Ions and electrons. What are ions - a large medical encyclopedia. Chemical and physical properties

IONS (from the Greek. ion-going, wandering), atoms or chem. radicals carrying electric charges.-Istoria. As Faraday established for the first time, the conduction of electric current in solutions is associated with the movement of material particles that carry electric charges. A substance conducting an electric current - an electrolyte - decomposes into positively and negatively charged radicals, which are attracted by the action of electrostatic forces - the first to the cathode, the second to the anode. Faraday called such atoms or atomic groups (radicals) moving in solution and carrying electric charges ions: positively charged ions (moving towards the cathode) are cations, negative ones are anions. Unlike metal conductors, in which the distribution of electricity is not associated with the transfer and decomposition of matter, electrolyte solutions are called "conductors of the second kind." Faraday believed that only when a galvanic current is passed through the solution by the action of external electric forces, some of the electrolyte molecules are split into ions. The founder of the theory of electrolytic dissociation Arrhenius (Sv. Arrhenius), on the basis of vast experimental material, showed that a certain part of the electrolyte molecules is constantly dissociated into ions, regardless of whether the solution is currently conducting electricity. current. This was the beginning of the concept of the existence of free ions in solution as a stable state of matter. The degree of dissociation of an electrolyte, indicating which part of its molecules breaks up into I., is the main value in the teachings of Arrhenius that characterizes the participation of an electrolyte in a number of processes occurring in solutions. The modern theory of electrolytic dissociation and the activity of electrolytes was further developed in the studies of Bjerrum, Debye, and Gyukkel (Bjerrum, Debye, Htickel) and others. electrostatic interactions. The influence of these electrostatic interionic forces made it possible to explain many features of electrolyte solutions that did not fit into the framework of the classical Arrhenius theory. The creators of the ionic theory did not have a concrete idea of ​​the structure of radiation and of the method of combining matter and charge in it. In the same way, the main property of I., his amazing chem. inertness compared to the corresponding neutral atom. So, sodium atoms react violently with water, decomposing it with the release of hydrogen; iodine gives a specific reaction with starch, etc. e. But a solution of NaJ, consisting of free I. sodium and iodine, does not reveal any of these reactions until the charge of its ions is destroyed (as is the case with electrolysis). These most important properties of ions could only be understood in the light of modern structural theory. atom(cm.). Ion structure. According to the theory of Rutherford and Bohr (Rutherford, Bohr), matter is built from positive and negative electric charges. The elementary positive charge is the proton, which has the mass of a hydrogen atom, while the free negative charge, the electron, has 1,800 times less mass. The atom is built from an extremely small central positive nucleus, around which, like the planets moving around the sun, electrons revolve in a complex system of orbits. The atomic nucleus consists of protons or a combination of protons with a smaller number of electrons. The number of positive charges in the nucleus (or the excess of positive charges over the number of intranuclear electrons) is equal to the number of electrons in the shell surrounding the nucleus. I This number increases uniformly by one as we move from H (the charge of the atomic nucleus 1) to each subsequent element, according to the order that they occupy in periodic system (cm.). The electron shell surrounding the atomic nucleus consists of a number of successive layers, each of which contains a certain number of electrons. The outer layer can contain up to 8 electrons (the exception is the first electron layer, directly adjacent to the nucleus; the largest number of electrons in it is two). If there is a total "number of electrons in the outer layer, the atom acquires a complete structure and an unusually stable electronic configuration, and, accordingly, complete chemical inertness. These are atoms of noble gases, the chemical valence of which is zero. The transition to the next element of the periodic system (alkali metal ) means the addition of a new electron located on a new outer electron layer. The continued construction of the atom in subsequent elements ends only with a new stable combination of electrons of the next noble gas. According to Kossel (Kos-sel), the electronic configuration of a noble gas (with an eight-electron outer layer) represents a stable state , an atom of each element strives for a transition in a swarm. This transition is accomplished by losing or capturing the missing electrons. It occurs most easily in alkali metals and halides, of which it is enough for the first to lose, and the second to acquire one electron, to become like the nearest noble at the gas Similarly, in other elements, the number of electrons that they must lose or gain in order to expose or complete the outer eight-electron layer is equal to the maximum number of positive or negative valences they detect. In this case, however, the electrical neutrality of the atom, the initial equality of its positive and negative charges, is violated. An atom is transformed into a positive or negative I., and the charge of the latter corresponds in sign and magnitude to the valence of the corresponding atom or radical. The electrostatic attraction of oppositely charged I. connects them into a heteropolar molecule. In media having, like water, a high dielectric constant, the effect of electrostatic forces is weakened, and the heteropolar molecule again decomposes into its ions. Thus, each I. has the electronic structure not of the atom from which it originated, but of the nearest noble gas. It differs from the latter only in its charge (and in the ease with which, losing it, it again turns into the original element). This structure of the ion fully explains its most important property, noted by Arrhenius: amazing chemical inertness, which is a feature of free I. in contrast to I from the atom into which it turns when it loses its charge. Approaching the structure of a stable, chemically inert noble gas, ions differ from each other only in the magnitude and distribution of their electric charge, i.e., in purely physical properties. Because of this, they represent an object primarily of physical methods of research, an object of physical chemistry. Hydration and sizes I. The most important physical. I.'s properties are its dimensions and the magnitude of the electric. charge. The charge density also depends on the ratio of these quantities, the greater, the smaller the size of the particle carrying a given charge. However, if we wanted to form an idea of ​​their relative magnitude from the structure of the I., from their electronic model, we would make a serious mistake. Ions Li -, Na", K", etc. in water consist not only of the indicated substances, but also of a significant amount of water molecules closely associated with them and moving together. The water molecule, like the molecule of many other substances, is a dipole, at opposite ends of which opposite charges are concentrated (on one pole there is a negative charge of oxygen, on the other a positive charge of hydrogen). Such dipoles are oriented around a charged particle, being attracted to it by their opposite pole. As a result, each ion in an aqueous solution is hydrated, surrounded by a shell built from water molecules. The farther from the center, the less accurate this orientation becomes, gradually turning into a chaotic distribution of free water molecules. That. I.'s hydration is caused by their electric charge (Born). As a result of hydration, the dimensions of I., as an independently moving particle, can increase significantly, and often ions that have smaller atomic dimensions, such as eg. Li, reach an even greater value than I., formed from larger atoms, like K. This implies another, no less paradoxical conclusion, which is of great importance for understanding certain problems of cell permeability: when a molecule breaks down into ions, the latter (together with the surrounding water lining!) can have larger dimensions than the molecule itself, which dissociates them. Mobility I. Certain actions are characteristic of I. along with neutral molecules. This is the osmotic pressure, which depends only on the kinetic energy of the dissolved particles. Others are due to the electric charge that makes the difference between I. and a neutral molecule. These properties include electrical conductivity. It is determined by the product of the number of ionic charges and the mobility of I. Each I. moves in an electric field with a speed proportional to the force acting on it and inversely proportional to the resistance it encounters. If the potential difference is one volt per 1 eat, then movement speed (in cm/sec. at 18°) will be expressed for several ions by the following figures: Cation U (cm/s) Anion V (cm/sec.) Na* K" Ag\ NH, 33.0. 10" 3.5.10" 4.6.10" 6.75. 10-* 5.7 .10- "6.7 .10" "OH" SG Br "G no; Mpo; 18.2 .yu-" 6.85.10-" 7.0 .1Q-" 6.95. )