What are hydrocarbons?

Hydrocarbons are organic compounds composed of carbon (C) and hydrogen (H) atoms. They form the basis of fuels like LPG, CNG, petrol, diesel, and coal gas and are also used in manufacturing polymers, dyes, and drugs.

What are the main types of hydrocarbons?

Hydrocarbons are classified based on carbon-carbon bonding:

• Saturated hydrocarbons (alkanes) → Contain only single bonds (C–C).
• Unsaturated hydrocarbons (alkenes and alkynes) → Contain double (C=C) or triple (C≡C) bonds.
• Aromatic hydrocarbons → Contain benzene rings and follow the rules of aromaticity.

What is the general formula of alkanes?

The general formula of alkanes is: C_nH_2n+2

where n = number of carbon atoms.

What is the structure and hybridization of alkanes?

Alkanes have a tetrahedral geometry with a bond angle of 109.5°.

The C-C and C-H bonds are σ (sigma) bonds formed by sp³ hybridization.

What are the physical properties of alkanes?

• Non-polar due to weak van der Waals forces.
• First four members (C₁ to C₄) are gases, C₅ to C₁₇ are liquids, and higher alkanes are solids.
• Insoluble in water but soluble in organic solvents.
• Boiling point increases with molecular mass but decreases with branching.

What are the important chemical reactions of alkanes?

Halogenation (Substitution reaction):

• Alkanes react with halogens in UV light to form alkyl halides.
• Example: CH₄+Cl₂ →CH₃Cl+ HCl

Combustion:

• Complete combustion produces CO₂ and H₂O with heat. 
• CH₄ + 2O₂ → CO₂ + 2H₂O + heat
• Incomplete combustion forms carbon (soot) and CO. 

Pyrolysis (Cracking):

• Breakdown of larger alkanes into smaller hydrocarbons at high temperature.

What is the general formula of alkenes?

The general formula of alkenes is: CnH₂n

What is the structure and hybridization of alkenes?

Trigonal planar geometry, bond angle 120°.

Double bond consists of:

• One σ (sigma) bond (sp² hybridization).
• One π (pi) bond (formed by sideways overlap of p orbitals).

What are the physical properties of alkenes?

Non-polar molecules with low boiling points.

Slightly soluble in water but highly soluble in organic solvents.

What are the important chemical reactions of alkenes?

Addition Reactions (Electrophilic Addition):

• Hydrogenation: C₂H₄ + H₂ →Ni/Pd C₂H₆
• Halogenation (Test for unsaturation – bromine water decolorizes): C₂H₄ + Br₂ → C₂H₄Br₂
• Hydrohalogenation (Markovnikov’s Rule): CH₃-CH=CH₂ + HBr → CH₃ - CHBr-CH₃
• Hydration (Formation of Alcohols): C₂H₄ + H₂O →H₂SO₄ C₂H₅OH

Oxidation Reactions:

• Baeyer’s Test (Cold KMnO₄ oxidation to form glycols).

Ozonolysis:

• Ozone cleavage of alkenes produces carbonyl compounds (aldehydes or ketones).

What is the general formula of alkynes?

The general formula of alkynes is: C_nH_2n−2

What is the structure and hybridization of alkynes?

Linear geometry, bond angle 180°.

Triple bond consists of:

• One σ (sigma) bond (sp hybridization).
• Two π (pi) bonds.

What are the important chemical reactions of alkynes?

1. Hydrogenation (Formation of alkenes and alkanes):

2. Electrophilic Addition:

• Halogenation:
  
• Hydrohalogenation (Follows Markovnikov's Rule):
  

3. Tautomerization (Formation of aldehydes and ketones from alkynes).

What is aromaticity?

A compound is aromatic if it satisfies Hückel’s Rule:

(4n+2)π-electrons

where n is a whole number (n = 0, 1, 2, …).

Example: Benzene (C₆H₆) has 6 π-electrons and is aromatic.

What are the important reactions of benzene?