Chapter 4: Carbon and Its Compounds

Introduction to Carbon

• Carbon is a versatile element due to its tetravalency and ability to form multiple bonds.
• Atomic number: 6
• Electronic configuration: 2,4
• Carbon can form covalent bonds by sharing electrons with other atoms.

Covalent Bonding In Carbon

Definition: A covalent bond is a chemical bond formed by the sharing of electrons between two atoms to achieve a stable electronic configuration (Octet Rule).

Carbon, having 4 valence electrons, cannot lose or gain electrons easily. Instead, it shares electrons to form stable compounds.

Why Does Carbon Form Covalent Bonds?

Does Not Lose Electrons:

• Losing 4 electrons to form C⁴⁺ is difficult as it requires a lot of energy.

Does Not Gain Electrons:

• Gaining 4 electrons to form C⁴⁻ would make it highly unstable.

Shares Electrons:

• Instead of losing or gaining electrons, carbon shares its valence electrons to form strong covalent bonds.

 

Types of Covalent Bonds

Covalent bonds are classified based on the number of shared electron pairs.

Type of Bond	Definition	Example
Single Covalent Bond	One pair (2 electrons) is shared between atoms	Hydrogen (H₂),         H-H Methane (CH₄)            H              |     H — C — H               |              H
Double Covalent Bond	Two pairs (4 electrons) are shared between atoms.	Oxygen (O₂),  —  O = O — Ethene (C₂H₄)   H – C = C – H           |      |          H    H
Triple Covalent Bond	Three pairs (6 electrons) are shared between atoms.	Nitrogen (N₂),        N≡N Ethyne (C₂H₂)    H – C ≡ C – H

 

Allotropes of Carbon

Introduction to Allotropes

Definition: Allotropes are different structural forms of the same element, having different physical properties but the same chemical properties.

Carbon exists in several allotropic forms due to its ability to form covalent bonds and different structural arrangements.

Types of Carbon Allotropes

(A) Crystalline Allotropes (Well-organized structure)

1 . Diamond

(A) Diamond – The Hardest Natural Substance

structure:

 

• Each carbon atom is tetrahedrally bonded to four other carbon atoms by strong covalent bonds.
• Forms a three-dimensional rigid network.

Properties:

✔ Extremely hard – Hardest known natural substance.

✔ High melting point – About 4000°C.

✔ Poor conductor of electricity – No free electrons.

✔ Transparent and shiny – High refractive index.

Uses:

🔹 Used in jewelry due to its brilliance.

🔹 Used in cutting and drilling tools (glass cutters, drill bits).

 

2. Graphite

(B) Graphite – A Good Conductor of Electricity

Structure:

 

• Carbon atoms are arranged in hexagonal layers.
• Each carbon is bonded to three other carbon atoms, leaving one free electron per atom.
• Layers are loosely held by weak Van der Waals forces, allowing them to slide over each other.

Properties:

✔ Soft and slippery – Used as a lubricant.

✔ Good conductor of electricity – Due to free-moving electrons.

✔ Opaque and black in color.

Uses:

🔹 Used in pencil lead (mixed with clay).

🔹 Used in electrodes of batteries due to high conductivity.

 

3. Fullerenes

(C) Fullerenes – The Molecular Cage of Carbon

Structure:

• First discovered fullerene is Buckminsterfullerene (C₆₀), shaped like a football (soccer ball).
• Carbon atoms are arranged in pentagons and hexagons, forming a hollow sphere or tube.

Properties:

✔ Lightweight and strong.

✔ Good conductor of electricity.

✔ Soluble in organic solvents.

Uses:

🔹 Used in nanotechnology and electronics.

🔹 Used in drug delivery systems in medicine.

 

Versatile Nature of Carbon

 

Why is Carbon Called a Versatile Element?

Carbon is called a versatile element because it forms a large number of compounds due to its unique bonding properties. It is the basis of organic chemistry and is essential for life.

