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24.11.202227.05.2017

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BROMINE(lat. Bromum), Br, chemical element of group VII of the periodic table, atomic number 35, atomic mass 79.904, belongs to halogens.

Natural bromine is a mixture of two nuclides with mass numbers 79 (in a mixture of 50.56% by mass) and 81. The configuration of the outer electron layer is 4s2p5. In compounds it exhibits oxidation states -1, +1, +3, +5 and +7 (valences I, III, V and VII), with the most characteristic oxidation states being -1 and +5.

Located in the fourth period in group VIIA of Mendeleev's periodic table of elements.

The radius of the neutral bromine atom is 0.119 nm, the ionic radii of Br-, Br3+, Br5+ and Br7+ are 0.182, respectively; 0.073; 0.045 and 0.039 nm. The energies of sequential ionization of a neutral bromine atom are, respectively, 11.84; 21.80; 35.9; 47.3 and 59.7 eV. Electron affinity 3.37 eV. According to the Pauling scale, the electronegativity of bromine is 2.8.

Name: due to the fact that bromine has a heavy, unpleasant odor of vapor (from the Greek bromos - stench).

Discovery history: The discovery of bromine was led by the research of the French chemist A. Balard, who in 1825, acting with chlorine on an aqueous solution obtained after washing seaweed ash, isolated a dark brown, foul-smelling liquid. He called this liquid, also obtained from sea water, murid (from Latin muria - saline solution, brine) and sent a message about his discovery to the Paris Academy of Sciences. The commission created to verify this message did not accept the name Balar and named the new element bromine. The discovery of bromine made the young and little-known scientist famous. After Balar’s article appeared, it turned out that bottles with a similar substance were awaiting research by German chemists K. Levig and J. Liebig. Having missed the opportunity to discover a new element, Liebig exclaimed: “It was not Balar who discovered bromine, but bromine who discovered Balar.”

Finding in nature: Bromine is a fairly rare element in the earth's crust. Its content in it is estimated at 0.37·10-4% (approximately 50th place). bromine element discovery application

Chemically, bromine is highly active and therefore does not occur in free form in nature. Part of a large number of different compounds (bromides sodium (Na), potassium (K), magnesium (Mg) etc.), accompanying sodium, potassium and magnesium chlorides. Bromine's own minerals are bromargyrite (bromide silver (Ag) AgBr) and embolite (mixed chloride and bromide silver (Ag)) are extremely rare. The source of bromine is the waters of bitter lakes, salt brines accompanying oil and various salt deposits, and sea water (65·10-4%), the Dead Sea is richer in bromine. Currently, bromine is usually extracted from the waters of some bitter lakes, one of which is located, in particular, in our country in the Kulunda steppe (in Altai).

Application: 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. Bromine-containing drugs are widely known. 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.

Features of working with bromine: When working with bromine, you should use protective clothing, a gas mask, and gloves. MPC of bromine vapor is 0.5 mg/m3. Already at a bromine content in the air at a concentration of about 0.001% (by volume), irritation of the mucous membranes, dizziness are observed, and at higher concentrations - spasms of the respiratory tract, suffocation. If ingested, the toxic dose is 3 g, the lethal dose is from 35 g. In case of bromine vapor poisoning, the victim should be immediately taken to fresh air; to restore breathing, you can use a swab moistened with ammonia for a short time, periodically bringing it to the body for a short time. the victim's nose. Further treatment should be carried out under the supervision of a physician. Liquid bromine causes painful burns if it comes into contact with the skin.

Due to the high chemical activity and toxicity of both bromine vapor and liquid bromine, it should be stored in a glass, tightly sealed, thick-walled container. Bottles with bromine are placed in containers with sand, which protects the flasks from destruction when shaken. Due to the high density of bromine, bottles containing it should never be picked up by the neck alone (the neck may come off, and then the toxic liquid will end up on the floor).

To neutralize spilled bromine, the surface containing it must be immediately covered with a slurry of wet soda Na2CO3.

