Question

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

Answer 1

Allotropes

• Allotropes are two or more forms of the same elements that exist in the same physical state (solid, liquid, or gas) but have physical and chemical properties that differ from one another.
• Allotropy is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.
• Example : Allotropes of carbon: Diamond, Graphite and Buckminsterfullerene.

Structure of diamond and graphite

The structure of a diamond is as follows:-

The structure of graphite is as follows:-

Impact of structure on the physical properties of diamond

• Each carbon atom in a diamond undergoes $s{p}^3$ hybridisation and is bonded to four other carbon atoms in a tetrahedral fashion.
• The structure expands throughout space, forming a hard three-dimensional carbon atom network.
• Throughout the lattice, directional covalent bonds are present.
• Diamond is the hardest substance on the Earth because it is extremely difficult to break extended covalent bonding.

Impact of structure on physical properties of Graphite

• In a hexagonal ring, the hybridization of each carbon atom is $s{p}^2$ .
• $\pi$ bond is formed by the fourth electron. The electrons are delocalized over the whole sheet.
• So, graphite conducts electricity along the sheet.
• Graphite is extremely slippery and soft because it cleaves easily between layers.
• As a result, graphite is commonly utilized as a dry lubricant in machines running at high temperatures.