ALLOTROPES OF CARBON

INTRODUCTION

  • Carbon is the seventeenth most copious element by mass in the earth’s crust.
  • It is extensively distributed in nature in free as well as in the combined state.
  •  In the elemental state, it is obtainable as coal, graphite, and diamond. However, it is present in metal carbonates, hydrocarbons, and carbon dioxide in the air in a combined state.
  • In the world, carbon is the most versatile element.
  •  Of all living organisms, it is an essential constituent.
  • Naturally, occurring carbon contains two stable isotopes: 12C and 13C. In addition to these, a third isotope, 14C is also present.
  • In carbon, only s and p orbitals are available for the bonding and therefore it can only accommodate 4 pairs of electrons around it.
  • Carbon also has the unique ability to form pπ -pπ multiple bonds with itself and with other atoms of smaller size.
  • Carbon atoms tend to link with one another through covalent bonds (bonds which are formed by the sharing of an electron pair between two atoms) to form chains and rings, this property is known as catenation.
  •  Carbon can show allotropic forms, due to its property of catenation and pπ-pπ bond formation.

ALLOTROPES OF CARBON – 

  • With widely varying physical properties, carbon occurs in different forms in nature.
  • Carbon exhibits many allotropic forms; both crystalline as well as amorphous. And the third form of carbon is known as fullerenes.
  • Diamond and graphite are two well-known crystalline forms of carbon, the difference lies in the manner in which the carbon atoms are bonded to one another.

DIAMOND

  • It has a crystalline lattice.
  •  Each carbon atom is linked to four other carbon atoms forming a rigid three-dimensional structure.
  •  In this structure, directional covalent bonds are present throughout the lattice.
  •  Diamond is the hardest substance on the earth because it is difficult to break down the extended covalent bonding.
  • It is used as an abrasive for sharpening hand tools, making dyes, and manufacturing tungsten filaments for electric light bulbs.
  •  By subjecting pure carbon to very high pressure and temperature, the diamond can be synthesized. These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.

GRAPHITE

  • Graphite has a layered structure.
  • Layers are grasped by van der Waals forces.
  • Each layer is composed of planar hexagonal rings of carbon atoms.
  • In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array.
  • Graphite is smooth and slippery.
  • Graphite is a very good conductor of electricity, unlike other non-metals.
  • Most stable allotrope of carbon.
  • The diamond and graphite both are having very different physical properties even though their chemical properties are the same.

FULLERENES

  • By heating graphite in an electric arc in the presence of inert gases such as helium or argon, fullerenes are made.
  • Fullerenes are the only pure form of carbon because they have a smooth structure without having dangling bonds.
  • Fullerenes are cage-like molecules.
  • C60 molecule has a shape like a soccer ball and is called buckminsterfullerene.
  • It contains twenty, six-membered rings and twelve, five-membered rings

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