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Electronic structure of the bromine atom

The bromine atom consists of a positively charged nucleus (+35), inside of which there are 35 protons and 45 neutrons, and 35 electrons move around in four orbits.

Fig.1. Schematic structure of the bromine atom.

The distribution of electrons among orbitals is as follows:

35Br) 2) 8) 18) 7 ;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 5 .

The outer energy level of the bromine atom contains 7 electrons, which are valence electrons. The energy diagram of the ground state takes the following form:

Each valence electron of a bromine atom can be characterized by a set of four quantum numbers: n(main quantum), l(orbital), m l(magnetic) and s(spin):

Sublevel

The presence of one unpaired electron indicates that the oxidation state of bromine can be -1 or +1. Since at the fourth level there are vacant orbitals 4 d-sublevel, then the bromine atom is characterized by the presence of an excited state:

That is why bromine also has an oxidation state of +3. It is known that bromine in its compounds is also capable of exhibiting oxidation states +5 and +7.

Examples of problem solving

EXAMPLE 1

Exercise

The element forms a gaseous compound with hydrogen containing 12.5% hydrogen. The highest oxide of this element has the formula RO 2. Indicate the number of electrons in the electron shell of an atom of this element.

Solution

Higher oxides of the composition RO 2 form elements located in group IV of the Periodic Table. Elements of this group form volatile compounds with hydrogen of the composition RH 4. Let us denote the desired element as X. Then its mass fraction in the composition of the hydrogen compound is equal to:

ω(X)=100 - 12.5 = 87.5%.

Let's find the relative atomic mass of this element:

A r (X) = ω(X)× n(H)/ω(H) = 87.5×4/12.5 = 28.

Silicon (Si) has this atomic mass. The formulas of the compounds specified in the problem statement will look like this: SiO 2 and SiH 4.

The total number of electrons in the electron shell of a silicon atom is equal to its serial number in the Periodic Table, i.e. 14.

Answer

The total number of electrons in the electron shell of a silicon atom is 14.

Among all the non-metal chemical elements, there is a special series - halogens. These atoms get their name from the special properties they exhibit in chemical interactions. These include:

chlorine;
bromine;
fluorine.

Chlorine and fluorine are poisonous gases with strong oxidizing properties. Under normal conditions, iodine is a crystalline substance of dark purple color with a pronounced metallic luster. Exhibits the properties of a reducing agent. What does the fourth halogen look like? What are the properties of bromine, the compounds it forms and its characteristics as an element and as a simple substance? Let's try to figure it out.

Bromine: general characteristics of the element

As a particle, bromine occupies a cell with serial number 35. Accordingly, its nucleus contains 35 protons, and the electron shell contains the same number of electrons. Outer layer configuration: 4s 2 p 5.

It is located in group VII, the main subgroup, and is part of the halogens - a group of chemical elements with a special properties. In total, about 28 different isotopic varieties of a given atom are known. Mass numbers vary from 67 to 94. There are two known stable and stable ones, as well as predominant in percentage content in nature:

bromine 79 - its 51%;
bromine 81 - its 49%.

The average atomic mass of the element is 79.904 units. The oxidation state of bromine varies from -1 to +7. It exhibits strong oxidizing properties, but is inferior to chlorine and fluorine, superior to iodine.

History of discovery

This element was discovered later than its colleagues in the subgroup. By that time, chlorine and iodine were already known. Who made this discovery? Three names can be named at once, since that is how many scientists almost simultaneously managed to synthesize a new element, which later turned out to be the atom in question. These names:

Antoine Jerome Balard.
Carl Levig.
Justus Liebig.

However, it is Balar who is considered the official “father”, since he was the first to not only obtain and describe, but also send to a scientific conference of chemists a new substance, which is an unknown element.

