a)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: Williemite `Zn_(2)(SiO_(4))`
ii)Puyrosilicates or sorosilicates or Disilicares:These contain `SiO_(7)^(-6)` units.Pyrosillicates are rare.
Ex:Thorveitite `Ln_(2)(Si_(2)O_(7))`
iii) Chain sillicates :They have the units `(SiO_(3))_(n)^(2n-)`
Ex:Spodumene LiAl `(SiO_(3))_(2)`
Amphiboles are one type chain siliates ,Generally double chains are formed in them .
iv)Cyclic silicates :They are silicates having ring structure .They may be formed of general formula `(SiO_(3))^(2n-)` .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)O_(18))`
v) Sheet silicates :When `SiO_(4)` units share three corners the structure formed is an inifinite two dimensional sheet.the empirical formula `(Si_(2)O_(5))_(n)^(2n-)`.These Compounds appear in layer structures .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 corners of a `SiO_(4)` Tetrahedrom results in thre dimensional lattice of formula `SiO_(2)`
Ex:Quartz,Tridmite,Cristobalite , Feldspar and ultramarine `(Na_(8)[Al_(6)Si_(6)O_(24)]S_(2))`,Zeolites .
b)Zeolites:The three dimensional structure metal ion an infinite three dimensional lattice is formed .Replacements of one or two silicon atoms in `[Si_(2)O_(8)]^(-2n)` Form zeolites.Zeolites act as ion ex-Changes and as molecular sieves.The structures of zeolites permit the formation of cavities of different sizes .Water molecules and a variety of other molecules like `NH_(3),CO_(2)` and ethanol can be trapped in these cavities.Then zeolites serve as molecular sieves .They trap `Ca^(+2)` ions from hard water and replace them by `Na^(+2)` ions .
USed of Zeolites :
`to` Zeolites are used as catalysts in petrochemical industries for carcking of hydrocarbonns and in isomerisation .
`to` Zeolite ZSM -5 used to convert alcohols directly into gasoline .
C)Fullerenes:
`to` Fullerences are one type of crystalline allotropes of carbon .
`to` these are formed by heating graphite in an electric arc in presence of inertgases such as Helium (or)Argon .
`to` These are formed smotth structure without dangling bonds.Hence Fullerenes are the only pure forms of carbon .
`to C_(60)` Molecule is called Buck mister fullerene and it.s shave was like a soccar ball.
`toC_(60)` contains twenty 6 memebered rings and twelve 5-memebared rings .
`to` In `C_(60)` 6 membered rings can combine with 5 (or) 6 -membered rings .
`to` In fullerens each carbon undergoes `sp^(2)` hybridisation
`to` Fullere has aromatic nature due to delocalisation of electrons in unhybrid p-orbitals.
`to` The C-C bond length in these compound lies between single and double bond lengths.
`to` Spherical fullerenc ate also named as bucky balls.
`to` The ball shaped molecules has 60 vertices.
`to` The C-C bond distance are 1.43 `A^(@)` and `1.38 A^(@)` respectively .
