DIAMOND	GRAPHITE
C is sp3 hybridised.	C is sp2 hybridised.
Three dimensional, tetrahedral structure.	Two dimensional, sheet like structure.
Crystalline, transparent with extra brilliance.	Crystalline, opaque and shiny substance.
It is hard with high density and high melting point.	It is soft with low density and high melting point.
Bad conductor of and electricity.	Good conductor of heat and electricity.

Silicates are classified into various types based on the way in which the tetrahedral units, [SiO₄]^4- are linked together.
(i) Ortho silicates (Neso silicates):
The simplest silicates which contain discrete [SiO₄]^4- tetrahedral units are called ortho silicates or nesosilicates.
Examples: Phenacite - Be₂SiO₄ (Be²⁺ ions are tetrahedrally surrounded by O^2- ions)
(ii) pyro silicate (or) Soro silicates: Silicates:
Which contain [Si₂O₇]^6- ions are called pyro silicates (or) Soro silicates.
Example: Thortveitite - Sc₂Si₂O₇
(iii) Cyclic silicates (or Ring silicates): 
Silicates which contain (SiO₃)₃^2n- ions which are formed by linking three or more tetrahedral SiO₄^4- units cyclically are called cyclic silicates.
Example: Beryl [Be₃Al₂ (SiO₃)₆] (an aluminosilicate with each aluminium is surrounded by 6 oxygen atoms octahedrally)
(iv) Inosilicates: Silicates which contain 'n':
number of silicate units liked by sharing two or more oxygen atoms are called inosilicates.
Example: They are further classified as chain silicates and double chain silicates.
(v) Chain silicates (or pyroxenes):
These silicates contain [(SiO₃)_n]^2n- ions formed: by linking 'n' number of tetrahedral [SiO₄]^4- units linearly. Each silicate unit shares two of its oxygen atoms with other units.
Example: Spodumene - LiAl(SiO₃)₂·
(vi) Double chain silicates (or amphiboles): 
These silicates contains \(\left[ { Si }_{ 4 }{ O }_{ 11 } \right] _{ n }^{ 6n- }\) ions. In these silicates there are two different types of tetrahedra:
(a) Those sharing 3 vertices
(b) those sharing only 2 vertices.
Example:
Asbestos: These are fibrous and non-combustible silicates.
(vii) Sheet or phyllo silicates: 
Silicates which contain \(({ Si }_{ 2 }{ O }_{ 5 })_{ n }^{ 2n- }\) are called sheet or phyllo silicates. In these, Each [SiO₄]^4- tetrahedron unit shares three oxygen atoms with others and thus by forming two dimensional sheets.
Example: Talc, Mica etc.
(viii) Three dimensional silicates (or tectosilicates): 
Silicates in which all the oxygen atoms of [SiO₄]^4- tetrahedra are shared with other tetrahedra to form three dimensional network are called three dimensional or tectosilicates.
Example: Quartz.

(i) Carbon monoxide can be prepared by the reaction of carbon with limited amount of oxygen.
2C + O₂ ⟶ 2CO
(ii) (a) On industrial scale carbon monoxide is produced by the reaction of carbon with air.
(b) The carbon monoxide formed will contain nitrogen gas also and the mixture of nitrogen and carbon monoxide is called producer gas.
(c) \(2C+{ O }_{ 2 }/{ N }_{ 2 }(air)\longrightarrow \underset { Producers \ Gas }{ 2CO } +{ N }_{ 2 }\)
(d) The producer gas is then passed through a solution of copper(I) chloride under pressure which results in the formation of CuCI(CO).2H₂O.
(e) At reduced pressures this solution releases the pure carbon monoxide.
(iii) Pure carbon monoxide is prepared by warming methanoic acid with concentrated sulphuric acid which acts as a dehydrating agent.
HCOOH + H₂SO₄ ⟶ CO + H₂O + H₂SO₄

Allotropism:
1. Some elements exist in more than one crystalline or molecular forms in the same physical state
(a) In Greek "allos" means ⇒ Another
(b) "trope" means ⇒ Change
2. The different forms of an element are called allotropes.
Allotropy of carbon:
Carbon exists as diamond, graphite, fullerenes, carbon nanotubes and graphene.
Graphite:
1. Graphite is the most stable allotropic form of carbon at normal temperature and pressure.
2. It is soft and conducts electricity.
3. It is composed of flat two dimensional sheets of carbon atoms.
4. Each sheet is a hexagonal.
5. It is "sp²" hybridised.
6. C-C bond length is 1.41 Å
7. Each C-atom forms three σ bonds with three neighbouring carbon atoms using three of its valence electrons and the fourth electron present in the unhybridised p-orbital form a π-bond.
8. The successive C-sheets are held together by weak Vander Waals forces.
9 The distance successive sheet is 3.40 Å.
10. It is used as a lubricant either on its own or as a graphited oil.

