose and fabrics (5-15%), for sanitary needs and disinfection (chlorination) of water.

Bromine

bromine is used in the preparation of a number of inorganic and organic substances in analytical chemistry. Bromine compounds are used as fuel additives, pesticides, flame retardants, and in photography. Widely known to contain bromine medications. It should be noted that the common expression: “the doctor prescribed bromine a tablespoon after meals” means, of course, only that an aqueous solution of sodium (or potassium) bromide was prescribed, and not pure bromine. The calming effect of bromide drugs is based on their ability to enhance inhibition processes in the central nervous system.

Iodine

iodine is used to obtain high-purity titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb) and other metals (so-called iodide refining of metals). During iodide refining, the original metal with impurities is converted into the form of volatile iodides, and then the resulting iodides are decomposed on a hot thin thread. The thread is made of pre-cleaned metal, which is subjected to refining. Its temperature is selected such that only the iodide of the metal being purified can decompose on the filament, while the remaining iodides remain in the vapor phase.
Iodine is also used in incandescent iodine lamps, which have a tungsten filament and are characterized by a long service life. As a rule, in such lamps, iodine vapor is in an environment of the heavy inert gas xenon (Xe) (lamps are often called xenon) and reacts with tungsten (W) atoms evaporating from the heated coil. Iodide, which is volatile under these conditions, is formed, which sooner or later ends up again near the helix. Immediate decomposition of the iodide occurs, and the released tungsten (W) again appears on the spiral. Iodine is also used in food additives, dyes, catalysts, photography, analytical chemistry.

Cl 2 + 2KI = I 2 + 2KCl

Molar mass of iodine, calculated using the table of chemical elements by D.I. Mendeleev, equal to – 254 g/mol. Let's find the amount of iodine formed:

v(I 2) = m(I 2)/M(I 2)

The halogens are located to the left of the noble gases in the periodic table. 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 halogen elements have seven valence electrons, they only need one extra electron to form a full octet. This characteristic makes them more reactive than other groups of nonmetals.

general characteristics

Halogens form diatomic molecules (type X2, where X denotes a halogen atom) - a stable form of 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 are never found uncombined in nature. Fluorine is the most active halogen, and astatine is the least.

All halogens form group I salts with similar properties. 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; for example Cl- is called "chloride".

Besides, Chemical properties halogens allow them to act as oxidizing agents - oxidizing metals. Majority chemical reactions, in which halogens participate - redox in an 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 organic compound, the prefix halo- can be used in a general sense, or the prefixes fluoro-, chloro-, bromo-, iodine- for specific halogens. Halogen elements can cross-link 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- ("salt") and -gen ("to form"). Together these words mean “salt-forming,” emphasizing the fact that halogens react with metals to form salts. Halite is the name for rock salt, a naturally occurring 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 thyroid hormones.

Chemical elements

Fluorine is an element with atomic number 9 and is designated 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 abundant 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 in the elemental diatomic state, in which its oxidation state is zero. Fluorine is extremely reactive and reacts 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 highly electronegative, its electronegativity does not determine acidity; HF is a weak acid due to the fact that the fluoride ion is basic (pH > 7). In addition, fluorine produces very powerful oxidizing agents. For example, fluorine can react with inert gas xenon and forms a strong oxidizing agent xenon difluoride (XeF2). Fluoride has many uses.

Chlorine is an element with atomic number 17 and the chemical symbol Cl. Discovered in 1774 by isolating it from hydrochloric acid. In its elemental state it forms the diatomic molecule Cl2. Chlorine has several COs: -1, +1, 3, 5 and 7. 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 form compounds. Chlorine reacts with metals to form salts called chlorides. Chlorine ions are the most common ions found in seawater. Chlorine also has two isotopes: 35Cl and 37Cl. Sodium chloride is the most common compound of all the chlorides.

Bromine – 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 COs are -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 salts dissolved in seawater. Behind last years The world's bromide production has increased significantly due to its availability and long shelf life. Like other halogens, bromine is an oxidizing agent and is very 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 solid purple. Iodine has one stable isotope - 127I. First discovered in 1811 using seaweed and sulfuric acid. Currently, iodine ions can be isolated in seawater. Although iodine is not very soluble in water, its solubility can be increased by using individual 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 the 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 very short period half-life, no longer than several hours. Obtained in 1940 as a result of synthesis. Astatine is believed to be similar to iodine. Differs in metallic properties.

