Carbon and Its Compounds: Why One Element Can Build an Entire World

If chemistry had a backbone, carbon would be it.
From the food we eat to the fuel we burn, from medicines to plastics, from clothes to fuels, everything important in daily life is built around carbon and its compounds.
This chapter explains:

• Why carbon is so special
• How carbon exists in different forms
• What hydrocarbons are
• How organic compounds are classified
• Why ethanol and ethanoic acid are so important

Let us understand this chapter slowly and clearly.

Introduction: Why Carbon Is Unique

Carbon is a non-metal, yet it forms an exceptionally large number of compounds.
No other element in the periodic table shows this behaviour to the same extent.
The reason lies in two special properties of carbon:

• Catenation
• Tetravalency

Catenation

Catenation is the ability of carbon atoms to bond with one another to form long chains, branches, and rings.
Carbon–carbon bonds are very strong.
Because of this, carbon can form:

• Long straight chains
• Branched chains
• Cyclic structures

This is why carbon compounds are so numerous.

Tetravalency

Carbon has four valence electrons.
To achieve stability, it forms four covalent bonds.
This allows carbon to bond with:

• Hydrogen
• Oxygen
• Nitrogen
• Halogens
• Other carbon atoms

As a result, carbon forms millions of stable compounds.

Allotropes of Carbon

Carbon exists in different forms in nature.
These different forms of the same element are called allotropes.
Allotropes have:

• Same chemical properties
• Different physical properties
  Carbon has two main types of allotropes:
• Crystalline allotropes
• Amorphous allotropes

Crystalline Allotropes of Carbon

Crystalline allotropes have a definite geometric structure.
The most important crystalline allotropes are diamond and graphite.

Diamond

In diamond:

• Each carbon atom is bonded to four other carbon atoms
• Bonds are very strong
• Structure is rigid

Properties:

• Extremely hard
• Does not conduct electricity
• Transparent
• High melting point

Uses:

• Cutting tools
• Jewellery
• Drilling machines

Diamond is hard because all carbon atoms are strongly bonded.

Graphite

In graphite:

• Each carbon atom is bonded to three other carbon atoms
• Layers are formed
• Weak forces exist between layers

Properties:

• Soft and slippery
• Good conductor of electricity
• Black in colour

Uses:

• Pencil leads
• Lubricants
• Electrodes

Graphite conducts electricity because it has free electrons.

Amorphous Allotropes of Carbon

Amorphous allotropes do not have a regular structure.
Examples:

• Coal
• Charcoal
• Coke
• Lamp black

They are mainly used as fuels and adsorbents.

Hydrocarbons

Hydrocarbons are organic compounds that contain only carbon and hydrogen.
They form the basic framework of organic chemistry.
Hydrocarbons are classified into:

• Saturated hydrocarbons
• Unsaturated hydrocarbons

Saturated Hydrocarbons (Alkanes)

Saturated hydrocarbons contain only single covalent bonds between carbon atoms.
General formula:

C_nH_2n+2

Examples:

• Methane (CH₄)
• Ethane (C₂H₆)

Properties:

• Less reactive
• Burn with clean flame

Uses:

• Fuels
• Cooking gas
• Heating

Unsaturated Hydrocarbons

Unsaturated hydrocarbons contain double or triple bonds.
They are of two types:

• Alkenes
• Alkynes

Alkenes

Contain at least one double bond.
General formula:

C_nH_2n

Example:

• Ethene (C₂H₄)

Alkynes

Contain at least one triple bond.
General formula:

C_nH_2n-2

Example:

• Ethyne (C₂H₂)

Unsaturated hydrocarbons are more reactive than saturated ones.

Homologous Series

A homologous series is a family of organic compounds having:

• Same functional group
• Similar chemical properties
• Gradual change in physical properties
  Successive members differ by –CH₂– unit.

Characteristics of a Homologous Series

• Same general formula
• Similar chemical reactions
• Gradual change in boiling point
• Molecular mass increases regularly

Example:

• CH₄
• C₂H₆
• C₃H₈

Each member differs by –CH₂–.

Functional Groups

A functional group is an atom or group of atoms that gives a compound its characteristic chemical properties.
Examples:

• –OH → Alcohol
• –COOH → Carboxylic acid
  Functional groups determine the behaviour of carbon compounds.

Ethanol: Properties and Uses

Ethanol (C₂H₅OH) is an important alcohol.

Physical Properties of Ethanol

• Colourless liquid
• Pleasant smell
• Soluble in water
• Volatile in nature

Chemical Properties of Ethanol

Combustion

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

Ethanol burns with a blue flame.

Reaction with Sodium

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂

This reaction shows that ethanol has acidic nature.

Uses of Ethanol

• Fuel
• Solvent
• Medicines
• Alcoholic beverages

Ethanoic Acid: Properties and Uses

Ethanoic acid (CH₃COOH) is a carboxylic acid.
It is commonly known as acetic acid.

Physical Properties of Ethanoic Acid

• Colourless liquid
• Sour smell
• Freezes at 16.6°C (glacial acetic acid)

Chemical Properties of Ethanoic Acid

Reaction with Metals

2CH₃COOH + Zn → (CH₃COO)₂Zn + H₂

Reaction with Bases

CH₃COOH + NaOH → CH₃COONa + H₂O

Reaction with Carbonates

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Uses of Ethanoic Acid

• Vinegar (food preservation)
• Manufacture of esters
• Laboratory reagent

---

FAQs – CARBON AND ITS COMPOUNDS (Exam-Focused)