Barium. barium properties
With the chemical formula BaSO 4 . It is an odorless white powder, insoluble in water. Its whiteness and opacity, as well as its high density, define its main applications.
Name history
Barium belongs to the alkaline earth metals. The latter are so named because, according to D. I. Mendeleev, their compounds form an insoluble mass of the earth, and oxides "have an earthy appearance." Barium is found in nature in the form of the mineral barite, which is barium sulfate with various impurities.
It was first discovered by the Swedish chemists Scheele and Hahn in 1774 as part of the so-called heavy spar. From here came the name of the mineral (from the Greek "baris" - heavy), and then the metal itself, when in 1808 it was isolated in its pure form by Humphry Devi.
Physical Properties
Since BaSO 4 is a salt of sulfuric acid, its physical properties are partly determined by the metal itself, which is soft, reactive and silvery white. Natural barite is colorless (sometimes white) and transparent. Chemically pure BaSO 4 has a color from white to pale yellow, it is non-flammable, with a melting point of 1580°C.
What is the mass of barium sulfate? Its molar mass is 233.43 g/mol. It has an unusually high specific gravity - from 4.25 to 4.50 g/cm 3 . Given its insolubility in water, its high density makes it indispensable as a filler for aqueous drilling fluids.
Chemical properties
BaSO 4 is one of the most sparingly soluble compounds in water. It can be obtained from two highly soluble salts. Take an aqueous solution of sodium sulfate - Na 2 SO 4. Its molecule in water dissociates into three ions: two Na + and one SO 4 2-.
Na 2 SO 4 → 2Na + + SO 4 2-
Let us also take an aqueous solution of barium chloride - BaCl 2, the molecule of which dissociates into three ions: one Ba 2+ and two Cl - .
BaCl 2 → Ba 2+ + 2Cl -
Mix an aqueous solution of sulfate and a mixture containing chloride. Barium sulfate is formed as a result of the combination of two ions with the same magnitude and opposite charge into one molecule.
Ba 2+ + SO 4 2- → BaSO 4
Below you can see the complete equation for this reaction (the so-called molecular equation).
Na 2 SO 4 + BaCl 2 → 2NaCl + BaSO 4
As a result, an insoluble precipitate of barium sulfate is formed.
Commodity barite
In practice, the feedstock for the production of commercial barium sulfate intended for use in drilling fluids when drilling oil and gas wells is, as a rule, mineral barite.
The term "primary" barite refers to commercial products that include raw material (obtained from mines and quarries) as well as products of simple enrichment by methods such as washing, settling, separation in heavy media, flotation. Most raw barite needs to be brought to a minimum purity and density. The mineral that is used as a filler is ground and sieved to a uniform size so that at least 97% of its particles are up to 75 microns in size, and no more than 30% are less than 6 microns. Primary barite must also be dense enough to have a specific gravity of 4.2 g/cm3 or higher, but soft enough not to damage the bearings.
Obtaining a chemically pure product
The mineral barite is often contaminated with various impurities, mainly iron oxides, which color it in various colors. It is processed carbothermally (heated with coke). The result is barium sulfide.
BaSO 4 + 4 C → BaS + 4 CO
The latter, unlike sulfate, is soluble in water and easily reacts with oxygen, halogens and acids.
BaS + H 2 SO 4 → BaSO 4 + H 2 S
Sulfuric acid is used to obtain a high purity end product. The barium sulfate formed by this process is often referred to as blancfix, which means "white fixed" in French. It is often found in consumer products such as paints.
Under laboratory conditions, barium sulfate is formed by combining barium ions and sulfate ions in solution (see above). Since sulfate is the least toxic salt of barium due to its insolubility, wastes containing other salts of barium are sometimes treated with sodium sulfate to bind all of the barium, which is quite toxic.
From sulfate to hydroxide and back
Historically, barite has been used to produce barium hydroxide, Ba(OH) 2 , needed in sugar refining. This is generally a very interesting and widely used compound in industry. It is highly soluble in water, forming a solution known as barite water. It is convenient to use for the binding of sulfate ions in various compositions through the formation of insoluble BaSO 4 .
We saw above that when heated in the presence of coke, it is easy to obtain water-soluble barium sulfide - BaS from sulfate. The latter, when interacting with hot water, forms a hydroxide.
