Carbon: Properties and Allotropes

Carbon: Properties and Allotropes

Properties and Allotropes

Introduction

• Carbon is a non-metal with an atomic number of 6 and a mass number of 12. It is placed in Group (IV) A, or Group 14, in the periodic table.

Allotropy of Carbon

• The substances which have the same chemical properties but different physical properties are called allotropes, and this property is known as allotropy.

Examples of Allotropes of Carbon

• Diamond

• Graphite

• Charcoal

Allotropes of Carbon

1. Diamond

• Purest form of carbon: Diamond is considered the purest form of carbon.

• Hardest natural substance: It is the hardest known natural substance.

• Transparent: Diamond is transparent, with a specific gravity of 3.52.

• Poor conductor: It is a poor conductor of electricity and heat.

• High refractive index: It has a very high refractive index of 2.415.

• Chemically inert: Diamond is chemically inert, and when heated above 1500°C, it converts into graphite.

• Crystal structure: It forms tetrahedral crystals, and the hybridisation of the carbon atoms is sp³.

• High melting point and density: Diamond has a high melting point and density.

• Black diamond (carbonado): Black diamonds, called carbonado, contain traces of graphite.

2. Graphite (Plumbago or Black Lead)

• Soft and greasy: Graphite is a soft, greasy, dark greyish-coloured crystalline solid.

• Good conductor: It is a good conductor of heat and electricity.

• Specific gravity: Its specific gravity is 2.3.

• Hexagonal structure: The hybridisation of carbon in graphite is sp², and it has a hexagonal layer structure.

• Chemically more reactive: Graphite is chemically more reactive than diamond.

• Layer structure: The layers in graphite are held together by weak Van der Waals forces.

• Uses of Graphite:

  • Used for lining and making electrodes in electric furnaces.

  • Used to make refractory crucibles.

  • Used in making lead pencils.

  • Used as a moderator in nuclear reactions.

  • Used as a lubricant in machinery.

  • Used as a reducing agent in steel manufacturing.

3. Forms of Amorphous Carbon (Obtained by Destructive Distillation)

• Wood Charcoal: Obtained from wood.

• Sugar Charcoal: Obtained from cane sugar.

• Bone or Animal Charcoal: Obtained from animal bones.

• Coke Charcoal: Obtained from coal.

Hydrocarbons

What are hydrocarbons?

Hydrocarbons are compounds made up of carbon and hydrogen atoms only. The natural source of hydrocarbons is petroleum.

Classification of Hydrocarbons

Hydrocarbons are classified into three main types:

1. Saturated Hydrocarbons

2. Unsaturated Hydrocarbons

3. Aromatic Hydrocarbons

1. Saturated Hydrocarbons

• Saturated hydrocarbons, also known as alkanes or paraffins, contain carbon atoms connected by single bonds.

• Alkanes are relatively unreactive under ordinary laboratory conditions, which is why they are also called paraffins (meaning "little reactive").

• General formula of alkanes: CₙH₂ₙ+₂

2. Unsaturated Hydrocarbons

The hydrocarbons in which carbon atoms are either doubly or triply bonded are called unsaturated hydrocarbons. Doubly bonded carbon atoms (C=C) in hydrocarbons are called alkenes. The general formula of alkynes is C_nH_2n.

Ethene (ethylene) is used for natural ripening of fruits. Triply bonded carbon: Carbon atoms containing hydrocarbons are called alkynes. The general formulas of alkynes are C_nH_2n-2

Example: Ethyne (Acetylene) – The molecular formula of ethyne is C₂H₂, and its structural formula is H-C≡C-H.

• • Uses: Acetylene is used for artificial ripening of fruit.

3. Aromatic Hydrocarbons

Aromatic hydrocarbons are homocyclic compounds that contain at least one benzene ring. In these rings, carbon atoms are linked to one another by alternating single and double bonds.

• Origin of Name: The word "aromatic" comes from the Greek word "aroma", meaning sweet smell. Compounds in this category often have a pleasant smell, hence the name aromatic compounds.

Isomerism

Isomerism is a phenomenon where two or more compounds have the same molecular formula but different physical and chemical properties. These compounds are called isomers.

Petroleum

The term 'petroleum' (from Latin 'petra', meaning 'rock', and 'oleum', meaning 'oil') refers to the dark-coloured oily liquid with an offensive odour found at various depths below the surface of the Earth. It is also called rock oil, mineral oil, or crude oil.

A complete list of petroleum products, approximate composition, boiling range and their uses is given ahead.

Fractional Distillation of Petroleum

Final Thoughts

Carbon, a versatile non-metal (atomic number 6), exhibits allotropy — existing as diamond, graphite, and amorphous carbon.

Diamond is the purest, hardest, and most transparent form, while graphite is soft, conductive, and layered. Amorphous forms like wood charcoal and coke arise from destructive distillation. Carbon combines with hydrogen to form hydrocarbons, which are classified as saturated (alkanes), unsaturated (alkenes and alkynes), and aromatic compounds like benzene.

The fractional distillation of petroleum yields useful products such as petrol, kerosene, diesel, lubricating oil, and paraffin wax, each varying in boiling range and carbon composition, serving vital roles as fuels, lubricants, solvents, and industrial materials in daily life.