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:

1. 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.

2. 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.

3. 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.

4. 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.

5. 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