Chemistry Notes – Set 15: Detailed Guide for UPSC, PCS, SSC Competitive Exams

Class 9: Chemical Bonding Basics

Detailed Concepts:

• Chemical Bonding: Force holding atoms together to form molecules or compounds.
  • Why Bonding Occurs: Atoms achieve stable electron configurations (e.g., noble gas-like, 8 valence electrons).
  • Valency: Number of bonds an atom can form (e.g., H: 1, O: 2, N: 3).
• Types of Bonds (Simplified):
  • Ionic Bond: Electron transfer between metal and non-metal (e.g., Na + Cl → NaCl, Na⁺Cl⁻).
    • Properties: High melting point, soluble in water, conducts in molten state.
  • Covalent Bond: Electron sharing between non-metals (e.g., H₂O, O shares electrons with 2H).
    • Properties: Low melting point, insoluble in water, non-conductive.
  • Metallic Bond: Delocalized electrons in metal lattice (e.g., Cu, electrons shared among Cu atoms).
    • Properties: Conducts heat/electricity, malleable.
• Chemical Interactions:
  • Ionic Compounds: Form crystals (e.g., NaCl lattice), used in salts.
  • Covalent Molecules: Form gases, liquids, or soft solids (e.g., CO₂, H₂O).
  • Metals: Form alloys (e.g., brass: Cu + Zn).
• Applications:
  • Industrial: NaCl in chemical synthesis, Cu in wiring.
  • Daily Life: H₂O in hydration, sugar (C₁₂H₂₂O₁₁, covalent) in food.
  • Environmental: CO₂ (covalent) in carbon cycle.
• Applications in Exams: Bonding types and their properties are key for objective and descriptive questions, especially for linking to material applications.

Formulas:

• Ionic Bond Formation: Na → Na⁺ + e⁻; Cl + e⁻ → Cl⁻; Na⁺ + Cl⁻ → NaCl.
• Covalent Bond Example: 2H + O → H₂O (shared electron pairs).
• Percentage Composition (e.g., NaCl): %Na = (23/58.5) × 100 ≈ 39.3%, %Cl = (35.5/58.5) × 100 ≈ 60.7%.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on bonding in materials (e.g., metals in construction) or environmental chemistry (e.g., CO₂).
  • SSC: Objective questions on bond types or properties (e.g., ionic vs. covalent).
  • Descriptive: Explain ionic bonding in NaCl or covalent bonding in H₂O.
• Real-World:
  • Industry: Al (metallic) in packaging, NaCl in food processing.
  • Environment: CO₂ in greenhouse effect, H₂O in ecosystems.
  • Daily Life: Sugar dissolution, metal utensils.
• Exam Tips:
  • Focus on properties of ionic vs. covalent compounds.
  • Link to environmental science (e.g., CO₂ emissions) for mains.

Diagram (Textual Description):

• Ionic vs. Covalent Bonding: Show NaCl (lattice of Na⁺ and Cl⁻ ions, electrostatic attraction) vs. H₂O (O with two H atoms, shared electron pairs). Label ionic bond (electron transfer), covalent bond (electron sharing), and properties (e.g., NaCl: high melting point; H₂O: liquid).

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Class 10: Environmental Chemistry

Detailed Concepts:

