Metals and Non-metals - Class 8 Notes & Olympiad Questions

Metals and Non-metals

Metals and non-metals are two distinct groups of chemical elements found in the periodic table. They have unique properties that set them apart from each other.

Physical Properties of Metals and Non-metals

Metals

Physical properties of metals are the characteristics that define their behaviour and appearance in a solid state at room temperature. These properties are unique to metals and set them apart from non-metals.

Some key physical properties of metals are:

1. Lustre

a) Metals have a characteristic shiny and reflective surface, known as lustre. This property is a result of the way metals interact with light, allowing them to reflect most of the incident light that falls on their surface.
b) For example, silver and gold are well-known for their lustre.

2. Malleability

a) Metals can be hammered or rolled into thin sheets without breaking. This property is known as malleability, and it allows metals to be shaped into different forms.
b) For instance, aluminium can be rolled into aluminium foil, and copper can be hammered into thin sheets.

3. Ductility

a) Metals can be drawn into thin wires without breaking. This property is called ductility, and it is important for making wires used in electrical circuits.
b) Copper and aluminium are commonly used for their ductility.

4. Conductivity

a) Metals are excellent conductors of both heat and electricity. This means they can efficiently transfer heat and electrical energy.
b) Copper is widely used in electrical wires due to its high electrical conductivity, while metals like silver and copper are used for thermal applications due to their high heat conductivity.

5. Sonority

a) Metals produce a ringing sound when struck, making them sonorous.
b) This property is utilised in musical instruments such as bells, cymbals, and brass instruments like trumpets.

6. Density

a) Metals are generally dense materials, meaning they have a high mass per unit volume.
b) This property contributes to their weight and strength, making them useful for structural applications.

7. Melting and Boiling Points

a) Metals generally have high melting and boiling points, making them resistant to high temperatures.
b) For example, iron has a high melting point, allowing it to withstand high temperatures in applications such as construction and manufacturing.

8. Solid State at Room Temperature

a) Most metals are solid at room temperature, with the exception of mercury and gallium, which are liquid.

Non-metals

The physical properties of non-metals distinguish them from metals and play a crucial role in their applications and uses.
Non-metals find applications in areas such as electronics, and chemical industries, and as essential elements in living organisms.

Some key physical properties of non-metals are:

1. Dullness

a) Non-metals have a non-reflective and dull appearance. Unlike metals, they do not have a shiny surface.

2. Brittleness

a) Non-metals are usually brittle, meaning they are easily broken or shattered when subjected to stress or pressure.
b) For instance, sulfur and phosphorus are brittle non-metals.

3. Non-Ductile

a) Non-metals cannot be drawn into thin wires like metals. They lack the property of ductility.

4. Non-Malleable

a) Similar to ductility, non-metals are non-malleable, meaning they cannot be hammered into thin sheets without breaking.

5. Poor Conductivity

a) Non-metals are poor conductors of both heat and electricity. They do not efficiently transfer heat and electrical energy.

6. Non-Sonorous

a) Non-metals do not produce a ringing sound when struck. Unlike metals, they are not sonorous.

7. Lower Density

a) Non-metals generally have lower densities compared to metals, meaning they have lower mass in relation to their volume.
b) For instance, hydrogen and helium are non-metals with low densities.

8. Varied States at Room Temperature

a) Non-metals can exist in various states at room temperature. They can be solids, liquids, or gases.
b) For example, sulfur is a solid, bromine is a liquid, and oxygen is a gas at room temperature.

Differences between Metals and Non-Metals

Chemical Properties of Metals and Non-metals

Metals

1. Reaction with Oxygen

Metals react with oxygen in the air to form metal oxides. This reaction is commonly known as oxidation.

Examples:
i) Magnesium reacts with oxygen to form magnesium oxide
2Mg(s) + O₂(g) → 2MgO(s)

ii) Iron reacts with oxygen to form iron oxide, commonly known as rust
4Fe(s) + 3O₂(g) → 2Fe₂O₃(s)

2. Reaction with Water

Some metals react with water to produce metal oxides and hydrogen gas.

Examples:
i) Sodium reacts with water to form sodium hydroxide and hydrogen gas
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

ii) Calcium reacts with water to form calcium hydroxide and hydrogen gas
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g) (s)

3. Reaction with Acids

Metals react with acids to produce metal salts and hydrogen gas. The reactivity of metals with acids varies.

Examples:
i) Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

ii) Magnesium reacts with sulfuric acid to form magnesium sulfate, water, and sulfur dioxide
Mg(s) + 2H₂SO₄(aq) → MgSO₄(aq) + 2H₂O(l) + SO₂(g)

4. Reaction with Bases

Some metals react with bases to produce hydrogen gas.

Examples:
i) Sodium reacts with sodium hydroxide to form sodium oxide and hydrogen gas
2Na(s) + 2NaOH(aq) → 2Na₂O(aq) + H₂(g)

ii) Zinc reacts with sodium hydroxide to form sodium zincate and hydrogen gas
Zn(s) + 2NaOH(aq) → Na₂ZnO₂(aq) + H₂(g)

5. Displacement Reactions

Metals can displace less reactive metals from their compounds in aqueous solutions. In the reactivity series, a metal is capable of displacing another metal positioned below it but cannot displace a metal positioned above it.

