Cheat Sheet: Carbon and its Compounds - Class 10 PDF Download

Importance of Carbon

• Elemental and Combined Forms: Carbon is vital in both elemental (diamond, graphite, fullerenes) and combined forms (e.g., food, clothes, medicines, living structures).

• Abundance: Earth's crust contains only 0.02% carbon (minerals like carbonates, coal, petroleum), and the atmosphere has 0.03% carbon dioxide.

• Significance: Despite low abundance, carbon’s versatility makes it essential due to its unique properties.

Bonding in Carbon - The Covalent Bond

• Carbon’s Electronic Configuration: Atomic number = 6, electron distribution: 1s² 2s² 2p², with 4 valence electrons.

• Covalent Bonding: Carbon shares electrons to achieve noble gas configuration (octet), forming covalent bonds instead of gaining/losing electrons (due to high energy requirements for C⁴⁻ or C⁴⁺).

• Types of Covalent Bonds:

  1. Single Bond: e.g., Hydrogen (H₂), Methane (CH₄).

  2. Double Bond: e.g., Oxygen (O₂), Ethene (C₂H₄).

  3. Triple Bond: e.g., Nitrogen (N₂), Ethyne (C₂H₂).

• Properties of Carbon Compounds:

  1. Low melting and boiling points (e.g., Acetic acid: 290 K melting, 391 K boiling; Methane: 90 K melting, 111 K boiling).

  2. Poor conductors of electricity (no ions formed).

  3. Weak intermolecular forces.

Electron Dot Structures:

• Methane (CH₄): Carbon shares 4 electrons with 4 hydrogen atoms.

• Ethane (CH₃-CH₃): Each Carbon shares 4 electrons with 3 hydrogen atoms.
  

• Ethene (CH₂-CH₂): Each carbon shares double bond with each other and single bond with 2 hydrogen.

Allotropes of Carbon

• Diamond: Each carbon bonded to 4 others in a rigid 3D structure; hardest substance, non-conductor.

• Graphite: Each carbon bonded to 3 others in hexagonal layers; smooth, slippery, good conductor.

• Buckminsterfullerene (C₆₀): Carbon atoms arranged in a football-like structure.

Versatile Nature of Carbon

• Catenation: Carbon’s ability to form long chains, branched chains, or rings by bonding with other carbon atoms.

• Tetravalency: Carbon’s valency of 4 allows bonding with up to 4 other atoms (carbon or other elements like H, O, N, S, Cl).

• Stability: Carbon forms strong bonds due to its small size, making compounds stable.

Organic Compounds:

• Initially thought to require a “vital force” (disproved by Wöhler’s synthesis of urea in 1828).

• Studied under organic chemistry (except carbides, oxides, carbonates, hydrogencarbonates).

Saturated and Unsaturated Carbon Compounds

1. Saturated Compounds (Alkanes):

• Single bonds, less reactive.

• Example: Ethane (C₂H₆) – H₃C–CH₃.

2. Unsaturated Compounds:

• Alkenes: One or more double bonds, e.g., Ethene (C₂H₄, H₂C=CH₂).

• Alkynes: One or more triple bonds, e.g., Ethyne (C₂H₂, HC≡CH).

Chains, Branches, and Rings

• Carbon Chains:

  1. Straight chains: e.g., Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

  2. Branched chains: e.g., Isobutane (C₄H₁₀).

  3. Cyclic: e.g., Cyclohexane (C₆H₁₂), Benzene (C₆H₆).

• Structural Isomers: Same molecular formula, different structures (e.g., butane vs. isobutane).

• Hydrocarbons:

  1. Alkanes: Saturated, single bonds (CₙH₂ₙ₊₂).

  2. Alkenes: One or more double bonds (CₙH₂ₙ).

  3. Alkynes: One or more triple bonds (CₙH₂ₙ₋₂).

Functional Groups

• Heteroatoms: Elements like Cl, Br, O, N, S replace hydrogen in hydrocarbons, forming functional groups.

Homologous Series

Series of compounds with the same functional group, differing by a –CH₂– unit.

Example (Alkanes):

• Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), etc.

• Differ by –CH₂– units.

• Molecular mass difference: 14 u (CH₂ = 12 u (C) + 2×1 u (H)).

Example (Alkenes):

• Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈).

• Differ by –CH₂– units.

Chemical Properties of Carbon Compounds

1. Combustion: Carbon compounds burn in oxygen to produce CO₂, water, and heat.

• Example: CH₄ + 2O₂ → CO₂ + 2H₂O + heat.

• Saturated hydrocarbons burn with a clean flame; unsaturated hydrocarbons give a sooty flame due to incomplete combustion.

2. Oxidation: Carbon compounds (e.g., alcohols) can be oxidized to carboxylic acids using oxidizing agents like alkaline KMnO₄ or acidified K₂Cr₂O₇.

• Example: Ethanol (C₂H₅OH) → Ethanoic acid (CH₃COOH).

3. Addition Reactions: Unsaturated hydrocarbons undergo addition reactions to become saturated.

• Example: Ethene (C₂H₄) + H₂ → Ethane (C₂H₆) (using Ni catalyst).

4. Substitution Reactions: Saturated hydrocarbons (e.g., alkanes) undergo substitution with halogens (e.g., Cl₂) in sunlight.

• Example: CH₄ + Cl₂ → CH₃Cl + HCl.

Some Important Carbon Compounds – Ethanol and Ethanoic Acid

1. Ethanol (C₂H₅OH):

Properties: Colorless, pleasant smell, volatile, soluble in water, flammable.

Reactions:

• Combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

• Oxidation: C₂H₅OH → CH₃COOH (with KMnO₄ or K₂Cr₂O�７).

• Dehydration: C₂H₅OH → C₂H₄ + H₂O (with conc. H₂SO₄ at 170°C).

Uses: Alcoholic beverages, solvent, fuel, antiseptic.

2. Ethanoic Acid (CH₃COOH):

Properties: Colorless, pungent smell, miscible with water, weak acid.

Reactions:

• With NaOH: CH₃COOH + NaOH → CH₃COONa + H₂O.

• With NaHCO₃: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂ (test for carboxylic acids).

• Esterification: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ (ethyl ethanoate) + H₂O.

Uses: Vinegar (5-8% solution), solvent, preservative.

Soaps and Detergents

Soaps:

• Sodium or potassium salts of long-chain carboxylic acids (e.g., sodium stearate, C₁₇H₃₅COONa).

• Structure: Hydrophilic head (–COO⁻Na⁺) and hydrophobic tail (long hydrocarbon chain).

• Cleansing Action: Forms micelles, trapping dirt/oil in the hydrophobic center, allowing it to be rinsed away by water.

• Limitation: Ineffective in hard water due to formation of insoluble calcium/magnesium salts (scum).

Detergents:

• Synthetic compounds (e.g., sodium alkyl sulphates or sulphonates).

• Effective in hard water, no scum formation.

• Advantage: Better cleansing in hard water; biodegradable options available.