Tellurium
atomic number	52
Appearance of a simple substance
Atom properties
Atomic mass (molar mass)	127.6 a. e.m. (g/mol)
Atom radius	160 pm
Ionization energy (first electron)	869.0 (9.01) kJ/mol (eV)
Electronic configuration	4d 10 5s 2 5p 4
Chemical properties
covalent radius	136 pm
Ion radius	(+6e) 56 211 (-2e) pm
Electronegativity (according to Pauling)	2,1
Electrode potential	0
Oxidation states	+6, +4, +2
Thermodynamic properties of a simple substance
Density	6.24 /cm³
Molar heat capacity	25.8 J /( mol)
Thermal conductivity	14.3 W/( )
Melting temperature	722,7
Melting heat	17.91 kJ/mol
Boiling temperature	1 263
Heat of evaporation	49.8 kJ/mol
Molar volume	20.5 cm³/mol
The crystal lattice of a simple substance
Lattice structure	hexagonal
Lattice parameters	4,450
c/a ratio	1,330
Debye temperature	n/a

Tellurium- a chemical element with atomic number 52 in the periodic system and atomic mass 127.60; denoted by the symbol Te (Tellurium), belongs to the family of metalloids.

Story

It was first found in 1782 in the gold ores of Transylvania by mining inspector Franz Josef Müller (later Baron von Reichenstein), on the territory of Austria-Hungary. In 1798, Martin Heinrich Klaproth isolated tellurium and determined its most important properties.

origin of name

From Latin tellus, Genitive telluris, Land.

Being in nature

Native tellurium is also found together with selenium and sulfur (Japanese telluric sulfur contains 0.17% Te and 0.06% Se).

An important source of tellurium is copper and lead ores.

Receipt

The main source is sludge from the electrolytic refining of copper and lead. The sludge is roasted, the tellurium remains in the cinder, which is washed with hydrochloric acid. From the resulting hydrochloric acid solution, tellurium is isolated by passing sulfur dioxide gas SO 2 through it.

Sulfuric acid is added to separate selenium and tellurium. In this case, tellurium dioxide TeO 2 precipitates, and H 2 SeO 3 remains in solution.

Tellurium is reduced from oxide TeO 2 with coal.

To purify tellurium from sulfur and selenium, its ability is used under the action of a reducing agent (Al) in alkaline environment go into soluble disodium ditelluride Na 2 Te 2:

6Te + 2Al + 8NaOH = 3Na 2 Te 2 + 2Na.

To precipitate tellurium, air or oxygen is passed through the solution:

2Na 2 Te 2 + 2H 2 O + O 2 \u003d 4Te + 4NaOH.

To obtain high purity tellurium, it is chlorinated.

Te + 2Cl 2 \u003d TeCl 4.

The resulting tetrachloride is purified by distillation or rectification. The tetrachloride is then hydrolyzed with water:

TeCl 4 + 2H 2 O \u003d TeO 2 + 4HCl,

and the resulting TeO 2 is reduced with hydrogen:

TeO 2 + 4H 2 \u003d Te + 2H 2 O.

Prices

Tellurium is a rare element, and a significant demand for a small amount of production determines its high price (about 200-300 dollars per kg, depending on the purity), but, despite this, the range of areas for its application is constantly expanding.

Physicochemical characteristics

Tellurium is a brittle, silvery-white substance with a metallic sheen. Red-brown in thin layers, golden yellow in pairs.

Tellurium is less active chemically than sulfur. It dissolves in alkalis, lends itself to the action of nitric and sulfuric acids, but in dilute hydrochloric acid dissolves weakly. Metallic tellurium begins to react with water at 100°C, and in the form of a powder it is oxidized in air even at room temperature, forming oxide Te0 2 .

When heated in air, tellurium burns out, forming Te0 2 . This strong compound is less volatile than tellurium itself. Therefore, to purify tellurium from oxides, they are reduced by running hydrogen at 500-600 °C.

In the molten state, tellurium is rather inert; therefore, graphite and quartz are used as container materials for its melting.

Application

Alloys

Tellurium is used in the production of lead alloys with increased ductility and strength (used, for example, in the manufacture of cables). With the introduction of 0.05% tellurium, the loss of lead for dissolution under the influence of sulfuric acid is reduced by 10 times, and this is used in the production of lead-acid batteries. It is also important that tellurium-doped lead does not weaken during plastic deformation, and this makes it possible to carry out the technology of manufacturing current collectors of battery plates by cold die cutting and significantly increase the service life and specific characteristics of the battery.