The Two Main Reasons for Carbon's Versatility:

Catenation (Self-Linking Ability)

Tetravalency (Forms Four Bonds)

 

1. Catenation

Catenation is the ability of carbon to form long chains, branched chains, or rings by bonding with other carbon atoms.

Why Does Carbon Show Catenation?

• Carbon forms strong covalent bonds with itself.
• It can form single (C–C), double (C=C), and triple (C≡C) bonds.
• Carbon can create long, stable chains and rings, leading to the formation of millions of organic compounds.

Examples of Catenation:

Straight Chain Compounds: Butane (C₄H₁₀)

Branched Chain Compounds: Iso-butane (C₄H₁₀)

Ring Structure Compounds: Cyclohexane (C₆H₁₂), Benzene (C₆H₆)

 

2. Tetravalency – Ability to Form Four Bonds

 

Carbon has 4 valence electrons (electronic configuration: 2,4). To achieve stability, it shares electrons with other atoms, forming covalent bonds.

Properties of Tetravalency:

• Carbon can bond with four different atoms or groups.
• It can form single, double, or triple bonds.
• Carbon bonds with various elements like H, O, N, Cl, etc., forming a vast number of compounds.

Examples:

Methane (CH₄): Carbon forms four single covalent bonds with hydrogen.

Ethene (C₂H₄): Carbon forms a double bond.

Ethyne (C₂H₂): Carbon forms a triple bond.

Saturated and Unsaturated Carbon Compounds

 

Definition of Hydrocarbons

Hydrocarbons: Compounds composed only of carbon (C) and hydrogen (H) atoms.

Two main types based on the types of bonds between carbon atoms:

Saturated Hydrocarbons (Single bonds only)

Unsaturated Hydrocarbons (Double or triple bonds)

1. Saturated Carbon Compounds

Definition: Hydrocarbons in which all carbon-carbon bonds are single bonds (C–C).

• General Formula: CₙH₂ₙ₊₂ (for alkanes)
• Properties of Saturated Hydrocarbons:
• Also known as alkanes or paraffins.
• Less reactive due to strong C–C bonds.
• Undergo substitution reactions (replace one atom with another).

Examples:

No of C atoms & Name	Formula	Structure
1. Methane	CH₄	H              |     H — C — H               |              H
2. Ethane	C₂H₆	H        H              |         |     H — C — C —H               |        |                       H      H
3. Propane	C₃H₈	H        H     H              |         |       |      H — C — C —C —H               |        |       |                         H      H      H
4. Butane	C₄H₁₀	H        H     H   H              |         |       |      |      H — C — C —C —C —H               |        |       |      |               H      H      H     H
5. Pentane	C₅H₁₂	H       H      H   H   H              |         |       |      |      |      H — C — C —C —C —C  —H               |        |       |      |       |               H      H      H     H     H
6. Hexane	C₆H₁₄	H       H      H     H     H           |         |       |      |      |       |   H — C — C —C —C —C —C —H            |        |       |      |       |       |            H      H      H     H     H     H

 

2. Unsaturated Carbon Compounds

Definition: Hydrocarbons in which at least one pair of carbon atoms are connected by a double bond (C=C) or a triple bond (C≡C).

Types:

Alkenes: Contain one or more double bonds (C=C).

Alkynes: Contain one or more triple bonds (C≡C).

Properties of Unsaturated Hydrocarbons:

• More reactive due to the presence of multiple bonds.
• Undergo addition reactions (atoms add across the double or triple bond).

