Chemistry is the science of substances and their transformations, as a result of which other substances with new properties are obtained from some substances.
From the point of view of the atomic-molecular theory of the structure of a substance, chemical transformations (reactions) are explained by the rearrangement of atoms in the molecules of the reacting substances, as a result of which others arise from one molecule with a different composition and internal structure.
Chemistry is divided into a number of major sections, representing independent chemical disciplines, interconnected with each other. Inorganic chemistry and organic chemistry are their subject of study of the composition and properties of inorganic and organic substances, respectively. The latter include substances containing a chemical element carbon . Many of these substances - proteins (see), fats (see), nucleic acids (see), carbohydrates (see) - are an integral part of organisms. The chemistry of biologically important substances and their transformations in organisms is dealt with by biological chemistry. (see Biochemistry). Physical chemistry is concerned with the study of the interconnection of physical and chemical phenomena; analytical chemistry - methods for determining the qualitative and quantitative composition of substances and their mixtures. The subject of hydrochemistry is the study of the chemical composition of natural waters, and the subject of histochemistry is the study of the localization of chemicals and biochemical reactions in cells and tissues. Theories of chemistry and chemical research methods are widely used in biology, physiology and medicine.
See also Nuclear Chemistry.