Introduction to Carbon and Its Compounds

  • Carbon is a key element in living and non-living things, found in forms like carbonates, coal, and petroleum (in small amounts: 0.02% in Earth’s crust and 0.03% as CO2 in the atmosphere).
  • Many daily-use items and all living structures are carbon-based.
  • Carbon compounds are important due to their unique bonding properties.

4.1 Bonding in Carbon – The Covalent Bond

Properties of Carbon Compounds:

  • Low Melting & Boiling Points: Indicates weak intermolecular forces.
  • Non-Conductive Nature: No ions are formed as bonding involves sharing of electrons.

Carbon’s Reactivity:

  • Carbon has 4 valence electrons (atomic number 6).
  • To achieve stability (noble gas configuration):
    • Gaining 4 electrons is hard (C⁴⁻ ion would be unstable).
    • Losing 4 electrons requires high energy (C⁴⁺ ion leaves the nucleus with too few electrons).
  • Solution: Carbon shares electrons to form covalent bonds.

Examples of Covalent Bonding:

  • Hydrogen Molecule (H₂): Two hydrogen atoms share one electron each to complete their shells.
  • Oxygen Molecule (O₂): Forms a double bond by sharing two pairs of electrons.
  • Nitrogen Molecule (N₂): Forms a triple bond, sharing three pairs of electrons.

Simple Carbon Compounds

  • Methane (CH₄): Carbon shares electrons with four hydrogen atoms, forming single covalent bonds.
  • Covalent bonds are strong within molecules but weak between them, resulting in low melting/boiling points.

Allotropes of Carbon

  • Diamond: Hardest known substance; carbon atoms arranged in a rigid 3D structure.
  • Graphite: Soft and slippery; carbon atoms form layers with hexagonal arrangements. A good conductor of electricity.
  • Fullerenes: Carbon atoms arranged in shapes like spheres (e.g., C-60 resembles a football).

4.2 Versatile Nature of Carbon

Unique Features:

  1. Catenation:
    • Carbon forms chains, branches, or rings by bonding with other carbon atoms.
    • Bonds can be single, double, or triple.
    • Strong carbon-carbon bonds enable stable structures.
  2. Tetravalency:
    • Carbon bonds with four atoms, forming diverse compounds with oxygen, hydrogen, nitrogen, etc.
    • Strong bonds due to carbon’s small size.

Organic Compounds

  • Saturated Compounds: Only single bonds between carbon atoms (e.g., methane, ethane).
  • Unsaturated Compounds: Contain double or triple bonds (e.g., ethene, ethyne).
  • Example:
    • Ethane (C₂H₆): All valencies satisfied with single bonds.
    • Ethene (C₂H₄): Contains a double bond.
    • Ethyne (C₂H₂): Contains a triple bond.

Structural Isomerism

  • Compounds with the same molecular formula but different structures (e.g., butane can have straight or branched chains).

Hydrocarbons

  • Alkanes: Saturated hydrocarbons with single bonds.
  • Alkenes: Unsaturated hydrocarbons with double bonds.
  • Alkynes: Unsaturated hydrocarbons with triple bonds.

Functional Groups and Homologous Series

  • Functional Groups: Specific atoms or groups (e.g., -OH, -CHO) replace hydrogen in hydrocarbons and define chemical properties.
  • Homologous Series:
    • A series of compounds with the same functional group and similar properties.
    • Example: Alcohols – Methanol (CH₃OH), Ethanol (C₂H₅OH), etc.

Additional Concepts for Competitive Exams

  1. Hybridization in Carbon: Explains shapes like tetrahedral (methane) and planar (ethene).
  2. Applications of Carbon Allotropes:
    • Diamonds: Cutting tools.
    • Graphite: Lubricants and electrodes.
    • Fullerenes: Drug delivery and nanotechnology.
  3. Synthesis of Organic Compounds: Friedrich Wöhler’s synthesis of urea disproved the “vital force” theory.
  4. Reactivity of Unsaturated Compounds: Double and triple bonds make them more reactive than saturated ones.