Examples:
i) Zinc displaces copper from copper sulfate solution, forming zinc sulfate and copper
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

ii) Iron displaces copper from copper sulfate solution, forming iron sulfate and copper
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

6. Reaction with Non-Metals

Metals can react with non-metals to form compounds.

Examples:
i) Sodium reacts with chlorine to form sodium chloride, commonly known as table salt
2Na(s) + Cl₂(g) → 2NaCl(s)

ii) Magnesium reacts with bromine to form magnesium bromide
2Mg(s) + Br₂(l) → 2MgBr(s)

7. Formation of Alloys

a) Metals can form alloys by combining with other metals or non-metals.
b) Alloys are mixtures of two or more elements, with at least one of them being metal. For example, brass is an alloy of copper and zinc.

8. Corrosion

a) Some metals, such as iron, can corrode when exposed to moisture and oxygen in the air.
b) Corrosion is the process of metals gradually getting damaged and converted into metal oxides over time.

Non-metals

1. Reaction with Oxygen

Non-metals also react with oxygen in the air, but their oxides are generally acidic in nature.

Examples:
i) Sulfur reacts with oxygen to form sulfur dioxide gas, which dissolves in water to form sulfurous acid.
S + O₂ → SO₂
SO₂ + H₂O → H₂SO₃

ii) Carbon reacts with oxygen to form carbon dioxide gas, which dissolves in water to form carbonic acid:
C + O₂ → CO₂
CO₂ + H₂O → H₂CO₃

2. Reaction with Water

Most non-metals do not react with water, but some highly reactive non-metals like phosphorus do.

3. Reaction with Acids

Non-metals generally do not react with acids, as they are usually poor conductors of electricity and do not readily release hydrogen gas.

4. Reaction with Bases

Non-metals may react with bases under certain conditions, but the reactions are more complex compared to metals.

5. Displacement Reactions

Non-metals do not typically undergo displacement reactions as metals do. They generally do not replace other non-metals from their compounds.

Uses of Metals and Non-metals

Metals

Metals have a wide range of applications due to their unique physical and chemical properties. Some common uses of metals include:

Construction: Metals like steel and aluminium are widely used in construction for buildings, bridges, and infrastructure due to their strength and durability.

Transportation: Metals such as iron, aluminium, and copper are used in automobiles, aeroplanes, trains, and ships because of their lightweight and good mechanical properties.

Electrical Conductors: Metals like copper and aluminium are excellent conductors of electricity and are used in electrical wiring and power transmission.

Electronics: Metals like silicon and gold are used in electronic devices and circuits.

Cooking Utensils: Metals like stainless steel are used in making cooking utensils due to their non-reactive nature and resistance to corrosion.

Currency: Metals like copper, nickel, and zinc are used to make coins.

Non-Metals

Non-metals also have various applications due to their specific properties. Some common uses of non-metals include:

Oxygen: Essential for respiration and combustion processes.

Carbon: Used in making fuels like coal and in various forms in the graphite and diamond industries.

Hydrogen: Used as a fuel and in the production of ammonia and other chemicals.

Nitrogen: Used in fertilisers and in various chemical processes.

Sulphur: Used in the production of sulfuric acid, fertilisers, and in the vulcanization of rubber.

Chlorine: Used in water purification and in the production of various chemicals.

Phosphorus: Used in fertilisers and in the production of detergents and matches.

Noble Gases: Used in lighting, such as neon lights and in helium for balloons.

Extraction of Metals

Each metal requires a different extraction process depending on its reactivity and the nature of its ore.

1. Highly Reactive Metals

a) Metals like sodium and potassium are very reactive and can't be extracted using simple methods. They are obtained by a process called electrolytic reduction, where an electric current is passed through their molten compounds to get the pure metal.
b) Example: Sodium metal is extracted from molten sodium chloride (table salt) through electrolysis.

2. Moderately Reactive Metals

a) Metals like zinc and iron are moderately reactive and are usually found as oxides or sulfides. They are extracted by roasting the ore to convert it into metal oxides and then reducing the oxides using carbon or carbon monoxide.
b) Example: Zinc is extracted from zinc oxide by heating with carbon.

3. Less Reactive Metals

a) Metals like copper and silver are less reactive and are found in their elemental form or as sulfides. They can be extracted by simply heating their ores with carbon or other reducing agents.
b) Example: Copper is extracted from copper sulfide by roasting and then reducing with carbon.

Corrosion of Metals

Corrosion is a natural process that occurs when metals react with substances like water and air, leading to the formation of unwanted compounds.
Two common examples of corrosion are:

1. Rusting of Iron

a) When iron comes in contact with oxygen in the air and water, it undergoes a chemical reaction and forms a brown-coloured powder known as rust.
b) Rust is actually iron oxide, and it weakens the metal, making it less durable.
c) The reaction involved is:

Iron + Oxygen + Water → Iron Oxide (Rust)
4Fe + 3O₂ + 6H₂O → 4Fe₂O₃ . 6H₂O

2. Corrosion of Copper

a) Copper can corrode in the presence of carbon dioxide and water, leading to the formation of a green coating. This green coating is a mixture of copper hydroxide and copper carbonate.
b) This green coating can compromise the integrity of the metal over time.
c) The reactions involved are:

i) Copper + Oxygen + Water → Copper Hydroxide
2Cu + O₂ + 2H₂O → Cu(OH)₂

ii) Copper Hydroxide + Carbon Dioxide → Copper Carbonate
Cu(OH)₂ + CO₂ → CuCO₃ + H₂O