Write a short note on silicates.

Explanation

Silicates : Many building materials are silicates.
Ex : Granites, slates, bricks and cement. Ceramics and glass are also silicates. The si-o bonds in silicates are very strong. They do not dissolve in any of the common solvents nor do they mix with other substances readily.
The silicates can be divided into six types. They are mentioned here.
i) Orthosilicate or Nesosilicates : Their general formula may be `M_(2)^(11) (SiO_(4))` .
Ex: Willemite `Zn_(2 )(SiO_(4))`
ii) Pyrosilicates or sorosilicates or Disilicates : These contain `SiO_(7)^(-6)` units. Pyrosilicates are rare.
Ex: Thorveitite Ln, `(Si_(2)O_(7))`.
iii)Chain silicates : They have the units `(SiO_(3))_(n)^(2n-)`.
Ex : Spodumene `LiAl (SiO_(3))_(2)` , Amphiboles are one type chain-silicates. Generally double chains are formed in them.
iv)Cyclic silicates. They are silicates having ring structures. They may be fornied of general formula `(SiO_(3))_(n)` Rings containing three, four, six and eight tetrahedral units are known. But rings with three and six are the most common.
Ex: Beryl `Be_(3)Al_(2)(Si_(6)OO_(16))`
v) Sheet silicates: When `SiO_(4)` units share three corners the structure formed is an infinite two dimensional sheet. The empirical formula `(Si_(2)O_(5))_(n)^(2n-)` . These compounds appear in layer struc tures. They can be cleaved.Ex: Kaolin `Al_(2) (OH)_(4)Si_(2)O_(5)`
vi) Frame work silicates or three dimensional silicates: Sharing all the four comers of a `SiO_(4)` tetrahedron results in three dimensional lattice of formula `SiO_(2)`.
Ex: Quartz, Tridymite, Cristobalite, Feldspar and ultramarine `(Na_(8) [Al_(6)Si_(6)O_(24)]`, zeolites.