P-Block Element and Their Compound – I: Allotropic Form of Carbon (For CBSE, ICSE, IAS, NET, NRA 2022)

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Allotropic Form of Carbon

Diamond and Graphite

  • Diamond and graphite are crystalline forms of carbon.
  • They are structurally different.
  • They show different properties due to different arrangement of carbon atoms.
  • In diamond, each carbon atom is hybridized and is linked to four other carbon atoms by strong covalent bonds in a tetrahedral fashion.
  • This gives rise to a three-dimensional arrangement (fig) .
Diamond and Graphite
  • In graphite, the carbon atoms are arranged in layers.
  • In each layer a particular carbon atom is hybridized and is linked to three other carbon atoms in a hexagonal arrangement.
  • The fourth electron is free and does not participate in bonding.
  • These different layers in graphite are held together by weak van der Waals forces (fig) .
Diamond and Graphite
  • Diamond is unreactive and burns in oxygen only if heated above forming carbon dioxide.
  • Diamond react with fluorine at giving carbon tetrafluoride.
  • Graphite is reactive and burns in air at to form .
  • Diamond is used for cutting and grinding hard substances such as rocks, glass etc.
  • Diamond is widely used in Jewellery.
  • Graphite is used as electrodes, as lubricant, for making crucibles, for casting of metals, for lead pencils and as a constituent of heat resistant paints.


  • Fullerene, a newly discovered allotrope of carbon is called “Buckminster Fullerene” .
  • Fullerene molecule has 60 carbon atoms and the carbon atoms are linked to create the shape of a hollow soccer ball.
  • Outer surface of fullerenes can be altered by the chemical reaction.

Oxides of Carbon and Silicon


  • Carbon forms two oxides, viz, carbon monoxide and carbon dioxide.
  • The bonding in carbon monoxide may be represented as, three electron pairs shared between the two atom.
  • The three electron pairs consist of one hybridized bond and two bonds.

  • The structure of carbon dioxide is linear .
  • Two bonds and two bonds in the molecule .
  • The carbon atom use hybrid orbitals to form bonds with oxygen atoms.
  • The remaining two orbitals of carbon overlap with orbitals one each from the two atoms to form the bonds.

Silicon forms two oxides:



  • Silicon monoxide is only known at high temperatures.
  • Silica is found as sand and quartz.


  • Carbon monoxide is a neutral oxide.
  • Carbon monoxide is a colorless, odorless and a poisonous gas and burns with a flame.
  • Carbon monoxide is toxic because it forms a complex with the hemoglobin in the blood which prevents the hemoglobin from carrying oxygen around the body which leads to oxygen deficiency resulting in unconsciousness or death.
  • Carbon dioxide is an acidic oxide.
  • is an acidic oxide and is unreactive in all its forms.
  • dissolves slowly in aqueous alkalis and more rapidly in fused alkalis or fused carbonates forming silicates.

Silica reacts with fluorine and to form silicon tetrafluoride.

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