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

 

Metals and Non-metals differ in terms of their physical and chemical properties.

 

Physical Properties of Metals and Non-metals

 

Physical Properties	Metals	Non-Metals
Conductivity	Metals (such as iron or copper) are good conductors of heat and electricity.	Non-metals (such as coal or sulphur) are poor conductors of heat and electricity. Graphite is an exception as it is a good conductor of electricity.
Ductility	Metals (such as aluminium and copper) are ductile, which means that they can be drawn into wires.	Non-metals are brittle (break down when struck) and hence, they cannot be drawn into wires.
Hardness	All metals are hard though there are some exceptions. Sodium and potassium are soft and can be cut with a knife.	Most non-metals are soft. Diamonds are exceptions as they are the hardest material found on Earth. However, they are also very brittle and break when struck with a hammer.
Lustre	Metals (such as gold, silver and copper) are lustrous, which means that they reflect light from their surface and can be polished.	Non-metals (such as coal) are generally dull and do not reflect light. Hence, they lack metallic lustre.
Malleability	Metals (such as silver and aluminium) are malleable, which means that they can be beaten into thin sheets.	Since non-metals break easily, they cannot be pounded into sheets.
Physical State	Most metals remain solid at room temperature, except mercury and gallium which remain liquid at room temperature.	Most non-metals exist in two of the three states of matter at room temperature: Gases (such as oxygen), and Solids (such as carbon).
Sonorous	Metals produce ringing sounds when they are struck and hence, they are sonorous, except Mercury which is liquid in nature.	Non-metals are non-sonorous and do not produce the typical metallic sound when they are struck.
Examples	Iron, copper, aluminium, calcium, magnesium, etc.	Sulphur, carbon, oxygen, phosphorus, etc.

Note: Copper Vessels also acquire a dull green coating (made up of copper hydroxide and copper carbonate) when they are exposed to moist air. It is called Verdigris.

Chemical Equation for Green Coating on Copper

Copper (Cu) + Moist Air (Water (H₂O) + Oxygen (O₂) + Carbon Dioxide (CO₂)) → Copper Hydroxide (Cu(OH)₂) + Copper Carbonate (CuCO₃)

2Cu + H₂O + CO₂ + O₂ → Cu (OH)₂ + CuCO₃

Copper carbonate and copper hydroxide are basic in nature.

Note: This green coating can be copper chloride if the copper reacts with sea air, or copper acetate if the copper reacts with acetic acid.

Chemical Properties of Metals and Non-metals

Reaction of Metals with Oxygen

When metals react with oxygen, they form metal oxide.

Metal + O₂ → Metal Oxide

For Example:

1. Copper + Oxygen → Copper Oxide (black)

2Cu + O₂ → 2CuO

2. Aluminium + Oxygen → Aluminium Oxide

4Al + 3O₂ → 2Al₂O₃

3. Magnesium + Oxygen → Magnesium Oxide

2Mg + O₂ → 2MgO

The reactivity of metals with oxygen differs. For Example:

• Sodium and Potassium react so vigorously with air that they catch fire when they are kept in open. Hence, they are immersed in kerosene to store them.

• The surfaces of Magnesium, Aluminium, Zinc and Lead are covered with a thin layer of oxide to make sure that they do not get oxidised anymore.

• While iron does not burn when heated, iron filings burn vigorously.

• Copper surface is coated with a thin layer of black copper oxide to prevent the process of further oxidation from taking place.

• Gold and silver do not react with Oxygen.

Amphoteric Oxides: Some metal oxides react both with acids and bases to produce salts and water. Such metal oxides are called amphoteric oxides. For example:

Aluminium Oxide + Hydrochloric Acid → Aluminium Chloride + Water

Al₂O₃ + 6HCl → 2AlCl₃ + H₂O

Aluminium Oxide + Sodium Hydroxide → Sodium Aluminate + Water

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

Reaction of Metals with Water

Metal + (cold) Water → Metal hydroxide + Hydrogen

Metal + Stream → Metal oxide + Hydrogen

For Example:

Sodium + Water → Sodium Hydroxide + Hydrogen + Heat

2Na + 2H₂O → 2NaOH + H₂ + Heat

Calcium + Water → Calcium Hydroxide + Hydrogen

Ca + 2H₂O → Ca(OH)₂ + H₂

Magnesium + Water → Magnesium Hydroxide + Hydrogen

Mg + 2H₂O → Mg(OH)₂ + H₂

Aluminium + Water → Aluminium Oxide + Hydrogen

2Al + 3H₂O → Al₂O₃ + 3H₂

Iron + Water → Iron Oxide + Hydrogen

3Fe + 4H₂O → Fe₃O₄ + H₂

The reactivity of metals with water differs. For Example:

• Sodium, Potassium and Calcium react with cold water.

• Magnesium reacts slowly with hot water to form slightly soluble magnesium hydroxide.

• Aluminium, Zinc and Iron react with steam.

• Lead, Copper, Silver and Gold do not react with water.