Examples:

Alkenes (General Formula: CₙH₂ₙ)

 

No of C atoms & Name	Formula: CₙH₂ₙ	Structure
1. Methene	Not possible	Not possible
2. Ethene (Ethylene)	C₂H₄	H  H        |   | H– C=C–H        |   |       H   H    H₂C=CH₂
3. Propene (Propylene)	C₃H₆	CH₂=CH—CH₃
4. Butene (Butylene)	C₄H₈	CH₂=CH—CH₂—CH₃
5. Pentene	C₅H₁₀	CH₂=CH—CH₂—CH₂—CH₃
6. Hexene	C₆H₁₂	CH₂=CH– CH₂– CH₂– CH₂– CH₃

 

Alkynes (General Formula: CₙH₂ₙ)

No of C atoms & Name	Formula: CₙH₂ₙ	Structure
1. Methyne	Not possible	Not possible
2. Ethyne (Acetylene)	C₂H₂	H– C=C–H   HC≡CH
3. Propyne	C₃H₄	CH≡C—CH₃
4. Butyne	C₄H₆	CH≡C—CH₂—CH₃
5. Pentyne	C₅H₈	CH≡C—CH₂—CH₂—CH₃
6. Hexyne	C₆H₁₀	CH≡C—CH₂—CH₂—CH₂—CH₃

 

What is Structural Isomerism?

Definition:

Structural isomerism occurs when compounds have the same molecular formula but different structural arrangements of atoms.

 Example:

1. Butane (C₄H₁₀) has two structural isomers:

• n-Butane (Straight-chain)

               CH₃-CH₂-CH₂-CH₃

• Iso-Butane (Branched-chain)

   CH₃

 |

CH₃ - CH - CH₃

 

2. Example: Pentane (C₅H₁₂)

• n-Pentane (Straight-chain)

CH₃-CH₂-CH₂-CH₂-CH₃

• Iso-Pentane (Branched-chain)

   CH₃

  |

           CH₃-CH-CH₂-CH₃

• Neo-Pentane (Highly branched):

   CH₃

|

CH₃  - C  - CH₃

 |

   CH₃

 

 

Homologous Series

Definition:

A homologous series is a group or family of organic compounds having the same functional group, similar chemical properties, and the same general formula. Each successive member differs from the previous one by a -CH₂ (methylene) group.

Characteristics of Homologous Series:

1. General Formula:

• • All members follow a common general formula.
  • Example: Alkanes follow CₙH₂ₙ₊₂.

2. Difference of CH₂ Group:

• • Each consecutive member differs by one CH₂ unit (14 amu in molecular mass).
  • Example:

Methane (CH₄) → Ethane (C₂H₆) → Propane (C₃H₈)

3. Gradation in Physical Properties:

• • Boiling point, melting point, and density gradually increase as the molecular mass increases.

4. Similar Chemical Properties:

• • Due to the presence of the same functional group, all members exhibit similar chemical behavior.
  • Example: All alcohols react similarly with sodium to produce hydrogen gas.

Examples of Homologous Series:

• Alkanes (Saturated Hydrocarbons)
  • General Formula: CₙH₂ₙ₊₂
  • Members:
    • Methane (CH₄)
    • Ethane (C₂H₆)
    • Propane (C₃H₈)
    • Butane (C₄H₁₀)
• Alkenes (Unsaturated Hydrocarbons with Double Bonds)
  • General Formula: CₙH₂ₙ
  • Members:
    • Ethene (C₂H₄)
    • Propene (C₃H₆)
    • Butene (C₄H₈)
• Alkynes (Unsaturated Hydrocarbons with Triple Bonds)
  • General Formula: CₙH₂ₙ₋₂
  • Members:
    • Ethyne (C₂H₂)
    • Propyne (C₃H₄)
    • Butyne (C₄H₆)
• Alcohols (Hydroxyl Group -OH)
  • General Formula: CₙH₂ₙ₊₁OH
  • Members:
    • Methanol (CH₃OH)
    • Ethanol (C₂H₅OH)
    • Propanol (C₃H₇OH)
• Carboxylic Acids (Carboxyl Group -COOH)
  • General Formula: CₙH₂ₙ₊₁COOH
  • Members:
    • Methanoic acid (HCOOH)
    • Ethanoic acid (CH₃COOH)
    • Propanoic acid (C₂H₅COOH)