• Note: Revisiting Set 7’s “Environmental Chemistry” with a focus on pollution control and green chemistry to avoid redundancy, tailored for Class 10 level and exam needs.
• Air Pollution:
  • Pollutants: CO, SO₂, NOₓ, particulate matter (PM), hydrocarbons.
  • Sources: Vehicles (CO, NOₓ), industries (SO₂), burning fuels (PM).
  • Effects: CO poisoning, SO₂ → acid rain (SO₂ + H₂O → H₂SO₃ → H₂SO₄).
  • Control: Catalytic converters (CO, NOₓ → CO₂, N₂), scrubbers for SO₂.
• Water Pollution:
  • Pollutants: Organic waste, heavy metals (Hg, Pb), fertilizers (NO₃⁻).
  • Effects: Eutrophication (NO₃⁻ → algal blooms → O₂ depletion), heavy metal toxicity.
  • Control: Filtration, activated carbon, biodegradable detergents.
• Soil Pollution:
  • Pollutants: Pesticides (e.g., DDT), industrial waste.
  • Effects: Bioaccumulation, reduced fertility.
  • Control: Bioremediation, organic farming.
• Green Chemistry:
  • Sustainable practices (e.g., using H₂O₂ instead of Cl₂ for bleaching).
  • Examples: Biodegradable plastics, renewable feedstocks.
• Applications:
  • Environmental: Pollution control, waste management.
  • Industrial: Green solvents, eco-friendly processes.
• Applications in Exams: Pollution types, control measures, and green chemistry are key for objective and descriptive questions.

Formulas:

• Acid Rain: SO₂ + H₂O → H₂SO₃; 2H₂SO₃ + O₂ → 2H₂SO₄.
• Catalytic Converter: 2CO + O₂ → 2CO₂; 2NO → N₂ + O₂.
• Eutrophication: NO₃⁻ → Algal growth → O₂ depletion.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on pollution control in environmental policy or green chemistry in industry.
  • SSC: Objective questions on pollutants or control measures.
  • Descriptive: Explain acid rain mitigation or green chemistry principles.
• Real-World:
  • Environment: Scrubbers in power plants, biodegradable soaps.
  • Industry: Green solvents in manufacturing.
  • Health: Water purification to remove heavy metals.
• Exam Tips:
  • Master pollution reactions and green chemistry solutions.
  • Link to environmental science (e.g., eutrophication) for mains.

Diagram (Textual Description):

• Catalytic Converter: Show exhaust gases (CO, NO) passing through Pt/Pd catalyst in a honeycomb structure, converting to CO₂, N₂. Label catalyst, redox reactions (CO → CO₂, NO → N₂), and cleaner emissions.

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Class 11: Classification of Elements and Periodicity in Properties

Detailed Concepts:

• Note: This topic complements Set 5 and Set 9’s periodic table discussions by focusing on Class 11-level depth, emphasizing trends and applications.
• Periodic Table:
  • Historical: Mendeleev (atomic mass), Moseley (atomic number).
  • Modern: Based on atomic number (Z), 7 periods, 18 groups.
  • Blocks: s, p, d, f based on orbital filling.
• Periodic Trends:
  • Atomic Radius: Decreases across period (higher nuclear charge), increases down group (more shells).
  • Ionization Energy: Increases across period (smaller size), decreases down group (larger size).
  • Electronegativity: Increases across period (e.g., F = 4.0), decreases down group.
  • Electron Affinity: Increases across period (more tendency to gain electrons).
  • Metallic Character: Decreases across period, increases down group.
• Group Properties:
  • Group 1 (Alkali Metals): Soft, reactive (e.g., Na + H₂O → NaOH + H₂).
  • Group 17 (Halogens): Reactive non-metals (e.g., Cl₂ in disinfectants).
  • Group 18 (Noble Gases): Inert (e.g., Ar in lighting).
• Applications:
  • Industrial: Alkali metals in batteries, halogens in water treatment.
  • Environmental: Noble gases in non-reactive applications.
• Applications in Exams: Periodic trends and group properties are key for objective and descriptive questions.

Formulas:

• Ionization Energy: M → M⁺ + e⁻ (energy required).
• Electron Affinity: X + e⁻ → X⁻ (energy released).
• Atomic Radius: ∝ 1/Nuclear charge (across period), ∝ Shells (down group).

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on periodic trends in materials or environmental applications (e.g., halogens).
  • SSC: Objective questions on trends or group properties.
  • Descriptive: Explain electronegativity or alkali metal reactivity.
• Real-World:
  • Industry: Li in batteries, F in toothpaste.
  • Technology: Ne in neon signs, Si in semiconductors.
  • Environment: Halogens in ozone depletion (CFCs).
• Exam Tips:
  • Memorize trends (radius, ionization energy).
  • Link to environmental science (e.g., CFCs) for mains.

