STRUCTURE OF SUBSTANCE

From Big Medical Encyclopedia

All known substances are constructed of the protons, neutrons and electrons representing elementary particles. Protons and neutrons form an atomic nucleus (see. atomic nucleus ). Atom (see) is the stable electroneutral system consisting of electrons and a kernel. Interaction between atoms leads to education molecules (see), stability the cut is explained by emergence of chemical communication between atoms. Depending on number of atoms in a molecule and its structures distinguish simple molecules (diatomic, triatomic, polyatomic), complicated molecules (consist of several simple atomic groups), polymeric molecules (consist of a large number of surface elements — monomer units). If intermolecular (interatomic) interactions are small and density of substance is small, and the sizes of molecules are comparable with intermolecular (interatomic) distances, then substance exists in gaseousness (see Gaza). In case of full ionization of atoms of gas there is a condition of substance with special characteristics called by plasma. At the big density intermolecular (interatomic) interactions become essential and substance passes into the condensed state. In this state the structure of substance is defined by a ratio of energy of thermal and intermolecular (interatomic) interface, and also degree of uniformity of substance.

So, substances, homogeneous on chemical structure, between molecules to-rykh there is an interaction in a certain interval of temperatures (from temperature of absolute zero up to the temperature of melting), can exist in the crystalline state (see Crystals) which is characterized by high degree of orderliness of a spatial relationship of molecules (atoms). Ionic and covalent crystals during the melting turn into liquid state (see. Liquids ), molecular crystals depending on properties of the molecules forming them — either in liquid, or in a liquid crystal state (see. Liquid crystals ).

S.'s studying is conducted in various sections of physics and chemistry century (e.g., physics of the condensed state, physics of plasma, quantum chemistry, the theory of solutions, nuclear and atomic physics, physical and colloid chemistry, etc.). Form the general theoretical basis of studying of S. of century quantum theory (see) and statistical mechanics. On their basis can be theoretically calculated as physical. - chemical properties of individual molecules, and properties of the macroscopic objects formed by these molecules (see. Polarization , Spectral analysis ).

Experimental methods of a research C. of century can be divided into methods of studying of structure of substance and into methods of studying of properties of molecules. Are among methods of the first group optical microscopy, including ultra-violet, infrared, luminescent, fazovokontrastny, interferential, polarizing (see. Microscopic methods of a research), and also submicroscopy (see), the X-ray crystallographic analysis (see), an elektronografiya, a neytronografiya, etc.

Methods of the second group conditionally divide on spectroscopic (see. Spectroscopy ), polarizing and optical (see. Optical techniques of a research), kinetic (connected with studying of the phenomena of transfer) and methods of studying of the superficial phenomena. Spectral techniques include methods of absorption optical spectroscopy (in the visible, infrared and ultra-violet ranges), methods of laser and nonlinear spectroscopy, radiospectroscopy, including an electronic paramagnetic resonance (see) and nuclear magnetic resonance (see), and also messbauerovsky, X-ray, photoelectronic spectroscopy and gamma spectroscopy. Polarization optical methods are based on studying of the phenomenon of double refraction (see). Methods of measurement of diffusion (see), viscosity (see), heat conductivity, osmotic properties, electrophysical properties (conductivity, photoelectric, galvanomagnigny and thermoelectric effects, electrolytic and membrane potentials, a potentsiometriya) belong to kinetic methods. Surface characteristics study by means of methods of measurement of adhesion, cohesion, adsorption, surface intention. Serves one of methods of definition of atomic composition of substance mass pektrometriya (see).

The century given about S. form theoretical base for studying of molecular structure biol. systems, molecular bases biol. processes; they are widely used in molecular biology (see), molecular genetics (see), biochemistry (see), bio-energetics (see) and molecular biophysics (see), representing a unified general basis of physical and chemical biology. So, at creation of models of structure and function biol. membranes (see Membranes biological) use representations of physics of a liquid crystal state, and for an explanation of dynamic properties biol. macromolecules, their interaction, processes intra-and intermolecular transfer of energy and a charge — representation of solid state physics. On the basis of achievements in the field of S.'s studying such directions of researches as quantum pharmacology, quantum genetics, the quantum theory of carcinogenesis, the quantum theory of muscle work form century, to-rye in general can be integrated within quantum biology.



Bibliography: Davydov A. S. Biology and quantum mechanics, Kiev, 1979; JI hell and to I. Quantum biochemistry for chemists and biologists, the lane with iy., M., 1975; X e d in and of the Item. Applied quantum chemistry, the lane with it., M., 1977.


M. M. Gorshkov.

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