INORGANIC RING
AND
CHAIN COMPOUNDS
DR. VIKAS A. THAKUR
DEPTT OF CHEMISTRY
RAYAT SHIKSHAN SANSTHA’S
K.B.P.COLLEGE, VASHI(AUTONOMOUS)
SILICATES
• Occurrence in the earth crust.
➢ Out of 100% total of earth’s crust , about 95% of the earth’s crust is composed of silicate minerals,
alumino silicates, clays or silica.
➢ These makes up bulk of all rocks, sands and their breakdown products, clays and soils.
➢ Many building materials are silicates , granite, slates, bricks and Cement.
➢ Ceramic and glass are also silicates.
➢ The three most abundant elements are Oxygen(4,55.000ppm), Silicon (2,72,000), Aluminium (83,000),
Iron (62,000) and Calcium( 46,000).
➢ Together these three elements make up 81% of the earth’s crust.
SILICATES
➢ That is four out of five atoms are one of thes or universe. as awhole
➢ This is much higher abundance than in the earth.
➢ During the cooling of the earth , the lighter silicate minerals crystallized and floated on the
surfaces .
➢ This results in icrease in concentration of silicates in the earths crust.
SEQUENCE IN WHICH MINERALS ARE
CRYSTALLIZED
• N.L.Bowen has summarized the sequence im whih these crystalline minerals appeared as the magma cooled.
• This is known as Bowen’s Reaction series.
• First ----
Olivine
M2(II) SiO4
•
Pyroxenes
•
Amphiboles
M7(II)(Al,Si)4 O11.(OH)2
•
Biotic Micas
(K,H)2(Mg, Fe(II))2(Al, Fe(III)2(SiO4)3
•
Orthoclose feldspars
•
Muscovite micas
• Last -------- Quartz
•
Zeolites
M2(II) (SiO3)2
KAlSi3O8
KAl2(Si3O10).(OH)2
SiO2
Na2(Al2Si3O10).2H2O
• Several points are arises :
➢ 1. Simpler silicate units crystallized first.
➢ 2.Hydroxyl groups appear in latter minerals and F may be substituted instead of OH.
• 3.Isomorphous replacement; changing one method for another without changing the
structure occurs particularly in latter elements.
• 4. The orthoclase feldspars, muscovite, mica and quartz are the major minerals of Granite.
• 5.As the silicates cooled further , they shrank and cracked.
• The hydrothermal (hot water) solution moved through the cracks nearer the surface to
regions of lower temperature and pressure.
• Where the elements precipitated and then combined with Sulphur(S) forming veins of
sulphides.
SOLUBLE SILICATES
• Silicates can be prepared by fusing an alkali metal carbonate with sand in an electric furnace at about 1400 0C.
•
• Na2CO3
1400 0C
-------
+ SiO2
CO2 + Na2O ---------Na4SiO4.(Na2SiO3)n + Others.
• The product is a soluble glass of sodium or potassium silicate.
• It is dissolved in hot water under pressure.
• It is filtered from any insoluble material.
• The composition of product varies but is approximately Na2Si2O5. 6H2O.
• In 1991, 2.6 million tonnes of soluble sodium silicates were produced(measured in terms of SiO2 content)..
• They are used in liquid detergent preparation to keep the pH high so that grease and fat can be dissolved by
forming soap.
• Soluble silicates must not be used if the twater is hard ortherwise they will be react with Ca2+ ions to form
insoluble calcium silicates
PRINCIPLES OF SILICATE STRUCTURES
➢ The majority of silicate minerals are very insoluble because they have an infinite ionic structures and great strength of the Si-O
bond.
➢ This makes difficult to study their structures and physical properties such as cleavage and the hardness of rocks originally
studied.
➢ The structural principles in silicate structures habe been only because of apparent since the structures have been solved by X-ray
crystallographic methods.
➢ 1. The electronegativity difference between Oxygen and Silicon is 1.7(3.5-1.8). This suggests bonds are almost 50% ionic and
50% covalent.
➢ 2. The structures therefore considered theoretically by both ionic and covalent methods.
➢ The radius ratio Si4+ : O2- :: is 0.29 which suggests that Si is four coordinate and surrounded by four atoms at the corners of a
tetrahedron.
