Learning Objectives
- Understand the unique bonding nature of carbon (covalent bonding)
- Learn about saturated and unsaturated hydrocarbons
- Understand homologous series and functional groups
- Study chemical properties of carbon compounds
- Learn about soaps and detergents
Key Concepts
Covalent Bonding in Carbon
Carbon has 4 valence electrons and forms covalent bonds by sharing electrons. Carbon can form:
- Single bonds (C-C) in saturated compounds (alkanes)
- Double bonds (C=C) in unsaturated compounds (alkenes)
- Triple bonds (C≡C) in unsaturated compounds (alkynes)
Carbon can bond with itself to form long chains (catenation), branched chains, and rings, leading to an enormous number of organic compounds.
Hydrocarbons
Saturated hydrocarbons (Alkanes): CₙH₂ₙ₊₂. Only single bonds. Example: CH₄ (methane), C₂H₆ (ethane).
Unsaturated hydrocarbons: Alkenes (CₙH₂ₙ) have double bonds; Alkynes (CₙH₂ₙ₋₂) have triple bonds.
Homologous Series
A series of compounds with the same functional group and similar chemical properties, where successive members differ by -CH₂- (14 u). Example: CH₃OH, C₂H₅OH, C₃H₇OH... (alcohol series).
Functional Groups
- -OH (Hydroxyl): Alcohols. Example: C₂H₅OH (ethanol)
- -CHO (Aldehyde): Aldehydes. Example: CH₃CHO (ethanal)
- -COOH (Carboxyl): Carboxylic acids. Example: CH₃COOH (ethanoic acid)
- -CO- (Ketone): Ketones. Example: CH₃COCH₃ (propanone)
- -X (Halogen): Haloalkanes. Example: CH₃Cl (chloromethane)
Chemical Properties of Carbon Compounds
Combustion: Carbon compounds burn in oxygen to produce CO₂ + H₂O + heat and light. Saturated compounds give clean flame; unsaturated give sooty flame.
Oxidation: Alcohols can be oxidised to carboxylic acids using alkaline KMnO₄ or acidified K₂Cr₂O₇. Example: CH₃CH₂OH → CH₃COOH
Addition reaction: Unsaturated compounds add H₂ (hydrogenation using Ni catalyst), Cl₂, etc. across double/triple bonds.
Substitution reaction: Saturated hydrocarbons undergo substitution (e.g., CH₄ + Cl₂ → CH₃Cl + HCl in sunlight).
Ethanol (C₂H₅OH) and Ethanoic Acid (CH₃COOH)
Ethanol: Liquid at room temperature, used as solvent and in beverages. Reacts with Na to give H₂. Long-term consumption damages liver.
Ethanoic acid (vinegar ~5-8%): Sour taste, reacts with NaHCO₃ to give CO₂. Freezes at 16.6°C (glacial acetic acid).
Soaps and Detergents
Soap: Sodium or potassium salt of long-chain fatty acid. Has a hydrophilic (water-loving) head and hydrophobic (water-repelling) tail. Forms micelles in water to clean grease.
Soaps do not work well in hard water (form scum). Detergents work in both hard and soft water.
Summary
Carbon forms covalent bonds and exhibits catenation, resulting in a vast number of organic compounds. Hydrocarbons are classified as saturated and unsaturated. Functional groups determine chemical properties. Homologous series show a gradual change in properties. Soaps and detergents clean through micelle formation.
Important Terms
- Catenation
- The ability of carbon to form bonds with other carbon atoms, creating long chains and rings
- Isomers
- Compounds with the same molecular formula but different structural arrangements
- Homologous Series
- A series of compounds with the same functional group, differing by CH₂
- Micelle
- A spherical cluster formed by soap molecules in water, with hydrophobic tails inward
Quick Revision
- Carbon has valency 4 and forms covalent bonds by sharing electrons
- Alkanes: CₙH₂ₙ₊₂; Alkenes: CₙH₂ₙ; Alkynes: CₙH₂ₙ₋₂
- Successive members of a homologous series differ by CH₂ (14 u)
- Saturated compounds undergo substitution; unsaturated undergo addition reactions
- Soaps form scum in hard water; detergents do not