Silicon , Silicone and Silicates.

LEARNING OUTCOME• Should able to describe the structure of

silicone and silicates (pyroxenes and amphiboles) , sheets (mica) and framework structure (quartz)

SILICATES• Silicon forms a strong bond with oxygen.• Silicon forms a class compound with oxygen called silicates.

SILICON + OXYGEN SILICATES (CLASS COMPOUND)

• The basic unit in all silicates is the tetrahedral ion ,[SiO4]4− .

• The classification of silicates depends on how the tetrahedral units are arranged.

Main classes of silicates

Orthosilicates

Pyrosilicates

Ring silicates

Chain silicates

Sheet silicates

Framework silicates

ORTHOSILICATES• The mineral that contains individual tetrahedral units are called

orthosilicates or nesosilicates .• This Orthosilicates have high densities and high refractive index .

Thus , they are used as gemstones.• Examples of Gemstones included Topaz , Phenacite and Zircon• Topaz is Aluminium Silicate Flouride Hydroxide .• The structure of Topaz is controlled by a chain like structure of connected

octahedrons. These octahedrons have an aluminum in the middle surrounded by four oxygen. Above and below the aluminum are the hydroxide or fluoride ions. The chains of octahedrons are held together by individual silicate tetrahedrons but it is the octahedron chains that give topaz its crystalline shape.

PYROSILICATES• When two tetrahedral units are joined by sharing one oxygen

atom per tetrahedron• So then pyrosilicates are formed.• Known as Sorosilicates.• Examples of pyrosilicates are thortveitite and hemimorphite.

RING SILICATES• This is formed when each tetrahedral unit shares two oxygen

atoms.• The most common ring silicates are composed of minimum three

tetrahedral forming triangular rings as in the mineral Benitoite.• Some of these minerals are also used as gemstones.

RING SILICATES

With four Tetrahedra is

Axinite

With six Tetrahedra is Tourmaline

CHAIN SILICATESSingle Chain Silicate (Pyroxene)• Two oxygen atoms per unit

tetrahedron are shared to form a single chain. The mineral pyroxene is formed.

• The tetrahedra are arranged in alternate positions to the left and the right along the chain. However, more complex chains may be spiral.

• Examples : Jadeite and Diopside

Double-chain Silicate (Amphibole)• Two Pyroxene chains are joined by

sharing another oxygen atom to form a double chain , Amphibole is formed.

• Some tetrahedra share two oxygen atoms while others share three.

• The most common amphibole : Asbestos• Asbestos is strong and hard but brittle. It

is cheap and resistant to heat, acids and alkalis . However , asbestos dust can cause lung cancer.

SHEET or LAYER SILICATES• When each tetrahedral unit shares three oxygen atoms, a two-

dimensional infinite sheet silicate will be formed.• Weak van der Waals forces hold the silicate sheets together. The

sheets can therefore slide over one another rather easily , making sheet silicates soft and slippery.

• Examples : Mica , talc , kaolinite and etc

FRAMEWORK SILICATES• All four oxygen atoms per unit tetrahedron are shared , a three-

dimensional structure of SiO2 will be formed.• Example of 3-D framework : quartz , trdymite and crystobalite.

SILICONE• Silicone is a synthetic organosilicon polymer

containing Si-O-Si bonds.• A typical silicone polymer can be

represented as follows, R represents an alkyl group , eg : Methy, -CH3

• Some common forms include - Silicone fluid - Silicone elastomer- Silicone resin

• Silicone resins usually contain cross-linked silicone polymers.

PROPERTIES & USES

Used to make sealants for glass,

ceramics and metals due to the strong Si-O which

resistant to chemical corrosion. Silicone Fluids are

used extensively as lubricants in high-

temperature equipment due to

its stability towards heat and

light.

Silicone Elastomer used to make

surgical implant . Why ? Coz its not

toxic.

Silicone resins used as an

insulator for wire casings & pot

holders.