 

Common Functional Groups in Carbon Compounds:

Functional Group	Formula	Example	Suffix/Prefix Used in	Naming Family Name
Alcohol	-OH	Ethanol (C₂H₅OH)	-ol (suffix)	Alcohols
Aldehyde	-CHO	Ethanal (CH₃CHO)	-al (suffix)	Aldehydes
Ketone	>C=O	Propanone (CH₃COCH₃)	-one (suffix)	Ketones
Carboxylic Acid	-COOH	Ethanoic acid (CH₃COOH)	-oic acid (suffix)	Carboxylic Acids
Alkene	C=C (double bond)	Ethene (C₂H₄)	-ene (suffix)	Alkenes (Unsaturated Hydrocarbons)
Alkyne	C≡C (triple bond)	Ethyne (C₂H₂)	-yne (suffix)	Alkynes (Unsaturated Hydrocarbons)
Halides (Haloalkanes)	-Cl, -Br, -I	Chloroethane (C₂H₅Cl)	Chloro-, Bromo-, Iodo- (prefix)	Haloalkanes
Amine	-NH₂	Aminoethane (C₂H₅NH₂)	-amine (suffix)	Amines
Ester	-COOR	Methyl ethanoate (CH₃COOCH₃)	-oate (suffix)	Esters

 

Nomenclature of Carbon Compounds (Examples)

1. Alcohols (-OH Functional Group)

• Suffix: -ol
• General Formula: CₙH₂ₙ₊₁OH

Name	Formula	Structure
Methanol	CH₃OH	H–CH₂–OH
Ethanol	C₂H₅OH	CH₃–CH₂–OH
Propanol	C₃H₇OH	CH₃–CH₂–CH₂–OH
Butanol	C₄H₉OH	CH₃–CH₂–CH₂–CH₂–OH
Pentanol	C₅H₁₁OH	CH₃–CH₂–CH₂–CH₂–CH₂–OH

 

2. Aldehydes (-CHO Functional Group)

• Suffix: -al
• General Formula: R-CHO

 

Name	Formula	Structure
Methanal	HCHO	H–CHO
Ethanal	CH₃CHO	CH₃–CHO
Propanal	C₂H₅CHO	CH₃–CH₂–CHO
Butanal	C₃H₇CHO	CH₃–CH₂–CH₂–CHO
Pentanal	C₄H₉CHO	CH₃–CH₂–CH₂–CH₂–CHO

 

3. Ketones (>C=O Functional Group)

• Suffix: -one
• General Formula: R–CO–R'

 

Name	Formula	Structure
Propanone	CH₃COCH₃	CH₃–CO–CH₃
Butanone	CH₃COC₂H₅	CH₃–CO–CH₂–CH₃
Pentanone	C₂H₅COCH₃	CH₃–CO–CH₂–CH₂–CH₃
Hexanone	CH₃COC₃H₇	CH₃–CO–CH₂–CH₂–CH₂–CH₃
Heptanone	CH₃COC₄H₉	CH₃–CO–CH₂–CH₂–CH₂–CH₂–CH₃

 

4. Carboxylic Acids (-COOH Functional Group)

• Suffix: -oic acid
• General Formula: R-COOH

 

Name	Formula	Structure
Methanoic Acid	HCOOH	H–COOH
Ethanoic Acid	CH₃COOH	CH₃–COOH
Propanoic Acid	C₂H₅COOH	CH₃–CH₂–COOH
Butanoic Acid	C₃H₇COOH	CH₃–CH₂–CH₂–COOH
Pentanoic Acid	C₄H₉COOH	CH₃–CH₂–CH₂–CH₂–COOH

 

5. Alkenes (C=C Double Bond)

• Suffix: -ene
• General Formula: CₙH₂ₙ

 

