Maarg Manthan · Topic 7.3

Carbon and Its Allotropic Forms

Science & Technology › Chemistry in Daily Life and Biomolecules · Topic 7.3

Carbon is a non-metal with atomic number 6 and four valence electrons, which allows it to form four bonds and to link with itself in long chains, a property called catenation. It forms more compounds than any other element, and is the base of organic chemistry and life. Allotropes are different forms of the same element in the same physical state. The crystalline allotropes of carbon are diamond, graphite, fullerenes, carbon nanotubes and graphene, and amorphous forms include coal, coke, charcoal and carbon black. Diamond is the hardest natural substance, graphite is soft and conducts electricity, buckminsterfullerene is a cage of 60 carbon atoms, and graphene is a single layer of carbon atoms. Andre Geim and Konstantin Novoselov received the Nobel Prize in Physics in 2010 for graphene.

5 min read · UPSC Prelims · Science & Technology · Chemistry in Daily Life and Biomolecules

At a Glance

Atomic number 6
Hardest allotrope Diamond
Conducting allotrope Graphite
Fullerene C60 (Kroto, Curl, Smalley)
Graphene Nobel Prize 2010
Exam link UPSC Prelims, Science & Technology: Chemistry in Daily Life and Biomolecules

Where Does It Fit?

This is the third topic of the macro on chemistry in daily life and biomolecules. It follows polymers and introduces the element that links organic chemistry and materials science. Previous topic: Chemistry of Pharmaceuticals. Next topic: Hydrocarbons and Their Derivatives.

What Are the Main Allotropes of Carbon?

Allotrope	Structure, properties and uses
Diamond	Each carbon is bonded to four others in a rigid three-dimensional network. Hardest natural substance, transparent, a very poor electrical conductor but a good conductor of heat, with a high refractive index. Used in jewellery, cutting and drilling tools
Graphite	Carbon atoms in flat hexagonal layers that slide over each other. Soft, slippery and a good conductor of electricity. Used in pencils, lubricants, electrodes and as a moderator in some nuclear reactors
Fullerenes	Hollow cages or balls of carbon, such as C60, called buckminsterfullerene, discovered in 1985 by Harold Kroto, Robert Curl and Richard Smalley, who received the Nobel Prize in Chemistry in 1996
Carbon nanotubes	Rolled sheets of graphene forming tubes. Identified by Sumio Iijima in 1991. Very strong and conducting, used in composites and electronics
Graphene	A single layer of carbon atoms in a honeycomb pattern. Very strong, thin, light and a good conductor, studied for batteries and sensors
Amorphous carbon	Coal, coke, charcoal, lamp black and carbon black. Without regular crystal structure. Used as fuel and in tyres and ink

What Makes Carbon Special?

Tetravalency: four valence electrons allow four covalent bonds.
Catenation: carbon atoms join to form long chains, branched chains and rings, which gives millions of compounds.
Multiple bonds: carbon can form double and triple bonds with itself and with other elements.
Isomerism: the same formula can have different structures and properties, as in Hydrocarbons and Their Derivatives.
Hybridisation: diamond has sp3 carbon, graphite has sp2 carbon, and acetylene has sp carbon.
Carbon cycle: carbon moves between air, plants, animals, soil and the ocean through photosynthesis, respiration and decay, as in Photosynthesis: Light Reaction and Dark Reaction.

What Else Should You Remember?

Carbon dating: radioactive carbon-14 is used to find the age of organic remains up to about 50,000 years, as in Structure of Atoms.
Carbon fibre: light and strong fibres used in aircraft, sports goods and rockets.
Lab-grown diamonds: made by high-pressure high-temperature or chemical vapour deposition methods. India announced a research programme on them at IIT Madras in the Union Budget 2023 to 2024, and Surat is a major diamond cutting centre.
Where diamonds occur: in kimberlite rocks, and in India in Panna in Madhya Pradesh, with historic ones from Golconda.
Carbon compounds: carbon dioxide, carbon monoxide, carbonates, hydrocarbons, carbohydrates and many more, as in Biomolecules: Carbohydrates, Proteins, Lipids, Nucleic Acids.
Carbon monoxide: a poisonous gas that binds haemoglobin, from incomplete burning, as in Respiratory System: External and Internal Respiration in Humans, Animals, Plants and Insects.
Carbon footprint and capture: measures of emissions, and methods to capture and store carbon dioxide are discussed for climate action.
Activated charcoal: highly porous carbon used to adsorb poisons and in water purifiers.
Carbon compounds in fuels: coal, petroleum and natural gas are carbon-rich fuels formed from ancient plants and animals, and their burning adds carbon dioxide to the air.
Coal types: coal ranks from peat to lignite, bituminous and anthracite, with the carbon content rising and anthracite being the highest grade.
Black carbon: soot from incomplete combustion warms the atmosphere and harms health, and it is a short-lived climate pollutant.

