Driving Question:
How can we identify and classify an unknown material using its physical properties?
Hypothesis:
Answer the driving question using: “if… then… because…”
Learning Objective:
Students will classify everyday objects as metals, non-metals, or alloys by observing and testing their physical properties and using a dichotomous classification key.
Success Criteria:
By the end of the investigation, I can:
- describe the physical properties of a material using scientific vocabulary;
- distinguish metals from non-metals using observable evidence;
- use a classification key to identify materials;
- explain why some materials are classified as alloys;
- justify my classification using evidence rather than appearance alone.
Materials:
- Container with assorted everyday objects
- Magnifying glasses
- Magnets
- Small containers or trays
- Rulers
- Balance
- Water droppers
- Classification Key
- School paper
PROCEDURES:
PART 1 — OBSERVE BEFORE YOU TEST
Choose several objects from the container.
Do not use the classification key yet.
For each object, carefully observe its physical properties.
Record:
- color;
- texture;
- surface appearance;
- hardness;
- flexibility;
- shape;
- luster;
- magnetic response;
- mass/weight;
- conductivity, if tested;
- any other relevant property.
Vocabulary Bank
| Property | Useful vocabulary |
|---|---|
| Luster | shiny / dull |
| Texture | smooth / rough |
| Hardness | hard / soft |
| Flexibility | flexible / rigid |
| Magnetic response | magnetic / non-magnetic |
| Density | light / heavy for its size |
| Electrical conductivity | conductor / poor conductor |
| Thermal conductivity | good conductor / poor conductor |
| Malleability | can be hammered or flattened / breaks or cracks |
| Appearance | metallic / non-metallic |
PART 2 — TEST THE OBJECTS
Use the available tests to collect evidence.
Test 1 — Magnetism
Bring the magnet close to the object.
Record:
Attracted / Not attracted
Remember: Not all metals are magnetic.
Test 2 — Flexibility
Carefully determine whether the object can bend.
Record:
Flexible / Rigid
Do not force or damage the objects.
Test 3 — Surface and Luster
Observe the object’s surface.
Record:
Shiny / Dull
Test 4 — Hardness
Compare the object’s hardness with other objects.
Record:
Hard / Soft
Test 5 — Mass and Size
Compare objects of similar size.
Record:
Relatively heavy / Relatively light
Test 6 — Conductivity
If your teacher provides an appropriate conductivity tester, test the objects.
Record:
Conductive / Poor conductor
PART 3 — USE THE CLASSIFICATION KEY
Now use the evidence you collected to classify each object.
Follow the key from the beginning.
Do not skip questions.
If the evidence is insufficient to make a decision, return to the object and perform another observation or test.
DICHOTOMOUS CLASSIFICATION KEY
START
1A. Does the object show metallic properties?
Examples of metallic properties include:
- metallic luster;
- relatively high hardness;
- good electrical/thermal conductivity;
- malleability;
- relatively high density.
YES → Go to 2
NO → Go to 7
2. Is the object made primarily of a single metallic element?
YES → CLASSIFY AS: METAL
Examples:
- copper;
- aluminum;
- iron.
NO / UNSURE → Go to 3
3. Does the material contain two or more elements, including at least one metal?
YES → CLASSIFY AS: ALLOY
Examples:
- steel;
- brass;
- bronze;
- stainless steel.
NO / UNSURE → Go to 4
4. Does the object have properties that are different from those expected for a pure metal?
Consider:
- hardness;
- strength;
- color;
- corrosion resistance;
- flexibility;
- density.
YES → Go to 5
NO / UNSURE → Go to 6
5. Could the different properties result from combining metals or a metal with another element?
YES → CLASSIFY AS: ALLOY
NO / INSUFFICIENT EVIDENCE → Ask for additional information or perform another test.
6. Is there enough evidence to identify the material as a pure metal?
YES → CLASSIFY AS: METAL
NO → Ask for additional information or perform another test.
7. Does the material show mainly non-metallic properties?
Examples:
- poor electrical conductivity;
- low luster;
- low density;
- flexibility or brittleness;
- lack of metallic appearance.
YES → CLASSIFY AS: NON-METAL
NO / UNSURE → Collect additional evidence.
IMPORTANT SCIENTIFIC NOTE
Appearance alone is not enough to identify a material.
For example:
- A shiny object is not necessarily a metal.
- A heavy object is not necessarily a metal.
- A magnetic object is not necessarily an alloy.
- A non-magnetic object is not necessarily a non-metal.
- Two objects may look similar but be made of different materials.
Scientists use multiple properties and multiple pieces of evidence to identify materials.
PART 4 — CLASSIFICATION TABLE
| Object | Metallic properties? | Magnetic? | Shiny? | Hard? | Flexible? | Conductive? | Final classification |
|---|---|---|---|---|---|---|---|
| Object 1 | |||||||
| Object 2 | |||||||
| Object 3 | |||||||
| Object 4 | |||||||
| Object 5 | |||||||
| Object 6 | |||||||
| Object 7 | |||||||
| Object 8 |
PART 5 — EVIDENCE AND REASONING
Choose three objects that were difficult to classify.
For each object, complete:
Object: ______________________
My classification: ______________________
Evidence 1:
Evidence 2:
Evidence 3
Therefore, I classified this object as __________________ because..
DISCUSSION:
Answer the questions using complete scientific sentences.
1. Which physical properties were most useful for distinguishing metals from non-metals?
2. Was magnetism a reliable way to identify all metals? Explain.
3. Why is it important to use more than one physical property when classifying a material?
4. Why might two objects made from metals have very different properties?
5. What is an alloy?
6. Why are alloys often used instead of pure metals?
7. How can changing the composition of a material change its properties?
8. Which objects in your collection were most difficult to classify? Why?
9. Did any object look like a metal but turn out to be a non-metal? Explain how your tests helped you identify it.
10. Did any objects look similar but receive different classifications? What does this tell you about using appearance to identify materials?
CONCLUSION:
Answer the questions below using complete scientific sentences and evidence collected during the investigation.
1. Which physical properties were the most useful for classifying the objects? Explain why.
2. How did the classification key help you identify and classify the materials?
3. What evidence allowed you to distinguish metals from non-metals?
4. Why is it important to use several physical properties instead of only one when classifying materials?
5. What are the main differences between metals, non-metals, and alloys?
6. Why are alloys often preferred over pure metals in everyday applications?
7. Was your initial hypothesis correct, partially correct, or incorrect? Use evidence from the investigation to justify your answer.
8. How does understanding the properties of materials help engineers and designers choose the best material for a specific product?