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Subject: Chemistry
Semester: 1
Period: 1
Week: 5
School Name:
Teacher’s Name:
Subject: Chemistry
Grade Level: Grade 12
Week & Period: Week 5, Period I
Date:
Topic: Hydrocarbons – Alkenes, Alkynes and Benzene
Subtopics:
- Alkenes: Sources, structure, uses, nomenclature, properties (physical and chemical), reactions.
- Alkynes: Sources, structure, nomenclature, physical properties, uses, and reactions.
- Benzene: Structure, physical and chemical properties, uses, reactions.
Learning Objectives: By the end of this lesson, learners should be able to:
- Describe the physical and chemical properties of alkenes and alkynes.
- Explain the structure and aromatic nature of benzene.
- Name simple alkenes and alkynes using IUPAC rules.
- Compare the reactivity of alkenes, alkynes, and benzene.
- Identify and discuss the major uses of benzene and its derivatives.
Previous Knowledge: Students have studied alkanes and petroleum refinement.
Instructional Materials:
- Molecular models of alkenes, alkynes, and benzene.
- Reaction mechanism charts.
- Benzene ring model (flat hexagon with delocalized electrons).
Anticipation (Warm-Up) – 5 minutes: Ask: “Why do some hydrocarbons burn more brightly than others?” Lead into discussion on multiple bonding and reactivity.
Building Knowledge (Main Lesson) – 25 minutes:
- Alkenes:
- Contain at least one carbon-carbon double bond. General formula: CₙH₂ₙ.
- Reactions: addition reactions with H₂, Cl₂, HCl, Br₂ (test with bromine water), polymerization.
- Naming based on longest chain with the double bond; number from the nearest end.
- Used in manufacture of plastics (polyethene), alcohols, detergents.
- Alkynes:
- Triple bond between carbon atoms. General formula: CₙH₂ₙ₋₂.
- Undergo similar reactions to alkenes, but more reactive due to triple bond.
- Acetylene (ethyne) is common alkyne used in welding.
- Benzene:
- Aromatic compound with delocalized π electrons over six carbon atoms.
- Undergoes substitution rather than addition reactions (preserves aromaticity).
- Used in synthesis of dyes, detergents, plastics, drugs.
Learners’ Activities:
- Draw and name first five alkenes and first two alkynes.
- Compare combustion of alkanes vs. alkenes in lab (demo).
- Construct benzene model using cut-out rings.
Consolidation (Review and Assessment) – 10 minutes:
- Quick matching quiz: compound type vs. reaction type.
- Review: List three uses each for alkenes, alkynes, benzene.
Homework / Assignment:
- Write balanced equations for addition reactions of ethene.
- Research a benzene derivative and its industrial use.
Notes – Detailed and Explained:
- Alkenes are more reactive than alkanes due to the presence of a double bond which can break to add atoms. They burn with a more sooty flame than alkanes and decolorize bromine water due to addition reactions.
- Alkynes contain a triple bond and are even more reactive. Ethyne is a key industrial alkyne used in oxyacetylene torches.
- Benzene is unique due to its aromatic nature. Instead of undergoing addition like alkenes, it prefers substitution reactions that maintain its stable ring system. Despite its usefulness in making dyes and drugs, it is carcinogenic, hence care is needed.
Expanded Notes / Instructions:
- Demonstrate bromine water test for alkenes (vs. alkanes).
- Link to environmental and health implications of benzene use.
- Relate polymerization of alkenes to plastic waste problems.
Inclusive / Differentiation:
- Model making and visual aids for ELL students.
- Guided drawing and naming for slower learners.
- Research extensions for gifted students.
Teacher’s Reflection (Post-Lesson Questions):
- Could learners differentiate between alkanes, alkenes, and alkynes?
- Did learners understand the structure and importance of benzene?
- Were they able to apply IUPAC naming rules effectively?