Thermoelectric materials

Bismuth telluride single crystal

Its role is also great in the production of semiconductor materials and, in particular, tellurides of lead, bismuth, antimony, cesium. In the coming years, the production of lanthanide tellurides, their alloys and alloys with metal selenides for the production of thermoelectric generators with a very high efficiency (up to 72–78%) will become very important, which will make it possible to use them in the energy sector and in the automotive industry.

So, for example, a very high thermo-EMF was recently discovered in manganese telluride (500 μV / K) and in its combination with bismuth, antimony and lanthanide selenides, which allows not only to achieve a very high efficiency in thermogenerators, but also to implement already in one stage of semiconductor refrigerator cooling down to the region of cryogenic (temperature level of liquid nitrogen) temperatures and even lower. The best tellurium-based material for the production of semiconductor refrigerators in last years tellurium alloy appeared,

DEFINITION

Tellurium is the fifty-second element of the Periodic Table. Designation - Te from the Latin "tellurium". Located in the fifth period, VIA group. Belongs to the family of metalloids. The core charge is 52.

Tellurium is one of the rare elements: its content in the earth's crust is only 0.000001% (mass).

In its free form, tellurium is a metal-like crystalline substance of silver-white color (Fig. 1) with a hexagonal lattice. Brittle, easily rubbed into powder. Semiconductor. Density 6.25 g/cm 3 . Melting point 450 o C, boiling point 990 o C.

Existence in an amorphous state is known.

Rice. 1. Tellurium. Appearance.

Atomic and molecular weight of tellurium

The relative molecular mass 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 the relative atomic mass of an element (Ar r) is how many times the average mass of atoms chemical element more than 1/12 of the mass of a carbon atom.

Since tellurium exists in the free state in the form of monatomic Te molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 127.60.

Isotopes of tellurium

It is known that tellurium can occur in nature in the form of eight stable isotopes, two of which are radioactive (128 Te and 130 Te): 120 Te, 122 Te, 123 Te, 124 Te, 125 Te and 126 Te. Their mass numbers are 120, 122, 123, 124, 125, 126, 128 and 130 respectively. The nucleus of the tellurium isotope 120 Te contains fifty-two protons and sixty-eight neutrons, and the other isotopes differ from it only in the number of neutrons.

There are artificial unstable isotopes of tellurium with mass numbers from 105 to 142, as well as eighteen isomeric states of nuclei.

tellurium ions

At the outer energy level of the tellurium atom, there are six 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 4 .

As a result of chemical interaction, tellurium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion or accepts electrons from another atom, i.e. is their acceptor and turns into a negatively charged ion:

Te 0 -2e → Te +;

Te 0 -4e → Te 4+;

Te 0 -6e → Te 6+;

Te 0 +2e → Te 2- .

Tellurium molecule and atom

In the free state, tellurium exists in the form of monatomic Te molecules. Here are some properties that characterize the tellurium atom and molecule:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise	Calculate the mass fractions of the elements that make up tellurium dioxide if its molecular formula is TeO 2 .
Solution	The mass fraction of an element in the composition of any molecule is determined by the formula: ω (X) = n × Ar (X) / Mr (HX) × 100%.

Tellurium is a non-metal that has a metallic luster. Its color is silvery white. This element is very rare and diffuse. It was discovered by the mining inspector Franz Josef Müller in 1782. Tellurium is extracted from polymetallic ore. This substance is contained in the form of compounds in hydrothermal deposits of gold and others.

Thallium is a brittle material that acquires plastic properties during heating. The density value of this non-metal is 6.25 g/cm3. Tellium begins to melt when the temperature reaches 450 °C, and boils at 990 °C. The material has the properties of a diamagnet and at 18 °C the value of the specific magnetic susceptibility is -0.31.10-6.

Tellurium is a p-type semiconductor when the ambient conditions are normal or when the material is heated to a boil. When a non-metal is cooled, at a transition of about -100 ° C, it changes its properties and acquires n-type conductivity. The band gap in width is 0.34 eV. The transition temperature decreases depending on the purity of the substance.

Thallium is used as an alloying additive in the production of lead. It improves strength and chemical resistance. Lead-tellurium alloy is used in cable and chemical production. Tellurium is also alloyed with copper and steel. This improves their mechanical processing.

Tellurium is also used in glass production. Glass, due to such an impurity, acquires a brown color, and its refractive index increases. In the rubber industry, tellurium is used to carry out the rubber vulcanization process.

Significant demand for tellurium is facilitated by its semiconductor properties. It is considered both a typical and technologically advanced semiconductor. This substance is used in microelectronics. It produces a thin film that melts at lower temperatures than many metals.

In its pure form, tellurium, in the form of a semiconductor, is rarely used because of its limited supply in the bowels of the Earth. In most cases, it is used in the manufacture of transistors and devices that are designed to measure the intensity of gamma radiation.

