Science · Grade 7 · Pure Substances and Mixtures · Term 3

Physical and Chemical Properties of Matter

Differentiating between physical properties (e.g., density, melting point) and chemical properties (e.g., flammability, reactivity).

• Ontario Curriculum Expectations
• MS-PS1-2

About This Topic

Physical and chemical properties classify matter by characteristics that define its behaviour. Physical properties include density, melting point, solubility, and colour, all observed without changing the substance's identity. Chemical properties, such as flammability, reactivity with acids, or oxidation, appear only during chemical changes that produce new substances. Grade 7 students explore these through examples like comparing densities of oils and water or noting how sugar dissolves but gasoline ignites.

This topic aligns with Ontario's Pure Substances and Mixtures unit, where students use physical properties to identify unknowns, such as distinguishing plastics by flexibility or metals by magnetism. They also predict safe handling based on chemical properties, like storing reactive metals away from moisture. These investigations build skills in observation, measurement, and evidence-based reasoning essential for scientific inquiry.

Active learning shines here because properties demand direct testing. Students conducting density columns, melting tests, or safe reactivity demos with vinegar and steel wool experience differences firsthand. Collaborative analysis of results clarifies distinctions, reinforces safety protocols, and connects classroom work to everyday materials, making concepts stick through tangible exploration.

Key Questions

1. Differentiate between a physical property and a chemical property with examples.
2. Analyze how observing physical properties can help identify an unknown substance.
3. Predict how a substance's chemical properties might influence its safe handling.

Learning Objectives

• Classify substances as having distinct physical properties such as density, melting point, or solubility.
• Compare and contrast physical and chemical properties, providing specific examples for each.
• Analyze how observing physical properties aids in the identification of unknown substances.
• Predict potential hazards associated with a substance's chemical properties, such as flammability or reactivity.
• Explain the difference between a physical change and a chemical change based on property observation.

Before You Start

States of Matter

Why: Students need to understand the basic states of matter (solid, liquid, gas) to comprehend properties like melting point and boiling point.

Introduction to Matter

Why: A foundational understanding of what matter is and that it has characteristics is necessary before exploring specific properties.

Key Vocabulary

Physical Property	A characteristic of a substance that can be observed or measured without changing the substance's chemical identity. Examples include color, density, and melting point.
Chemical Property	A characteristic of a substance that describes its potential to undergo a chemical change or reaction by virtue of its composition. Examples include flammability and reactivity.
Density	The mass of a substance per unit volume, often expressed in grams per cubic centimeter (g/cm³). It helps determine if a substance will float or sink in another substance.
Flammability	A chemical property that describes a substance's ability to burn or ignite easily. It indicates how readily a material will combust in the presence of an oxidant, usually oxygen.
Reactivity	A chemical property that describes how readily a substance combines or reacts with other substances. High reactivity means a substance easily undergoes chemical changes.

Watch Out for These Misconceptions

Common Misconception

Melting or dissolving always means a chemical change.

What to Teach Instead

These are physical changes because the original substance reforms unchanged, like ice to water. Hands-on melting demos let students evaporate water to recover salt, building evidence against the idea. Group discussions refine their models through shared observations.

Common Misconception

Chemical properties describe appearance only, like colour.

What to Teach Instead

Chemical properties require reactions to observe, unlike static physical traits. Safe reactivity stations show colour change during fizzing but not before, helping students distinguish. Peer teaching during rotations reinforces the need for change.

Common Misconception

All properties are physical; chemical ones do not exist for common items.

What to Teach Instead

Everyday items have both, like wood's flammability. Inquiry labs with household samples reveal chemical traits safely, shifting views. Collaborative predictions before demos highlight overlooked properties.

Active Learning Ideas

Stations Rotation: Physical Property Stations

Prepare stations for density (layer liquids by pouring carefully), melting point (heat paraffin and chocolate on hot plates), solubility (test salt and oil in water), and magnetism (test everyday objects). Groups rotate every 10 minutes, recording data on charts. Debrief with class sharing of patterns.

50 min·Small Groups

Prediction Challenge: Chemical Properties

Show safe demos like steel wool in vinegar (reactivity) or paper near flame (flammability). Students predict outcomes in pairs, observe, then classify as chemical. Discuss why new substances form, linking to property definitions.

30 min·Pairs

Unknown Substance ID: Property Testing

Provide coded samples (e.g., sand, salt, iron filings). Students test physical properties: mass for density, solubility in water, response to magnet. Groups hypothesize identities and present evidence to class.

40 min·Small Groups

Gallery Walk: Property Cards

Distribute cards with examples like 'rusting iron' or 'boiling water'. Pairs sort into physical or chemical categories on posters. Whole class gallery walk allows voting and corrections with justifications.

35 min·Pairs

Real-World Connections

• Materials scientists use knowledge of physical properties like tensile strength and melting point to select appropriate materials for building bridges and aircraft, ensuring structural integrity and safety.
• Food chemists analyze chemical properties such as oxidation rates and reactivity with preservatives to determine the shelf life and safety of packaged foods, preventing spoilage and ensuring consumer health.
• Firefighters assess the flammability and reactivity of materials at a scene to develop safe and effective strategies for extinguishing fires and protecting themselves and the public.

Assessment Ideas

Quick Check

Present students with a list of properties (e.g., 'boils at 100°C', 'rusts in air', 'is magnetic', 'explodes when heated'). Ask them to label each as either a 'physical property' or a 'chemical property' and briefly justify their choice for two examples.

Exit Ticket

Provide students with scenarios involving common substances (e.g., 'Water freezing', 'Wood burning', 'Iron rusting', 'Sugar dissolving'). Ask them to identify the primary property being demonstrated in each scenario and state whether it is physical or chemical.

Discussion Prompt

Pose the question: 'Imagine you found a new, unlabelled solid. What physical properties would you test first to try and identify it, and why? What chemical property might you be hesitant to test directly, and what safety precautions would you consider?' Facilitate a class discussion on their responses.

Frequently Asked Questions

What are key examples of physical and chemical properties for grade 7?

Physical: density (mass per volume), melting point (temperature substance changes state), solubility (dissolves in water), conductivity. Chemical: flammability (burns in air), reactivity (fizzes with acid), oxidation (rusts). Use tables for students to list and test five examples each, connecting to identification tasks in the unit.

How do you teach differentiating physical from chemical properties?

Start with definitions and visuals, then hands-on tests. Have students observe no-change tests (density, melting) versus reaction demos (vinegar on chalk). Charts comparing 'before/after substance identity' clarify. Follow with application to unknowns, ensuring 80% accuracy before advancing.

How can active learning help students understand properties of matter?

Active methods like property stations and prediction challenges engage senses, making abstract ideas concrete. Students measure densities, watch melting, and see safe reactions, building mental models through evidence. Group rotations foster discussion, correcting errors in real time, while safety focus teaches responsible inquiry. Retention improves as they link tests to daily items like cooking oil flammability.

Why focus on chemical properties for safe handling in grade 7 science?

Chemical properties predict hazards, like reactivity guiding storage away from water. Students analyze scenarios, such as handling bleach, to prioritize safety. This builds lab skills and real-world awareness, aligning with curriculum expectations for responsible science practices and risk assessment.