Among the fundamental sciences, chemistry is a field of human knowledge, the subject of study of which is the composition and characteristics of compounds, as well as their mutual transformations. One of the central questions of chemistry seems to be the following: what are the classes of substances? Special sections of science, such as inorganic and organic chemistry, examine the structural features and properties of compounds, and also reveal their practical significance.
What is a chemical substance, how to separate physical bodies and materials, what is a variety of substances - these and other questions will be addressed by us in this work.
The basic concept of chemistry
In every branch of human knowledge there are main ones - basic ideas and concepts on which the entire harmonious building of science is held. For mathematics, this is a number; in programming, it is data abstraction. In chemistry, the central place is occupied by matter - the form of matter, the structural units of which are atoms, molecules or ions. Combining in various combinations, they form a fantastic amount of all kinds of compounds having different chemical and physical properties of the substance.
Body and material
Based on the ideas about the state of aggregation, it is possible to determine what substance is in vivo: solid, liquid or gaseous. Organized in the form of crystal lattices, the structural units of chemical compounds form bodies. Substances whose particles (atoms, molecules or ions) are used by a person for certain needs and requirements are called material. So, cement, glass are artificial, and wood, sand, granite are natural materials.
What are pure substances
In chemistry, it is customary to distinguish between individual substances and mixtures. The latter in nature are several orders of magnitude more: sea water, blood, milk, rocks, the air we breathe are combinations of several compounds. You can get acquainted with pure substances in an ordinary school chemical laboratory. The reagents in it are distributed by degree of purity. So, in their especially pure species, the mass fraction of impurities does not exceed 0.0001%, but in high-tech industries such as microelectronics, robotics, space industry, such a degree of purity of the substance is insufficient.
For example, in semiconductors of 10 billion germanium atoms, no more than one impurity atom is allowed. To determine what a substance can be in terms of purity, modern chemical analysis techniques such as dispersion, solubilization, and colloid-chemical purification are used. After liberation from impurities, its chemical and physical properties of the substance become unique.
Language of chemistry
Being an exact science, operating with the concept of substances, chemistry uses the symbols of elements. They denote the qualitative and quantitative composition of molecules. So, the definition of the formulas of organic substances includes several possible options, for example, according to the general formula of the compound, its chemical properties, and combustion products.
Compounds are simple and complex
Continuing to look for the answer to the question of what substance happens, it is worth recalling one of the very first classifications studied in chemistry lessons - the separation of substances into simple and complex. The former contain atoms of only one chemical element. For example, oxygen is O 2 , sulfur is S, calcium is Ca. Others, also called compounds, consist of two atoms (binary substances H 2 O, CuS) and more chemical elements. For example, Na 2 CO 3 , Ba (OH) 2 . Simple substances, in turn, can be divided into metals and non-metals.
The main differences between them relate primarily to such characteristics as physical properties. The substances βmetalsβ are easily recognizable by their characteristic silvery sheen; they conduct heat and electric current very well, being conductors of the first kind. Non-metals are in the vast majority of cases dielectrics. They also conduct poorly and warmly. However, such a division of substances is conditional. Since between metals and non-metals it is difficult to draw a clear line. For example, germanium and graphite, widely used in electrical engineering, are non-metals.
Classes of Complex Substances
By systematizing knowledge explaining the chemical and physical properties of a substance, scientists divided inorganic and organic compounds into classes. Oxides, acids, salts and bases are studied in detail at chemistry classes in grades 7β9, and classes of organic substances (hydrocarbons, alcohols, aldehydes) are introduced into the program of grades 10β11.
Studying the classes of chemical compounds broadens the horizons of man, contributes to the formation of a real picture of the world, consisting of a huge variety of substances. So, when considering oxides, we learn not only about what happens in this class of material by its physical or chemical properties, but also get acquainted with the distribution of oxides in nature, and also determine their use in industry and everyday life. So, silicon oxide SiO 2 is part of sand, clay, granite, quartz, forming the Earth's lithosphere.
It is the most important raw material for the building materials industry, in the production of glass, cement, and ceramics. Iron oxides FeO, Fe 2 O 3 , Fe 3 O 4 are the main components of various types of iron ores that form deposits, for example, Kryvyi Rih, Kursk, Kachkanar. Both carbon oxides, especially carbon dioxide, and nitrogen oxides are widely represented in the atmosphere.
Salts - as the most extensive class of chemicals
Above, we examined the characteristics of oxides - binary compounds of oxygen with metals and non-metals. Now let us dwell on one of the largest classes of inorganic substances - salts. Their physical properties are explained by ionic crystal lattices. First of all, this is the ability to conduct electric current both in solutions and in melts, as well as high melting points. For example, in ordinary table salt it is equal to 801 Β° , in calcium silicate - 1544 Β° .
Salts take part in chemical processes with metals, alkalis, acids, and can also react with each other in solutions, entering into exchange reactions. Chemistry studies not only what a substance is in terms of its chemical and physical properties, but also pays great attention to its use in industry, agriculture or in everyday life. For example, sodium chloride, which we use to salt food, is a multi-ton raw material for the production of hydrochloric acid, soda, and chlorine. Potassium salts, such as chloride nitrate and sulfate, are mineral fertilizers that increase crop yields. Calcium carbonate, found in nature, is widely used in construction.
Properties of psychotropic substances
Natural or artificially synthesized compounds that affect both the parts of the central nervous system and the peripheral part are called psychoactive substances or antipsychotics. Focusing on the negative properties and their ability to cause dependence in humans, the term "drugs" is often used. To clarify the effect of psychotropic substances on the nervous system as a whole, we recall that compounds of this series can both increase the rate of transmission of excitation to the brain and spinal cord, and inhibit the work of the entire nervous system as a whole.
They are specific stimulants of various types of receptors: pain, auditory, visual, tactile. This can cause a person to have a special state of consciousness called altered. Natural psychoactive substances with a milder effect on the human body are well known. They are found in coffee beans, tea leaves, nutmeg fruits.
Nicotine, a standard, and ibotenic acid contained in the extract of poisonous mushrooms have a fairly pronounced toxic effect. Many painkillers used in anesthesia, such as morphine, codeine, ephedrine, are obtained from plants. They are also strong psychotropic compounds. The most severe, leading to the complete destruction of the human body are semisynthetic and synthetic antipsychotics: amphetamine, heroin, LSD. The use of all psychotropic drugs is strictly controlled, and the use is under the mandatory supervision of a physician.
Substances with unique properties
In the total mass of chemical compounds can be called those that have certain, special properties. For example, the most ductile metal in nature is considered to be gold, the sweetest substance is -L-Ξ±-aspartyl aminomalonic acid. It is 40 thousand times sweeter than edible sugar. But when asked what substance has the most fetid odor, there is no definite answer, since a number of mercury-sulfur compounds with the general formula RSH, called mercaptans, smell disgusting. They are secreted during the decay of dead organics, are present in the feces of birds and mammals, and even are part of the odorous glands of some animals, for example, skunk.
As you can see, the world of substances is huge and interesting, and chemistry is a science that allows us to study their structure, properties and significance in human life.