5. Nomenclature of Carbon Compounds:

  1. Naming Organic Compounds:
    • Names are based on the carbon chain, modified by prefixes or suffixes to indicate functional groups.
    • Example: Alcohols like methanol, ethanol, propanol, etc.
  2. Steps for Naming:
    • Step 1: Count the carbon atoms in the compound (e.g., 3 carbons = propane).
    • Step 2: Identify functional groups (e.g., alcohol, ketone, carboxylic acid).
    • Step 3: Add a suffix (e.g., “ol” for alcohol) or prefix for functional groups.
    • If the functional group starts with a vowel, remove the final ‘e’ from the base name (e.g., propane → propanone for a ketone).
  3. Unsaturation:
    • For double bonds, replace “ane” with “ene” (e.g., propene).
    • For triple bonds, replace “ane” with “yne” (e.g., propyne).
  4. Homologous Series:
    • A family of compounds differing by a –CH₂ unit. Example: CH₃OH → C₂H₅OH → C₃H₇OH (methanol, ethanol, propanol).

Key Functional Groups and Naming Rules (from Table 4.4):

ClassPrefix/SuffixExample
HaloalkanesPrefix: Chloro, BromoChloropropane
AlcoholsSuffix: -olPropanol
AldehydesSuffix: -alPropanal
KetonesSuffix: -onePropanone
Carboxylic AcidsSuffix: -oic acidPropanoic Acid
AlkenesSuffix: -enePropene
AlkynesSuffix: -ynePropyne

Chemical Properties of Carbon Compounds:

  1. Combustion:
    • Carbon burns in oxygen to form CO₂, releasing heat and light.
    • Examples:
      • C + O₂ → CO₂ + heat
      • CH₄ + O₂ → CO₂ + H₂O + heat.
    • Saturated hydrocarbons burn clean (blue flame), while unsaturated give yellow, sooty flames due to incomplete combustion.
  2. Oxidation:
    • Alcohols can oxidize to acids (e.g., ethanol → ethanoic acid).
    • Oxidizing agents like alkaline potassium permanganate and potassium dichromate are used.
  3. Addition Reactions:
    • Unsaturated hydrocarbons (alkenes/alkynes) can add hydrogen to form saturated ones using catalysts (e.g., Ni, Pd).
    • Example: Hydrogenation of vegetable oils.
  4. Substitution Reactions:
    • Saturated hydrocarbons react with chlorine under sunlight (e.g., CH₄ + Cl₂ → CH₃Cl + HCl).

Important Carbon Compounds:

  1. Ethanol (Alcohol):
    • Physical Properties:
      • Liquid at room temperature, dissolves in water.
    • Uses: Solvent, ingredient in alcoholic drinks, medicines.
    • Reactions:
      • With sodium: Produces hydrogen gas.
      • Dehydration: Ethanol → Ethene with conc. H₂SO₄.
  2. Ethanoic Acid (Acetic Acid):
    • Physical Properties:
      • 5-8% solution is vinegar; freezes in cold climates (glacial acetic acid).
    • Reactions:
      • With alcohol: Forms esters (sweet-smelling substances).
      • With bases: Produces salt and water.
      • With carbonates: Produces CO₂, water, and a salt.

Soaps and Detergents:

  1. Micelle Formation:
    • Soap molecules have two ends:
      • Hydrophilic: Attracts water.
      • Hydrophobic: Attracts oil.
    • Helps in cleaning by trapping oil/dirt in water.
  2. Cleaning Action:
    • Forms emulsions by surrounding dirt particles.

Extra Knowledge for Competitive Exams:

  1. Key Properties of Functional Groups:
    • Alcohols: React with sodium, undergo dehydration.
    • Carboxylic Acids: React with bases and carbonates to produce salt and CO₂.
  2. Tips for Nomenclature:
    • Prioritize functional groups when naming.
    • Remember “ane” → “ene” for double bonds; “ane” → “yne” for triple bonds.
  3. Combustion and Pollution:
    • Incomplete combustion produces CO and soot (major pollutants).
    • Fuels like coal/petroleum release sulfur/nitrogen oxides.
  4. Fossil Fuels:
    • Coal: Formed from plant remains under high pressure.
    • Petroleum: Derived from marine organisms buried under silt.

THESE ALL ARE THE NOETS OF CHAPTER 4. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