Carbon and its Compounds

• Introduction to Carbon

  • Symbol: C, Atomic Number: 6
  • Versatile element in living and non-living things
  • Tetravalent: Valency of 4
  • Forms covalent bonds by sharing electrons

• Bonding in Carbon: Covalent Bonding

  • Definition: Sharing of valence electrons between atoms
  • Properties of Covalently Bonded Compounds
    • Low melting and boiling points
    • Poor conductors of electricity
    • Weak intermolecular forces
  • Types of Covalent Bonds
    • Single bond (e.g., $CH_4$)
    • Double bond (e.g., $O_2$, $C_2H_4$)
    • Triple bond (e.g., $N_2$, $C_2H_2$)

• Versatile Nature of Carbon

  • Catenation: Ability to form long chains and rings with other carbon atoms
  • Tetravalency: Bonding with four other atoms (H, O, N, S, Halogens)
  • Formation of Isomers (Same molecular formula, different structures)

• Hydrocarbons and Carbon Compounds

  • Definition: Compounds containing only carbon and hydrogen
  • Types of Hydrocarbons
    • Saturated Hydrocarbons: Alkanes ($C_n2_{n+2}$, single bonds, e.g., Methane)
    • Unsaturated Hydrocarbons
      • Alkenes ($C_nH_{2n}$, double bonds, e.g., Ethene)
      • Alkynes ($C_nH_{2n-2}$, triple bonds, e.g., Ethyne)
  • Functional Groups
    • Heteroatom replacing hydrogen
    • Halo- (Chloro/Bromo): $-Cl, -Br$
    • Alcohol: $-OH$
    • Aldehyde: $-CHO$
    • Ketone: $>C=O$
    • Carboxylic acid: $-COOH$
  • Homologous Series
    • Series of compounds with same functional group
    • Difference of $-CH_2-$ unit between successive members
    • Gradation in physical and similar chemical properties

• Chemical Properties of Carbon Compounds

  • Combustion
    • Oxidation in air to release $CO_2$, heat, and light
    • Saturated hydrocarbons: Clean blue flame
    • Unsaturated hydrocarbons: Sooty yellow flame
  • Oxidation
    • Conversion of alcohols to carboxylic acids using oxidizing agents (alkaline $KMnO_4$ or acidified $K_2Cr_2O_7$)
  • Addition Reaction
    • Hydrogenation of unsaturated hydrocarbons using nickel/palladium catalyst
  • Substitution Reaction
    • Replacement of one type of atom by another (e.g., Chlorination of methane in sunlight)

• Important Carbon Compounds: Ethanol and Ethanoic Acid

  • Ethanol ($CH_3CH_2OH$)
    • Properties: Liquid at room temperature, active ingredient of all alcoholic drinks, good solvent
    • Reactions: With sodium (gives hydrogen gas), dehydration with hot conc. $H_2SO_4$ (gives ethene)
  • Ethanoic Acid / Acetic Acid ($CH_3COOH$)
    • Properties: Commonly called acetic acid, 5-8% solution in water is vinegar, melts at 290K (glacial acetic acid)
    • Reactions: Esterification (forms sweet-smelling esters), reaction with bases and carbonates (gives salt, water, and $CO_2$)

• Soaps and Detergents

  • Soap
    • Sodium or potassium salts of long-chain carboxylic acids
    • Effective only in soft water
    • Structure: Hydrophilic (polar) head and Hydrophobic (non-polar) tail
  • Detergent
    • Ammonium or sulphonate salts of long-chain carboxylic acids
    • Effective in both hard and soft water (do not form scum)
  • Cleansing Action
    • Formation of micelles
    • Hydrophobic tail attaches to dirt/oil; hydrophilic head dissolves in water
    • Emulsification of dirt to wash it away