TEACHGYAN • CLASS 7 SCIENCE • CURIOSITY
Chapter 4 — The World of Metals and Non-metals
Properties • Uses • Reactivity • Materials • Everyday Connections
🌟 Chapter at a Glance
Metals and non-metals have characteristic physical and chemical properties, but the useful question is not simply “which is better?” It is: which material is suitable for a particular job, and why?
| Property | Many metals | Many non-metals |
|---|---|---|
| Lustre | Often lustrous | Often dull |
| Malleability | Generally malleable | Generally not malleable |
| Ductility | Generally ductile | Generally not ductile |
| Conductivity | Generally good conductors | Generally poor conductors |
These are broad patterns, not rules without exceptions. Scientific classification is based on evidence.
🔨 1. Physical Properties
Lustre describes a shiny appearance. Malleability is the ability to be beaten into sheets. Ductility is the ability to be drawn into wires. Metals often show these properties, which explains their use in utensils, wires and structures.
⚡ 2. Why Copper for Wires?
Copper is a good conductor and can be drawn into wires, making it useful for electrical connections. Its usefulness is therefore connected to several properties working together.
🧪 3. Chemical Behaviour
Materials can also be compared by how they react with air, water or other substances. Some metals react readily; others are much less reactive. Non-metals also show characteristic reactions, and the products formed can have different properties.
🛡️ 4. Rusting and Protection
Iron can react with oxygen and moisture to form rust. Keeping air or moisture away from the surface can slow this process. Painting, oiling, coating and galvanising are examples of protection methods.
| Method | How it helps |
|---|---|
| Painting | Creates a barrier |
| Oiling/greasing | Reduces contact with moisture and air |
| Galvanising | Protects iron/steel with a zinc coating |
🌱 5. Uses Depend on Properties
Aluminium is useful for some containers because it is relatively light and workable. Iron and steel are useful for structures because of their strength. Non-metals also have important uses: oxygen supports respiration, carbon has several forms and uses, and chlorine is used in water treatment under controlled conditions.
🧠 Worked Examples
- Why is aluminium used in some aircraft parts? Its low density is one relevant property.
- Why is rubber used around electrical wires? It is a useful insulating material and provides a protective covering.
- Why is iron painted? Painting helps prevent contact with moisture and oxygen, reducing rusting.
🎯 Concept Check
- Define malleability and ductility.
- Why are many metals useful for electrical wires?
- What conditions promote rusting?
- Name two ways to protect iron from rust.
🧩 Interactive MCQs
- The ability to be drawn into wires is: A ductility B malleability C solubility D hardness
- A common metal used for electrical wires is: A copper B sulphur C rubber D wood
- Rusting of iron needs oxygen and generally: A moisture B darkness only C sugar D salt only
- Galvanising commonly uses a coating of: A zinc B copper C carbon D sulphur
Answers: 1-A, 2-A, 3-A, 4-A
📌 Case-Based Learning — Choosing a Cooking Pan
A designer must choose materials for a cooking pan, handle and electrical heating connection.
- Which properties would be important for the pan?
- Why might the handle use a non-metallic insulating material?
- Why is electrical conductivity useful in some parts but undesirable in the handle?
- Explain why material selection depends on purpose.
🔥 HOTS / Competition Corner
- A material is shiny and conducts electricity but is brittle. Would you classify it using only one property? Explain.
- Design an experiment to compare the conductivity of three materials safely.
- Why can’t “all metals are hard” be treated as a perfect scientific rule?
📝 Worksheet
| Level | Task |
|---|---|
| 1 | Identify common metal/non-metal properties. |
| 2 | Match properties to uses. |
| 3 | Explain rusting and prevention. |
| 4 | Interpret material-selection situations. |
| 5 | Design a property-testing investigation. |
🏆 Mastery Checklist
- ☐ I can explain malleability and ductility.
- ☐ I can connect properties with uses.
- ☐ I understand rusting and prevention.
- ☐ I can compare materials using evidence.