Chemistry · Grade 12

Active learning ideas

Lewis Acids and Bases

Active learning helps students visualize the invisible electron pair transfers central to Lewis acids and bases. Hands-on model building, lab observations, and sorting tasks make abstract concepts concrete, reducing misconceptions about what counts as an acid or base.

• Ontario Curriculum Expectations
• Ontario Curriculum, Grade 12 Chemistry (SCH4U), Strand D: Energy Changes and Rates of Reaction, D3.4: explain the concept of entropy, and predict the direction of spontaneous change for a variety of chemical reactions.
• Ontario Curriculum, Grade 12 Chemistry (SCH4U), Strand D: Energy Changes and Rates of Reaction, D3.5: explain the relationship between the spontaneity of a reaction, and the change in enthalpy (ΔH), the change in entropy (ΔS), and the temperature of the system (T), using the Gibbs free energy equation.
• Ontario Curriculum, Grade 12 Chemistry (SCH4U), Strand D: Energy Changes and Rates of Reaction, D2.1: use appropriate terminology related to energy changes and rates of reaction, including, but not limited to: enthalpy, entropy, free energy, activation energy, and specific heat capacity.

• 20–35 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Concept Mapping
• 30 min · Small Groups

Model Building: Lewis Adducts

Distribute molecular model kits or software. Have small groups assemble Lewis acids like BF3 or AlCl3, then pair with bases such as NH3 or OH- to form adducts. Students draw before-and-after diagrams, noting electron pair arrows. Discuss how bonds form without protons.

Differentiate between Brønsted-Lowry and Lewis definitions of acids and bases.

Facilitation Tip

During Model Building, circulate to ensure students rotate models to view empty orbitals and lone pairs from multiple angles, reinforcing the 3D geometry of adduct formation.

What to look for

Present students with several reaction equations, some involving proton transfer and others involving electron pair donation/acceptance without protons. Ask them to label the Lewis acid and Lewis base in each reaction and briefly justify their choices.

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Activity 02

• Concept Mapping
• 35 min · Pairs

Observation Lab: Metal-Ligand Reactions

Prepare solutions of Cu2+ or Fe3+ salts. Pairs add ligands like ammonia or water, observe color changes, and classify species as Lewis acid or base. Record videos for analysis and predict outcomes for new combinations.

Identify Lewis acids and bases in various chemical reactions.

Facilitation Tip

In the Observation Lab, have students record color changes and precipitate formation firsthand, then connect these visual cues to electron pair donation and acceptance.

What to look for

Facilitate a class discussion using the prompt: 'How does the Lewis definition of acids and bases provide a broader understanding of chemical reactivity compared to the Brønsted-Lowry definition? Provide at least two examples of species that can be classified as acids or bases only under the Lewis theory.'

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Activity 03

• Concept Mapping
• 25 min · Small Groups

Card Sort: Reaction Classification

Create cards with chemical reactions, formulas, and roles. Small groups sort into Brønsted-Lowry, Lewis only, or both categories, justifying choices. Class shares and debates borderline cases.

Explain how the Lewis theory expands the range of substances considered acids and bases.

Facilitation Tip

For the Card Sort, monitor groups to prevent misclassification by asking them to verbalize their reasoning for each card placement.

What to look for

Provide students with the reaction between BF3 and NH3. Ask them to: 1. Identify the Lewis acid and Lewis base. 2. Draw the product formed, showing the coordinate covalent bond. 3. Write one sentence explaining why BF3 is a Lewis acid.

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Activity 04

• Concept Mapping
• 20 min · Pairs

Virtual Simulation: Electron Flow

Use PhET or ChemCollective simulations. Individuals or pairs manipulate molecules to show electron donation in reactions like H+ with H2O versus BF3 with F-. Export screenshots with annotations for a class gallery walk.

Differentiate between Brønsted-Lowry and Lewis definitions of acids and bases.

Facilitation Tip

Run the Virtual Simulation in real time so students can pause and discuss electron flow snapshots as a class.

What to look for

Present students with several reaction equations, some involving proton transfer and others involving electron pair donation/acceptance without protons. Ask them to label the Lewis acid and Lewis base in each reaction and briefly justify their choices.

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

A few notes on teaching this unit

Start with a quick diagnostic question to surface prior knowledge about acids and bases. Teach Lewis theory by contrasting it with Brønsted-Lowry, emphasizing the broader scope of electron pair behavior. Use analogies like 'electron pair magnets' to build intuition, but transition quickly to formal definitions. Avoid over-reliance on proton transfer examples, and always connect back to the Lewis framework to prevent confusion.

Students will confidently identify Lewis acids and bases in reactions, explain coordinate covalent bond formation, and compare Lewis and Brønsted-Lowry definitions using evidence from their work. Success looks like accurate labeling, clear explanations, and applying the definitions beyond textbook examples.

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Watch Out for These Misconceptions

• During the Model Building activity, watch for students who assume all acids must contain hydrogen.

  Use the model kits to point out BF3’s empty p-orbital and NH3’s lone pair, then ask students to physically demonstrate how the pair moves into BF3’s orbital, linking the visual to the definition.

• During the Observation Lab, watch for students who label metal cations like Fe3+ as bases because they 'accept' something in reactions.

  Have students revisit their lab notes and highlight where Fe3+ accepts electron pairs from ligands, then reclassify it as a Lewis acid using the reaction evidence in front of them.

• During the Card Sort activity, watch for students who group all acids and bases based solely on proton transfer.

  Ask groups to justify their placements by describing electron pair movement, and prompt them to re-sort cards like BF3 + NH3 or AlCl3 + Cl- using Lewis definitions.

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Methods used in this brief

• Concept Mapping