Introduction

Carbon is one of the most important elements in nature. It is present in all living organisms and in substances like coal, petroleum, and natural gas. Carbon exhibits catenation (carbon-carbon bonding), which allows it to form long chains, branched structures, or rings. This chapter explores the tetravalency (forms four bonds), covalent bonding (electron sharing), and diverse compounds of carbon in our daily lives.

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1. Unique Nature of Carbon
Carbon is unique due to its two main properties:

(i) Catenation
Carbon atoms bond with other carbon atoms, forming long chains, rings, and branched structures.
This property explains why millions of carbon compounds exist.

(ii) Tetravalency
Carbon has four valence electrons, forming covalent bonds with elements like hydrogen, oxygen, nitrogen, and sulfur.
It shares electrons rather than gaining or losing them.

2. Allotropes of Carbon
Carbon exists in different allotropic forms, including:

(i) Diamond
Hard, non-conductor of electricity.
Used in jewelry and cutting tools.

(ii) Graphite
Soft, conductor of electricity.
Used in pencil lead and lubricants.

(iii) Fullerene
Spherical structure (Buckyballs).
Used in nanotechnology.

3. Covalent Bonding in Carbon Compounds
Carbon forms covalent bonds by electron sharing:

Single Bond (C-C) → Example: Methane
Double Bond (C=C) → Example: Ethene
Triple Bond (C≡C) → Example: Ethyne

Properties of Covalent Compounds:
Low melting and boiling points.
Do not conduct electricity.
Generally insoluble in water.

4. Hydrocarbons – Compounds of Carbon and Hydrogen
Hydrocarbons are classified as:

(i) Saturated Hydrocarbons (Alkanes)

Contain single bonds (C-C).
General formula: C?H????.
Example: Methane (CH?), Ethane (C?H?).

(ii) Unsaturated Hydrocarbons
Contain double (C=C) or triple (C≡C) bonds.
General formula:
Alkenes (C=C) → C?H?? (Example: Ethene C?H?).
Alkynes (C≡C) → C?H???? (Example: Ethyne C?H?).

5. Functional Groups in Organic Compounds

Functional groups define the chemical properties of a compound.

6. Homologous Series
A homologous series consists of compounds with:

Same general formula.
Gradation in physical properties.
Similar chemical behavior.
Example: Alcohol series (Methanol, Ethanol, Propanol, etc.).

7. Chemical Properties of Carbon Compounds

(i) Combustion (Burning of Carbon Compounds)
Carbon compounds burn in oxygen to produce carbon dioxide and energy.
Fuels like petrol, diesel, LPG, and CNG undergo combustion.

(ii) Oxidation
Alcohols oxidize to acids using oxidizing agents like potassium permanganate.

(iii) Addition Reaction (Unsaturated Compounds Only)
Hydrogenation converts unsaturated hydrocarbons into saturated ones using a nickel catalyst.

(iv) Substitution Reaction (Saturated Compounds Only)
Alkanes react with chlorine in sunlight, replacing hydrogen atoms.

8. Ethanol and Ethanoic Acid – Important Carbon Compounds

(i) Ethanol (C?H?OH) – Alcohol
Solvent, fuel, used in alcoholic beverages.
Reacts with sodium, releasing hydrogen gas.

(ii) Ethanoic Acid (CH?COOH) – Acetic Acid
Present in vinegar, used as a preservative.
Undergoes esterification to form esters (fruity-smelling compounds).

9. Soaps and Detergents

(i) Soaps
Natural, work in soft water.
Micelles trap dirt and remove grease.

(ii) Detergents
Synthetic, work in hard water.
Used in laundry and household cleaning.

10. Importance of Carbon Compounds in Daily Life

Fuels: Petrol, diesel, LPG, CNG.
Food Components: Carbohydrates, proteins, fats.
Medicines: Aspirin, antibiotics, painkillers.
Plastics and Polymers: Used in synthetic fibers, rubber, and household items.

FAQs – Frequently Asked Questions

Q1: Why is carbon important?
Carbon forms millions of compounds due to catenation and tetravalency.

Q2: Why do covalent compounds have low melting and boiling points?
Due to weak intermolecular forces.

Q3: Why is diamond hard but graphite soft?
Diamond has a rigid 3D structure, while graphite has layers that slide.

Q4: What happens when ethanol reacts with sodium?
It produces hydrogen gas and sodium ethoxide.

Q5: Why are alkanes called saturated hydrocarbons?
They contain only single bonds (C-C).

Q6: What is the difference between soaps and detergents?
Soaps are natural and don’t work well in hard water. Detergents are synthetic and work in both.

Q7: Why is vinegar used in cooking?
Vinegar contains acetic acid, enhancing flavor and preservation.

Q8: What is the role of catalysts in hydrogenation?
Nickel or palladium speeds up the addition of hydrogen to unsaturated compounds.