Chemistry · Grade 12

Active learning ideas

Reactions of Hydrocarbons

Move beyond simply naming and drawing molecules to explore how they actually behave and transform. This topic uncovers the fundamental rules that govern how hydrocarbons react, forming the basis of organic synthesis.

• Ontario Curriculum Expectations
• Ontario Curriculum: SCH4U, Strand B - Organic Chemistry, B2: Investigate the molecular structures and the properties of organic compounds, and carry out organic reactions.

• 20–30 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Collaborative Problem-Solving
• 30 min · Pairs

Modelling Reaction Mechanisms

Students use molecular model kits to physically break and form bonds for a substitution and an addition reaction. This hands-on approach helps them visualize the movement of atoms and the structural changes that occur.

Compare the mechanism of a free-radical substitution reaction with an electrophilic addition reaction.

Facilitation Tip

Encourage students to narrate the process as they manipulate the models to reinforce the steps of the mechanism.

What to look for

Use 'Predict the Product' exit tickets. Provide students with the starting hydrocarbon and a reagent, and ask them to draw and name the major organic product.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 02

• Collaborative Problem-Solving
• 25 min · Small Groups

Markovnikov's Rule Challenge

Provide students with worksheets containing various unsymmetrical alkenes and reagents (e.g., HBr, H2O). In small groups, they predict the major and minor products, drawing the carbocation intermediates to justify their answers.

Explain Markovnikov's rule for the addition of hydrogen halides to asymmetrical alkenes.

Facilitation Tip

Circulate and probe groups about why a tertiary carbocation is more stable than a primary one.

What to look for

A unit test section containing problems where students must identify the reaction type, predict products for a variety of reactions (including applying Markovnikov's rule), and draw a simple reaction mechanism.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

Activity 03

• Collaborative Problem-Solving
• 20 min · Small Groups

Reaction Type Card Sort

Students are given a set of cards, each with a different hydrocarbon reaction. They must sort these cards into three categories: Substitution, Addition, and Elimination, and then justify their reasoning to their group.

Identify the products formed from the complete and incomplete combustion of a hydrocarbon.

Facilitation Tip

Include combustion as a fourth category to review prior knowledge and add a layer of complexity.

What to look for

Provide a checklist of the learning objectives. Students rate their confidence level (e.g., from 1 to 5) for each objective, such as 'I can explain why a tertiary carbocation is the most stable'.

• Apply
• Analyze
• Evaluate
• Create
• Relationship Skills
• Decision-Making
• Self-Management

A few notes on teaching this unit

Start by visually contrasting the single bonds of ethane with the double bond of ethene, emphasizing the pi bond as a site of reactivity. Use analogies, like a pi bond being a 'handle' for other molecules to grab onto, to explain the reactivity of unsaturated compounds. When introducing Markovnikov's rule, focus on the 'why' (carbocation stability) before the 'what' (the rule itself) to promote deeper understanding over memorization.

Students will be able to analyze a given set of reactants, identify the most likely reaction to occur, and predict the major products formed.

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Watch Out for These Misconceptions

• Alkanes undergo addition reactions just like alkenes.

  Alkanes are saturated, meaning they only have single bonds and cannot 'add' more atoms without first breaking a strong C-C or C-H bond. They undergo substitution, where one atom is swapped for another.

• Markovnikov's rule is just a random rule to memorize.

  Markovnikov's rule is based on the stability of the carbocation intermediate formed during the reaction. The reaction proceeds through the most stable intermediate (tertiary > secondary > primary), which leads to the formation of the major product.

• In an addition reaction, the double bond simply disappears.

  The double bond consists of one sigma bond and one pi bond. The weaker, more accessible pi bond breaks to form two new, stronger sigma bonds with the atoms being added. The original sigma bond between the carbons remains intact.

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Methods used in this brief

• Collaborative Problem-Solving