➢ This can be predicted also be from the use of 3s and three 3p orbitals by Si for bonding.
➢ Thus silicates are based on (SiO4 4-) tetrahedral units.
PRINCIPLES OF SILICATE STRUCTURES
➢ 3. The Sio4 tetrahedron may exist discrete units or may polymerized into larger units by
sharing the corners. I,e. sharing ‘’O’’ atom .
➢ 4. The ‘’O’’ atom are often close-packed ar nearly close-packed.
➢ Close packed structures have tetrahedral and octahedral holes and metal ions may
occupy either octahedral or tetrahedral sited depends upon their size.
CLASSIFICATION OF SILICATES
• A convenient classification of many silicate minerals are based on the way in which the ( SiO4)4tetrahedral units are linked.
❖ 1.Ortho-Silicates(Neso-Silicates):
➢ A wide variety of minerals contain discrete ( SiO4)4- tetrahedra i,e. they share no corners.
➢ They have the formula M2II[SiO4]where M= Be, Mg, Fe, Mn or Zn.
➢ Or MIV[SiO4] e.g. ZrSiO4.
➢ Different Structures are formed depending upon the coordination number adopted by the metal.
➢ In Wilemite, Zn2[SiO4] and Phenacite Be2[SiO4] the Zn and Be atoms have a
coordination Number of 4 and occupy tetrahedral holes.
➢ In Forstevite Mg2[SiO4], the Mg has coordination number of 6 and occupy octahedral
holes.
➢ When octahedral sites ae occupied, it is quite common to get isomorphus replacement of
one divalent metal ion by another similar size without changing the structure.
➢ The mineral Olivine (Mg,Fe)2 [SiO4] has the same structure as forsterite.
➢ But about one tenth of Mg2+ ion in forsterite are replaced by Fe2+ ions.
➢ The ions have the same charge and similar radii.(Mg2+ -0.72A0, Fe2+ -0.78A0) and occupy the
same type of hole.
➢ This substitution of one metal for another does not change the structure.
➢ This mineral also have Mn(II) in some octahedral sites.
➢ Thus giving [Mg, Fe, Mn]2 [SiO4].
➢ These are all related to hexagonal close-packed.
➢ Zircon, ZrSiO4 is used as a germ stone as it can be cut to like a diamond. But it is much cheaper.
➢ Zircon is much softer than diamond.
➢ Zircon has coordination number 8.
➢ Structure is not closed packed.
PYRO SILICATES(SORO SILICATES, DISILICATES)
• Two tetrahedral units are joined by sharing the ‘Oxygen’’ atom at one corner.
• This gives the unit ( Si2O7)6• This is the simplest of the condensed silicate ions.
• The name pyro came from the similarity in structure with pyrophosphates such as
• These were named because they can be made by heating Orthophosphates.
• Pyro silicates are rare.
• One example is Sc2[Si2O7].
• A number of lanthanide disilicates have similar formulae, Ln2[Si2O7].
Na4P O
2 7
PYRO SILICATES(SORO SILICATES, DISILICATES)
• These are not quite the same as Si-O-Si angle is not 180 0 as in the Sc compound but varies
down to 133 0.
• The coordination number of the metal changes from 6 to 7 and then to 8 as the size of metal
increases.
• Hemimorphite Zn4(OH)2[Si2O7]. H2O is another example.
• But the structure studies show no difference in the length of bridging and terminal Si-O bonds.
• Thus the representation as a disilicate ion may be misleading.
• The structure may be better considered as [ SiO4] and [ ZnO3(OH)] tetrahedron linked to give
a three dimensional network.
CYCLIC SILICATES
➢ If two oxygen atoms per tetrahedron are shared, ring structure may be formed having general formula
(SiO3)n2n-
➢ Rings containing three, four, six and eight tetrahedral units are known.
➢ But rings containing with three and six are the most common.
➢ The cyclic ions Si3O96- occurs in Wollastonite Ca3[Si3O9]
➢ and in Benitoite BaTi [Si3O9]
➢ The Si6O18 12- unit occurs in Beryl , Be3Al2[Si6O18].
➢ In Beryl the Si6O18 units are aligned one above the other, leaving channels.
➢ Na+, Li+ and Cs+ are commonly found in these channels.