Diamond:
1. It is very hard.
2. It is "sp³" hybridised.
3. C-C bond length is 1.54 Å
4. It is used for sharpening hard tools, cutting glasses, making bores and rock drilling.

Fullerenes:
1. These allotropes are discrete molecules such as \(C_{32}, C_{50}, C_{60}, C_{70}, C_{76}\) etc.
2. It has cage like structure
3. The C₆₀ molecules have a "soccer" ball like structure and is called buckminster fullerene or buckyballs.
4. It has a fused ring structure consists of 20 six membered rings and 12 five membered ring.
5. Each carbon atom is "sp²" hybridised.
6. It has three σ bonds and a delocalised π bond giving aromatic character to these molecules.
7. The C-C bond distance is 1.44 Å
8. The C=C bond distance is 1.38 Å.

Carbon nanotubes:
1. Carbon nanotubes, another recently discovered allotropes, have graphite like tubes with fullerene ends.
2. Along the axis, these nanotubes are stronger than steel and conduct electricity.
3. These have many applications in nanoscale electronics, catalysis, polymers and medicine.
Graphene:
 It has a single planar sheet of "sp²" hybridised carbon atoms that are densely packed in a "honeycomb crystal" lattice.

(i) Borax - Na₂[B₄O₅.(OH)₄].8H₂O
(ii) Kernite - Na₂[B₄O₅(OH)₄]·2H₂O

(i) In the elements of 4^th, 5^th and 6^th period of the p-block the electrons present in the intervening d and f - orbitals do not shield the s-electrons of the valence shell effectively.
(ii) As a result, ns²-electons remains more tightly held by the nucleus and hence do not participate in bonding. This is called inert pair effect.

(i) Silicon tetrachloride is used in the production of semiconducting silicon.
(ii) It is used as a starting material in the synthesis of silica gel, silicic esters, a binder for ceramic materials.

The equilibrium involved in the reaction between carbon dioxide and hydrogen, has many industrial applications and is called water gas equilibrium.
CO₂ + H₂ ⇌ CO + H₂O
                   water gas

On heating to 475 K potash alum loses water of hydration and swells up. The swollen mass is known as burnt alum.

(i) Boranes are colourless diamagnetic compounds with low thermal stability.
(ii) Diborane is a gas at room temperature with sweet smell and it is extremely toxic.
(iii) It is also highly reactive At high temperatures it forms higher boranes liberating hydrogen.

Boric acid can be extracted from borax and colemanite.
Na₂B₄O₇ + H₂SO₄ + 5H₂O ⟶ Na₂SO₄ + 4H₃BO₃
Ca₂B₆O₁₁ + 11H₂SO₄ + SO₂ ⟶ Ca(HSO₃)₂ + 6H₃BO₃

CO acts as a strong reducing agent.
Example: 3CO + Fe₂O₃ \(\longrightarrow \)  2Fe + 3CO₂
It reduces metallic. oxides into metals.

When boric acid or borate salt is heated with ethyl alcohol in presence of conc. sulphuric acid, an ester, trialkylboranes is formed.
The vapour of this ester burns with a green edged flame
This reaction is used to identify the presence of triethyl borate.
\({ H }_{ 3 }{ BO }_{ 3 }+{ 3C }_{ 2 }{ H }_{ 5 }OH\overset { Conc }{ \underset { { H }_{ 2 }{ SO }_{ 4 } }{ \longrightarrow } } B\left( { OC }_{ 2 }{ H }_{ 5 } \right)_3 +3{ H }_{ 2 }O\)
                       Ethyl borate
                        (Green edged flame)

(i) Icosogens → B, Al, Ga, In, Tl
(ii) Tetragens → C, Si, Ge, Sn, Pb
(iii) Pnictogens → N, P, As, Sb, Bi
(iv) Chalcogens → O, S, Se, Te, Po

Diborane adds on to alkenes and alkynes in ether solvent at room temperature. This reaction is called hydroboration.
\({ B }_{ 2 }{ H }_{ 6 }+6RCH=CHR\longrightarrow 2B(RCH_2-{ CH }R)_{ 3 }B\)

(i) In diborane two BH₂ units are linked by two bridged hydrogens.
(ii) It has eight B-H bonds.
(iii) Diborane has only 12 valance electrons.
(iv) The four terminal B-H- bonds is "2c - 2e" bond (two centre - two electron bond.)
(v) Two three centred B - H - B bonds two electrons each. "(3c - 2e)"
(vi) In diborane, the boron is "sp³" hybridised
(vii) Three of the four "sp³" hydridised orbitals contains single electron and the fourth orbital is empty.

Oxides of Carbon	Structure	Parameters
CO		Three electron pairs are shared between carbon and oxygen. The C-O bond distance is 1.128\(\overset{o}{A}\).
CO2		Equal bond distance for the both C-O bonds. Two C-O sigma bond, It has 3c-4e bond.