BaS + 2H 2 O → Ba(OH) 2 + H 2 S
Barium hydroxide and sodium sulfate, taken in solutions, when mixed, will give an insoluble precipitate of barium sulfate and sodium hydroxide.
Ba(OH) 2 + Na 2 SO 4 = BaSO 4 + 2NaOH
It turns out that natural barium sulfate (barite) is first industrially converted into barium hydroxide, and then serves to obtain the same sulfate when cleaning various salt systems from sulfate ions. In the same way, the reaction will also take place during the purification of SO 4 2- ions from a solution of copper sulphate. If you make a mixture of "barium hydroxide + copper sulfate", the result is copper hydroxide and insoluble barium sulfate.
CuSO 4 + Ba(OH) 2 → Cu(OH) 2 + BaSO 4 ↓
Even in reaction with sulfuric acid itself, its sulfate ions will be completely bound by barium.
Use in drilling fluids
About 80% of the world production of barium sulfate, purified and ground barite, is consumed as a component of drilling fluids in the creation of oil and gas wells. Adding it increases the density of the fluid injected into the well to better resist high reservoir pressure and prevent breakouts.
When a well is drilled, the bit passes through various formations, each with its own characteristics. The greater the depth, the greater the percentage of barite must be present in the structure of the solution. An additional advantage is that barium sulfate is a non-magnetic substance, so it does not interfere with various downhole measurements using electronic devices.
Paint and paper industry
Most of the synthetic BaSO 4 is used as a component of the white pigment for paints. So, blancfix mixed with titanium dioxide (TiO 2) is sold as a white oil paint used in painting.
The combination of BaSO 4 and ZnS (zinc sulfide) gives an inorganic pigment called litopone. It is used as a coating for certain grades of photographic paper.
More recently, barium sulfate has been used to brighten paper intended for inkjet printers.
Applications in the chemical industry and non-ferrous metallurgy
In the production of polypropylene and polystyrene, BaSO 4 is used as a filler in proportions up to 70%. It has the effect of increasing the resistance of plastics to acids and alkalis, as well as imparting opacity to them.
It is also used to produce other barium compounds, notably barium carbonate, which is used to make LED glass for television and computer screens (historically in cathode ray tubes).
Molds used in metal casting are often coated with barium sulfate to prevent adhesion to the molten metal. This is done in the manufacture of anode copper plates. They are cast into copper molds coated with a layer of barium sulfate. When liquid copper solidifies into a finished anode plate, it can be easily removed from the mold.
pyrotechnic devices
Since barium compounds emit green light when burned, salts of this substance are often used in pyrotechnic formulas. Although nitrate and chlorate are more common than sulfate, the latter is widely used as a component in pyrotechnic strobe lights.
X-ray contrast agent
Barium sulfate is a radiopaque agent used to diagnose certain medical problems. Since such substances are opaque to x-rays (blocking them as a result of their high density), the areas of the body in which they are localized appear as white areas on x-ray film. This creates the necessary distinction between one (diagnosed) organ and other (surrounding) tissues. The contrast will help the doctor see any special conditions that may exist in that organ or body part.
Barium sulfate is taken by mouth or rectally with an enema. In the first case, it makes the esophagus, stomach or small intestine opaque to x-rays. So they can be photographed. If the substance is administered with an enema, then the large intestine or intestines can be seen and fixed with x-rays.
The dose of barium sulfate will be different for different patients, it all depends on the type of test. The drug is available in the form of a special medical barium suspension or in tablets. Different tests that require contrast and x-ray equipment require different amounts of suspension (in some cases, a drug in tablet form is necessary). The contrast agent should only be used under the direct supervision of a physician.
Barium is an element of the main subgroup of the second group, the sixth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 56. It is designated by the symbol Ba (lat. barium). A simple substance is a soft, ductile silver-white alkaline earth metal. Possesses high chemical activity.
History of the discovery of bariumBarium was discovered in the form of oxide BaO in 1774 by Karl Scheele. In 1808, the English chemist Humphrey Davy produced a barium amalgam by electrolysis of wet barium hydroxide with a mercury cathode; after evaporating the mercury on heating, he isolated barium metal.