Diagram (Textual Description):

• Periodic Trends: Show a periodic table section (Groups 1, 2, 13–18; Periods 2–4). Draw arrows for atomic radius (increases down, decreases across), ionization energy (increases across), and electronegativity. Label key elements (e.g., Li, F).

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Class 12: p-Block Elements

Detailed Concepts:

• Note: This topic extends Set 9’s Class 11 p-Block Elements to Class 12 level, focusing on advanced compounds, reactions, and applications.
• p-Block Elements: Groups 13–18, valence electrons in p-orbitals (ns²np¹⁻⁶).
• Group-Wise Overview:
  • Group 13 (Boron Family):
    • Boron: B₂H₆ (diborane, electron-deficient), Al₂O₃ (amphoteric).
    • Compounds: Borax (Na₂B₄O₇·10H₂O), used in glass.
  • Group 14 (Carbon Family):
    • Carbon: Allotropes (diamond, graphite, graphene).
    • Silicon: SiO₂ (silica), silicates in cement.
  • Group 15 (Nitrogen Family):
    • Nitrogen: N₂ (inert), NH₃ (Haber process), HNO₃ (oxidizing).
    • Phosphorus: P₄, allotropes (white, red), P₂O₅ (dehydrating agent).
  • Group 16 (Oxygen Family):
    • Oxygen: O₂, O₃ (ozone, protects from UV).
    • Sulphur: S₈, H₂SO₄ (contact process).
  • Group 17 (Halogens):
    • Fluorine: Most reactive, forms HF (strong acid).
    • Chlorine: Cl₂ in bleaching, HClO in disinfectants.
  • Group 18 (Noble Gases):
    • Xenon: XeF₂, XeO₃ (reactive compounds).
• Key Reactions:
  • Ammonia Synthesis: N₂ + 3H₂ ⇌ 2NH₃ (Fe catalyst).
  • Sulphuric Acid: 2SO₂ + O₂ → 2SO₃ (V₂O₅); SO₃ + H₂O → H₂SO₄.
  • Ozone Formation: 3O₂ ⇌ 2O₃ (UV light).
• Applications:
  • Industrial: H₂SO₄ in fertilizers, Si in semiconductors.
  • Environmental: O₃ in UV protection, CFCs in ozone depletion.
• Applications in Exams: Compounds, reactions, and applications are key for objective and descriptive questions.

Formulas:

• Ammonia: N₂ + 3H₂ ⇌ 2NH₃.
• Sulphuric Acid: SO₃ + H₂O → H₂SO₄.
• Boric Acid: H₃BO₃ + H₂O ⇌ B(OH)₄⁻ + H⁺.
• Xenon Fluoride: Xe + F₂ → XeF₂.

Applications:

• Competitive Exams:
  • UPSC/PCS: Questions on p-block compounds in industry (e.g., H₂SO₄) or environmental issues (e.g., CFCs).
  • SSC: Objective questions on reactions or group properties.
  • Descriptive: Explain H₂SO₄ production or ozone’s role.
• Real-World:
  • Industry: NH₃ in fertilizers, Cl₂ in water treatment.
  • Environment: O₃ in UV protection, SO₂ in acid rain.
  • Technology: Si in electronics, Xe in lamps.
• Exam Tips:
  • Master group-wise reactions and applications.
  • Link to environmental science (e.g., ozone depletion) for mains.

Diagram (Textual Description):

• Contact Process for H₂SO₄: Show SO₂ + O₂ → 2SO₃ (V₂O₅ catalyst) in a reactor, then SO₃ + H₂O → H₂SO₄ in absorption tower. Label catalyst, exothermic reaction, and H₂SO₄ collection.