Carbon and Its Compounds - Exam Notes

Carbon and its Compounds

• Carbon has an atomic number of 6.
• Electronic configuration: 2, 4.
• To attain stability, carbon needs to gain or lose 4 electrons, which requires a lot of energy. Therefore, carbon shares its valence electrons with other atoms, forming covalent bonds.

Covalent Bonding

• Covalent bonding involves the sharing of electrons between atoms to achieve a noble gas configuration.
• Examples:
  • Hydrogen molecule (H₂): Two H atoms share electrons to form a single covalent bond.
  • Chlorine molecule (Cl₂): Two Cl atoms share electrons to form a single covalent bond.
  • Oxygen molecule (O₂): Two O atoms share two pairs of electrons to form a double bond.
  • Nitrogen molecule (N₂): Two N atoms share three pairs of electrons to form a triple bond.
  • Methane (CH₄): Carbon shares electrons with four hydrogen atoms.

Properties of Covalent Bonds

• Low melting and boiling points due to weak intermolecular forces.
• Electrons are shared, so no charged particles are formed.

Allotropes of Carbon

• Allotropy: An element existing in multiple forms with different physical properties but identical chemical properties.
  • Diamond:
    • Very hard and non-conductive.
    • Used as a cutting instrument and in jewelry.
  • Graphite:
    • Slippery and conducts electricity.
    • Used as a lubricant, in electric cells, and in pencil leads.
  • Fullerenes:
    • The first known fullerene was $C_{60}$, also known as Buckminsterfullerene.

Versatile Nature of Carbon

• Catenation: Carbon atoms link through covalent bonds to form long, straight, branched chains and rings due to its small size and strong C-C bond.
• Tetravalency: Carbon has 4 valence electrons, enabling it to bond with four other atoms.
• Multiple Bonds: Carbon forms double and triple bonds by sharing more than one electron pair.

Hydrocarbons

• Compounds made of hydrogen and carbon only.
  • Saturated Hydrocarbons (Alkanes): Linked by single bonds.
    • General formula: $C<em>nH</em>{2n+2}$
  • Unsaturated Hydrocarbons: Having double or triple bonds.
    • Alkenes: At least one double bond.
      • General formula: $C<em>nH</em>{2n}$
    • Alkynes: One or more triple bonds.
      • General formula: $C<em>nH</em>{2n-2}$

IUPAC Nomenclature

• Prefix + Suffix
  • Prefix: Based on the number of carbon atoms in the chain.
    • C₁: Meth-
    • C₂: Eth-
    • C₃: Prop-
    • C₄: But-
    • C₅: Pent-
    • C₆: Hex-
  • Suffix: Based on whether the hydrocarbon is an alkane, alkene, or alkyne.
    • Alkane: -ane
    • Alkene: -ene
    • Alkyne: -yne

Functional Groups

• An atom or group of atoms that makes a carbon compound reactive and determines its chemical properties.
• Nomenclature:
  • Prefix: Chloro-, Bromo-
  • Suffix: -ol (alcohol), -one (ketone), -oic acid (carboxylic acid)

Homologous Series

• A group of organic compounds with similar structures and chemical properties, where successive compounds differ by a $CH_2$ group.
• Characteristics:
  • All members have the same general formula.
  • Adjacent members differ by a $CH_2$ group and 14u in molecular mass.
  • Show similar chemical properties.

Structural Isomerism

• Compounds with identical molecular formulas but different structures.

Important Carbon Compounds

• Ethanol ($CH<em>3CH</em>2OH$):
  • Commonly called alcohol, used in medicines.
  • Obtained by fermentation.
• Ethanoic Acid ($CH_3COOH$):
  • Commonly called acetic acid.
  • 5-8% solution is called vinegar.
  • Carboxylic acids are weak acids.

Chemical Properties of Carbon Compounds

• Combustion: A chemical reaction where heat and light are given out.
  • Saturated hydrocarbons burn with a clear flame in sufficient oxygen; otherwise, a sooty flame.
  • Unsaturated hydrocarbons burn with a yellow flame and black smoke.
• Oxidation: Carbon compounds are easily oxidized on combustion. Alkaline $KMnO<em>4$ and acidified $K</em>2Cr<em>2O</em>7$ act as oxidizing agents.
• Addition Reaction: Unsaturated hydrocarbons add hydrogen in the presence of catalysts (Palladium or Nickel) to give saturated hydrocarbons.
• Substitution Reaction: One functional group is replaced by another.
• Reactions of Ethanol: Reaction with sodium to produce sodium ethoxide and hydrogen. Dehydration to give unsaturated hydrocarbons using hot concentrated $H<em>2SO</em>4$.
• Reactions of Ethanoic Acid: Esterification (reaction with alcohol to give ester). Saponification (reaction used in soap preparation).

Soaps and Detergents

• Soaps: Sodium or potassium salts of long-chain carboxylic acids.
• Detergents: Ammonium or sulfonate salts of long-chain carboxylic acids.
• Cleaning Action: Soap molecules form micelles, dissolving oil in water.
• Hardness of Water: Soap reacts with calcium and magnesium salts in hard water, forming scum. Detergents are effective in hard water as they do not form insoluble precipitates.