Name	Formula	Structure
Ethene	C₂H₄	CH₂=CH₂
Propene	C₃H₆	CH₂=CH–CH₃
Butene	C₄H₈	CH₂=CH–CH₂–CH₃
Pentene	C₅H₁₀	CH₂=CH–CH₂–CH₂–CH₃
Hexene	C₆H₁₂	CH₂=CH–CH₂–CH₂–CH₂–CH₃

 

6. Alkynes (C≡C Triple Bond)

• Suffix: -yne
• General Formula: CₙH₂ₙ₋₂

 

Name	Formula	Structure
Ethyne	C₂H₂	CH≡CH
Propyne	C₃H₄	CH≡C–CH₃
Butyne	C₄H₆	CH≡C–CH₂–CH₃
Pentyne	C₅H₈	CH≡C–CH₂–CH₂–CH₃
Hexyne	C₆H₁₀	CH≡C–CH₂–CH₂–CH₂–CH₃

 

7. Halides (Haloalkanes) (-Cl, -Br, -I Functional Groups)

• Prefix: Chloro-, Bromo-, Iodo-
• General Formula: R–X (X = Cl, Br, I)

 

Name	Formula	Structure
Chloromethane	CH₃Cl	CH₃–Cl
Bromoethane	C₂H₅Br	CH₃–CH₂–Br
Iodopropane	C₃H₇I	CH₃–CH₂–CH₂–I
Chlorobutane	C₄H₉Cl	CH₃–CH₂–CH₂–CH₂–Cl
Bromopentane	C₅H₁₁Br	CH₃–CH₂–CH₂–CH₂–CH₂–Br

 

8. Amines (-NH₂ Functional Group)

• Suffix: -amine
• General Formula: R–NH₂

Name	Formula	Structure
Methanamine	CH₃NH₂	CH₃–NH₂
Ethanamine	C₂H₅NH₂	CH₃–CH₂–NH₂
Propanamine	C₃H₇NH₂	CH₃–CH₂–CH₂–NH₂
Butanamine	C₄H₉NH₂	CH₃–CH₂–CH₂–CH₂–NH₂
Pentanamine	C₅H₁₁NH₂	CH₃–CH₂–CH₂–CH₂–CH₂–NH₂

 

9. Esters (-COOR Functional Group)

• Suffix: -oate
• General Formula: R–COO–R'

Name	Formula	Structure
Methyl Methanoate	HCOOCH₃	H–COO–CH₃
Methyl Ethanoate	CH₃COOCH₃	CH₃–COO–CH₃
Ethyl Ethanoate	CH₃COOC₂H₅	CH₃–COO–CH₂–CH₃
Propyl Methanoate	HCOOC₃H₇	H–COO–CH₂–CH₂–CH₃
Butyl Ethanoate	CH₃COOC₄H₉	CH₃–COO–CH₂–CH₂–CH₂–CH₃

 

Chemical Properties of Carbon Compounds 

1. Combustion Reactions

Definition:

Combustion is a chemical reaction in which carbon compounds react with oxygen to release energy (heat and light), usually forming carbon dioxide (CO₂) and water (H₂O).

• Saturated hydrocarbons (alkanes) burn with a blue, non-sooty flame.
• Unsaturated hydrocarbons (alkenes and alkynes) burn with a yellow, sooty flame due to incomplete combustion.
• Incomplete combustion can lead to the formation of carbon monoxide (CO), which is a toxic gas.

For example :

(i). C + O₂ –> CO₂ + heat and light

(ii). CH₄ +O₂  –> CO₂ + H₂O + heat and light

(iii). CH₃CH₂0H + O₂  –> CO₂  + H₂O  + heat and light

 

2. Oxidation Reaction:

Definition: Oxidation is a chemical reaction in which a substance gains oxygen or loses hydrogen. It is often associated with the release of energy.

Example:

• Burning of carbon
  • C + O₂ –> _CO2
• Oxidation of alcohol to carboxylic acid
  • c

3. Addition Reaction: