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 Multiple Choice QuestionsLong Answer Type

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131.

What are allotropes? Sketch the structure of two allotropes of carbon family namely diamond and graphite. What is the impact of structure on physical properties of two allotropes?


Allotropes. Allotropes are defined as the different forms of an element which have different physical but similar chemical properties.

Both diamond and graphite are network covalent solids in which the carbon atoms are linked by covalent bonds.

In diamond: Each carbon atom is sphybridised. It is bonded tetrahedrally to four other carbon atoms by simple covalent bonds. Thus, it has a three-dimensional network of strong covalent bonds in which C–C bond length is 154 pm and each bond angle is 109° – 28'. Due to sphybridization, the carbon atoms in diamond are closely packed and all the valence electrons are involved in bonding, leaving no free electrons, so, diamond is very hard, bad conductor of electricity and has high melting point.

In graphite: Each carbon atom is sp2 hybridised and is bonded to three other carbon atoms through covalent bonds forming hexagonal planar rings. The C–C covalent bond distance in rings is 142 pm. Graphite has a two-dimensional sheet-like structure. Due to sp2 hybridization, one p-unhybridised orbital of the carbon atom in graphite



is not involved in bond formation. Thus, one valence electron of each carbon atom is free to move (mobile electron) from one point to other and this accounts for the electrical conductivity and soft nature of graphite.

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 Multiple Choice QuestionsShort Answer Type

132.

Give reasons:
Graphite is used as lubricant.

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133.

Give reasons:
Diamond is used as an abrasive.

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 Multiple Choice QuestionsFill In the Blanks

134.

The atoms in __________ are arranged in layers.

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135.

The atoms in diamond are arranged in __________ pattern which account for its __________

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136.

When wood is heated in the absence of air, the residue is called ________

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137.

The residue can absorb fuel gases and is, therefore used in ___________

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138.

The residue is also used for _________ of substances, e.g. sugar. 

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 Multiple Choice QuestionsLong Answer Type

139.

Difference between diamond and graphite.

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 Multiple Choice QuestionsShort Answer Type

140.

Give two important uses of each of diamond and graphite.

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