Silicone Fluid used to make Car polish and other water-proof materials . Coz, it’s a good water repellant due to its alkyl

group .

USES OF SILICON• Silicon is a metalloid• It is used widely as semiconductors for

intergrated circuits in microchips , transistors an solar batteries.

• The conductivity of silicon can be replaced by increasing its temperature and by doping with phosphorous and boron.

USES OF SILICATES• Always depends on their physical properties.• QUARTZ – to make electronic equipment, watches ,

gems and lenses.• MICA – to make electrical insulator in high voltage

electrical equipment and in capacity.• ASBESTOS – is a heat insulator. To make fire retardant

coating, ceiling sheets, vehicle brake linings, exhaust manifolds and gaskets.

• Used widely in ceramics , cement and glass.

CEMENTS• Is made by heating a mixture of limestone which is

calcium carbonate , silicate clay and sand to a high temperature.

• Mostly widely used in construction industry.

GLASS• When silicon(IV) oxide is heated to its melting point ,

the Si-O bonds break and it melts to form a viscous liquid. When cooled rapidly, silicate glass is formed.

• The silicon and oxygen atoms in glass are not arranged in a regular manner . This makes the glass an AMORPHOUS SOLID.

• Glass is soluble in hot obviously , concentrated alkalis as it contains silicon dioxide which is acidic.

SiO2 (s) + 2NaOH (aq) Na2SiO3 (aq) + H2O (l)• Hence, hot and concentrated alkalis should not be stored

in glass containers.

Properties of Glass (can be modified by

adding oxides of other elements)

Transparent

Inert towards many

chemicals

Hard Brittle

Non-porous

CERAMICS• The aluminium ion can easily substitute for the silicon ion to form

aluminosilicates. However, the charge on an aluminium ion is +3 while that on a silicon ion is +4 . To balance the charge, other cations are incorporated in the structure.

• Ceramics are one of the examples of ALUMINOSILICATES.• Advanced ceramics incorporate carbides, oxides and nitrides in their structure.

Some examples include silicon carbide , aluminium oxide and silicon nitride. Some of the advanced ionic ceramics can be made into superconductors when cooled by liquid nitrogen.

PROPERTIES USES EXAMPLESHard and strong Building materials Bricks, Tiles ,

CementAttractive in appearance

Decorative Items Porcelain plates and vases.

Electrical insulators

Make insulating parts in electrical equipment

Insulators in toasters and iron , spark plugs.

Chemically inert and non-corrosive

Householdmaterials

Plates, bowls , cooking utensils.

Heat resistant Heat insulating layers

Refractory lining of furnace and outer body of space shuttles.

ZEOLITES• Some aluminosilicates lose water when heated to forms a porous

structure with a large surface area.• These aluminosilicates are called ZEOLITES.

USES

OF Z

EOLI

TES AS MOLECULAR SIEVES

- Used as molecular sieves where they can retain molecules that can fit into their molecular cavities.

- Is to separate straight-chain hydrocarbons from branched-chain hydrocarbons in gas chromatography.

AS ION EXCHANGERS- Used in exchange (ions) columns where the ions in zeolites can be exchanged with other ions.-This process needs Soften Hard Water. When hard water containing Ca2+ and Mg2+ ions will

pass through zeolite, then the Ca2+ and Mg2+ ions will be replaced with Na2+ ions

Na2Z + Ca2+ (aq) <--> CaZ + 2Na+

AS CATAYLST- Have the ability to act as catalyst for chemical reactions

which take place within internal cavities.- Used in many organic reactions

TIN ALLOYS

USES OF TIN & LEAD

TIN- Used in

electroplating industry (Iron

and Steel)

TIN PLATED IRON

- Used to make tin cans for food (Tin is not toxic)

TIN & LEAD- Used to

make alloys

ALLOYSSOLDER

• Consist of 70% of Pb and 30% of Sn

• Used as soldering electronic parts.

PEWTER• Consists of 96% of Sn , 3%

of Cu and 1% of Sb• Used as souvenirs ,

décorative items.