Metals, Non-metals and Synthetic Materials: Class 8 Study Guide
The materials we choose depend on their properties. Knowing them explains why we use copper for wires and plastic for handles.
Metals such as iron, copper, aluminium and gold are usually shiny (lustrous), hard, malleable (can be hammered into sheets), ductile (can be drawn into wires), and good conductors of heat and electricity. They usually produce a ringing sound when struck (sonorous). Mercury is a liquid metal at room temperature.
Non-metals such as carbon, sulphur, oxygen and iodine are usually dull, brittle if solid and poor conductors (graphite, a form of carbon, is an exception). Some elements, called metalloids, have properties of both.
Comparing metals and non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Lustre | shiny | dull (iodine is shiny) |
| Hardness | usually hard (sodium is soft) | usually soft or brittle (diamond is very hard) |
| Conductivity | good | poor (graphite conducts) |
| Malleability | malleable and ductile | brittle |
| State at room temperature | solid (mercury is a liquid) | solids, liquids or gases |
Chemical properties
Most metals react with oxygen to form metal oxides that are basic; non-metal oxides are acidic. Many metals react with acids to give hydrogen gas. Reactive metals such as sodium and potassium are stored under oil; gold and silver react little, which is why they stay shiny. Corrosion is the gradual damage of metals by air and moisture. Iron rusts when exposed to oxygen and water. Rust can be prevented by painting, oiling, galvanising (a zinc coating) or using stainless steel.
Dry air, water, oil-covered water.
Observe.
Rust forms where air and water meet iron.
Both are needed.
Synthetic materials
Synthetic fibres (nylon, polyester, acrylic) are made from chemicals, and are strong, wrinkle-resistant and quick-drying, but many do not break down easily and melt in heat. Plastics are polymers that can be moulded; some are thermoplastics (soften on heating, such as PVC) and others thermosetting (harden permanently, such as Bakelite). Plastic waste harms the environment, so reduce, reuse and recycle, and choose bio-degradable options where possible.
Worked example and common misconceptions
Example: Aluminium is used for foil because it is malleable and resists corrosion by forming a thin oxide layer. Common misconceptions: thinking all metals are heavy and hard, that rust only happens in water (it needs oxygen too) and that plastic is biodegradable. Wear gloves and goggles when handling chemicals.
Check your understanding: model answers
1. For example, they conduct electricity and can be hammered into sheets. 2. By painting, oiling or galvanising it. 3. A plastic that softens when heated and can be remoulded.
✨ Key Takeaways
- Metals are lustrous, malleable, ductile and conductive.
- Non-metals are usually dull and brittle.
- Rusting needs oxygen and water.
- Reduce, reuse and recycle plastics.
💬 Questions for Discussion & Reflection
- Name two properties of metals.
- How can iron be protected from rusting?
- What is a thermoplastic?
Print a periodic table study sheet →