METAVALENT CHEMICAL COMPOUNDS OF THE TYPE AIBVCVI2 (AI – Li, Na, K, Rb, Cs; BV – As, Sb, Bi; CVI – Se, Te)

The concept of chemical bonding is one of the key concepts in the modern chemical science. The main types of chemical bonds traditionally distinguished in the scientific literature are ionic, covalent and metallic; whereas hydrogen bonds and intermolecular interaction forces are usually taken as secondary bonds. It should be noted, however, that there are no sharp boundaries for the above types of chemical bonds.In order to predict the type of chemical bond between atomic particles, a special atomic property called the electronegativity [i.e. the ability of a given atom in a molecule to attract electron density (or valent electrons)] is widely used. The concept of electronegativity and the first scale of electronegativities of chemical elements were proposed by L. Pauling in 1932; later, several alternative scales of electronegativities were developed, including those by Mulliken and by Allred–Rochow.Using the difference between the electronegativities of atoms (DEN) and the sum of the electronegativities of atoms (SEN), one can obtain quantitative parameters which characterize the chemical bonds in specific compounds. In particular, the difference in the electronegativities of the A and B atoms characterizes the degree of ionicity for the A–B bond, while the sum of electronegativities indicates either the degree of covalency (at relatively large SEN values) or the degree of metallicity (at low SEN values). The sum of electronegativities can be replaced, if necessary, by the average electronegativity (ENav.) of the compound. Taking the elementary substances Cs and F2 and the binary compound CsF as reference points in the coordinates ENav.–DEN, a diagram triangle was constructed, which conveniently and clearly illustrates the type of chemical bond of different chemical compounds.The analysis of the ternary chalcogenide AIBVCVI2 (AI – Li, Na, K, Rb, Cs; BV – As, Sb, Bi; CVI – Se, Te) compounds (which have been studied for a long time by the researchers of the Uzhhorod National University) by using the aforementioned diagram triangle in the coordinates ENav.–DEN has revealed the fact that the considered compounds are characterized by the combined (so-called "metavalent") chemical bonding recently identified in the specialized scientific literature as a separate bonding type.