The table below shows the structure of halogen atoms and the structure of the outer layer of electrons.

This structure of the outer layer of electrons means 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 simple substances halogens change with increasing atomic number of the element. For better understanding and greater clarity, we offer you several tables.

The melting and boiling points of a group increase as the molecular size increases (F

Table 1. Halogens. Physical properties: melting and boiling points

Kernel size increases (F< Cl < Br < I < At), так как увеличивается число протонов и нейтронов. Кроме того, с каждым периодом добавляется всё больше уровней энергии. Это приводит к большей орбитали, и, следовательно, к увеличению радиуса атома.

Table 2. Halogens. Physical properties: atomic radii

If the outer valence electrons are not located near the nucleus, then it will not take much energy to remove them from it. Thus, the energy required to eject an outer electron is not as high in the lower part of the element group, since there are more energy levels there. Additionally, high ionization energy causes the element to exhibit non-metallic qualities. Iodine and display astatine exhibit metallic properties because the ionization energy is reduced (At< I < Br < Cl < F).

Table 3. Halogens. Physical properties: ionization energy

The number of valence electrons in an atom increases with increasing energy levels at progressively lower levels. Electrons are progressively further away from the nucleus; Thus, the nucleus and electrons are not 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

As atomic size increases with increasing period, electron affinity tends to decrease (B< I < Br < F < Cl). Исключение – фтор, сродство которого меньше, чем у хлора. Это можно объяснить меньшим размером фтора по сравнению с хлором.

Table 5. Electron affinity of halogens

The reactivity of halogens decreases with increasing period (At

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, forming halides of the form HX:

Hydrogen halides easily dissolve in water to form hydrohalic acid (hydrofluoric, hydrochloric, hydrobromic, hydroiodic) acid. The properties of these acids are given below.

Acids are formed by the following reaction: HX (aq) + H2O (l) → X- (aq) + H3O+ (aq).

All hydrogen halides form strong acids, with the exception of HF.

The acidity of hydrohalic acids increases: HF

Hydrofluoric acid can etch glass and some inorganic fluorides for a long time.

It may seem counterintuitive that HF ​​is the weakest hydrohalic acid, since fluorine has the highest electronegativity. 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 high dissociation energy. Of all the hydrogen halides, HF has the shortest bond length and the highest bond dissociation energy.

Halogen oxoacids

Halogen oxo acids are acids with hydrogen, oxygen and halogen atoms. Their acidity can be determined by structural analysis. The halogen oxo acids are given below:

In each of these acids, a proton is bonded to an oxygen atom, so comparing proton bond lengths is not useful here. Electronegativity plays a dominant role here. Acid activity increases with the number of oxygen atoms associated with the central atom.

Appearance and state of the substance

The basic physical properties of halogens can be summarized in the following table.

Explanation of appearance

The color of halogens results from the absorption of visible light by molecules, which causes electrons to be excited. Fluorine absorbs violet light and therefore appears light yellow. Iodine, on the other hand, absorbs yellow light and appears violet (yellow and violet 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 in the form of a colored gas.

Although the color of astatine is unknown, it is assumed to be darker than iodine (i.e., black) according to the observed pattern.

Now, if you are asked: “Characterize the physical properties of halogens,” you will have something to say.

Oxidation state of halogens in compounds

Oxidation number is often used instead of the concept of halogen valence. Typically, the oxidation state is -1. But if a halogen is bonded to oxygen or another halogen, it can take other states: oxygen CO -2 takes precedence. In the case of two different halogen atoms bonded together, the more electronegative atom prevails and accepts 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 an CO of -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 the halogen in elemental form (X2), where its CO is zero.

Why is CO fluorine always -1?

Electronegativity increases with increasing period. Fluorine therefore has the highest electronegativity of all the elements, as evidenced by its position on the periodic table. Its electron configuration is 1s2 2s2 2p5. If fluorine gains another electron, the outermost p orbitals are completely filled and form a full octet. Since fluorine has high 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 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 using oxidizing agents. For example, chlorine is produced by hydrolysis of a solution of table salt. The use of halogens and their compounds is diverse.