CBSE Class 8 Science Revision Notes Chapter 4 Materials: Metals and Non-metals

Class 8 science chapter 4 metals and non-metals quick revision notes to revise whole the chapter in less time during exams.

Introduction

• There are number of materials in our surroundings. Some of them are made up of metals and some are non-metals.

• Metals and non-metals can be distinguished on the basis of their physical and chemical properties.

Physical properties of metals and non-metals:

1. Hardness: Generally metals are very hard and non metals are soft.

Exceptions:

• Sodium is a metal but it is very soft metal and can be cut using a knife.

• Diamond is a non metal but it is very hard.

• Mercury is a metal but it is found in liquid state at room temperature.

2. Appearance: Metals have lustrous (shiny) appearance while non metals are dull in appearance.

Exception:

• Iodine is a non metal but it is lustrous (shiny).

3. Malleability: The property of metals by which they can be beaten into thin sheets is called malleability.

For example aluminium foils are used for wrapping food. (Aluminium is a metal and it is beaten into sheets to make aluminium foils.)

Metals are malleable while non-metals are non-malleable.

4. Ductility: The property of metals by which it can be drawn into wires is called ductility.

for example electrical wires are made up of copper and aluminium. (aluminium and copper are metals) Metals are ductile but non-metals are non-ductile.

5. Sonorous: When metals struck hard they produce ringing sound, so they are called sonorous.

All metals produce ringing sound so they are said to be sonorous.

Non-metals are non sonorous because they do not produce ringing sound on hitting with hard substance.

6. Conduction of heat and electricity: Metals can conduct heat and electricity easily, so metals are good conductor of heat and electricity.

Non-metals are poor conductor of heat and electricity.

Exception: Graphite is a non metal but it is good conductor of heat and electricity.

Chart of Physical properties of metals and non-metals:

Chemical properties of metals and non-metals:

1. Reaction with oxygen: Metals react with oxygen to form metallic oxides and non-metals react with oxygen to form non metallic oxides.

For example;

Magnesium (Mg) + Oxygen (O2) -----> Magnesium oxide (MgO)

(Metal) (Metallic oxides)

Sulphur (S) + Oxygen (O2) -----> Sulphur dioxide (SO2)

(Non-metal) (Non-mettalic oxide)

• Metallic oxides are basic in nature and non metallic oxides are acidic in nature.

2. Reaction with water: Some metals reacts vigorously with water but some others do not.

for example sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. It is therefore stored in kerosene.

• Iron reacts with water very slowly.

• Generally non metals do not react with water.

• Phosphorus is very reactive non-metal. It catches fire if exposed to air.Therefore to protect its contact with atmospheric oxygen it is stored in water.

3. Reaction with acids: Metals react with acids and produce hydrogen gas.

Non-metals generally do not react with acids.

4. Reaction with bases: Metals react with sodium hydroxide (a base) to produce hydrogen gas.

Reaction of non-metals with bases are complex.

Displacement reaction:

In displacement reaction a more reactive metal displaces a less reactive metal from its salt solution.

For example:

Iron (Fe) + Copper sulphate (CuSO4) -----> Iron sulphate (FeSO4) + copper (Cu)

Here iron is more reactive than copper. Therefore it displaced copper from copper sulphate (salt solution).

Reactivity series of metals:

Reactivity decreases as we move down.

K - Potassium. ( Most reactive metal)

Na - Sodium

Ca - Calcium

Mg - Magnesium

Al - Aluminium

Zn - Zinc

Fe - Iron

Pb - Lead

H - Hydrogen

Cu - Copper

Hg - Mercury

Ag - Silver

Au - Gold (Least reactive metal)

Examples of displacement reaction :

Copper sulphate (CuSO4) + Zinc (Zn) ------> Zinc sulphate (ZnSO4) + copper (Cu)

Iron sulphate (FeSO4) + Zinc (Zn) -----> Zinc sulphate (ZnSO4) + Iron (Fe)

Silver Sulphate ( (Ag)2SO4 ) + Copper (Cu) -----> Copper sulphate (CuSO4) + Silver(Ag)

Uses of Metals and Non-metals:

Metals are used in:

making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils, water boilers etc.

Non-metals are used:

• for breathing (Oxygen).

• Nitrogen is used in fertilizers.

• chlorine is used in water purification.

• Iodine is used in antiseptic.

• Phosphorus is used for making crackers