• Because of these channels , the mineral is permeable to gases consisting of small atoms or
molecules .e,g. Helium.
• Beryl and emerald are both germ stones.
• Beryl is found with granite and usually forms pale green crystals which are six sided prisms.
• Emerald has the same formula as beryl except that it contains 1-2% Cr which gives it a strong
green colour.
CHAIN SILICATES
➢ Simple Chain silicates or Pyroxenes are formed by the sharing of the Oxygen atom on two corners of each
tetrahedron with other tetrahedra.
➢ This gives the formula (SiO3)n2n➢ A large number of important minerals form chains.
➢ But there are a variety of different structures are formed.
➢ Because the arrangement of the tetrahedra in space may vary.
➢ This affect the repeat distance along the chain.
➢ The most common arrangements repeats after every second tetrahedra.
➢ E.g. in Spodumene, LiAl(SiO3)2]. It is the main source of Li.
CHAIN SILICATES
➢ Enstatite, Mg2((SiO3)2].
➢ Wollastanite, Ca3[(SiO3)3] has a repeat unit of three tetrahedra.
➢ Others are known with repeat unit of 4,5,6,7,9 & 12.
➢ Double chains can be formed when two simple chains are joined together by shared
oxygens.
➢ These minerals are called amphiboles and they are well known.
➢ There are several ways of forming double chains giving formula ( Si2O5)n2n-, (Si4 O11)n6n- ,
(Si6O17)n10n- and others.
➢ The most numerous and the best known amphiboles are the asbestos minerals.
➢ These are based on the structural unit
.
➢ In this structure, some tetrahedra share two corners while others share three
corners.
➢ Examples are tremolite, Ca2Mg5[((Si4O11)2] (OH)2
➢ Crocidolite Na2Fe3(II)Fe(III)[(Si4O11)2] (OH)2
➢ Amphiboles always contain hydroxyl groups which are attached to metal ions.
➢ Asbestos minerals come from two different group of silicates.
➢ 1. The amphiboles.
➢ 2.The sheet silicates.
• Though asbestos is chemically inert, it presents a serious health hazard.
• Inhaling asbestos dust causes asbestosis or scarring of the lungs.
• It also causes lung cancer.
• Blue asbestos appears to be the worst hazard.
• The disease may have latent period of 20-30years.
• The best control is to minimize asbestos dust and to handle asbestos wet if possible.
SHEET SILICATES (PHYLLO-SILICATES)
• When SiO4 units are shared there corners, the structure formed is an infinite two-dimensional sheet of
empirical formula (Si2O5)n 2n-.
• There are strong bonds within Si-O sheet, but much weaker forces hold each sheet to the next one.
• Thus these minerls tend to cleave into thin sheets.
• Structures with simple planar sheets are rare.
• A large number of sheet silicates are important and well known.
• These have slightly more complicated structure.
• These are made up of either two or three layers joint together.
• These includes
1.
Clay minerals (Kaolinite, Pyrophyllite, Talc)
2.
White asbestos (Chrysotile, Biotite)
3.
Micas (Muscovite and Margarite)
4.
Montmorillonites (Fullers earth, Bentonite and Vermiculite)
Let us see the formation of two layer structures:
• If we start with simple silicate sheet, then one side of the sheet contains all the unshared (singly
bound) oxygen atom.
• The pure hydroxides Al(OH)3 and Mg(OH)2 both crystallize with layer structures.
• Al and Mg are six-coordinate and occupy octahedral sites.
• The unshared O in the silicate sheet have almost the same relative positions as 2/3rd of OH groups
on each side of the hydroxide layer.
➢ If Si2O5 layer is placed alongside a layer of ϒ-Gibbsite , Al(OH)3 , then many of the
oxygen atoms will coincide.
➢ The OH group in Al(OH)3 can be removed and an electrically neutral two layer structure is
formed.
➢ These double layers stacked parallel give the mineral Kaolinite having formula
Al2(OH)4[Si2O5].
➢ It is a white solid formed by the decomposition of granite.
➢ The world production of Kaolinite was 22.5 million tonnes in year 1992(USA 41%, UK 11% and South Korea – 8%)
➢ China clay or kaolin is mixed in Cornwall.
