Chalcogenes - a group of elements to which sulfur belongs. Its chemical sign is S - the first letter of the Latin name Sulfur. The composition of a simple substance is recorded using this symbol without an index. Consider the main points regarding the structure, properties, preparation and application of this element. Sulfur characteristics will be presented as detailed as possible.
Common signs and differences of chalcogenes
Sulfur belongs to a subgroup of oxygen. This is the 16th group in the modern long-period form of the image of the periodic system (PS). An outdated version of the number and index is VIA. Names of the chemical elements of the group, chemical signs:
- oxygen (O);
- sulfur (S);
- selenium (Se);
- tellurium (Te);
- polonium (Po).
The external electronic shell of the above elements is arranged identically. In total, it contains 6 valence electrons, which can participate in the formation of chemical bonds with other atoms. Hydrogen compounds correspond to the composition of H 2 R, for example, H 2 S - hydrogen sulfide. Names of chemical elements that form two types of compounds with oxygen: sulfur, selenium and tellurium. The general formulas of the oxides of these elements are RO 2 , RO 3 .
Chalcogenes correspond to simple substances, which differ significantly in physical properties. The most common of all chalcogenes in the earth's crust are oxygen and sulfur. The first element forms two gases, the second - solids. Polonium - a radioactive element - is rarely found in the earth's crust. In the group from oxygen to polonium, non-metallic properties decrease and metallic properties increase. For example, sulfur is a typical non-metal, while tellurium has a metallic luster and electrical conductivity.
Element No. 16 of the periodic system D.I. Mendeleev
The relative atomic mass of sulfur is 32.064. Of the natural isotopes, 32 S is the most common (more than 95% by weight). Nuclides with an atomic mass of 33, 34, and 36 are found in smaller amounts. Characteristics of sulfur by position in the PS and atomic structure:
- serial number - 16;
- the atomic nucleus charge is +16;
- atom radius - 0.104 nm;
- ionization energy —10.36 eV;
- relative electronegativity - 2.6;
- the degree of oxidation in the compounds is +6, +4, +2, -2;
- valencies - II (-), II (+), IV (+), VI (+).
Sulfur is in the third period; The electrons in the atom are located at three energy levels: on the first - 2, on the second - 8, on the third - 6. Valence are all external electrons. When interacting with more electronegative elements, sulfur gives off 4 or 6 electrons, acquiring typical oxidation states +6, +4. In reactions with hydrogen and metals, an atom attracts the missing 2 electrons to fill an octet and achieve a stable state. The oxidation state in this case decreases to -2.
Physical properties of rhombic and monoclinic allotropic forms
Under ordinary conditions, sulfur atoms join together at an angle in stable chains. They can be closed in rings, which suggests the existence of cyclic sulfur molecules. Their composition is reflected by the formulas S 6 and S 8 .
The sulfur characteristics should be supplemented by a description of the differences between allotropic modifications with different physical properties.
Rhombic, or α-sulfur is the most stable crystalline form. These are bright yellow crystals composed of S 8 molecules. The density of rhombic sulfur is 2.07 g / cm3. Light yellow monoclinic crystals are formed by β-sulfur with a density of 1.96 g / cm3. The boiling point reaches 444.5 ° C.
Amorphous Sulfur Production
What is the color of sulfur in a plastic state? This is a dark brown mass, completely unlike yellow powder or crystals. To obtain it, you need to melt the rhombic or monoclinic sulfur. At temperatures above 110 ° C, a liquid forms, with further heating it darkens, at 200 ° C it becomes thick and viscous. If molten sulfur is quickly poured into cold water, it will solidify with the formation of zigzag chains, the composition of which is reflected by the formula S n .
Sulfur Solubility
Some modifications of the substance are dissolved in carbon disulfide, benzene, toluene and liquid ammonia. If organic solutions are slowly cooled, acicular crystals of monoclinic sulfur are formed. When liquids evaporate, transparent lemon-yellow crystals of rhombic sulfur are released. They are fragile, they can easily be ground into powder. Sulfur is not soluble in water. The crystals sink to the bottom of the vessel, and the powder can float on the surface (not wetted).
Chemical properties
In reactions typical non-metallic properties of element No. 16 are manifested:
- sulfur oxidizes metals and hydrogen, is reduced to an ion S 2- ;
- during combustion in air and oxygen, sulfur dioxide and trioxide are formed, which are acid anhydrides;
- in reaction with another more electronegative element - fluorine - sulfur also loses its electrons (oxidizes).
Free sulfur in nature
In terms of prevalence in the earth's crust, sulfur is in 15th place among chemical elements. The average content of S atoms in rocks and minerals is 0.05% of the mass of the earth's crust.
What color is sulfur in nature (native)? This is a light yellow powder with a characteristic odor or yellow crystals with a glass luster. Deposit in the form of placer, crystalline layers of sulfur are found in areas of ancient and modern volcanism: in Italy, Poland, Central Asia, Japan, Mexico, the USA. Often during mining, beautiful Druze and giant single crystals are found.
Hydrogen sulfide and oxides in nature
In areas of volcanism, gaseous sulfur compounds come to the surface. The Black Sea at a depth of over 200 m is lifeless due to the release of hydrogen sulfide H 2 S. The formula of bivalent sulfur oxide is SO 2 , trivalent - SO 3 . The listed gaseous compounds are present in some oil, gas, and natural water deposits. Sulfur is a part of coal. It is necessary for the construction of many organic compounds. When chicken egg proteins rot, hydrogen sulfide is released, so it is often said that this gas has the smell of rotten eggs. Sulfur is a nutrient, it is necessary for the growth and development of man, animals and plants.