Why Does It Matter for the Exam?

Property questions: why graphite conducts but diamond does not, and why diamond is hard.
Discovery questions: who discovered fullerene and who got the Nobel Prize for graphene.
Technology link: nanomaterials, batteries and lab-grown diamonds.
Industry link: India’s gem and jewellery sector.
Common errors: saying that diamond conducts electricity or that graphite is hard.

As an analytical point, the same element can behave very differently depending on how its atoms are joined. Structure decides properties, which is a central idea in materials science.

Why Is This Topic Important?

Facts Allotropes and Nobel asked
Concept Structure and property
Link Nanotechnology

What Came Next?

The next topic covers hydrocarbons and their derivatives. Next topic: Hydrocarbons and Their Derivatives.

Key People and Terms

Allotrope Different form of the same element
Catenation Self-linking of atoms
Fullerene Cage of carbon atoms
Graphene One-atom-thick carbon sheet
Kimberlite Rock that holds diamonds
Amorphous Without regular structure

Exam Corner

Points to Remember

Diamond hardest; graphite conducts.
C60: Kroto, Curl, Smalley, 1996.
Graphene: Nobel 2010.
Nanotubes: Iijima, 1991.
Carbon has four valence electrons.

Do Not Confuse With

Diamond and graphite 3D network versus layers
Graphene and nanotube Flat sheet versus rolled tube
Allotrope and isotope Different form versus different neutron number

Memory Hook

Diamond sp3 hard and bright, graphite layers slip and conduct; C60 ball by Kroto’s three, graphene sheet, Nobel twenty ten.

Mains Angle

Questions link carbon materials with technology. These points add depth.

Allotropes Structure and properties
Uses Industry and electronics
Future Graphene and nanotubes

A Question You May Face

An original practice question, not a past paper question.

“Explain how the structure of the allotropes of carbon determines their properties and uses.”

How to Answer

Carbon Tetravalency.
Allotropes Diamond, graphite.
Nano forms Fullerene, graphene.
Use Industry.

GS Relevance

Prelims: allotropes, structures and properties, discoverers, uses. GS Paper 3: science and technology, materials.

Frequently Asked Questions

What are allotropes of carbon?

Allotropes are different structural forms of carbon in the same physical state. The crystalline ones are diamond, graphite, fullerenes, carbon nanotubes and graphene, and they differ in the way carbon atoms are arranged, which gives very different properties such as hardness and electrical conductivity.

Why is diamond hard and graphite soft?

In diamond each carbon atom is joined to four others by strong covalent bonds in a rigid three-dimensional network, so it is extremely hard. In graphite the atoms lie in flat layers held together by weak forces, so the layers slide over each other, which makes graphite soft and a good lubricant.

Why does graphite conduct electricity?

In graphite each carbon atom uses three of its four valence electrons for bonding within a layer, leaving one electron free to move between atoms along the layer. These free electrons carry electric current, so graphite conducts, whereas diamond has no free electrons and is an insulator.

What is graphene?

Graphene is a single layer of carbon atoms arranged in a honeycomb pattern. It is extremely thin, strong, light and an excellent conductor, and Andre Geim and Konstantin Novoselov received the Nobel Prize in Physics in 2010 for isolating it. It is being studied for batteries, sensors and electronics.

What is a fullerene?

A fullerene is a form of carbon made of atoms joined in a hollow cage, sphere or tube. The first one, C60 or buckminsterfullerene, has 60 carbon atoms in a shape like a football, and was discovered in 1985 by Harold Kroto, Robert Curl and Richard Smalley, who received the 1996 Nobel Prize in Chemistry.

PYQ Practice — Statement Analysis

1 Graphite is a good conductor of electricity.

True

It has free electrons.

2 Diamond conducts electricity well.

False

It is an insulator.

3 C60 is called buckminsterfullerene.