Most often, not a pure non-metal is used in industry, but its compounds with metals, which are called tellurides. With their use, important parts of thermoelectric generators are produced.

Sale of non-ferrous metals in Moscow -.

Physical Properties
Tellurium exists in two modifications - crystalline and amorphous.
Crystalline tellurium is obtained by cooling tellurium vapor, and amorphous tellurium is obtained by reducing telluric acid with sulfur dioxide or another similar reagent:

Amorphous tellurium is a fine black powder that transforms into metallic tellurium when heated. The density of amorphous tellurium is 5.85-5.1 g/cm3.
For crystalline tellurium, two polymorphic varieties are known: α-Te and β-Te. The α→β transition occurs at 354°C. Crystalline tellurium has a white-silver color. Its density is 6.25 g/cm2. Hardness of crystalline tellurium 2.3; at ordinary temperatures it is brittle, easily broken into powder, and at higher temperatures it becomes so plastic that it can be pressed.
The melting point of tellurium is 438-452 ° C, and the boiling point is 1390 ° C. Tellurium is characterized by high vapor pressure, which, depending on temperature, is expressed by the following numbers:

Tellurium has a semiconductor nature of conductivity. The electrical resistance of polycrystalline tellurium at 0°C is 0.102 ohm*cm. With increasing temperature, the electrical resistivity of tellurium decreases:

In contrast to selenium, the electrical resistance of tellurium is not very sensitive to illumination. However, at low temperatures, the influence of lighting still affects; so, at -180 ° C, the electrical resistance of tellurium under the influence of illumination decreases by 70%.
Chemical properties
By their own chemical properties tellurium is similar to selenium, but has a more pronounced metallic character. At room temperature, compact tellurium is resistant to air and oxygen, but when heated, it oxidizes and burns with a blue flame with a green border, forming TeO2.
In the dispersed state and in the presence of moisture, tellurium is oxidized at ordinary temperature. Tellurium reacts with halogens at room temperature and forms chemically stronger halides (TeCl4; TeBr4) than selenium.
Tellurium does not combine directly with hydrogen under ordinary conditions, but when heated, it forms H2Te. When heated with many metals, tellurium forms tellurides: K2Te, Ag2Te, MgTe, Al2Te, etc.
Metallic tellurium reacts with water at 100-160°C, and freshly deposited (amorphous tellurium) at room temperature:

Te + 2H2O → TeO2 + 2H2.

Tellurium does not dissolve in CS2; dissolves very slowly in dilute HCl. In concentrated and dilute HNO3, tellurium is oxidized to form H2TeO3:

3Te + 4HNO3 + H2O = 3H2TeO3 + 4NO.

Tellurous acid is easily decomposed by sulfur dioxide with the release of tellurium:

H2TeO3 + 2SO2 + H2O → Te + 2H2SO4.

This reaction is used to obtain pure tellurium.
Tellurium is an almost constant companion of heavy non-ferrous metals in sulfides (iron and copper pyrite, lead luster), but it also occurs in the form of sylvanite, calaverite (Au, Ag)Te2 minerals, etc.
The main source of industrial tellurium is the waste processing of sulfide ores of copper and lead - dust, in which tellurium is present in the form of TeO2, obtained by roasting sulfide ores; as well as anode sludge obtained from the electrolytic refining of copper and lead.

17.03.2020

The creation of three-dimensional models today is relevant not only for animation, but also for technical purposes. Also often with the help of 3D modeling create interior models....

16.03.2020

Like the currently popular laminate flooring, modern parquet boards are quite easy to install. Lay it on the floor in a residential or technical room at the owner's...

16.03.2020

Registration on the portal is almost instant, you can create an account by entering your email address or use your own account in one of 20...

16.03.2020

No matter what gadget you have, you can play through the mobile version even from the oldest smartphone. To start the game, first of all, you have to register ....

16.03.2020

Among floor coverings, carpet is particularly interesting because it combines excellent insulating qualities, luxurious appearance and simple laying technology ....

16.03.2020

First you need to understand how industrial chillers work. Such a device resembles an ordinary refrigerator, a special pump pumps out liquid, cooling ...

15.03.2020

When planning repairs in your home, you first need to decide on the spectrum of action. Depending on the condition of the premises, area, will depend ...

14.03.2020

Owners can use drywall panels in various occasions. Especially often drywall is used for wall cladding ....

13.03.2020

V modern world it is difficult to imagine at least one high-profile festive event without the use of various pyrotechnics, which is represented, in simple terms, by colorful ...

13.03.2020

Paving slabs - used to create a hard surface of streets, decoration of pedestrian areas, roads, etc. Can be formed from various materials. They...