Modern chemistry is studying transformations in which molecules of one compound exchange atoms with molecules of other compounds, break up into molecules with fewer atoms, and also enter into chemical reactions, as a result of which new substances are formed. Atoms undergo some changes in chemical processes only in external electronic shells, the atomic nucleus and internal electronic shells do not change.
In determining the subject matter of chemistry is often emphasized that it is, above all, the compounds of atoms and the transformation of these compounds, occurring with the breakage of one and the formation of other interatomic bonds.
Different chemical sciences differ in the fact that they study either different classes of compounds (such a difference is the basis for the distinction between organic and inorganic chemistry), or different types of reactions (radiochemistry, radiation chemistry, catalytic synthesis, polymer chemistry), or the use of different research methods (physical chemistry in its various directions). The distinction between one chemical discipline and another, which in the present conditions preserves historically established dividing lines, is relative.
Until the end of the XIX, century chemistry was basically a unified science. Its internal division into organic and inorganic did not break this unity. But the numerous discoveries that followed, both in chemistry itself and in biology, gave rise to rapid differentiation of physics.
Modern chemical science, relying on solid theoretical foundations, is continuously developing in width and depth. In particular, new, qualitatively different discrete chemical particles are discovered and studied. Thus, in the first half of the XIX century, during the study of electrolysis, ions were discovered - special particles formed from atoms and molecules, but electrically charged. Ions are structural units of many crystals, metal lattices, they exist in the atmosphere, in solutions, etc.
In the early 20th century, chemists discovered radicals as one of the active forms of a chemical substance. They are formed from molecules by splitting off individual atoms or groups and contain atoms of elements in an unusual for them valence state, which is associated with the presence of single (unpaired) electrons, explaining their exceptional chemical activity.
Macromolecules also belong to special forms of chemical substance. They consist of hundreds and thousands of atoms and as a result, acquire qualitatively new properties in contrast to the usual molecule.
The process of deep internal differentiation, which is characteristic of the newest chemistry, as well as for the whole science of the XX century, is largely connected with the discovery of this qualitative variety of chemical substances. Their structure, transformations, and properties have become the subject of study of special branches of chemistry: electrochemistry, chemical kinetics, polymer chemistry, the chemistry of complex compounds, colloid chemistry, and chemistry of high-molecular compounds.
By the beginning of the 20th century, general and inorganic chemistry, as well as organic chemistry, were clearly distinguished within chemistry itself. The subject of the study of general and closely related inorganic chemistry was chemical elements, the simplest inorganic compounds they form and their general laws (first of all, the Periodic Law of D.I. Mendeleev).
A strong impetus for the development of inorganic chemistry was given by the penetration into the depths of the atom and the study of nuclear processes. The search for the elements most suitable for decomposition in nuclear reactors contributed to the study of poorly studied elements and the synthesis of new ones utilizing nuclear reactions. The study of their properties, as well as physicochemical bases and chemical properties of radioactive isotopes, methods of their isolation and concentration was carried out by radiochemistry, which appeared in the second quarter of the XX century.
Organic chemistry was finally formed into an independent science in the second half of the 19th century. The determining factor for all organic compounds is the peculiarities of the valence state of carbon - the ability of its atoms to bind together as a single and double, triple bond in long linear and branched chains. Due to the infinite variety of forms of carbon atomic bonding, the presence of isomerism and homologous series in almost all classes of organic compounds, the possibility of obtaining these compounds is virtually unlimited.
In the XX century, many sections of organic chemistry began to gradually turn into large, relatively independent branches with their own objects of study. Thus, the chemistry of organ element compounds, the chemistry of polymers, the chemistry of high-molecular compounds, the chemistry of antibiotics, dyes, fragrant compounds, pharmacochemistry, etc. appeared.
At the end of the 20th century, the chemistry of organometallic compounds i.e. compounds containing one (or more) direct connection between metal and carbon, appeared. Until the end of the century, organic compounds of mercury, cadmium, zinc, and lead were discovered
The most important features of modern chemistry include
- Differentiation of the main branches of chemistry into separate, largely independent scientific disciplines. This differentiation is based on the distinction between objects and methods of research. Thus, physical chemistry is divided into a significant number of rapidly developing disciplines.
- Integration of chemistry with other sciences. As a result of this process, biochemistry, bioorganic chemistry, and molecular biology have emerged that study chemical processes in living organisms. On the boundary between chemistry and geology, geochemistry is developing, investigating the patterns of behavior of chemical elements in the Earth's crust. The tasks of cosmochemistry are to study the peculiarities of the elemental composition of space bodies (planets and meteorites) and various compounds contained in these objects.
- The appearance of new, mainly Physico-chemical, physical methods of research (structural X-ray analysis, mass spectroscopy, radio spectroscopy, etc.)