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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
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Allotropes of Carbon - Class 10 Tutorial - Amrita University

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許藝菊 2015 年 9 月 18 日 に公開
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