Carbon and Its Compounds

📌 Introduction

Carbon is a versatile element that forms the backbone of all living organisms and many non-living substances. The study of carbon compounds is extremely important in understanding life processes, fuels, synthetic materials, and medicines. This chapter deals with the structure, properties, and reactions of carbon and its compounds.

🔹 Carbon – The Element

Symbol: C
Atomic Number: 6
Electronic Configuration: 1s² 2s² 2p²
Valency: 4 (tetravalent)

Carbon has the unique ability to form a vast number of compounds due to the following reasons:

1. Tetravalency

Carbon has four electrons in its outer shell and requires four more to complete its octet. It forms four covalent bonds with other atoms like hydrogen, oxygen, nitrogen, and other carbon atoms.

2. Catenation

Catenation is the property of an element to form long chains with atoms of the same element. Carbon can form long straight chains, branched chains, and ring structures due to strong carbon-carbon bonding.

🔹 Types of Carbon Compounds

1. Saturated Compounds (Alkanes)

Only single covalent bonds between carbon atoms.
General formula: CnH₂n+₂
Example: Methane (CH₄), Ethane (C₂H₆)

2. Unsaturated Compounds

Contain one or more double or triple bonds between carbon atoms.

a. Alkenes

Have at least one double bond.
General formula: CnH₂n
Example: Ethene (C₂H₄)

b. Alkynes

Have at least one triple bond.
General formula: CnH₂n−2
Example: Ethyne (C₂H₂)

🔹 Types of Covalent Bonds in Carbon Compounds

Carbon atoms form covalent bonds by sharing electrons.

Single bond (–): Sharing of one pair of electrons (Alkanes)
Double bond (=): Sharing of two pairs (Alkenes)
Triple bond (≡): Sharing of three pairs (Alkynes)

Covalent compounds are generally:

Poor conductors of electricity (no free ions)
Low melting and boiling points
Mostly insoluble in water but soluble in organic solvents

🔹 Homologous Series

A homologous series is a group of organic compounds with a similar general formula, functional group, and chemical properties, differing by a CH₂ group.

Examples:

Alkanes: CH₄, C₂H₆, C₃H₈…
Alkenes: C₂H₄, C₃H₆, C₄H₈…
Alkynes: C₂H₂, C₃H₄, C₄H₆…

Characteristics:

Each successive member differs by -CH₂.
Gradation in physical properties (boiling point, melting point).
Same functional group.

🔹 Functional Groups

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

Functional Group	Formula	Example
Alcohol	–OH	CH₃OH (Methanol)
Aldehyde	–CHO	CH₃CHO (Ethanal)
Ketone	>C=O	CH₃COCH₃ (Propanone)
Carboxylic Acid	–COOH	CH₃COOH (Acetic Acid)
Halogen	–X	CH₃Cl (Chloromethane)

🔹 Nomenclature of Organic Compounds

To systematically name carbon compounds, we use the IUPAC system:

Rules:

Identify the longest carbon chain (parent chain).
Number the chain from the end nearest to the functional group or double/triple bond.
Name the substituents (branches or functional groups).
Combine names using prefixes/suffixes.

Example:
CH₃–CH₂–OH → Ethanol
CH₃–CH=CH₂ → Propene

🔹 Chemical Properties of Carbon Compounds

1. Combustion

Carbon compounds burn in oxygen to produce carbon dioxide, water, and energy (heat and light).

Example:
CH₄ + 2O₂ → CO₂ + 2H₂O + energy

Saturated hydrocarbons burn with a blue flame.
Unsaturated hydrocarbons burn with a sooty (yellow) flame.

2. Oxidation

Carbon compounds get oxidized in the presence of oxidizing agents like alkaline KMnO₄ or acidified K₂Cr₂O₇.

Example:
CH₃CH₂OH → CH₃COOH (ethanol to ethanoic acid)

3. Addition Reaction

Occurs in unsaturated compounds where hydrogen or halogens are added across double/triple bonds.

Example:
CH₂=CH₂ + H₂ → CH₃–CH₃ (in presence of nickel catalyst)

4. Substitution Reaction

Occurs in saturated hydrocarbons where one hydrogen atom is replaced by another atom or group.

Example:
CH₄ + Cl₂ → CH₃Cl + HCl (in presence of sunlight)

🔹 Important Carbon Compounds

1. Ethanol (C₂H₅OH)

Properties:

Colorless, volatile liquid.
Soluble in water.
Burns with a blue flame.

Uses:

As an antiseptic (in hand sanitizers).
In alcoholic beverages.
As a solvent.

Reactions:

With sodium:
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑
Dehydration (loss of water):
C₂H₅OH → C₂H₄ + H₂O (in presence of H₂SO₄)

2. Ethanoic Acid (CH₃COOH)

Also known as acetic acid.

Properties:

Sour taste and pungent smell.
Freezes into ice-like crystals (glacial acetic acid).
Soluble in water.

Reactions:

With base:
CH₃COOH + NaOH → CH₃COONa + H₂O
With carbonates:
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
With alcohol (Esterification):
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (pleasant-smelling ester)

🔹 Soaps and Detergents

1. Soaps

Sodium or potassium salts of long-chain carboxylic acids.
Made by saponification:
Oil + NaOH → Soap + Glycerol

2. Detergents

Made from petrochemicals.
Effective in hard water.

Difference:
Soaps do not work well in hard water due to formation of scum, while detergents work well in both hard and soft water.

🔹 Micelle Formation

In water, soap molecules form clusters called micelles. Each soap molecule has:

Hydrophilic head (water-loving)
Hydrophobic tail (water-repelling)

Micelles trap grease/dirt in the center and allow it to be washed away with water.

🧾 Summary

Carbon shows tetravalency and catenation, forming a huge variety of compounds.
Carbon compounds are covalent, have low melting/boiling points, and do not conduct electricity.
The homologous series shows gradual changes in physical properties and similar chemical behavior.
Functional groups give characteristic properties to organic molecules.
Important reactions include combustion, oxidation, addition, and substitution.
Ethanol and ethanoic acid are common carbon compounds with many industrial and household uses.
Soaps and detergents help in cleaning through micelle formation.

📘 Conclusion

Carbon is truly a “miracle element” due to its ability to form millions of compounds. The study of carbon and its compounds is crucial for understanding life processes, the pharmaceutical industry, fuels, and synthetic materials. This chapter provides the foundation for advanced organic chemistry in higher classes.