➢ It is a high grade of Kaolinite
➢ When small amount of SiO2 and mica are removed, it can be mixed with water to give a
white or nearly white plastic clay.
➢Small amounts are used for making porcelain, china cups and plates, sanitary
wares and other ceramics.
➢And for chromatography as a treatment for indigestion and for poultices.
➢One Al(OH)3 layer has two equivalent sides.
➢A Si2O5 layer was combined with one side in Kaolinite but a second
Si2O5sheet can combine with the other side , thus giving a three layer
structure.
➢This is made up of Silicate, Al(OH)3 silicate.
➢Pyrophyllite [Al2(OH)2] [ Si2O5)2] has this three layer structure.
➢ A layer of Brucite, Mg(OH)2, may be combined with Si2O5 layer to form two=layer structure.
➢ This gives the mineral Chrysotile, Mg3(OH)4 [ Si2O5](White asbestos) Which is considerable
commercial importance.
➢ Alternatively, Brucite may combine with two SiO2 layers , forming a triple sheet structure called as
talk or Soap stone, Mg(OH)2 [ Si2O5)4].
➢ These triple sheets are electrically neutral and there are no metal ions holding one sheet to the next
so that structure breaks very easily and is very soft.
➢ Soapstone has a slippery feeling . Hence it is as named.
➢ It is act as dry lubricant.
➢ In 1992, World production of talc was 8.4 million tonnes.
➢ It is mainly used in making ceramics, paper and mint. A small amount are used in Cosmetics.
➢ A talc can be ground into a fine powder and used as a talcum powder.
• A substitution of atoms may occur in the triple layer structures of the pyrophyllite types.
• If Si is partly replaced by Al(in tetrahedral holes), then the sheet becomes negatively charged.
• These charges are balanced by positively charged metal ions which are placed between the
layers.
• This give rise to the mica minerals.
• Muscovite has the formula KAl2(OH)2[AlSi3O10] and is called white mica,
• Margarite has the formula CaAl2(OH)2[ AlSi3O10].
• Micas are much harder than talc and other minerals because of the electrostatic attractin between
the negatively charged triple sheets and positive metal ions.
• World production of mica in 1992 was 214000 tonnes.
• The main sources are USA 40%, Soviet Union 16% and Canada 8%.
➢ Mica sheet is used as an electrical insulator and in electric heating elements(as electric
iron).
➢ It is also used in electric capacitors and for windows in furnaces.
➢ Finely ground mica is used as filter in plastics and rubbers.
➢ The clay minerals are formed from other silicates by weathering or by hydrothermal
process I,e by action of water under heat and pressure.
➢ They contain electrically neutral layers. E,g. Kaolinite and pyrophyllite.
➢ The clay minerals also include montmorillionites which have negatively charged layers.
➢ But number of charges is much lower than in the micas.
➢ Not all but some of the octahedral Al(III) in prrophyllite Al2(OH)2(Si2O5)] are
replaced by Mg(II) ions giving (Mg0.33Al0.67) (OH)2 (Si2O5)2.
THREE DIMENSIONAL SILICATES
➢ Sharing all four corners of a SiO4 tetrahedron, results in a three dimensional lattice of formula
SiO2(Quartz, tridymite, Cristobalite etc.)
➢ These contain no metal ions but three dimensional structures can form the basis of silicate structures
if there is isomorphous replacement of some of the Si4+ ions by Al3+ plus an additional metal ion.
➢ This gives an infinite three dimensional lattice and additional cations occupy holes in the lattice.
➢ Replacing one quarter of the Si4+ in SiO2 with Al3+ gives a framework ion AlSi3O8.
➢ The cations are usually the larger metal ions such as K+, Na+, Ca2+ or Ba2+.
➢ The smaller ions Fe3+, Cr3+ and Mn2+ which were common in the chain.
➢ Sheet silicates do not occur in the three dimensional silicates because the cavities in the
lattice are too large.
➢ Replacement of one quarter or one half of the Si atoms are quite common, giving
structures M(I)[AlSi3O8] and M(II)[ Al2Si2O8].
➢ Such replacements results in three groups of Minerals.
➢ 1.Feldspars
➢ 2. Zeolotes
➢ 3. Ultramarines.
FELDSPARS
➢ The feldspars are the most important rock forming minerals and constitute two third of the igneous rocks.