Catenation is an ability of an element to form chain of atoms.
The conditions for catenation.
(a) The valency of element is greater than or equal to two.
(b) Element should have an ability to bond with itself
(c) The self bond must be as strong as Its bond with other elements
(d) Kinetic inertness of catenated compound towards other molecules.
(e) Carbon possesses all the above properties and forms a wide range of compounds with itself and with other elements such as H, O, N, S and halogens.

(i) CO being a good reducing agent, reduces several metal oxides into crude metal. Hence it is used in extraction of metals.
(ii) CO forms carboxy-hemoglobin complex with hemoglobin of blood which is about 300 times mores stable than oxygen - hemoglobin complex and thus it stops the supply of oxygen and hence, leads to death of the person.
(iii) Solid CO₂, produce cooling and sublimes directly into vapour state, hence used for refrigeration.

(i) Graphene is an allotropic form of carbon.
(ii) It has a single planar sheet of sp² hybridised carbon atoms that are densely packed in a honeycomb crystal lattice.

(i) Carbon nanotubes, have graphite like tubes with fullerene ends.
(ii)  Along the axis, these nanotubes are stronger than steel and conduct electricity.
(iii) These have many applications in nanoscale electronics, catalysis, polymers and medicine.

(i) Graphite is the most stable allotropic form of carbon at normal temperature and pressure.
(ii) It is soft and conducts electricity. It is composed of flat two dimensional sheets of carbon atoms.
(iii) Each sheet is a hexagonal net of Sp² hybridised carbon atoms with a C-C bond length of 1.41 Å which is close to the C-C bond distance in benzene (1.40 Å).
(iv) Each carbon atom forms three a bonds with three neighbouring carbon atoms using three of its valence electrons and the fourth electron present in the unhybridised p orbital forms a π-bond.
(v) These π electrons are delocalised over the entire sheet which is responsible for its electrical conductivity.
(vi) The successive carbon sheets are held together by weak van der Waals forces. The distance between successive sheet is 3.40 Å.
(vii) It is used as a lubricant either on its own or as a graphited oil.

(i) When aluminium metal or aluminium hydroxide is treated with hydrochloric acid, aluminium trichloride is formed.
(ii) The reaction mixture is evaporated to obtain hydrated aluminium chloride.
2Al + 6HCl ⟶ 2AICl₃ + 3H₂
Al(OH)₃ + 3HCl ⟶ AlCl₃ + 3H₂O

At high temperatures it forms higher boranes liberating hydrogen.
\(5{ B }_{ 2 }{ H }_{ 6 }\overset { 388K }{ \underset { U-tube }{ \longrightarrow } } 2{ B }_{ 5 }{ H }_{ 11 }+4{ H }_{ 2 }\)
\(2{ B }_{ 2 }{ H }_{ 6 }\overset { 198-373K }{ \longrightarrow } { B }_{ 4 }{ H }_{ 10 }+{ H }_{ 2 }\)
\(5{ B }_{ 2 }{ H }_{ 6 }\overset { 373K }{ \underset { sealed\ tube }{ \longrightarrow } } { B }_{ 10 }{ H }_{ 14 }+8{ H }_{ 2 }\)
\(5{ B }_{ 2 }{ H }_{ 6 }\overset { 473-523K }{ \longrightarrow } 2{ B }_{ 5 }{ H }_{ 9 }+6{ H }_{ 2 }\)
\(10{ B }_{ 2 }{ H }_{ 6 }\overset { 523K }{ \longrightarrow } 2{ B }_{ 5 }{ H }_{ 9 }+2{ B }_{ 5 }{ H }_{ 10 }+11{ H }_{ 2 }\)
\({ B }_{ 2 }{ H }_{ 6 }\overset { Red \ hot }{ \longrightarrow } 2B+3{ H }_{ 2 }\).

A hydride of 2^nd period alkali metal (A) is lithium hydride (LiH).
Lithium hydride (A) reacts with diborane (B) to give lithium borohydride (C) which is acts as a reducing agent.
B₂H₆ + 2 LiH \(\xrightarrow[]{ether}\) 2 LiBH₄
[Diborane (B)]   [Lithium hydride (A)]  [Lithium borohydride (C)]
Result:

Compound	Formula	Name
A	LiH	Lithium hydride
B	B2H6	Diborane
C	LiBH4	Lithium borohydride

Fusion of urea with B(OH)_3' in an atmosphere of ammonia at 800 - 1200 K gives boron nitride.
B(OH)₃ + NH₃ \(\overset { \Delta }{ \longrightarrow } \) BN+ 3H₂O

(i) Silicones are used for low temperature lubrication and in vacuum pumps, high temperature oil baths etc.
(ii) They are used for making water proofing clothes.
(iii) They are used as insulting material in electrical motor and other appliances.
(iv) They are mixed with paints and enamels to make them resistant towards high temperature, sunlight, dampness and chemicals.