SILICATES

TUMKUR UNIVERSITY
TUMKUR
DEPARTMENT OF STUDIES AND RESEARCH IN ORGANIC CHEMISTRY
“SILICATES’’
SHOBHA V T
I MSC I Sem
1

CONTENTS
 INTRODUCTION
 DEFINATION OF SILICATES
 CLASSIFICATION OF SILICATES
 APPLICATIONS OF SILICATES
 CONCLUSION
 REFERENCES
2

INTRODUCTION
A silicate is an anions consisting of silicon and oxygen.
Silicates occur in earth’s crust in abundantly in the form of silicate minerals and
aluminosilicate clay.
Silicate anions are often large polymeric molecules with an extense variety of
structures,including chains and rings.double chains and sheets.
Silicates are extremely important materials, both natural and artificial, for all sorts
of technological and artistic activities.
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PRINCIPLES OF SILICATE STRUCTURE
The majority of silicates minerals are very insoluble because they have an infinite
ionic structure and because they have an infinite ionic structure and because of the
great strength of the Si-O bond. This made it difficult to study their structure and
physical properties such as cleavage and the hardness of rocks were originally
studied.The structural principles in silicates structure have only become apparent
since the structure have been solved by X-ray crystallographic methods.
1. The electronegativity diffence between O and Si 3.5-1,8 =1.7 such that the bond
are almost 50% ionic and 50%covalent.
2. The structure may therefore be considered theoretically by both ionic and
covalent methods. The radius ratio S𝑖4+
,𝑂2−
is 0.29 which suggests that Si is
four –coordinate and is surrounded by four O atoms at the corners of a
tetrahedron. This can also be predicted from the use of the 3s and three 3p
orbitals by Si for bonding thus silicates are based on (Si𝑂4)4− tetrahedral units.
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3. The Si𝑂4 tetrahedral may exist as discrate units,or may polymerize into large
units by sharing corners that is by sharing O atom.
4. The O atoms are aften close –packed or nearly close –packed close packed
structures have tetrahedral and octahedral holes and metal ions may occupy either
octahedral or tetrahedral sites depending on their size to fit one type of
hole,through A𝑙+3
can fit into either.thus Al can replace either a metal in one of the
holes or a silicon atom in the lattice this is particularly important in the
aluminosilicates

SILICATE
Silicates are the minerals containing silicon and oxygen in tetrahedral Si𝑂4
4−
units
which are linked together in several patterns.About 95% of the earth’s crust is
composed of silicates minerals,alumino silicate clays or silica.
Silicate structure consists of (Si𝑂4)4−units which are formed by s𝑝3
hybridisation of Si orbitals.
 The electron configuration of silicon atom in the excited state is 3𝑠1
𝑝𝑥
1
𝑝𝑦
1
𝑝𝑧
1
thus it forms four bonds with oxygen atom by utilizing s𝑝3 hybrid orbits and
yielding (Si𝑂4)4−
units.
 The oxygen atoms pickup one electron each
from some metal in order to complete their octets.
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CLASSIFICATION OF SILICATES
1. Orthosilicates (neso-silicates)
2. Pyrosilicates (soro-silicates,disilicates)
3. Chain silicates (pyroxenes)
4. Double chain silicates (Tecto silicates)
5. Sheet silicates (phyllo-silicates)
6. 3D silicates (Tecto silicates)
7

Orthosilicates(neso-silicates)
If the corner oxygens are not shared with other Si𝑂4
4−
tetrahedrans each tetrahedran
will be isolated thus this group is aften referred to as the island silicate group.the
basic structural unit is then Si𝑂4
4−
in this group the oxygen are shared with
octahedral group that contain other cations like M𝑔+2, Z𝑟+2, or C𝑎+2 simple.
Example: silicates of magnesium(M𝑔2Si𝑂4)
and zirconium(ZrSi𝑂4)
Uses:
• Jewelry :Orthosilicates like garnet and topaz are used
Jewelry due to their attractive colours and durability.
• Abrasives:Orthosilicates like garment are used as abrasives in sandpaper and
other abrasive material due to their hardness and toughness.
• welding rods:Orthosilicates like fayalite are used in welding roads as a flux to
remove impurities from the metal and promote better fusion. 8

