2014-01-27
692
Theme: structure crystal силикатов. Development of representations about structure силикатов. Features of structures of knitting substances. Structural classification силикатов. Structure боридов, карбидов, нитридов and силицидов.
Lecture № 6.
1. Structure crystal силикатов.
2. Development of representations about structure силикатов.
3. Feature of structures of knitting substances.
4. Structural classification силикатов.
5. Structure боридов, карбидов, нитридов and силицидов.
Structure силикатов - тетраэдр [SiO4]
Карборунд - карбид of silicon
Силикаты and алюмосиликаты - most widespread minerals in terrestrial коре. They make more thirds of all minerals.
The majority natural силикатов has complex(difficult) structure and, as a rule, insolubly in water. This long time complicated an establishment of their structure. Therefore in a history of study силикатов it is possible clearly to allocate 5 stages.
The first stage is connected to only chemical study силикатов. In this перид the items of information on their structure collected. The empirical formulas силикатов entered the name as оксидов in ascending order of charge катиона. For example Na2O·Al2O3·6SiO2 - альбит, СaO·Al2O3·2SiO2 - анортит.
In a basis of classification силикатов the attitude(relation) of number of atoms of oxygen connected to silicon, to number of atoms of oxygen connected to others катионами was necessary. On this classification силикаты were divided on моно-, ди-, трисиликаты etc. So СaO·Al2O3·2SiO2 is моносиликатом, because the number of atoms of oxygen connected to silicon, is equal to number of atoms of oxygen connected with кальцием and aluminium (4). On similar accounts лейцит К2O·Al2O3·4SiO2 is дисиликатом, and альбит Na2O·Al2O3·6SiO2 - трисиликатом. Thus the substances, close on a nature, (field шпаты - альбит, ортоклаз, анортит) got in different classes, and various - in one of a class.
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The second stage is connected to representation about силикатах, as about salts of hypothetical polysilicon acids - метакремниевой Н2SiO3, ортокремниевой Н4SiO4 and ортодикремниевой Н6Si2O7. However question on a structure силикатов and here remained unsolved.
The third stage in development силикатов is closely connected to a name of outstanding Russian scientist В.И.Вернадского (1863-1945г), which in 1891 has put forward idea about the special role of aluminium in силикатах, that has facilitated decoding their structures.
At the fourth stage of study силикатов was connected to successes of stereochemistry of complex connections. By analogy with четырехвалентной by platinum, which in complex connections has coordination number 6, the same coordination number attributed also to silicon. The structural formulas constructed on these principles, further have appeared incorrect.
The modern (fifth) stage of development of representations about structures силикатов is closely connected to successes рентгеноструктурного of the analysis. Leaning(basing) on rules of education ионных of crystals formulated Л.К. Полингом in 1929г., В.Л.Брегу and Ф.Махачки it was possible to decipher the first structures силикатов. Has appeared, that силикаты are not ионными crystals. A primary type of communication(connection) in силикатах is ионно-ковалентная communication(connection). Now are deciphered a structure and structure many complex(difficult) силикатов. The especially large merit in it belongs to the Soviet school кристаллографии, based акад. Н.В.Беловым.
