Chain sheet

When the ratio MO/SiOj is a little less than 2/1, silica dimers form (Fig. 16.4b). One oxygen is shared between two tetrahedra it is called a bridging oxygen. This is the first step in the polymerisation of the monomer to give chains, sheets and networks. 

Hornsby, P. R., Merson, S., Prosser, H. J. Wilson, A. D. (1982). The formation and properties of mineral-polyacid cements. Part 2. Chain, sheet and three-dimensional silicates. Journal of Materials Science, 17, 3575-92. 

Most of the isolated borate anions shown above may polymerize in a variety of ways to form extended chains, sheets, and networks. Polymerization occurs by either sharing an exocyclic oxygen atom or by sharing an intracyclic tetrahedral boron atom. These are exemplified by the structures of the important industrial minerals colemanite [29], Ca[6304(0H)3] H2O... 

However, explanations for growth limitation based on repulsion of metal ions may be somewhat oversimplified. Elements other than vanadium, niobium, tantalum, molybdenum, and tungsten do not form isopoly anions. Other ions which have appropriate radii (e.g., Al,+, 67 pm Oa5+, 76 pm I7"1. 67 pm) for discrete isopoly anion formation instead form chains, sheets, or three-dimensional frameworks. Why does polymerization stop for isopoly anions An oxygen atom in a terminal position in an isopoly anion is strongly n bonded to a transition metal such as Mo(V ) or W (VI). These terminal oxygen atoms are never found trans to one another because they avoid... 

Infinite chains, sheets and three-dimensional lattices 563... 

The phenomenon of increased hardness occurs principally in minerals of sheet and chain structures, which link together through the cations (silicates and aluminosilicates, as well as hydrated sheet minerals, such as glauconite, melilite and gypsum—M ranging from 0 to about 1.25), and also in minerals of skeletal structures (borates, phosphates, sulphates, nitrates, carbonates, such as calcite, dolomite and others—Ah from 0 to about 1.15). For this reason, the hardness analysis of minerals with weak bonds demands consideration of the fact that just as the basic crystallo-chemical factors, so is hardness influenced by the form of domains (component parts of structures) in all anisodesmic minerals of chain, sheet or skeletal structure. Depending on the form of domain (and also according... 

Palygorskile and Sepiolite. Palygorskite (anapalgite) and sepiolitc arc day minerals in which the 2 1 layers are linked together in chain-likc or a combination of chain-sheet structures. 

Since the Braggs first determination, thousands of structures, most of them far more complicated than that of sodium chloride, have been determined by x-ray diffraction. For covalently bonded low molecular weight species (such as benzene, iodine, or stannic chloride), it is often of interest to see just how the discrete molecules are packed together in the crystalline state, but the crystal structures affect the chemistry of such substances only to a minor degree. However, for most predominantly ionic compounds, for metals, and for a large number of substances in which atoms are covalently bound into chains, sheets, or three dimensional networks, their chemistry is very largely determined by the structure of the solid. 

In addition to having relatively stiff chains, cellulose forms an extensive network of hydrogen bonds (some of which involve water molecules), resulting in the formation of microfibrils from extended chain sheets (Figure 9-35). There are also some amorphous polysaccharides present in a fiber such as cotton and the aggregated microfibrils have extensive pores capable of holding relatively large amounts of water (which makes them useful components of diapers ). 

Following the structural hierarchy developed for uranyl compounds [11, 12], the orthophosphates and orthoarsenates of the hexavalent actinides may be divided into three general classes based on the polymerization of polyhedra of higher bond-valence chain, sheet, and framework structures. Among the sheet and framework stmctures, there is some overlap as the phosphuranylite-type sheet is exhibited mainly by sheet stmctures but also by frameworks, and is discussed in the section on sheet stmctures. Similarly, the uranophane sheet-anion topology is adopted by some sheets but mainly by frameworks and is discussed in the latter section. 

Show how the fundamental silicate tetrahedral unit (Si04 ) links to other silicate tetrahedra to form rings, chains, double chains, sheets, and space-filling crystalline networks (Section 22.1, Problems 1-4). 

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