Metal bond briefly. Metal bond: mechanism of formation. Metal chemical bond: examples. Examples of bond formation in metals

As already indicated in paragraph 4.2.2.1, metal connection- electronic connection of atomic nuclei with minimal localization of shared electrons both on individual (as opposed to an ionic bond) nuclei, and on individual (as opposed to a covalent bond) bonds. As a result, it is a multi-center chemical bond with a deficiency of electrons, in which socialized electrons (in the form of “electron gas”) provide communication with the maximum possible number of nuclei (cations) that form the structure of liquid or solid metallic substances. Therefore, the metallic bond as a whole is non-directional and saturated; it should be considered as limiting case of delocalization of a covalent bond. Let us recall that in pure metals the metallic bond appears primarily homonuclear, i.e. cannot have an ionic component. As a result, a typical picture of the electron density distribution in metals is spherically symmetrical cores (cations) in a uniformly distributed electron gas (Fig. 5.10).

Consequently, the final structure of compounds with a predominantly metallic type of bond is determined primarily by the steric factor and packing density in the crystal lattice of these cations (high CN). The BC method cannot interpret metallic bonds. According to MMO, a metallic bond is characterized by a deficiency of electrons compared to a covalent bond. Strict application of MMO to metallic bonds and connections leads to band theory (electronic model of a metal), according to which in the atoms included in the crystal lattice of a metal, there is an interaction of almost free valence electrons located in external electron orbits with the (electric) periodic field of the crystal lattice. As a result, the energy levels of electrons split and form a more or less wide band. According to Fermi statistics, the highest energy band is populated by free electrons up to complete filling, especially if the energy terms of an individual atom correspond to two electrons with antiparallel spins. However, it can be partially filled, which provides the opportunity for electrons to move to higher energy levels. Then

this zone is called the conduction zone. There are several basic types of relative arrangement of energy bands, corresponding to an insulator, a monovalent metal, a divalent metal, a semiconductor with intrinsic conductivity, a -type semiconductor and an impurity semiconductor/b-type. The ratio of energy bands also determines the type of conductivity of a solid.

However, this theory does not allow quantitative characterization of various metal compounds and has not led to a solution to the problem of the origin of real crystal structures of metal phases. The specific nature of chemical bonds in homonuclear metals, metal alloys and intermetallic heterocompounds is considered by N.V. Ageev)