The crystalline allotrope of carbon is

Concept:

Crystals:

• Crystals are formed by the symmetrical arrangement of constituent atoms.
• The atoms are arranged in repeating units and the basic unit is called a unit cell.
• There are three types of unit cells depending on the arrangement of atoms.
• A unit cell tells us about the number of atoms and the nature of the arrangement.
• Multiple unit cells put together in an ordered manner give us Crystal lattice.

Allotropes:

• Depending on the conditions of formation like temperature and pressure, different forms of compounds of the same element may be formed.
• These compounds are called allotropes and the element is said to exhibit allotropy.
• Carbon occurs in nature abundantly in both free and compound forms.
• Carbon has allotropes in crystalline as well as amorphous forms.
• The allotropes of carbon like a diamond, graphite, etc are crystalline solid but wood, and stone are non-crystalline solid.

Explanation:

• Graphite:
  • Graphite is an allotropic form of carbon that has units of six carbon atoms grouped together forming a crystal structure.
  • The units in the crystal structure are arranged in an ordered hexagonal manner.
  •  In each of the hexagonal unit cells, the carbon atoms are attached to the neighbouring three carbon atoms.
  • Graphite has hexagonal layers of carbons that can slip on each other and thus it is slippery in nature.
  • Graphite is lustrous and brittle in nature.
  • The structure of graphite is given as follows:

Hence, the crystalline allotrope of carbon is Graphite.

Additional Information

• Amorphous compounds are compounds that have no ordered manner of arrangement of atoms. Amorphous forms of carbon are coal, coke, charcoal, lamp black and gas carbon.