Topic: Organic Chemistry – Alkanes
Lesson 1: Structure and Bonding in Alkanes
| Section | Details |
|---|---|
| Objective | – State that alkanes have single covalent bonds.- Define alkanes as saturated hydrocarbons. |
| Activities | – Starter (5 mins): Show molecular models of methane, ethane, and propane and ask: “What do these molecules have in common?”- Main (25 mins): 1. Define alkanes as hydrocarbons with only single covalent bonds. 2. Explain the term “saturated hydrocarbon” (no double or triple bonds). 3. Provide examples: methane (CH4CH_4), ethane (C2H6C_2H_6), propane (C3H8C_3H_8), butane (C4H10C_4H_{10}). 4. Students practice drawing structural and displayed formulae for simple alkanes.- Plenary (10 mins): Students complete a worksheet identifying alkanes and explaining why they are saturated hydrocarbons. |
| Resources | Molecular models, periodic table, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Draw the structural and displayed formulae for the first five alkanes. |
| Assessment | Worksheet: Identify alkanes based on structural or displayed formulae. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/20 Q6(b) – Structure and bonding in alkanes. |
Lesson 2: Properties of Alkanes
| Section | Details |
|---|---|
| Objective | – Describe the general properties of alkanes.- Explain that alkanes are generally unreactive except for combustion and substitution reactions. |
| Activities | – Starter (5 mins): Burn a small sample of an alkane (e.g., candle wax) and ask: “What happens when alkanes burn?”- Main (25 mins): 1. Discuss the physical properties of alkanes: – Nonpolar. – Insoluble in water. – Low reactivity. 2. Explain chemical properties: – Combustion (complete and incomplete): CH4+2O2→CO2+2H2OCH_4 + 2O_2 → CO_2 + 2H_2O (complete combustion). – Substitution reaction with chlorine (requires UV light). 3. Highlight why alkanes are generally unreactive due to strong single covalent bonds.- Plenary (10 mins): Students classify a list of reactions as involving alkanes or not. |
| Resources | Candle or alkane sample, worksheets, reaction equations. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write the balanced equations for complete and incomplete combustion of ethane. |
| Assessment | Worksheet: Describe the properties of alkanes and predict combustion products. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/19 Q6(a) – Properties of alkanes. |
Lesson 3: Substitution Reaction of Alkanes
| Section | Details |
|---|---|
| Objective | – Define substitution reactions.- Describe and draw the substitution reaction of alkanes with chlorine as a photochemical reaction. |
| Activities | – Starter (5 mins): Show a UV lamp and ask: “Why is UV light needed for some chemical reactions?”- Main (25 mins): 1. Define substitution reaction: One atom or group of atoms is replaced by another. 2. Explain photochemical substitution in alkanes: – Reaction with chlorine in the presence of UV light. – Example with methane: CH4+Cl2→CH3Cl+HClCH_4 + Cl_2 → CH_3Cl + HCl (monosubstitution). – Highlight the role of UV light as the source of activation energy. 3. Practice drawing structural and displayed formulae for the reaction.- Plenary (10 mins): Students complete a worksheet drawing and naming substitution products. |
| Resources | UV lamp, reaction diagrams, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Draw the structural formula for the products of propane reacting with chlorine (monosubstitution). |
| Assessment | Worksheet: Write equations and draw structures for monosubstitution reactions of alkanes. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q6(b) – Substitution reactions of alkanes. |
Key Notes for Students:
- Structure of Alkanes:
- Single covalent bonds only (saturated hydrocarbons).
- Examples: Methane (CH4CH_4), Ethane (C2H6C_2H_6), Propane (C3H8C_3H_8).
- Properties of Alkanes:
- Nonpolar, insoluble in water, low reactivity.
- Combustion produces CO2CO_2 and H2OH_2O (complete combustion).
- Substitution Reaction:
- Example: CH4+Cl2→CH3Cl+HClCH_4 + Cl_2 → CH_3Cl + HCl (UV light required).
- Chlorine replaces one hydrogen atom (monosubstitution).
Notes for Teachers:
- Use molecular models to show single bonds in alkanes.
- Demonstrate real-life examples of alkanes and their combustion.
- Reinforce the role of UV light in substitution reactions with practical demonstrations or simulations.
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