1. INDUSTRIALLY IMPORTANT MATERIALS
BS.c Chemistry
Semester 6
JOFRIN J

2. CARBIDES
Carbides are the binary compounds in which carbon has combined with elements of lower or equal electronegativity than carbon.

3. Types of carbides Carbides are mainly classified into three
1. Ionic carbides
2. Covalent carbides
3. Interstitial or metallic carbides

4. IONIC CARBIDES
Ionic carbides are formed by the combination of carbon with alkali, alkaline earth metals, Sc, Ag, Thorium and aluminium.
These carbides are usually prepared by heating the metals or metal oxide with carbon or CO or CO2

5. IONIC CARBIDES Ionic carbides are further classified into three.
a) Acetylides
b) Methanides
c) Allylides

6. IONIC CARBIDES Acetylides
These carbides yield acetylene on hydrolysis.
They contain [C2 ]2- group.
Example: Calcium carbide CaC2.
CaC2+ 2H2O------Ca(OH)2+ C2H2(acetylene)
Since these carbides yield acetylene on hydrolysis, they are called acetylides

7. IONIC CARBIDES Methanides These carbides yield methane on hydrolysis.
They contain C4- .
Examples: Be2C, Al4C3
Be2C+ 4H2O 2Be(OH)2+CH4
Al4C3+12H2O  4Al(OH)3+3CH4.

8. IONIC CARBIDES Allylides
These ionic carbides on hydrolysis yield allylene.
[C3 ]4- is the common group found in these type of carbides.
Example: Mg2C3
Mg2C3 +4H2O  2 Mg(OH)2+ C3H4.

9. COVALENT CARBIDES
Binary compounds of carbon with elements of similar electronegativity are called covalent carbides.
Examples: Silicon carbide (SiC) or Carborandum & Boron carbide (B4C3).

10. INTERSTITIAL / METALLIC CARBIDES
In these carbides, small carbon atoms occupy interstitial positions in the crystal lattices of metals. So they are also called interstitial carbides
Examples : TiC, ZrC, VC, W2C
These carbides are also extremely hard as diamond. It has been estimated that the radius of the metal atom should be greater than 1.3 A0 to form the interstitial carbides.
So metals like Cr, Fe, Ni, Co which possess smaller atomic radii than 1.3 A0 do not form interstitial carbides.

11. Applications of carbides
Since they are very hard they are used as abrasive, drilling tools, cutting tools.
As reducing agents in metallurgy
Aluminium carbide is used for producing methane while calcium carbide is used to produce acetylene.
Carbides are used as furnace lining
Boron carbide is used for cutting diamond, making lamp filaments, drilling holes in rocks

12. NITRIDES
Nitrides are binary compounds of nitrogen with elements which are less electronegative than nitrogen.
Depending on the bond between the metal and nitrogen nitrides have been classified as
(a) Ionic nitrides
(b) covalent nitrides
(c) Interstitial nitides

13. IONIC NITRIDES
These nitrides are formed by the elements like Mg, Ca, Ba, Sr, Zn, Cd, Lithium etc.
They contain the common group N3-
Eg: Ca3N2, Li3N
6Li+ N 2Li3N
3Mg+N Mg3N2
These nitrides on hydrolysis yield NH3.
Eg: Li3N+3H2O 3LiOH+NH3

14. COVALENT NITRIDES
These nitrides are formed sharing electrons between nitrogen and elements like Boron, Carbon, Aluminium, Silicon , Fe etc.
Eg: cyanogen (CN)2, disulphur dinitrogen (S2N2), (S4N4).

15. NITRIDES INTERSTITIAL NITRIDES
Transition metals of group 3,4, 5 absorb nitrogen on heating into their lattice to form interstitial nitrides.
Eg: ScN, TiN, VN

16. BORIDES
These are binary compounds of boron with transition metals. There are a large group of borides with different stoichiometries.
(i) Boron rich borides (MB to MB66)
(ii) Metal rich borides. These borides range from M2B to M10B11

17. BORIDES Applications of Borides (March 2014)
1. Boron coated reaction vessels are used in making crucibles.
2. Borides are used as high temperature semi-conductors
3. ZrB2 and CrB2 find application as turbine blades and rocket nozzles.
4. Lanthanide hexaborides are good thermionic emitters.

18. GRAPHITE Graphite is an allotropic form of carbon.
It has a two dimensional structure.
In Graphite each carbon is sp2 hybridized.
Each carbon atom uses three hybrid orbitals to form three covalent bonds with three neighbouring carbon atoms.
Clearly the structure of graphite is a two dimensional sheet like; consisting of hexagonal rings of carbon atoms fused together. Distance between carbon atoms is 142 pm and the distance between sheets are 340 pm.
The large distance between the layers points to the formation of intercalation or lamellar compounds.

19.
The fourth valence electron in the unhybrid orbital of each carbon atom remains free.
These electrons can move from one carbon to another carbon under an applied field.
These free electrons make the graphite a good conductor of electricity

20. Properties of graphite........
It is slowly oxidised to carbon dioxide by chromic acid
It is oxidised by Conc.Nitric acid to give graphitic acid C11H4O5
When graphite is treated with potassium permanganate and conc. Sulphuric acid, graphite oxide is formed.
It reacts with Fluorine at 5000C to give carbon mono fluoride.

21. 8C+K-------------------C8K
Intercalation compounds or lamellar compounds of graphite with alkali metals
Graphite reacts with potassium metal at 3000C to give intercalation compound having the formula C8K
8C+K C8K
In the same method we can prepare C8Rb, C8Cs.
The compound C8M (M=K,Rb,Cs ) is formed through four stages.
First C48M is formed. This then converted into C36M , then to C24M and finally to C8M.

22. Intercalation compounds of graphite with metal halides
These lamellar compounds are prepared by reacting metal halides in presence of the free halogens with graphite.
The intercalated halides are lewis acids such as FeCl3, BeCl2, NiCl2, AlCl3, SbCl5
Graphite + xFeCl Graphite(FeCl3)x.
The product formed is a charge transfer complex.
The d-orbitals of Fe3+ ion receive charge from the graphite π system.

23. CARBON MONOFLUORIDE
Fluorine reacts with graphite at 5000C to give carbon monofluoride. (C2F and C4F are also formed)
C+F CFx (x= 0.68 to 0.99).
The colour of CFx depends on the fluorine content.
The colour deepens with decrease in fluorine content. When x=0.99 the colour is white.
But it may turn to black when x=0.7