In 1774, the Swedish chemist Carl Wilhelm Scheele and his friend Johan Gottlieb Hahn investigated one of the heaviest minerals, heavy spar BaSO 4 . They managed to isolate the previously unknown "heavy earth", which was later called barite (from the Greek βαρυς - heavy). And after 34 years, Humphry Davy, having subjected wet barite earth to electrolysis, obtained from it a new element - barium. It should be noted that in the same 1808, a little earlier than Davy, Jene Jacob Berzelius and his co-workers obtained amalgams of calcium, strontium and barium. This is how the element barium was born.
Ancient alchemists calcined BaSO 4 with wood or charcoal and obtained phosphorescent "Bolognese gems". But chemically, these gems are not BaO, but barium sulfide BaS.
origin of name
It got its name from the Greek barys - "heavy", since its oxide (BaO) was characterized as having an unusually high density for such substances.
Finding barium in natureThe earth's crust contains 0.05% barium. This is quite a lot - much more than, say, lead, tin, copper or mercury. In its pure form, it does not exist in the earth: barium is active, it is included in the subgroup of alkaline earth metals and, naturally, it is quite firmly bound in minerals.
The main barium minerals are the already mentioned heavy spar BaSO 4 (more often called barite) and witherite BaCO3, named after the Englishman William Withering (1741 ... 1799), who discovered this mineral in 1782. In a small concentration of barium salts are found in many mineral waters and sea water. The low content in this case is a plus, not a minus, because all barium salts, except for sulfate, are poisonous.
Types of barium depositsBy mineral associations, barite ores are divided into monomineral and complex. Complex ones are subdivided into barite-sulfide (contain lead, zinc, sometimes copper and iron pyrite sulfides, less often Sn, Ni, Au, Ag), barite-calcite (contain up to 75% calcite), iron-barite (contain magnetite, hematite, and goethite and hydrogoethite in the upper zones) and barite-fluorite (except for barite and fluorite, they usually contain quartz and calcite, and zinc, lead, copper, and mercury sulfides are sometimes present as small impurities).
From a practical point of view, hydrothermal vein monomineral, barite-sulfide and barite-fluorite deposits are of the greatest interest. Some metasomatic sheet deposits and eluvial placers are also of industrial importance. Sedimentary deposits, which are typical chemical sediments of water basins, are rare and do not play a significant role.
As a rule, barite ores contain other useful components (fluorite, galena, sphalerite, copper, gold in industrial concentrations), so they are used in combination.
Isotopes of bariumNatural barium consists of a mixture of seven stable isotopes: 130 Ba, 132 Ba, 134 Ba, 135 Ba, 136 Ba, 137 Ba, 138 Ba. The latter is the most common (71.66%). Radioactive isotopes of barium are also known, the most important of which is 140 Ba. It is formed during the decay of uranium, thorium and plutonium.
Obtaining bariumThe metal can be obtained in various ways, in particular, by electrolysis of a molten mixture of barium chloride and calcium chloride. It is possible to obtain barium by restoring it from the oxide by the aluminothermic method. To do this, witherite is fired with coal and barium oxide is obtained:
BaCO 3 + C → BaO + 2CO.
Then a mixture of BaO with aluminum powder is heated in vacuum to 1250°C. Vapors of reduced barium condense in the cold parts of the tube in which the reaction takes place:
3BaO + 2Al → Al 2 O 3 + 3Ba.
It is interesting that barium peroxide BaO 2 is often included in the composition of ignition mixtures for aluminothermy.
Obtaining barium oxide by simple calcination of witherite is difficult: witherite decomposes only at temperatures above 1800°C. It is easier to obtain BaO by calcining barium nitrate Ba (NO 3) 2:
2Ba (NO 3) 2 → 2BaO + 4NO 2 + O 2.
Both electrolysis and aluminum reduction produce a soft (harder than lead, but softer than zinc) shiny white metal. It melts at 710°C, boils at 1638°C, its density is 3.76 g/cm 3 . All this fully corresponds to the position of barium in the subgroup of alkaline earth metals.
There are seven natural isotopes of barium. The most common of these is barium-138; it is more than 70%.
Barium is highly active. It self-ignites on impact, easily decomposes water, forming a soluble barium oxide hydrate:
Ba + 2H 2 O → Ba (OH) 2 + H 2.
An aqueous solution of barium hydroxide is called barite water. This "water" is used in analytical chemistry to determine CO 2 in gas mixtures. But this is already from the story about the use of barium compounds. Metallic barium finds almost no practical application. In extremely small quantities, it is introduced into bearing and printing alloys. An alloy of barium and nickel is used in radio tubes, pure barium is used only in vacuum technology as a getter (getter).