➢ E,g. Granite is made up of feldspars with some micas and quartz.
➢ Feldspars are divided into two classes.
❑ Orhoclase feldspars
➢ 1.Orthoclase K[AlSi3O8]
➢ 2.Celsian
Ba[Al2Si2O8]
❑ Plagioclase feldspars
➢ 1.Albite Na[AlSi3O8]
➢ 2. Anortnite Ca[ Al2Si2O8]
ZEOLITES
➢ The Orthoclases are more symmetrical than plagioclases.
➢ Because K+ and Ba2+ are just the right size to fit into the lattice.
➢ While Na+ and Ca2+ are being smaller allow distortions.
❑ 2. Zeolites :
➢ Zeolites have much more open structure than the feldspars.
➢ The anion skeleton is penetrated by channels giving a honey comb like structure.
➢ These channels are large enough to allow them to exchange certain ions.
➢ They can also absorb r lose water and outer small molecules without the structure breaking down.
➢ Zeolites are often used as ion-exchanger materials and as a molecular sieves.
➢ Natrolite, Na2[Al2Si3O10]. 2 H2O is a natural ion exchanger.
➢ Zeolites take Ca2+ ions from hard water and replace these by Na+.
➢ Thereby softening of water.
➢ The sodium zeolite natrolite gradually becomes a calcium zeolite.
➢ It eventually regenerated by treatment with strong soluion of NaCl, when the reverse process takes
place.
➢ In addition to naturally ocuring minerals, many synthetic zeolites have been made.
➢ Zeolites also acts as molecular sieves by absorbing molecules which are small enough to enter the
caities.
➢ But they are not too big to enter.
➢ They can absorb water, CO2, NH3 and EtOH.
➢ They are also useful for separating straight chain hydrocarbons from branched chain compounds.
➢ Some other zeolites are neulandite, Ca[Al2Si7O18].6H2O, Chabazite Ca[Al2Si4O12.6H2O]
➢ Molecular sieves cn be made with appropriate size to remove small molecules selectively.
ULTRAMARINES
➢ The mineral Lapiz lazuli is a splendid blue colour and was highly prized as a pigment for oil paintings in
the middle ages.
➢ It contains ultramarines Na8[(AlSiO4)6] in which the colour is produced by the polysulphide ions.
➢ The ultramarines are a group of related compounds which do not contain water.
➢ But it contains cations such as Cl-, SO4 2- and S2-.
➢ Some examples of Ultramarines are
➢ Ultramarine
Na8[(AlSiO4)6]S2
➢ Sodalite
Na8[(AlSiO4)6]Cl2
➢ Nosean
Na8[(AlSiO4)6]SO4
➢ The ultramarines are now produced synthetically.
➢ Ultramarine itself is made by igniting Kaolinite, Sodium carbonate and sulphur in
the absence of air.
➢ The product may be green, blue or red depending on the particular polysulphide
species present.
➢ Typically it is used as a blue pigment in oil based pigments and ceramics.
➢ Before the days of detergents with artificial brightners, synthetic ultramarines was
used as blueing agent(Called dolly blue) to make domestic washings appear white
by masking any yellowness.
SILICATES IN TECHNOLOGY
➢ Many silicates are used as a direct result of their physical properties.
➢ E,g. Clay minrals are used for absorbing chemicals, micas are used for electrical insulation
➢ Asbestos is used for thermal insulation, agate and clints are used as hard or sharp surfaces.
➢ In addition to this, a variety of germstones are used for ornaments and jewellary.
➢ Silicates are extremely important because cement, ceramic and glasss industries are based on their
chemistry.
➢ Metallurgical extraction processes often produce silicates as a waste products or slag.
➢ It is due to either because that minerals are silicates or because the minerals contain silicate impurities.
TECHNOLOGICAL APPLICATIONS OF SILICATES
➢ Some of the main technological applications of silicates are :
❖ Alkali Silicates :
➢ These are mainly used as a glue.
❖ Cement :
➢ Both Portland and high alumina cement are of this kind.
❖ Ceramics:
➢ Ceramics are inorganic materials that can be made into a paste and shaped at normal temperature.
➢ The shape is then ‘fired’ at a high temperature.