Antoine Balard studied the composition of sea salt. After conducting numerous tests over it, one day he passed chlorine through the solution and saw that some kind of yellow compound was being formed. Taking this as a product of the interaction of chlorine and iodine in solution, he began to further investigate the resulting product. Subjected to the following treatments:

influenced by ether;
soaked in ;
treated with pyrolusite;
kept in a sulfuric acid environment.

As a result, he received a volatile brownish-red liquid with an unpleasant odor. This was bromine. He then conducted a thorough study of the physical and chemical characteristics of this substance. Afterwards he sent a report about it, describing the properties of bromine. The name that Balar gave to the element was murid, but it did not stick.

Today's common name for this atom is bromine, which in Latin means “smelly”, “fetid”. This is fully confirmed by the properties of its simple substance. The year of discovery of the element is 1825.

Possible oxidation states of bromine

There are several of these. Indeed, thanks to its properties, bromine can exhibit both oxidizing and reducing properties, with a clear predominance of the former. There are five possible options in total:

-1 - lowest oxidation state of bromine;

In nature, only those compounds are found that contain the element in a negative value. +7 is the maximum oxidation state of bromine. It manifests itself in the composition of bromic acid HBrO 4 and its bromate salts (NaBrO 4). In general, this oxidation state of bromine is extremely rare, just like +2. But connections with -1; +3 and +5 are very common and are important not only in the chemical industry, but also in medicine, technology and other sectors of the economy.

Bromine as a simple substance

Under normal conditions, the element in question is a diatomic molecule, but it is not a gas, but a liquid. Very poisonous, smoking in the air and emitting an extremely unpleasant odor. Even low concentrations of vapor can cause burns to the skin and irritation of the mucous membranes of the body. If you exceed the permissible limit, then suffocation and death are possible.

The chemical formula of this liquid is Br 2. Obviously, the symbol is derived from the Greek name for the element - bromos. The bond between atoms is single, covalent, nonpolar. The atomic radius is relatively large, so bromine reacts quite easily. This allows it to be widely used in chemical syntheses, often as a reagent for the qualitative determination of organic compounds.

It is not found in nature as a simple substance, as it easily evaporates in the form of reddish-brown smoke, which has a corrosive effect. Only in the form of various multicomponent systems. The degree of oxidation of bromine in compounds of various kinds depends on which element the reaction takes place with, that is, with which substance.

Physical properties

These characteristics can be expressed in several points.

Solubility in water is average, but better than other halogens. The saturated solution is called bromine water and has a reddish-brown color.
The boiling point of the liquid is +59.2 0 C.
Melting point -7.25 0 C.
The smell is pungent, unpleasant, suffocating.
Color - reddish-brown.
The physical state of a simple substance is a heavy (high density), thick liquid.
Electronegativity on the Pauling scale is 2.8.

These characteristics affect the methods for obtaining this compound, and also impose obligations to exercise extreme caution when working with it.

Chemical properties of bromine

From a chemical point of view, bromine behaves in two ways. Exhibits both oxidative and reducing properties. Like all other elements, it is capable of accepting electrons from metals and less electronegative nonmetals. It is a reducing agent with strong oxidizing agents, such as:

oxygen;
fluorine;
chlorine;
some acids.

Naturally, the oxidation state of bromine also varies from -1 to +7. What exactly is the element in question capable of reacting with?

With water, the result is a mixture of acids (hydrobromic and hypobromic).
With various iodides, since bromine is able to displace iodine from its salts.
With all non-metals directly, except oxygen, carbon, nitrogen and noble gases.
With almost all metals as a strong oxidizing agent. With many substances even flammable.
In ORR reactions, bromine often promotes the oxidation of compounds. For example, sulfur and sulfites are converted into sulfate ions, iodides into iodine, as a simple substance.
With alkalis to form bromides, bromates or hypobromates.

The chemical properties of bromine are of particular importance when it is part of the acids and salts formed by it. In this form, its properties as an oxidizing agent are very strong. Much more pronounced than that of a simple substance.

