CBSE Class 8 Science notes Chapter 4 Materials: metals and non-metals
Do you know what metals and Non-metals are? In our surrounding everything falls into the category of either metals or non-metals, its important to understand their characteristics. In this chapter, we will understand metal and nonmetal properties and applications in various fields. Here is a diagram to differentiate between metal and non-metal around us.
1.0Physical Properties of Metals and Non-metals
Physical Properties of Metals:
- Hard, shiny, and malleable (can be shaped into sheets).
- Ductile (can be drawn into wires).
- Good conductors of heat and electricity.
- Produce a ringing sound (sonorous).
- Examples: Iron, copper, and aluminium (used in construction and wiring).
Physical Properties of Non-metals:
- Soft, brittle, and dull.
- Lack malleability and ductility.
- Poor conductors of heat and electricity.
- Do not produce sound when struck.
- Examples: Sulfur, and carbon (used in insulation, and chemical processes).
Below is a comparison of the physical properties of metals and non-metals:
2.0Chemical Properties of Metals and Non-metals
Metals and non-metals react differently with oxygen, water, acids, and bases, showcasing their unique chemical behaviors. Let's explore these reactions with examples:
- Reaction with Oxygen:
- Metals: Metals react with oxygen to form metal oxides, which are generally basic in nature.
- Example: Magnesium reacts with oxygen to form magnesium oxide.
2 Mg + O2 → 2MgO
Magnesium oxide, when dissolved in water, turns red litmus blue, indicating a basic solution.
- Non-metals: Non-metals form acidic oxides when they react with oxygen.
- Example: Sulfur reacts with oxygen to form sulfur dioxide.
S + O2 → SO2
When dissolved in water, sulfur dioxide forms sulfurous acid, turning blue litmus red.
- Reaction with Water:
- Metals: Some metals react vigorously with water, while others react slowly.
- Example: Sodium reacts violently with water to produce sodium hydroxide and hydrogen gas.
2Na + 2H2O → 2NaOH + H2
- Example: Iron reacts slowly with water to form iron(III) oxide and hydrogen gas.
3Fe + 4H2O → Fe3O4 + 4H2
- Non-metals: Non-metals generally do not react with water. For example, phosphorus is stored in water to prevent it from reacting with oxygen in the air, as it is highly reactive.
- Reaction with Acids:
- Metals: Metals react with acids to produce hydrogen gas.
- Example: Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
Zn + 2HCl → ZnCl2 + H2
- The release of hydrogen gas can be confirmed by the characteristic ‘pop’ sound.
- Non-metals: Non-metals generally do not react with acids. For instance, carbon and sulfur do not produce hydrogen gas when reacting with acids.
- Reaction with Bases:
- Metals: Some metals react with strong bases like sodium hydroxide to produce hydrogen gas.
- Example: Aluminum reacts with sodium hydroxide to form sodium aluminate and hydrogen gas.
2Al + 2NaOH + 6H2O → 2NaAl(OH)4 + 3H2
- Non-metals: Reactions of non-metals with bases are complex and less common.
- Displacement Reactions:
- Metals: A more reactive metal can displace a less reactive metal from its compound.
- Example: Zinc displaces copper from copper sulfate solution, forming zinc sulfate and depositing copper.
Zn + CuSO4 → ZnSO4 + Cu
3.0Uses of Metals and Non-metals