Barium metal is obtained from oxide by aluminum reduction in vacuum at 1200-1250°C:
4BaO + 2Al \u003d 3Ba + BaAl 2 O 4.
Barium is purified by vacuum distillation or zone melting.
Preparation of barium titanium. Getting it is relatively easy. Witherite BaCO 3 at 700 ... 800 ° C reacts with titanium dioxide TYu 2, it turns out just what you need:
BaCO 3 + TiO 2 → BaTiO 3 + CO 2.
Main prom. a method for obtaining metallic barium from BaO is its reduction with A1 powder: 4BaO + 2A1 -> 3Ba + BaO * A1 2 O 3. The process is carried out in a reactor at 1100-1200°C in an Ar atmosphere or in a vacuum (the latter method is preferable). The molar ratio of BaO:A1 is (1.5-2):1. The reactor is placed in a furnace so that the temperature of its "cold part" (the formed barium vapors condense in it) is about 520 ° C. By distillation in vacuum, barium is purified to an impurity content of less than 10 ~ 4% by weight, and when using zone melting - up to 10 ~ 6%.
Small amounts of barium are also obtained by the reduction of BaBeO 2 [synthesized by fusion of Ba (OH) 2 and Be (OH) 2] at 1300 ° C with titanium, as well as by decomposition at 120 ° C Ba (N 3) 2, formed during exchange p- cations of barium salts with NaN 3 .
Acetate Ba (OOCHN 3), - colorless. crystals; m.p. 490°С (decomp.); dense 2.47 g/cm 3 ; sol. in water (58.8 g per 100 g at 0°C). Below 25 ° C, trihydrate crystallizes from aqueous solutions, at 25-41 ° C - monohydrate, above 41 ° C - anhydrous salt. Get interaction. Ba (OH) 2, VaCO 3 or BaS with CH 3 CO 2 H. Used as a mordant when dyeing wool and chintz.
Manganate(VI) BaMnO 4 - green crystals; does not decompose up to 1000°C. Obtained by calcining a mixture of Ba(NO 3) 2 with MnO 2 . A pigment (kassel or manganese green) commonly used for fresco painting.
Chromate (VI) ВаСrO 4 - yellow crystals; m.p. 1380°C; - 1366.8 kJ/mol; sol. in inorg. to-max, not sol. in water. Get interaction. aqueous solutions of Ba (OH) 2 or BaS with alkali metal chromates (VI). Pigment (barite yellow) for ceramics. MPC 0.01 mg / m 3 (in terms of Cr0 3). Pirconate ВаZrО 3 - colorless. crystals; m.p. ~269°С; - 1762 kJ/mol; sol. in water and aqueous solutions of alkalis and NH 4 HCO 3, decomposed by strong inorg. to-tami. Get interaction. ZrO 2 with BaO, Ba(OH) 2 or BaCO 3 when heated. Ba zirconate mixed with ВаТiO 3 -piezoelectric.
Bromide BaBr 2 - white crystals; m.p. 847°C; dense 4.79 g/cm 3 ; -757 kJ/mol; well sol. in water, methanol, worse - in ethanol. From aqueous solutions, the dihydrate crystallizes, turning into a monohydrate at 75 ° C, into an anhydrous salt - above 100 ° C. In aqueous solutions, the interaction. with CO 2 and O 2 of air, forming VaCO 3 and Br 2. Get BaBr 2 interaction. aqueous p-ditch Ba (OH) 2 or VaCO 3 with hydrobromic acid.
Iodide BaI 2 - colorless. crystals; m.p. 740°С (decomp.); dense 5.15 g/cm 3 ; . -607 kJ/mol; well sol. in water and ethanol. From hot water solutions, the dihydrate crystallizes (dehydrated at 150 ° C), below 30 ° C - hexahydrate. Get VaI 2 interaction. water p-ditch Ba (OH) 2 or VaCO 3 with hydroiodic acid.
Physical properties of bariumBarium is a silvery-white malleable metal. It breaks on a sharp blow. There are two allotropic modifications of barium: α-Ba with a cubic body-centered lattice is stable up to 375 °C (parameter a = 0.501 nm), β-Ba is stable above.