Receipt

The fact that the substance we are considering is important and significant from a chemical point of view is confirmed by the fact of its annual production in the amount of 550 thousand tons. Leading countries for these indicators:

China.
Israel.

The industrial method of extracting free bromine is based on processing salt solutions of lakes, wells, and seas. From them, the salt of the desired element is isolated, which is converted into an acidified form. It is passed through a powerful stream of air or water vapor. Thus, bromine gas is formed. Then it is processed and a mixture of sodium salts is obtained - bromides and bromates. Their solutions are acidified and come out with a free liquid substance.

Laboratory synthesis methods are based on the displacement of bromine from its salts with chlorine, as a stronger halogen.

Being in nature

The substance we are considering does not occur in nature in its pure form, since it is a highly volatile liquid that fumes in air. It is mainly included in compounds in which the minimum oxidation state of bromine is -1. These are salts - bromides. A lot of this element accompanies natural chlorine salts - sylvite, carnallite and others.

The minerals of bromine itself were discovered later than he himself. The three most common of them are:

embolite - a mixture of chlorine and bromine with silver;
bromarginite;
bromosylvinite - a mixture of potassium, magnesium and bromine with bound water (crystalline hydrate).

Also, this element is necessarily included in the composition of living organisms. Its deficiency leads to various diseases of the nervous system, disorders, sleep disturbances and memory impairment. In worse cases, it threatens infertility. Fish are capable of accumulating bromine in significant quantities in the form of salts.

In the earth's crust, its mass content reaches 0.0021%. Sea water and the Earth's hydrosphere in general contain a lot.

Bromine compounds with the lowest oxidation state

What is the oxidation state of bromine in its compounds with metals and hydrogen? The lowest possible for a given element is minus one. It is these compounds that are of greatest practical interest to humans.

HBr - hydrogen bromide (gas), or hydrobromic acid. In the gaseous aggregate state it has no color, but it has a very strong and unpleasant smell and smokes heavily. It has a corrosive effect on the mucous membranes of the body. It dissolves well in water, forming an acid. She, in turn, is a good restorer. Easily transforms into free bromine under the action of sulfuric, nitric acids and oxygen. It is of industrial importance as a source of bromide ion for the formation of salts with metal cations.
Bromides are salts of the above acid, in which the oxidation state of bromine is also equal to -1. Of practical interest are: LiBr and KBr.
Organic compounds containing bromide ion.

Compounds with the highest oxidation state

These include several basic substances. The highest oxidation state of bromine is +7, which means that in these compounds it should exhibit exactly that.

Bromic acid - HBrO 4. The strongest of all acids known for this element, however, it is also the most resistant to attacks by strong reducing agents. This is explained by the special geometric structure of the molecule, which in space has the shape of a tetrahedron.
Perbromates are salts above the designated acid. They are also characterized by the maximum degree of oxidation of bromine. They are strong oxidizing agents, which is why they are used in the chemical industry. Examples: NaBrO 4, KBrO 4.

Application of bromine and its compounds

Several areas can be identified in which bromine and its compounds find direct application.

Production of dyes.
For the production of photographic materials.
As medicines in medicine (bromine salts).
In the automotive industry, namely as an additive in gasoline.
Used as an impregnation to reduce the flammability level of some organic materials.
In the manufacture of drilling fluids.
In agriculture in the manufacture of insect-protective sprayers.
As a disinfectant and disinfectant, including for water.

Biological effect on the body

Both excess and lack of bromine in the body have very unpleasant consequences.

Pavlov was the first to determine the influence of this element on living beings. Experiments on animals have proven that a long-term lack of bromine ions leads to:

disruption of the nervous system;
sexual function disorder;
miscarriages and infertility;
decreased growth;
decreased hemoglobin levels;
insomnia and so on.

Excessive accumulation in organs and tissues leads to suppression of the brain and spinal cord and various external skin diseases.

In the modern sphere of the national economy, bromine is actively used for the production of fire retardants, that is, products that protect materials of organic origin from ignition. It is also used for the manufacture of non-flammable paints, fabrics and plastics, and impregnation of wooden products.