Pyrosilicates(soro-silicates,disilicates)
In this types of silicates, two tetrahedral unit are joined by sharing the oxygen at one
corner. The structural units of pyrosilicates are (S𝑖2 𝑂7)6−. This is the simplest of
condensed silicate ions these are also known as soro silicate.
Example : Thortveitite S𝑐2yt[S𝑖2𝑂7]
Henimorphite Z𝑛4[(OH)2[𝑆𝑖2𝑂7].𝐻2O
Uses:
• Insulation: pyrosilicates used as insulation material in industries such as
aerospace,automotive,and construction.
• Water treatement : in water treatement application as coagulants and flocculants
to remove impurities from water.
• Agriculture : used in agriculture as soil conditioners to improve soil fertility and
crop yield.
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Cyclic silicates(ring-silicates)
In this types of silicates two oxygen atoms per tetrahedral unit are shared to form a
ring type of structure. The general formula of cyclic silicate is
(Si𝑂3)𝑛
2𝑛−. rings containing three,four six and eight tetrahedral unit are known.but
three and six are more common.
Example : cyclic silicates(wollastonite C𝑎3[S𝑖3𝑂7]
beryl B𝑒3 A𝑙2[S𝑖6𝑂18]
Uses :
• chemical industry : cyclic silicates are used in the
• chemical industry as catalysts in various chemical reactions.
• Environmental remediation : cyclic silicates are used in environmental
remediation to remove pollutants from soil.
• Medicinal industry : filler or binder in tablet formulations.
10

Chain silicates (pyroxenes)
Simple chain silicates are formed by sharing oxygen atom on two corners of each
tetrahedral.
The general formula of cyclic silicates is (Si𝑂3)𝑛
2𝑛−.
Example : spodumene –LiA(Si𝑂3)2
diopsidecamg(Si𝑂)2
Uses :
• Ceramics industry : used as a fluxing
Agent,which lower the melting point of
Ceramics materials and helps to improve their hardness and durability.
• Cement : used in filler and concrete to improve their strength and durability.
• Glass industry : used as a fluxing agent to lower the melting point of glass and
improve its properties. 11

Sheet silicates(phyllo-silicates)
when Si𝑂4 units share three corners an infinite two dimensional sheet is formed
called sheet silicates. The empirical formula is (S𝑖2𝑂)𝑛
2𝑛− three are strong bonds
within the Si-O sheet but much weaker forces hold each sheet to the next one
Example : Al(OH)3 gibbsite sheet
Mg(OH)2 brucite sheet
Uses
• Ceramics:sheet silicates like kaolinite
are used in production of ceramics.
• Petroleum industry:sheet silicates like montmorillonite and bentonite are use as
drilling fluids in the viscosity and rheological properties of fluid.
• Construction:sheet silicates like mica and vermiculite are used as cement and
plaster to improver their workability, strength, and durability.
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Three –dimensional silicates
In the structure of the three –dimensional silicates all the four corner oxygen atom
of Si𝑂4 units are shared with others. the three – dimentional lattice formula is
Si𝑂2(quartz,tridymite cristabalite) these are not contain no metal ions but three –
dimensional structures can form the basis of silicate structure if there is
isomophous replacement of some of the S𝑖+4by A𝑙3+ plus additional ion.
Example: feldspars
zeolites
ultramarines
Uses:
• Glass production : used as silica And feldspars, are used as
raw materials in the production.
• Industrial catalysts : used as catalysts in various industrial processes due to their
porous structure and ability to adsorb and desorb molecules. 13

CONCLUSION
 Alkali silicates are used mainly as glue
 Silicates are extremely important in the cement ceramic and glass
indrustries
 Quartz is another example of silicates with an ideal capability to give a
high rhythmic frequency vibration these charecterstics make quartz
crystals to be used in radio’s pressure gauges and watches
 Industries use silicates to treat waste water as an iron flocculent and
alum coagulant
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REFERENCE
 Inorganic chemistry by – J.D.Lee (fifth edition)
page number : (432-445)
 Inorganic chemistry by - Puri sharma kalia
page number : (480-483)
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