Organic chemistry, covalent bonds, homologous series, functional groups, soaps and detergents
Catenation: Carbon can bond with itself to form long chains, branched chains, and rings. No other element shows this property to such a great extent.
Tetravalency: Carbon has valency 4 — it forms 4 covalent bonds. This allows enormous variety in organic compounds.
Carbon always forms covalent bonds (sharing of electrons) — never ionic bonds with other carbon atoms.
Carbon has 4 electrons in outer shell. To complete octet, it needs to gain or lose 4 electrons. Gaining 4 electrons → C⁴⁻ (too much negative charge). Losing 4 electrons → C⁴⁺ (requires too much energy). So carbon SHARES 4 electrons — forming 4 covalent bonds. This is most stable!
| Allotrope | Structure | Properties | Uses |
|---|---|---|---|
| Diamond | Each C bonded to 4 others (tetrahedral, 3D network) | Hardest substance, non-conductor, transparent | Jewellery, cutting tools, drills |
| Graphite | Layered hexagonal rings; 3 bonds + 1 free electron | Soft, slippery, conducts electricity | Pencils, lubricants, electrodes |
| Fullerene (C₆₀) | Hollow sphere of 60 C atoms (soccer ball shape) | Special electronic properties | Nanotechnology, drug delivery |
Saturated hydrocarbons (Alkanes): Only single C–C bonds. General formula: CₙH₂ₙ₊₂
Example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)
Unsaturated hydrocarbons:
Alkenes: Double C=C bond. Formula: CₙH₂ₙ. Example: Ethene C₂H₄
Alkynes: Triple C≡C bond. Formula: CₙH₂ₙ₋₂. Example: Ethyne C₂H₂
| Functional Group | Name | Example |
|---|---|---|
| –OH | Alcohol (hydroxyl) | Ethanol: C₂H₅OH |
| –CHO | Aldehyde | Ethanal: CH₃CHO |
| –COOH | Carboxylic acid | Acetic acid: CH₃COOH |
| –CO– | Ketone | Acetone: CH₃COCH₃ |
| –Cl, –Br | Haloalkane | Chloromethane: CH₃Cl |
A homologous series is a series of compounds with same functional group, differing by –CH₂– (14 mass units), with a general formula, and showing a gradual change in properties.
Methanol: CH₃OH (1C) → Ethanol: C₂H₅OH (2C) → Propanol: C₃H₇OH (3C)
Each differs by –CH₂– group. General formula: CₙH₂ₙ₊₁OH
CH₄ + 2O₂ → CO₂ + 2H₂O + heat & light
Complete combustion → blue flame (clean)
Incomplete combustion → yellow sooty flame (carbon particles)
CH₂=CH₂ + H₂ → CH₃–CH₃ (Ethene + Hydrogen → Ethane, using Ni catalyst)
This converts vegetable oil (unsaturated, liquid) → vanaspati ghee (saturated, solid)
CH₄ + Cl₂ → CH₃Cl + HCl (in presence of UV light)
One H replaced by Cl — characteristic of alkanes
Soap molecule has two ends: Hydrophilic head (–COO⁻Na⁺, loves water) and Hydrophobic tail (long hydrocarbon chain, hates water, loves oil/grease).
Micelle: When soap is added to water with oil, soap molecules surround the oil droplet (hydrophobic tails inside with oil, hydrophilic heads outside in water). This forms a micelle — a spherical structure that keeps oil suspended in water → allows rinsing.
Soap: Sodium/potassium salt of long-chain fatty acids. Made by saponification (fat + NaOH → soap + glycerol). Does NOT work in hard water (forms scum with Ca²⁺/Mg²⁺ ions).
Detergent: Ammonium or sulphonate salts of long-chain acids. Works in hard water too. More effective, but may not be biodegradable.