The chemical reactions are used for the direct receipt of electric current, as it takes place, for example, in storage batteries, so for the receipt of electric current by transformation of thermal energy appearing at chemical reaction in energy of steam and, in the end, into electric energy by means of the steam-turbine and electric generator mechanically related to her on thermal power-stations that work with the use of organic fuel. More ecologically cleaner technological processes of indirect receiving of electrical energy are utilized on the thermal sun power-stations at chemical transformations of salts absorbing infra-red radiation of the Sun or on the stations of electrolyze of water for receiving of hydrogen.

The chemical reactions take place under action of external factors: mechanical forces, ultrasonic waves, heating, electric current, electromagnetic radiations, and etc.

The chemical reactions are accompanied by the discharging or absorption of energy, appearance of charged particles (ions and electrons), appearance of electromagnetic radiation of a different spectral range.

The physical and chemical Nature of substance is fully determined by its chemical and crystal-chemical composition or, in other words, by the aggregate of power, geometrical and quantum-chemical characteristics: energy, length and spatial orientation (angle) of bond.

Chemical bond is an interaction of atoms in a molecule that is conditioned by ceiling of electronic clouds of linked particles. These chemical bonds are accompanied by the reduction of complete energy of the system (molecule, crystal).

Chemical bonds arise up as a result of electrons transfer from one atom to other (Ron effect), or as a result of sharing of electrons by pair or group of atoms. The forces that stipulate chemical bonds have coulomb nature, but it is impossible to describe fully the chemical bonds within the framework of electrostatics, so as electrostatics takes into account the quantum phenomena.

The basic types of chemical bonds are ionic (electrovalent) bond and covalent (homopolar) bond.

The ionic chemical bond appears at transfer of lone valent electrons from one atom to other and is stabilized by electrostatic attractive interaction between the appearing positive and negative ions.

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds. In short, attraction-to-repulsion stability that is crated between atoms when they share electrons is known as covalent bonding. Such bonds lead to stable molecules if they share electrons in such a way as to create a noble gas configuration for each atom. In the polar covalent bonds the sharing of the electron pair is unequal, with the electrons spending more time around the more nonmetallic atom. In such a bond there is a charge separation with one atom being slightly more positive and the other more negative, i.e., the bond will produce a dipole moment. The ability of an atom to attract electrons in the presence of another atom is a measurable property called electronegativity.

Energy of bonds is usually found within 200…1000 kJ/mole.

Hydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. The nitrogen and oxygen which makes up the bulk of the atmosphere also exhibits covalent bonding in forming diatomic molecules.

The energy of bond is a measure of its solidity. Its value is determined by the work necessary for the break of bond or by the winning in energy at creation of substance from separate atoms. For example, the energy of chemical bond in the molecule of hydrogen N-N is equal 435 kJ/mol. It means that at formation of one mole of gaseous molecular hydrogen from the separate isolated atoms of hydrogen about 435 kJ of energy is discharged. The same amount of energy is expended on a disintegration of 1 mole of hydrogen to the atomic state (energy of atomization of a molecule). The mean values of energy of bond of atoms of methane and water are accordingly 412 kJ and 462 kJ. To determine the energy of single bond it is necessary the mean value of energy to divide on an Avogadro’s constant. The energy of breakdown (energy of dissociation) can substantially differ from the mean value. The concept of energy of bonding is universal for molecules and condensed state of substance.

At creation of the crystal from the molecules of gases there is a winning in energy, which is explicated by the well-organized disposing of atoms in a crystalline grating.

To define the value of winning of energy, it is necessary to compare the energies of break of bond in a crystal and gaseous molecule. The break of bond in a gaseous molecule can be executed hemiletically with formation of neutral atoms, and heterolytically with formation of ions. For the molecule of culinary salt it is necessary to spend 414 kJ/mole of energy in first case and 548 kJ/mole - in other case. In other words, the energy of break grows on 134 kJ/mole.

The break of bond in a crystal can also be executed homiletically or heterolytically (phenomenon of sublimation). In the first case it is necessary to spend 644 kJ/mole of energy, in other case - 778 kJ/mole.  The energy of bond in a crystalline grating is on 230 kJ/mole greater than that is for a gaseous molecule. The energy of break of bond at homiletical or heterolytical methods in a molecule and crystal differs on the same value - 134 kJ/mole. She is equal to a difference between the energy of ionization of sodium (- 495,3 kJ/mole) and energy of bringing together to the electron for to the chlorine (-361,5 kJ/mole) and determines the energy necessary for creation of gaseous ions of sodium and chlorine from the isolated atoms. There are three basic conformities to the law:

·     energy of bond diminishes at the increase of atomic number of element;

·     energy of bond in a crystal is always greater than an energy of bond in the proper molecule;

·     energy of dissociation at a homiletical mechanism is below for molecules and for the crystal, than the energy at heterolytical mechanism.  

In the total at heating these bonds disintegrate onto the atoms, and not onto the ions.

The other fundamental value of bond is a length– the distance between the centers of nucleus of atoms in a molecule and crystal, when the attractive forces are balanced by the repulsive forces and the sum energy of the system is minimal. The length of bond is determined experimentally by means of spectral data. The calculation methods are approximate, so as the real bond in the compounds is determined by the aggregate of ionic, covalent and metallic bonds. 

 The length of bond is multiplied with the increase of the atomic number of element.

The atoms in the molecules and crystals hesitate round a position of equilibrium. The frequency of vibrations is characteristic for every bond and does not rely on a temperature. In the same time the amplitude of vibrations is determined by the temperature of substance. The characteristic frequencies of vibrations lie in an interval 10(14) Hz (for light atoms) …10(12) Hz (for heavy atoms). These parameters correspond to the wavelengths of 1…10 µm. The oscillations of the linked atoms that take place in the direction of bond are named the valent oscillation. Except of these oscillations the deformation vibrations are possible, as a result of which the angles between bonds are changed. The valent vibrations can be symmetric and asymmetric.

To change the length of the system of two linked atoms on the value of 1 nm it is necessary to act by the force equivalent to the value of power constant k. For the system of H-Br the value is equal k = 3,8х10-7 N/nm.

By Vasil Sidorov on October 19, 2009 in Queltanews.com

sidorovvasil@gmail.com