Note: Calcium and magnesium float on water as bubbles of hydrogen stick to their surface.

Reaction of Metals with Solutions of Other Metal Salts

Metal A + Salt Solution of Metal B → Salt Solution of Metal A + Metal B

More reactive metals replaces less reactive metals.

Less reactive metals cannot replace more reactive metals.

For Example:

Iron + Copper Sulphate → Iron Sulphate + Copper

Fe + CuSO₄ → FeSO₄ + Cu

The reactivity series is given below:

Reaction of Different Metals and Non-metals with Acids

Metal/Non-metal	Reaction with Dilute Hydrochloric Acid		Reaction with Dilute Sulphuric Acid
	Room Temperature	Warm	Room Temperature	Warm
Magnesium (ribbon)	Magnesium (Mg) + Hydrochloric Acid (HCl) → Magnesium Chloride (MgCl2) + Hydrogen (H2) Mg + 2HCl →  MgCl2 + H2	Magnesium (Mg) + Hydrochloric Acid (HCl) →  Magnesium Chloride (MgCl2) + Hydrogen (H2) Mg + 2HCl →  MgCl2 + H2	Magnesium (Mg) + Sulphuric Acid (H2SO4) →  Magnesium Sulphate (Mg2SO4) + Hydrogen (H2) 2Mg + H2SO4 →  MgSO4 + H2	Magnesium (Mg) + Sulphuric Acid (H2SO4) →  Magnesium Sulphate (Mg2SO4) + Hydrogen (H2) 2Mg + H2SO4 →  MgSO4 + H2
Aluminum (foil)	Aluminum (Al) + Hydrochloric Acid (HCl) →Aluminum Chloride (AlCl3) + Hydrogen (H2) 2Al + 6HCl → 2AlCl3 + 3H2	Aluminum (Al) + Hydrochloric Acid (HCl) →Aluminum Chloride (AlCl3) + Hydrogen (H2) 2Al + 6HCl → 2AlCl3 + 3H2	Aluminum (Al) + Sulphuric Acid (H2SO4) + Water (H2O) →Aluminum Sulphate (Al2SO4) HexaHydrate (6H2O) + Hydrogen (H2) 2Al + 3H2SO4 + 6H2O →Al2(SO4)3•6H2O + 3H2	Aluminum (Al) + Sulphuric Acid (H2SO4) + Water (H2O) →Aluminum Sulphate (Al2SO4) HexaHydrate (6H2O) + Hydrogen (H2) 2Al + 3H2SO4 + 6H2O →Al2(SO4)3 • 6H2O + 3H2
Iron (filings)	Iron does not react with hydrochloric acid at room temperature.	Iron (Fe) + Hydrochloric Acid (HCl) →Iron Chloride (FeCl2) + Hydrogen (H2) 2Fe + 2HCl → 2FeCl2 + H2	Iron does not react with diluted sulphuric acid at room temperature.	Iron (Fe) + Diluted Sulphuric Acid (H2SO4) →Ferrous Sulphate (FeSO4) + Hydrogen (H2) Fe + H2SO4 → FeSO4 + H2
Copper (peeled flexible wire)	Copper does not react with hydrochloric acid at room temperature.	Copper does not react with hydrochloric acid (even when it is heated)	Copper does not react with diluted sulphuric acid at room temperature.	Copper (Cu)+ conc. Sulphuric Acid (H2SO4)  → Copper Sulphate (CuSO4) + Sulphur Dioxide (SO2) + Water (H2O) Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
Charcoal (powder)	Charcoal does not react with hydrochloric acid at room temperature.	Charcoal does not react with hydrochloric acid (even when it is heated).	Charcoal does not react with sulphuric acid at room temperature.	Charcoal (C)+conc. Sulphuric Acid (H2SO4) → Carbon Dioxide (CO2) + Sulphur Dioxide (SO2) + Water (H2O) C + 2H2SO4 → CO2 + 2SO2 + 2H2O
Sulphur (powder)	Sulphur does not react with hydrochloric acid at room temperature.	Sulphur does not react with hydrochloric acid (even when it is heated).	Sulphur does not react with sulphuric acid at room temperature.	Sulphur does not react with sulphuric acid (even when it is heated).

Note:

• When metals react with acids, they produce hydrogen gas with produce a 'pop' sound when it burns.

• Iron reacts with hydrochloric acid and sulphuric acid on heating.

• Copper does not react with hydrochloric acid (even when it is heated) but reacts with sulphuric acid on heating.

Uses of Metals and Non-metals

As discussed above, metals are hard, malleable, ductile, and sonorous and are hence, can be used for:

• Making machinery

• Making automobiles, trains, and aeroplanes

• Making cooking utensils  and water boilers

• Making industrial gadgets and satellites etc.

Non-metals also have several uses, such as:

• Essential for life (such as oxygen)

• Used as fertilizers (such as nitrogen and phosphorus)

• Used to purify water (such as chlorine)

• Applied on wounds as an antiseptic (such as purple-coloured iodine solution)

• Used in crackers (such as sulphur)