Hardness on a mineralogical scale 1.25; on the Mohs scale 2.
Barium metal is stored in kerosene or under a layer of paraffin.
Chemical properties of bariumBarium is an alkaline earth metal. It oxidizes intensively in air, forming barium oxide BaO and barium nitride Ba 3 N 2, and ignites when heated slightly. Vigorously reacts with water, forming barium hydroxide Ba (OH) 2:
Ba + 2H 2 O \u003d Ba (OH) 2 + H 2
Actively interacts with dilute acids. Many barium salts are insoluble or slightly soluble in water: barium sulfate BaSO 4, barium sulfite BaSO 3, barium carbonate BaCO 3, barium phosphate Ba 3 (PO 4) 2. Barium sulfide BaS, unlike calcium sulfide CaS, is highly soluble in water.
Natural barium has seven stable isotopes since May. ch. 130, 132, 134-137 and 138 (71.66%). The cross section of capture of thermal neutrons is 1.17-10 28 m 2 . External configuration electron shell 6s 2 ; oxidation state + 2, rarely + 1; ionization energy Ba° -> Ba + -> Ba 2+ resp. 5.21140 and 10.0040 eV; Pauling electronegativity 0.9; atomic radius 0.221 nm, ionic radius Ba 2+ 0.149 nm (coordination number 6).
Easily reacts with halogens to form halides.
When heated with hydrogen, it forms barium hydride BaH 2 , which, in turn, with lithium hydride LiH gives the Li complex.
Reacts on heating with ammonia:
6Ba + 2NH 3 = 3BaH 2 + Ba 3 N 2
Barium nitride Ba 3 N 2 reacts with CO when heated, forming cyanide:
Ba 3 N 2 + 2CO = Ba(CN) 2 + 2BaO
With liquid ammonia, it gives a dark blue solution, from which ammonia can be isolated, which has a golden sheen and easily decomposes with the elimination of NH 3. In the presence of a platinum catalyst, ammonia decomposes to form barium amide:
Ba (NH 2) 2 + 4NH 3 + H 2
Barium carbide BaC 2 can be obtained by heating BaO with coal in an arc furnace.
With phosphorus it forms the phosphide Ba 3 P 2 .
Barium reduces the oxides, halides and sulfides of many metals to the corresponding metal.
Application of bariumAn alloy of barium with A1 (alba alloy, 56% Ba) is the basis of getters (getters). To obtain the getter itself, barium is evaporated from the alloy by high-frequency heating in an evacuated flask of the device; barium mirror (or diffuse coating during evaporation in a nitrogen atmosphere). The active part of the overwhelming majority of thermionic cathodes is BaO. Barium is also used as a Cu and Pb deoxidizer, as an additive to antifrictions. alloys, ferrous and non-ferrous metals, as well as alloys, from which typographic fonts are made to increase their hardness. Barium alloys with Ni are used for the manufacture of electrodes for glow plugs in internal engines. combustion and in radio tubes. 140 Va (T 1/2 12.8 days) is an isotope indicator used in the study of barium compounds.
Barium metal, often in an alloy with aluminum, is used as a getter in high vacuum electronic devices.
Anti-corrosion materialBarium is added together with zirconium to liquid metal coolants (alloys of sodium, potassium, rubidium, lithium, cesium) to reduce the aggressiveness of the latter to pipelines, and in metallurgy.
Barium fluoride is used in the form of single crystals in optics (lenses, prisms).
Barium peroxide is used for pyrotechnics and as an oxidizing agent. Barium nitrate and barium chlorate are used in pyrotechnics to color flames (green fire).
Barium chromate is used in the production of hydrogen and oxygen by the thermochemical method (Oak Ridge cycle, USA).
Barium oxide, together with oxides of copper and rare earth metals, is used to synthesize superconducting ceramics operating at liquid nitrogen temperatures and above.
Barium oxide is used to melt a special type of glass used to coat uranium rods. One of the widespread types of such glasses has the following composition - (phosphorus oxide - 61%, BaO - 32%, aluminum oxide - 1.5%, sodium oxide - 5.5%). In glassmaking for the nuclear industry, barium phosphate is also used.
Barium fluoride is used in solid state fluorine batteries as a component of the fluoride electrolyte.
Barium oxide is used in powerful copper oxide batteries as a component of the active mass (barium oxide-copper oxide).
