Carbon and its compounds are widely distributed in nature. It is found in living organism, coal, earth crust, outer space, planetary objects etc. It is found in 3-forms in nature which are called as allotropes of carbon. The phenomenon of existence of an element in different forms which have different physical properties but similar chemical properties is known as allotropy or allotropes. Many elements show allotropy forms like hydrogen, carbon, sulphur, phosphorous etc. Carbon shows 3-allotropic forms namely: crystalline form, amorphous form and newly discovered fullerene.
Crystalline forms of carbon
The allotropes of carbon which posses fixed characteristic geometrical shapes, sharp melting point, bonded with strong intermolecular forces and are anisotropic in nature are crystalline forms of carbon. Diamond and graphite are 2 crystalline forms of carbon.
It is the purest, densest and hardest form of carbon. It is found naturally inside eath crust as well as made artificially nowdays. Inside earth crust, it is formed from coal when high pressure is created inside it. Coal is abundantly founded inside eath crust which are remains of dead trees and logs deposited millions of year ago. Diamond is formed only when all requirements are created naturally inside earth bed. Henry Moissan in 1895 first attempted to produce artifical diamond by heating pure sugar charcoal and iron in a graphite crucible at above 4000°C in electric arc furnance. Naturally it is found in many parts of the world such as Russia, Brazil, South Africa, the Belgian Congo, British Guiana etc. Russia is the top diamond mining country in the world.
Structure of diamond
The carbon atoms in diamond are linked to each other in a tetrahedral structure. Each carbon atom is sp3hybridised and linked to its neighbouring C-atom by 4 single covalent bond. Three dimensional network is created due to covalent bond formed by C-atoms which makes it hard, compact and with very high melting and boiling point. The bond length in between C-C atom is 1.54A° and bond angle is 109.5°. It refractive index is 2.418. Since, all valence electron of carbon atoms(valence electron of carbon=4) are used in C-C bond formation, no electron is left free that's why diamond is bad conductor of electricity.
Natural occuring diamonds are in the form of transparent octahedral crystals having curved surface and do not have bright shinings. It is cut at proper angles to produe large total internal refraction which then shines brighter.
Physical properties of diamond
- It is hard, shiny crystalline solid.
- It is tetrahedral with sp3hybridisation.
- It is bad conductor of electricity. The four valence electron of carbon atom in daimond are involved in bonding. Free electron is need to conduct electricity in solids. Since, no electron is left free no conduction of electricity occurs making diamond bad conductor of electricity.
- It's refractive index is 2.418.
Uses of diamond
- It is hard, shiny precious allotropes of carbon.
- It is used in making different kinds of precious juwelery.
- It is used as decorative purposes.
- Due to hardness nature, it is used in cutting class, drilling rocks etc.
It is also called as plumbago or black lead. It is soft and widely distributed in nature. Graphite is formed from diamond which is very slow process and might takes about a millions years. Artifically it is prepred by heating coke and sand in electric furnance at 3000°C.
Structure of graphite
The carbon atom in graphite are arranged in regular hexagonal in parallel layers. Each C-atoms in graphite is sp2 hybridised. The type of bond formed between C-C atoms in each layers is covelent bond. But, each parallel layers is bonded to adjacent layers by weak Vander waal force which makes each layers to slide over each other. So, both covalent bond and vander waal force is present in graphite. Out of 4 valence electron of cabon, only 3 are involved in bonding whereas one electron is free which makes some double bond character in graphite.
It is good conductor of elctricity because of this one non bonded free electron. The C-C bond lenght is 1.42A° and distance between two adjacent layers is 3.5A°.
Physical properties of graphite
- It is soft, regular hexagonal structure.
- It is good conductor of heat and electricity due to presence of one free electron.
- It's melting point is 3500°C and has density 2.2.
Uses of graphite
- Due to soft and slippery nature, it is used as lubricant in motor.
- It is used in making electrodes in electric furance as it conduct electricity through it.
- It is used in lead pencils.
- It is used in stone paints.
- It is used in manufacture of gramophone records and graphite crucible.
Amorphous forms of carbon
The allotropes of carbon which do not posses characteristic geometrical shapes, not has sharp melting point and are isotropic in nature are amorphous forms of carbon. It includes coal, charcoal, lamp black, carbon black, gas carbon, petroleum coke etc.
Coal is formed from fallen woods buried inside earth crust by the process of carbonization. Carbonization is the process of conversion of wood to caol under the influence of high temperature and pressure in absence of air. Coal is used in various ways including burning, running coal engines, running factories, producing producer gas, water gas and manufacturing coal tar, coke, coal gas etc.
Charcoal are of various types like wood charcoal, animals charcoals and sugar charcoal. Wood charcoal is formed from destructive distillation of wood which are used as good reducing agent, fuel, making gun powder. Animals charcoal is obtained by destructive distillation of bone which is also called as bone black. It is used in sugar refining for deashing agent and decolarisation of sugar. Sugar charcoal is formed by destructive distillation of cane sugar in absence of air. Sugar charcoal is the purest form of amorphous carbon.
When tar and vegetable oil rich in carbon content are burnt in insufficient suply of air, lamp black is formed. It is used in making ink, printer's ink, black paint, cabon paper etc.
It is prapared by burning naturalk gas in limited supply of air. It is used in making automobiles tyres.
Gas carbon and petroleum coke
They are used for making electrodes in dry cell.
It is newly discovered allotrope of carbon. It is also called as Buckminster fullerene in honor of it's structure designer R. Buckminster Fuller. It has one special character of having fixed number of carbon atoms in each molecule. One of the famous fullerene is C60. Other fullerene have also been discoverd like C20, C70, C72, C80, C120 etc.
Structure of fullerene
The carbon atoms in fullerene forms a ring shape structure which are fused with other rings within same molecule. All the carbon present in fullerene C60 are sp2 hybridised. Each carbon atom in C60 bends to form soccer ball shaped molecule which is also called as bucky ball. Each ring consists of 20 six member ring and 12 five member rings which makes the most symmetrical possible molecule.
Uses of fullerene
- It is used in super conductor as it offers no resistance even at room temperature.
- It is used in different nanomaterials.
- It is used in medicinal science as drugs carrier in the body.