Читать книгу Material science. Жаратылыстану факультеттерінің студенттеріне арналған әдістемелік құрал - Шолпан Гумарова - Страница 2

There are ionic, atomic (covalent), metallic, and molecular bonds between the atoms of substances. The materials obtained from substances, which display various types of chemical bonding greatly differ in electric and other properties.

Na⁺ – Cl^-, Li⁺ – F^-

The ionic bond is attributed to the forces of electrostatic attraction between positive and negative ions. Such a bond is most characteristic of inorganic dielectrics whose compositions contain ions of unlike charges, such as

The atomic (covalent) bond is created between atoms owing to the formation of shared pairs of valence electrons of its neighbor. Such an electron pair strongly binds the atoms by virtue of the exchange interaction between oppositely spin-type and orbital magnetic moments of electrons. Unlike the ionic bond, the atomic bond displays a directional character, i.e. it is oriented in the direction of the most dense population of paired electrons. Therefore, substances with atomic bonding are generally hard and brittle. Example of such substances are crystals of germanium, silicon, diamond, and compounds SiC and BN, whose elements fall into middle groups of the periodic table. Atomic bonding is also typical for the molecules of such gases as H₂, O₂, N₂, and also for the molecules of many organic compounds, such as polyethylene, (C₂H₄)n, and polytetrafluoroethylene, (C₂F₄)n.

The metallic bond is the bond established between positively charged metal ions by collective valence electrons that have detached from atoms. The electron gas has a cementing action on the crystal structure of metals and responsible for their high thermal and electric conductivity. The nondirectional character of bonding accounts for high ductility of metal.

The molecular bond occurs between individual molecules which cling together due to the electrostatic forces of attraction (van der Waals forces) between unlike charges of the molecules. The bonds of this type hold together the molecules of solid hydrogen H₂, nitrogen N₂, carbon dioxide CO₂, many organic compounds. Because the molecular bonds here are inherently weak the substances easily disintegrate with thermal motion of molecules and have low melting and boiling temperatures.

Exercises:

I. Memorize the following words and word combinations:

II. Find the Kazakh (Russian) equivalents to the following word combinations:

А) attributed to the forces of attraction; formation of shared pairs; exchange interaction; detached from atoms; thermal motion of molecules; high ductility of metal.

В) тепловое движение молекул; высокая пластичность металлов; обусловленные силами притяжения; обменное взаимодействие; оторванные от атома; образование общих пар.

С) молекулалардың жылулық қозғалыстары; металдардың жоғары майысқыштығы; тартылыс күштеріне негізделген; ауыспалы өзара әрекеттесу; атомдардан алынған; жалпы жұптардың құрылуы.

III. Translate into English using the active vocabulary of the lesson:

IV. Translate at sight

A valuable contribution to the advancement of the science of materials has been made by Russian scientists. P.P. Anosov (1799-1851) was the first to establish definite correlations between the structure and properties of steels. D.K. Chernov (1839-1921) discovered polimorphic transformations in steels and has been recognized worldwide as the founder of scientific physical metallurgy. The work of N.S. Kurnakov (1860-1941) and his disciples was of large importance for the development of physico-chemical methods of analysis and for the classification of complex phases in metal alloys. The development of the theory and technology of heat treatment of steels is associted with the names of S.S. Steinberg (1872-1940) and N.A. Minkevich (1883-1942).

A.M. Butlerov (1828-1886), one of the outstanding Russian chemists, worked out the theory of chemical structure of organic substances, the scientific basis for the manufacture of polymer materials. The research work of S.V. Lebedev opened the possibility of industrial production of synthetic rubber. The advancement of polymer technology owes much to the structural studies carried out by V.A. Kargin and his disciples.

V. Give definitions for the following bonds between the atoms of substances: ionic, atomic, metallic, molecular bonds.

VI. Retell the text