Barium sulfate is used as a negative electrode active mass expander in the production of lead-acid batteries.
Barium carbonate BaCO 3 is added to the glass mass to increase the refractive index of the glass. Barium sulfate is used in the paper industry as a filler; the quality of paper is largely determined by its weight, barite BaSO 4 makes the paper heavier. This salt is necessarily included in all expensive grades of paper. In addition, barium sulfate is widely used in the production of white lithopone paint, a product of the reaction of solutions of barium sulfide with zinc sulfate:
BaS + ZnSO 4 → BaSO 4 + ZnS.
Both salts, having a white color, precipitate, pure water remains in the solution.
When drilling deep oil and gas wells, a suspension of barium sulfate in water is used as a drilling fluid.
Another barium salt finds important uses. This is barium titanate BaTiO 3 - one of the most important ferroelectrics (ferroelectrics are polarized on their own, without exposure to an external field. Among dielectrics, they stand out in the same way as ferromagnetic materials among conductors. The ability for such polarization is maintained only at a certain temperature. Polarized ferroelectrics differ higher dielectric constant), which are considered very valuable electrical materials.
In 1944, this class was supplemented by barium titanate, the ferroelectric properties of which were discovered by the Soviet physicist B.M. Vulom. A feature of barium titanate is that it retains ferroelectric properties in a very wide temperature range - from close to absolute zero to +125°C.
Barium has also been used in medicine. Its sulfate salt is used in the diagnosis of gastric diseases. BaSO 4 is mixed with water and allowed to be swallowed by the patient. Barium sulfate is opaque to x-rays, and therefore those parts of the digestive tract, through which the "barium porridge" goes, remain dark on the screen. So the doctor gets an idea about the shape of the stomach and intestines, determines the place where an ulcer can occur.
The effect of barium on the human body
Routes of entry into the body.
The main way barium enters the human body is through food. Thus, some marine inhabitants are able to accumulate barium from the surrounding water, and in concentrations 7-100 (and for some marine plants up to 1000) times higher than its content in sea water. Some plants (soybeans and tomatoes, for example) are also able to accumulate barium from the soil by 2-20 times. However, in areas where the concentration of barium in the water is high, drinking water can also contribute to the total barium intake. The intake of barium from the air is negligible.
Health hazard.
In the course of scientific epidemiological studies conducted under the auspices of WHO, data on the relationship between mortality from cardiovascular diseases and the content of barium in drinking water have not been confirmed. In short-term studies in volunteers, there was no adverse effect on the cardiovascular system at barium concentrations up to 10 mg/l. True, in experiments on rats, when the latter consumed water even with a low content of barium, an increase in systolic blood pressure was observed. This indicates the potential danger of an increase in blood pressure in humans with prolonged use of water containing barium (USEPA has such data).
USEPA data also suggests that even a single drink of water that contains far more than the maximum barium content can lead to muscle weakness and abdominal pain. However, it is necessary to take into account that the barium standard established by the USEPA quality standard (2.0 mg/l) significantly exceeds the value recommended by WHO (0.7 mg/l). Russian sanitary standards set an even more stringent MPC value for barium in water - 0.1 mg/l. Water removal technologies: ion exchange, reverse osmosis, electrodialysis.
DEFINITION
Barium is located in the sixth period of the II group of the main (A) subgroup of the Periodic Table.
belongs to the family s-elements. Metal. Designation - Ba. Ordinal number - 56. Relative atomic mass - 137.34 a.m.u.
The electronic structure of the barium atom
The barium atom consists of a positively charged nucleus (+56), inside which there are 56 protons and 81 neutrons, and 56 electrons move around in six orbits.
Fig.1. Schematic structure of the barium atom.
The distribution of electrons in orbitals is as follows:
56Ba) 2) 8) 18) 18) 8) 2 ;
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 2 .
The outer energy level of the barium atom contains 2 electrons, which are valence. The energy diagram of the ground state takes the following form:
The barium atom is characterized by the presence of an excited state. Electrons 6 s- sublevels are unpaired and one of them occupies a vacant orbital 6 p- sublevel:
The presence of two unpaired electrons indicates that barium has an oxidation state of +2.
