Unit 18HYDROCARBONS
The chemistry of carbon and hydrogen — from simple methane to complex alcohols. Explore alkanes, alkenes, alkynes, and their remarkable reactions.
What are Hydrocarbons?
Compounds formed exclusively by carbon (C) and hydrogen (H) atoms are called hydrocarbons. They are the foundation of organic chemistry.
Carbon — The Foundation
- → Atomic number: 6, Atomic mass: 12
- → Group 14 of the periodic table
- → Has 4 valence electrons — forms 4 covalent bonds
- → Property of catenation — forms long chains and rings
- → Makes up about 18% of the human body
Main Sources of Hydrocarbons
- → Petroleum — complex mixture of hydrocarbons
- → Natural gas — mainly methane (CH₄)
- → LPG — mainly propane and butane
- → Examples: CH₄ (methane), C₂H₆ (ethane), C₃H₈ (propane)
Saturated vs Unsaturated Hydrocarbons
🔵 Saturated Hydrocarbons
Carbon atoms are bonded with single bonds only (C−C). Called alkanes (paraffins). Do NOT undergo addition reactions.
General formula: CₙH₂ₙ₊₂
🟢 Unsaturated Hydrocarbons
Carbon atoms have double (C=C) or triple (C≡C) bonds. Called alkenes and alkynes. DO undergo addition reactions.
Alkene: CₙH₂ₙ | Alkyne: CₙH₂ₙ₋₂
Alkanes · Alkenes · Alkynes
Three main series of hydrocarbons — each with a unique bond type and general formula.
Alkanes
C₂H₆ → Ethane (n=2)
C₃H₈ → Propane (n=3)
C₄H₁₀ → Butane (n=4)
Alkenes
C₃H₆ → Propene (n=3)
C₄H₈ → But-1-ene (n=4)
C₅H₁₀ → Pent-1-ene (n=5)
Alkynes
C₃H₄ → Propyne (n=3)
C₄H₆ → 1-Butyne (n=4)
C₄H₆ → 2-Butyne
| n | Mol. Formula | IUPAC Name | Structural Formula | State (Room Temp) |
|---|---|---|---|---|
| 1 | CH₄ | Methane | H−C−H (4 bonds) | Gas |
| 2 | C₂H₆ | Ethane | CH₃−CH₃ | Gas |
| 3 | C₃H₈ | Propane | CH₃−CH₂−CH₃ | Gas |
| 4 | C₄H₁₀ | Butane | CH₃−CH₂−CH₂−CH₃ | Gas |
| 5 | C₅H₁₂ | Pentane | CH₃(CH₂)₃CH₃ | Liquid |
| 6 | C₆H₁₄ | Hexane | CH₃(CH₂)₄CH₃ | Liquid |
| 7 | C₇H₁₆ | Heptane | CH₃(CH₂)₅CH₃ | Liquid |
| 8 | C₈H₁₈ | Octane | CH₃(CH₂)₆CH₃ | Liquid |
| 9 | C₉H₂₀ | Nonane | CH₃(CH₂)₇CH₃ | Liquid |
| 10 | C₁₀H₂₂ | Decane | CH₃(CH₂)₈CH₃ | Liquid |
| Molecular Formula | IUPAC Name | Structural Formula | Note |
|---|---|---|---|
| C₂H₄ | Ethene | CH₂=CH₂ | Simplest alkene |
| C₃H₆ | Prop-1-ene | CH₂=CH−CH₃ | |
| C₄H₈ | But-1-ene | CH₂=CH−CH₂−CH₃ | |
| C₄H₈ | But-2-ene | CH₃−CH=CH−CH₃ | Isomer of But-1-ene |
| C₅H₁₀ | Pent-1-ene | CH₂=CHCH₂CH₂CH₃ |
| Molecular Formula | IUPAC Name | Structural Formula | Note |
|---|---|---|---|
| C₂H₂ | Ethyne (Acetylene) | H−C≡C−H | Used in welding |
| C₃H₄ | Propyne | CH≡C−CH₃ | |
| C₄H₆ | 1-Butyne | HC≡C−CH₂−CH₃ | |
| C₄H₆ | 2-Butyne | CH₃−C≡C−CH₃ | Isomer of 1-Butyne |
Homologous Series Explorer
Drag the slider to change carbon number (n) and instantly see how name, formula, and mass change.
📏 Homologous Series — Key Rules
- → All members have the same general formula
- → All contain the same functional group
- → Have similar chemical properties
- → Physical properties change gradually with mass
- → Consecutive members differ by −CH₂ (14 amu)
- → Each step: +1 carbon, +2 hydrogens
Alcohols — Hydroxy Derivatives
Alcohols are organic compounds containing the −OH (hydroxyl) functional group. They are derivatives of alkanes where H atoms are replaced by −OH.
Ethanol (C₂H₅OH)
Propanol (C₃H₇OH)
HOCH₂−CH₂OH
Propan-1,3-diol
(Glycerol / Glycerin)
Found in soaps, lotions
- Fuel and fuel additive
- Raw material for formaldehyde (plastics)
- Solvent for paints, varnishes, inks
- Pharmaceutical manufacturing
- ⚠️ Toxic — causes blindness if consumed
- Alcoholic beverages (beer, wine)
- Antiseptic and disinfectant
- Biofuel in vehicles
- Solvent for perfumes and cosmetics
- Used in medicines and cough syrups
- Antifreeze in automobile coolants
- Raw material for polyester (PET plastic)
- Heat transfer fluid in cooling systems
- Solvent for paints and inks
- Pharmaceuticals: cough syrups, ointments
- Sweetening agent in food and drinks
- Cosmetics: creams, lotions, toothpaste
- Raw material for nitroglycerin (explosives)
⚗️ Preparation of Ethanol from Ethene
Ethanol is prepared from ethene by addition of water (hydration):
Ethene + Water → Ethanol
(Catalyst: H₂SO₄, Heat & Pressure)
This is an addition reaction — water adds across the double bond of ethene.
Functional Groups & IUPAC Naming
A functional group is the most reactive part of an organic molecule — it determines the compound's chemical properties.
IUPAC Naming = Word Root + Suffix
2 → Eth-
3 → Prop-
4 → But-
5 → Pent-
C=C → -ene
C≡C → -yne
−OH → -ol
C₂H₄ → Ethene
C₂H₂ → Ethyne
C₂H₅OH → Ethanol
Multiple Choice Questions
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Short & Long Answer Questions
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