Bromine is highly soluble in alcohol and ether, as well as organic solvents, hydrocarbons and chloroform. It dissolves a little less well in water.

Application in the production of bromine compounds

Its compounds, such as bromochloromethane, are used as a filler in fire extinguishers. Elemental bromine is used in water purification and water treatment workflows.

Bromine feedstocks are actively used in the production of insecticides and pesticides, and they are used as fuel additives. Even for photo printing, bromine is needed.

There are frequent cases of using this element for soft water in public water to reduce the risk for people who are hypersensitive to chlorine compounds.

The essential value of this element in the form of sodium or calcium bromide is used to produce drilling fluids that are injected into wells for the important purpose of increasing the amount of oil produced. This material is also used in the production of high-quality rubber, that is, bromobutyl rubber and
pharmaceuticals.

The healing abilities of halogen compounds

Bromine salts are also widely used in medical practice as a remedy when it is necessary to relieve nervous excitement, hysteria, insomnia due to nervous fatigue, and irritability. They have epilepsy and other convulsive diseases based on increased excitability of the brain.

Bromides are also used for diseases that are associated with certain organ problems (peptic ulcers, some stages of hypertension).

In addition, lenses are now being made that perfectly transmit the infrared part of the spectrum from potassium bromide crystals. The bactericidal properties of this salt help to store fruits and vegetables for a long time.

Studying the scope of bromine, it should be noted that this common halogen and its starting materials are quite widely used in various areas of human activity, in agriculture and medicine, which cannot be said about its other brothers.

DEFINITION

Bromine- a chemical element located in the fourth period in group VIIA of the Periodic Table D.I. Mendeleev.

The atomic number is 35. The structure of the atom is shown in Fig. 1. Non-metal of the p-family.

Rice. 1. Scheme of the structure of the bromine atom.

Under normal conditions, bromine is a red-brown liquid with a strong, unpleasant odor. Poisonous. Density 3.19 g/cm 3 (at t 0 = 0 o C). When boiling (t 0 = 58.6 o C), bromine changes from a liquid state to a gaseous state - it forms brown-brown vapor.

The relative atomic mass of atomic bromine is 79.904 amu. Its relative molecular mass will be 79.904 and its molar mass:

M(Br 2) = M r (Br 2) × 1 mol = 79.904 g/mol.

It is known that the bromine molecule is diatomic - Br 2, then the relative atomic mass of the bromine molecule will be equal to:

A r (Br 2) = 79.904× 2 = 159.808 amu

The relative molecular weight of the bromine molecule will be 159.808, and the molar mass will be:

M(Br 2) = M r (Br 2) × 1 mol = 159.808 g/mol or simply 160 g/mol.

Examples of problem solving

EXAMPLE 1

Exercise

Write the reaction equations in accordance with the transformation scheme:

Br 2 → NaBr → Br 2 → HBr → KBr → AgBr.

Answer

In order to obtain sodium bromide from bromine water, it is necessary to treat it with a dilute solution of sodium hydroxide. The reaction takes place at a temperature of 0 - 5 o C.

Br 2 + 2NaBr dulute = NaBr + NaBrO + H 2 O.

It is possible to obtain bromine from sodium bromide if dilute sulfuric acid (10-50%) is added to the salt (in a solid aggregate state):

2NaBr + H 2 SO 4(dilute) = Na 2 SO 4 + 2HBr.

To obtain hydrogen bromide from bromine water, hydrogen must be added to the reaction mixture:

Br 2 + H 2 = 2HBr.

Potassium bromide is formed as a result of the interaction of dilute solutions of hydrogen bromide and potassium hydroxide:

HBr dilute + KOH dilute = KBr + H 2 O.

A yellow precipitate - silver bromide - can be obtained by treating silver nitrate with a solution of potassium bromide:

KBr + AgNO 3 = AgBr↓ + KNO 3.

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