The valence electrons of a barium atom can be characterized by a set of four quantum numbers: n(chief quantum), l(orbital), m l(magnetic) and s(spin):
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sublevel |
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Examples of problem solving
EXAMPLE 1
DEFINITION
Barium is the fifty-sixth element of the Periodic Table. Designation - Ba from the Latin "barium". Located in the sixth period, group IIA. Refers to metals. The core charge is 56.
Barium occurs in nature mainly as sulfates and carbonates, forming the minerals barite BaSO 4 and witherite BaCO 3 . The content of barium in the earth's crust is 0.05% (wt.), which is much less than the content of calcium.
In the form of a simple substance, barium is a silvery-white metal (Fig. 1), which in air is covered with a yellowish film of products of interaction with the constituent parts of air. Barium is similar in hardness to lead. Density 3.76 g/cm 3 . Melting point 727 o C, boiling point 1640 o C. It has a body-centered crystal lattice.
Rice. 1. Barium. Appearance.
Atomic and molecular weight of barium
DEFINITION
Relative molecular weight of a substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.
Since barium exists in the free state in the form of monatomic Ba molecules, the values of its atomic and molecular masses coincide. They are equal to 137.327.
Isotopes of barium
It is known that barium can occur in nature in the form of seven stable isotopes 130Ba, 132Ba, 134Ba, 135Ba, 136Ba, 137Ba, and 138Ba, of which 137Ba is the most common (71.66%). Their mass numbers are 130, 132, 134, 135, 136, 137 and 138, respectively. The nucleus of the atom of the barium isotope 130 Ba contains fifty-six protons and seventy-four neutrons, and the remaining isotopes differ from it only in the number of neutrons.
There are artificial unstable barium isotopes with mass numbers from 114 to 153, as well as ten isomeric states of nuclei, among which the 133 Ba isotope with a half-life of 10.51 years is the longest-lived.
barium ions
At the outer energy level of the barium atom, there are two electrons that are valence:
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 2 .
As a result of the chemical interaction, barium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:
Ba 0 -2e → Ba 2+.
Barium molecule and atom
In the free state, barium exists in the form of monatomic Ba molecules. Here are some properties that characterize the barium atom and molecule:
Examples of problem solving
EXAMPLE 1
In 1808, Davy Humphrey obtained barium in the form of an amalgam by electrolysis of its compounds.
Receipt:
In nature, it forms the minerals barite BaSO 4 and witherite BaCO 3 . Obtained by aluminothermy or decomposition of azide:
3BaO+2Al=Al 2 O 3 +3Ba
Ba(N 3) 2 \u003d Ba + 3N 2
Physical properties:
A silvery white metal with a higher melting and boiling point and greater density than the alkali metals. Very soft. Tm.= 727°C.
Chemical properties:
Barium is the strongest reducing agent. In air, it quickly becomes covered with a film of oxide, peroxide and barium nitride, ignites when heated or when simply crushed. Vigorously interacts with halogens, when heated with hydrogen and sulfur.
Barium reacts vigorously with water and acids. Store, like alkali metals, in kerosene.
In compounds, it exhibits an oxidation state of +2.
The most important connections:
barium oxide. A solid that reacts vigorously with water to form hydroxide. Absorbs carbon dioxide, turning into carbonate. When heated to 500 ° C, it reacts with oxygen to form peroxide
barium peroxide BaO 2 , white substance, poorly soluble, oxidizing agent. Used in pyrotechnics, to produce hydrogen peroxide, bleach.
barium hydroxide Ba(OH) 2 , Ba(OH) 2 octahydrate *8H 2 O, colorless. crystal, alkali. Used to detect sulfate and carbonate ions, to purify vegetable and animal fats.
barium salts colorless crystals. substances. Soluble salts are highly toxic.
Chloride barium is obtained by the interaction of barium sulfate with coal and calcium chloride at 800°C - 1100°C. Reagent for sulfate ion. used in the leather industry.
Nitrate barium, barium nitrate, a component of green pyrotechnic compositions. When heated, it decomposes to form barium oxide.
Sulfate barium is practically insoluble in water and in acids, therefore it is slightly toxic. used for bleaching paper, for fluoroscopy, barite concrete filler (protection from radioactive radiation).
Application:
Barium metal is used as a component of a number of alloys, a deoxidizer in the production of copper and lead. Soluble barium salts are poisonous, MPC 0.5 mg/m 3 . See also:
S.I. Venetsky About rare and scattered. Metal stories.