The value of natural sulfides and sulfates
The sulfur characteristic will be incomplete, if not to say that the element is found not only in the form of a simple substance and oxides. The most common natural compounds are salts of hydrogen sulfide and sulfuric acid. Sulfides of copper, iron, zinc, mercury, lead are found in the minerals chalcopyrite, pyrite, sphalerite, cinnabar and galena. Sulphates include sodium, calcium, barium, and magnesium salts, which form minerals and rocks in the nature (mirabilite, gypsum, selenite, barite, kizerite, epsomite). All these compounds are used in various sectors of the economy, are used as raw materials for industrial processing, fertilizers, building materials. Great medical value of some crystalline hydrates.
Getting
The yellow substance in the free state is found in nature at different depths. If necessary, sulfur is smelted from rocks, not lifting them to the surface, but pumping superheated water vapor and compressed air to a depth . Another method involves sublimation from crushed rocks in special furnaces. Other methods include carbon disulfide dissolution or flotation.
Industrial needs for sulfur are great, therefore, its compounds are used to obtain the elementary substance. In hydrogen sulfide and sulfides, sulfur is in reduced form. The oxidation state of an element is -2. Sulfur is oxidized, increasing this value to 0. For example, according to the Leblanc method, sodium sulfate is reduced with carbon to sulfide. Then calcium sulfide is obtained from it, it is treated with carbon dioxide and water vapor. The resulting hydrogen sulfide is oxidized with atmospheric oxygen in the presence of a catalyst: 2H 2 S + O 2 = 2H 2 O + 2S. The determination of sulfur obtained in different ways sometimes gives low purity values. Refining or purification is carried out by distillation, rectification, treatment with mixtures of acids.
The use of sulfur in modern industry
Granular sulfur goes to various production needs:
- Production of sulfuric acid in the chemical industry.
- Production of sulfites and sulfates.
- The release of drugs for plant nutrition, the fight against diseases and pests of crops.
- Sulfur-containing ores are processed at mining and chemical plants to produce non-ferrous metals. Related production is sulfuric acid.
- Introduction to the composition of some grades of steel to give special properties.
- Thanks to the vulcanization of rubber , rubber is obtained.
- Production of matches, pyrotechnics, explosives.
- Use for the preparation of paints, pigments, artificial fibers.
- Tissue whitening.
Toxicity of sulfur and its compounds
Dusty particles with an unpleasant odor irritate the mucous membranes of the nasal cavity and respiratory tract, eyes, and skin. But the toxicity of elemental sulfur is not considered particularly high. Inhalation of hydrogen sulfide and dioxide can cause severe poisoning.
If during the firing of sulfur-containing ores at metallurgical plants, the exhaust gases are not captured, then they enter the atmosphere. Combining with drops and water vapor, the oxides of sulfur and nitrogen give rise to the so-called acid rain.
Sulfur and its compounds in agriculture
Plants absorb sulfate ions along with the soil solution. A decrease in sulfur content slows down the metabolism of amino acids and proteins in green cells. Therefore, sulfates are used for fertilizing crops.
For the disinfection of poultry houses, cellars, vegetable stores, a simple substance is burned or treated with modern sulfur-containing preparations. Sulfur oxide has antimicrobial properties, which has long been used in the production of wines, in the storage of vegetables and fruits. Sulfur preparations are used as pesticides for the control of diseases and pests of crops (powdery mildew and spider mites).
Medical use
Great importance was given to the study of the healing properties of yellow powder by the great healers of antiquity Avicenna and Paracelsus. Later it was found that a person who does not receive enough sulfur with food weakens, experiences health problems (these include itching and peeling of the skin, weakening of hair and nails). The fact is that without sulfur, the synthesis of amino acids, keratin, and biochemical processes in the body is disrupted.
Medical sulfur is included in the composition of ointments for the treatment of skin diseases: acne, eczema, psoriasis, allergies, seborrhea. Sulfur baths can relieve pain in rheumatism and gout. For better absorption by the body, water-soluble sulfur-containing preparations have been created. This is not a yellow powder, but a white crystalline substance. When used externally, this compound is incorporated into a cosmetic skin care product.
Gypsum has long been used in the immobilization of injured parts of the human body. Glauber's salt is prescribed as a laxative. Magnesia lowers blood pressure, which is used in the treatment of hypertension.
Sulfur in history
Even in ancient times, non-metallic yellow substance attracted the attention of man. But only in 1789 did the great chemist Lavoisier establish that the powder and crystals found in nature are composed of sulfur atoms. It was believed that the unpleasant odor arising from its burning scares away all evil spirits. The formula for sulfur oxide produced by combustion is SO 2 (dioxide). It is a toxic gas; inhalation is hazardous to health. Scientists explain several cases of mass extinction of people by entire villages on the coasts in the lowlands by the release of hydrogen sulfide or sulfur dioxide from the earth or water.
The invention of black gunpowder increased military interest in yellow crystals. Many battles were won thanks to the ability of the masters to combine sulfur with other substances in the manufacturing process of explosives. The most important compound - sulfuric acid - also learned to use a very long time. In the Middle Ages, this substance was called vitriol, and salts - vitriol. Copper sulfate CuSO 4 and iron sulfate FeSO 4 still have not lost their importance in industry and agriculture.