NCERT Revision Notes Chapter 4 Materials: Metals and Non-metals Class 8 Science
CBSE NCERT Revision Notes1
Answer
• Introduction
• Metals
→ Physical properties of metals
→ Chemical Properties of metals
→ Reaction of metals with water
• Non-metals
→ Physical properties of non-metals
• Difference between metals and non-metals
• Reaction with Acids
• Reaction with Bases
• Uses of metals
• Uses of non-metals
• Types of Reactions
→ Displacement Reactions
→ Double-displacement Reactions
• Alloys
→ Ferrous alloys
→ Non ferrous alloys
2
Answer
→ Materials are classified in two types i.e. metals and non-metals.
→ Metals can be distinguished from non-metals on the basis of their physical and chemical properties.
3
Answer
→ They have shining surface in their pure state. It is also called metallic lustre.
→ They are generally hard. The hardness varies from metal to metal.
→ Metals are malleable. This means it can be made thin sheets by beating.
→ Ductile which means it can be drawn into thin wires. As an example, Gold is highly ductile metal.
→ The are good conductors of heat and have high melting point.
→ The conduct electricity.
→ Most of metals are sonorous which means it can produce sound.
4
Answer
→ Metals combine with oxygen to form metal oxides.
2Cu + O2 → 2CuO
4Al + 3O2 → 2Al2O3
→ Most metal oxides are insoluble in water.
If metal oxides are soluble, they form alkali.
Na2O + H2O → 2NaOH
K2O + H2O → 2KOH
→ Sodium, potassium react very easily with O2. So, they are kept immersed in kerosene.
→ Mg, Al, Zn, Pb form thin layers of oxides when kept in open.
5
Answer
→ Metals produce metal oxide + H2 on reaction with water.
If oxide is soluble, then metal hydroxide is formed.
→ Magnesium doesn't react with cold water.
→ Al, Zn, Fe do not react with H2O, but react with steam.
2Al + 3H2O → Al2O3 + 3H2
3Fe + 4H2O → Fe3O4 + 4H2
6
Answer
→ Non-metals are found in all the three states i.e. solid, liquid and gas, at room temperature.
→ Iodine (non-metal) has lustre.
→ Carbon has allotropes which means it exists in different forms.
→ Diamond is hard and Graphite conducts electricity.
7
Answer
Metals | Non-metals |
Generally, these are hard and lustrous. | These are soft and have no lustre. |
These are malleable and ductile. | These are non-malleable and non-ductile |
These are sonorous (produce ringing sound when struck). | These are not sonorous. |
These are good conductors of heat and electricity. | These are poor conductors of heat and electricity. |
These react with oxygen to produce metal oxides, which are basic in nature. | These react with oxygen to form non-metallic oxides, which are acidic in nature. |
These react with acids to produce metal salts and hydrogen gas. | These do not react with acids. |
Some metals react with bases to produce hydrogen gas. | Reactions of non-metals with bases are complex. |