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  • ALLOTROPES OF CARBON

  • Carbon is a well known non-metallic chemical element which is present in all life forms.

  • The element carbon occurs in different forms in nature with wide variety of physical properties.

  • It is abundantly found in the Earth's crust.

  • Let's now try to have a better understanding of Carbon and its compounds'.

  • Carbon is represented by the symbol C. Its atomic number is 6. ie, it contains 6 protons

  • and 6 electrons. Carbon exists in two forms: Crystalline and

  • Amorphous. In crystalline solids the constituent particles are arranged in a definite order

  • but in amorphous solids the constituent particles have no definite order of arrangement.

  • Coal, coke and charcoal are amorphous form of carbon. and Diamond, Graphite and fullerene

  • are crystalline forms of carbon. Both these forms are called allotropes of

  • carbon. Allotropes are forms of the same element which

  • exhibit different physical properties but with same chemical composition.

  • Let's now classify Carbon according to its shape, structure and physical properties:

  • Accordingly let us understand the crystalline forms -- Diamond.

  • Diamond is the hardest crystalline form of carbon.

  • In diamond, each carbon atom is linked to four other carbon atoms by covalent bonds

  • forming a rigid three dimensional structure. Each C-C bond length is 154pm. Diamond's density

  • is equal to 3.5 g/cc. Here, no free electrons are available as they

  • are involved in bond formation. Because of the absence of free electrons, diamond is

  • a bad conductor of electricity Diamond has high melting point 4000 Kelvin

  • or more. Let's now learn about other crystalline allotropic

  • form of carbon in Free State ' Graphite.

  • In graphite, each carbon atom is linked to three other carbon atoms by covalent bonds,

  • resulting in hexagonal rings which are arranged in layers one above the other. One of the

  • carbon- carbon bonds is double bond thus the valency of carbon is satisfied.

  • Since one electron of each carbon atom in graphite is free to move about, graphite is

  • a good conductor of electricity The Carbon to Carbon bond length is 142 pm.

  • These layers are held together by weak force of attraction and the distance between the

  • layers is 335 pm. Due to its structure, Graphite is not hard

  • as diamond and is greasy. It has grey color. It has a metallic luster and it is opaque.

  • Its density varies from 2.0 to 2.25 g/cc and it melts at about 1800 Kelvin.

  • We will examine another carbon allotrope ' Fullerene. Chemically fullerenes are formed by the combination

  • of a large number of carbon atoms. The first one to be identified was C60.Its

  • structure has been established on the basis of investigations carried by Buckminster Fuller,

  • an American architect. So Fullerenes are often called Bucky balls.

  • The shape of Fullerene resembles that of a soccer ball with six membered as well as five

  • membered rings. There are 12 five membered rings and 20 six membered rings.

  • In fullerene, all the carbon atoms are found to be equivalent, and are connected by both

  • single and double bonds. [ Bond length of single bonds = 145.3 pm, Bond length of double

  • bonds = 138.3 pm].

  • THINGS TO REMEMBER:

  • Carbon is represented by the symbol 'C'. Its atomic number is 6 i.e., it contains 6 protons

  • and 6 electrons. Carbon exists in two forms as Crystalline

  • and Amorphous form. These forms are known as allotropes of carbon.

  • The crystalline forms of carbon are diamond, graphite and Fullerene.

  • Diamond is the hardest crystalline form of carbon. Each C-C bond length is 154pm

  • Graphite is not hard as diamond and is a greasy substance. The Carbon to Carbon bond length

  • is 142 pm. Fullerene resembles as a soccer ball and has

  • 6 membered as well as 5

ALLOTROPES OF CARBON

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B2 carbon crystalline diamond graphite bond pm

Allotropes of Carbon - Class 10 Tutorial - Amrita University

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    許藝菊 posted on 2015/09/18
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