➢ Firing gives the product strength either by sintering the crystallite together or partly
meetry the paste.
➢ A number of carbides, oxides and in particular clays are treated in this way.
➢ The process is important for making bricks, tiles and pottery.
➢ A porosity of product depends on the temperature reached.
➢ If the firing emperature is high, the product does not absorb liquid.
➢ The presence of Fe3+ in the clay imparts red purple colour.
➢ A clay with a high proportion of CeO gives a yellow or buff coloured products.
➢ Most ceramics except bricks and floor tiles covered with a glassy coatings called a
glaze.
➢ Pigments may be applied either before glazing(underglaze colour) or after firing and on
the top of the glaze when second firing is required.
GLASS
➢ A small amount of glass is made up of Silica.
➢ This has excellent properties.
➢ But a very high temperature are needed to produce it. Silica glass is too expensive for general use.
➢ But it is used in Scientific instruments.
➢ The temp.required for melting can be reduced by adding various oxides to the melt.
➢ Thus it produce Silicate glass.
➢ A number of oxides may be used includes Na2O, K2O, MgO, CaO, BeO, B2O3, Al2O3, PbO and ZnO.
➢ Glass is a solid solution and hence its composition may vary.
➢ The amount of oxide added is not very large. Hence SiO4 tetrahedra have a
significant role in the structure.
➢ If Na2O or K2O were used, the glass would be water soluble.
➢ Normal domestic glass for windows is a Calcium alkali silicate glass by fusing the
alkali metal carbonate, CaCO3 and SiO2.
➢ If Na2CO3 is used, soda glass is produced. It is used for cheap laboratory
glassware.
➢ By using K2CO3 potash glass is produced.
➢ Most of the CaO may replaced by PbO giving lead glass which has higher
refractive index.
➢ It is used for making optical parts and glass ornaments.
• If Al2O3 is used, Al3+ may be present in the structure as a free metal ion or
• It may replace Si4+ in SiO4 skeleton.
• Borosilicate glasses containing Boron and sometimes Aluminium also are important.
• They have low Coefficient of expansion.
• They can withstand heat changes without cracking.
• They contain less alkali and hence are less prone to chemical attack.
• Such glasses are widely used for laboratory equipment as in pyrex glassware.
USES OF MICA
➢ The mineral mica is abundantly used in items that you use everyday like Cosmetics and electrical
appliances.
➢ Since mica has excellent dielectric strength, it is used in many electrical components like capacitors.
➢ Uses of Ground Mica :
❖ 1. Ground mica is used in Gypsum wall board as a wadding to remove its imperfection and enhance
its work ability.
❖ 2. In paints to improve the quality and add shine.
❖ 3.It is added to plastic products to strengthen their mechanical properties.
❖ 4. It is added to rubber products like tyres as it serve anti-sticking agents.
❖ It is added to product like eye liners, nail polish, lipstic, foundation etc.
❑Sheet Mica :
❖1. Mica sheet are useful in electric appliances due to their dielectric and insulating property.
❖2. Heating appliances like hot plates, soldering, iron etc.
❖3.Control devices like regulators.
❖4. Lighting equipment like neon lights., incandescent lamp etc.
QUARTZ
➢ The sand that glass makes uses to create glass, are hundred percent containing quartz.
➢ Quartz is the main material of glass maker and an important mineral and inorganic compound.
➢ In the wristwatch, the material of the glass is always made from quartz.
➢ Quartz has precious solid and durable material.
➢ Hence it is ideal material for creating glass of watch .
➢ It is also used as material of the glass in clock.
➢ It is used as good material for germstone jewellary because they have beautiful colors and are
more affordable.
➢ It is used as abrasive material. Quartz sand is good for sand blasting, sand
sawing and grininding. Quartz is also anti corrosive material materials.
➢ Quartz is also sturdy and not get attacked by chemical corrosion. It is durable
material for household.
➢ Quartz can be used as a Research material as a outstanding isolator . Product
made from quartz are more resistant to electricity than thse with others.
➢ Quartz can endure any temp. as well as weather conditions.
➢ Due to hardness, quartz used to sharpen other materials. Sharpening tools for
knives and cutting tools.
➢ It is used in UV prisms and lenses.
➢ Ideal material for household furnitures.