Crystalline form of Carbon | Properties of Diamond and Carbon

Crystalline forms of carbon 

      1:- Diamond 

      2:- Graphite 

  

 DIAMOND 

   • Occurence :- Diamond occur in nature in many parts of the world. They have also been synthesize by subjecting pure carbon to very high pressure (50,000-60,000) and high temperature. The synthetic are small in size but are otherwise indistinguishable from natural diamond. 

 • Structure:- Each carbon atoms in Diamond is joined to four carbon atoms in such a way that one carbon atom is present at the centre of a regular tetrahedron while four others surrounding carbon atoms occupy the four vertices of this tetrahedron. The angle between any two Tetrahedron adjacent carbon atoms is 109°28'. This angle is called tetrahedral angle. As a result of this tetrahedral arrangement of carbon atoms, a crystal of diamond ia a giant molecule that appears to be a closely there dimensional rigid structure. 

Properties. 

  1:- Appearance:- Raw diamonds do not shine. To make them shine, they cut and polished so that their angled faces reflect light  and  break  into different  colours. Pure diamonds are transparent and colourless. The presence of impurities imparts colour to diamonds. 

2:- Hardness:-  The thre- dimensional network structures of diamond makes it heavy and hard  it is the hardest natural substances known. 

 3:- High melting point:-  A large amount of energy is required to break the 3- dimensional network structure of diamond, therefore, the melting point of diamond is very high (3939°C or 4203°K).

 4:- Electrical Conductor :- Since all the four valence electrons are firmly held in carbon-carbon single bonds, there are book free electrons in a diamond crystal. This makes diamond a bad conductor of electricity. 

 5:- Thermal Conductivity :- Diamonds has the highest thermal conductivity of any know substances. Therefore, the diamond topped tools do not overheat and so  are used extensively for drilling and cutting purpose. 

 6:-  Diamonds are burns on string heating to form carbon dioxide. 

         C+O2  →  CO2↑

   This shows the diamond is made up of carbon only. 

 

Uses of Diamonds. 

1:- Because of its brilliant shine, it is used in jewellery. 

2:-  Diamond knives are used by eye surgeons in duplicate eye surgeries. 

3:-  As bearing in watches. 

4:- As needles for long- playing record players. 

5:- Because diamond can withstand high radiations in space, so it is used for making radiation proof windows for spacecraft and satellite. 

GRAPHITE.  

Structure of graphite

  1:- Occurence :-  It is greyish bleck substances which occurs in nature (Sri Lanka, Siberia, China, India, New Zealand, etc.) Mixed with mica, quartz and silica. 

2:- Preparation :- It is prepared artificially from carbon by heating in an electric furnace to a temperature of about 3000°C.

3:-  Structure of Graphite :- The structure of graphite is entirely different from that of diamond. 

  In graphite molecule each carbon atom is linked with three neighbouring carbon atoms, in the same plane this forming hexagonal rings. These hexagonal rings of atom are arranged as layers or sheets piled on top of the other. 

4:- Properties of Graphite :- 

 (i) Graphite is a greyish black, opaque substances, with a metallic lustre. 

(ii) Low Density :- Due to wide spacing between the two layers, the carbon atoms in graphite are less closely packed and hence the density of graphite (2.22g cm-³) is much lower than that of diamond (3.51g cm-³). 

(iii) Softness :- The layers of carbon atoms in graphite are held together by weak forces and hence can slide over one another. This makes graphite soft and slippery. 

(iv) Electrical Conductivity :- Carbon has 4 valence electrons but in graphite crystal, each carbon atom is joined to three carbon atoms by covalent bonds. Hence, one valence electrons of each carbon atom is free to move, thus making carbon a good conductor of electricity. 

(v) Thermal Conductivity :- It is a good conductor of heat. 

Uses of graphite. 

1:- Due to it's softness, graphite is used with petroleum jelly as grease or lubricant. It is used as solid lubricant for heavy machinery operating at high temperatures. 

2:- Being soft and black graphite mark, the paper black so mixed with wax or  clay, it is used for making the cores of lead pencils. 

 3:- Being a good conductor of electricity, graphite is used for making electrode for dry cells and electric accessories. 

 4:- for making carbon brushes for electric motors. 

 5:- For making crucibles for melting metals. 

   

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