Metals and Non-Metals: Complete Guide for Class 8

Metals and non-metals form the building blocks of all materials around us. From the air we breathe to the devices we use, understanding these elements is crucial for science students.

Why This Topic Matters:

• Forms 10-15% of your Science exam
• Essential for understanding chemistry concepts
• Helps explain everyday phenomena (rusting, cooking, etc.)
• Foundation for higher chemistry studies

Earth's crust contains various elements in different states. More than 75% of known elements are metals, while only 22 are non-metals. This chapter explores their properties, reactions, and applications.

Important Concepts & Definitions

What are Elements?

Elements are pure substances made up of only one type of atom. Though millions of substances exist, they are all composed of a limited number (about 118) of basic elements.

Classification of Elements

Elements are broadly classified into:

1. Metals - Elements with characteristic shine, conductivity, and malleability
2. Non-metals - Elements lacking metallic properties
3. Metalloids - Elements showing properties of both metals and non-metals
4. Noble gases - Inert gaseous elements

Important Terms Explained

Malleability: The property of metals to be hammered into thin sheets without breaking.

• Example: Gold can be beaten into extremely thin foils used in sweets decoration.

Ductility: The ability of metals to be drawn into thin wires.

• Example: Copper is drawn into wires for electrical connections.

Sonority: The property of producing a ringing sound when struck.

• Example: Church bells are made of metals due to this property.

Luster: The shiny appearance of metals when freshly cut or polished.

• Example: Gold and silver jewelry shine due to metallic luster.

Conductivity: The ability to allow heat or electricity to pass through.

• Example: Copper wires conduct electricity efficiently.

Physical Properties of Metals

1. Physical State

• Metals: Crystalline solids at room temperature (except mercury - liquid)
• Non-metals: Can be solids, liquids, or gases (bromine is the only liquid non-metal)

2. Metallic Luster

• Metals: Shine when polished; can reflect light
• Non-metals: Dull appearance (exceptions: graphite, iodine)

3. Density

• Metals: Generally high density (exception: sodium, potassium, lithium - float on water)
• Non-metals: Low density (exception: diamond has high density)

4. Hardness

• Metals: Hard solids (exceptions: sodium and potassium - can be cut with knife)
• Non-metals: Soft and brittle if solid (exception: diamond - hardest natural substance)

5. Melting and Boiling Points

• Metals: High melting/boiling points (exceptions: sodium ~98°C, potassium ~63°C)
• Non-metals: Low melting/boiling points (exceptions: carbon, silicon, boron have high values)

6. Malleability

• Metals: Can be hammered into sheets
  • Gold, silver, aluminum are highly malleable
  • Gold is most malleable - 1 gram can cover 0.5 m²
• Non-metals: Brittle; break into powder when hammered

7. Ductility

• Metals: Can be drawn into wires
  • Gold is most ductile - 1 gram makes 2 km wire
  • Exceptions: zinc, arsenic, antimony
• Non-metals: Not ductile (exception: carbon fiber)

8. Tensile Strength

• Metals: High - can withstand stress without breaking
• Non-metals: Low tensile strength (exception: carbon fiber)

9. Thermal and Electrical Conductivity

• Metals: Excellent conductors
  • Silver is best conductor
  • Used in electrical wiring, cooking utensils
• Non-metals: Poor conductors/insulators (exception: graphite)

10. Sonority

• Metals: Produce ringing sound when struck
  • Used in bells, musical instruments
• Non-metals: Non-sonorous; no characteristic sound

Physical Properties Comparison Table

Chemical Properties of Metals

1. Reaction with Oxygen

General Equation:

Metal + Oxygen → Metal Oxide (Basic)

Examples:

a) Highly Reactive Metals (Na, K)

• React vigorously even at room temperature
• Must be stored in kerosene

4Na + O₂ → 2Na₂O (sodium oxide) 4K + O₂ → 2K₂O (potassium oxide)

b) Moderately Reactive Metals (Mg, Al, Zn, Fe, Pb, Cu)

• React on heating
• Form basic oxides (insoluble in water)

2Mg + O₂ --heat→ 2MgO (magnesium oxide) 2Cu + O₂ --heat→ 2CuO (copper oxide - black) 4Fe + 3O₂ --heat→ 2Fe₂O₃ (ferric oxide - rust)

c) Unreactive Metals (Ag, Au, Pt)

• Do not react even on strong heating
• Called noble metals

Point: Metal oxides are basic in nature they form salt and water with acids.

2. Reaction with Water

General Equation:

Metal + Water → Metal Hydroxide/Oxide + Hydrogen gas

Classification by Reactivity:

a) Very Reactive Metals (Na, K)

• React vigorously with cold water
• Reaction produces heat (exothermic)
• Can cause fire/explosion

2Na + 2H₂O --vigorous→ 2NaOH + H₂↑ + Heat 2K + 2H₂O --very vigorous→ 2KOH + H₂↑ + Heat

b) Moderately Reactive (Ca)

• Reacts with cold water, but less vigorously

Ca + 2H₂O --moderate→ Ca(OH)₂ + H₂↑

c) Less Reactive Metals (Mg, Al, Zn, Fe)

• React with hot water or steam only
• Form metal oxides

Mg + H₂O --steam→ MgO + H₂↑ 3Fe + 4H₂O --steam→ Fe₃O₄ + 4H₂↑

d) Unreactive Metals (Cu, Ag, Au, Hg)

• Do not react with water or steam

3. Reaction with Acids

General Equation:

Metal + Acid → Salt + Hydrogen gas

Important Notes:

• Only dilute acids are used (HCl, H₂SO₄)
• Not nitric acid - it oxidizes H₂ to water
• Reactivity varies by metal

Examples:

a) Highly Reactive (Na, K)

• React explosively with dilute acids
• Too dangerous to perform

2Na + 2HCl --vigorous→ 2NaCl + H₂↑

b) Moderately Reactive (Mg, Zn, Fe)

• React at moderate speed

Zn + H₂SO₄ → ZnSO₄ + H₂↑ Fe + 2HCl --slow→ FeCl₂ + H₂↑ Mg + 2HCl → MgCl₂ + H₂↑

c) Unreactive Metals (Cu, Ag, Au, Pb)

• Do not react with dilute acids
• Some react with concentrated acids only

Cu + 2H₂SO₄(conc.) → CuSO₄ + SO₂ + 2H₂O

Chemical Properties of Non-Metals

1. Reaction with Oxygen

General Equation:

Non-metal + Oxygen → Non-metallic Oxide (Acidic)

Examples:

C + O₂ --heat→ CO₂ (carbon dioxide - acidic) S + O₂ --heat→ SO₂ (sulphur dioxide - acidic) 4P + 5O₂ → 2P₂O₅ (phosphorus pentoxide)

Special Case - Hydrogen:

2H₂ + O₂ → 2H₂O (neutral oxide)

Point: Non-metal oxides are acidic in nature they turn blue litmus red.

2. Reaction with Water

Non-metal oxides dissolve in water to form acids.

Examples:

CO₂ + H₂O → H₂CO₃ (carbonic acid) SO₂ + H₂O → H₂SO₃ (sulphurous acid)

Natural Phenomenon: During thunderstorms, lightning causes:

N₂ + O₂ --lightning→ nitrogen oxides Nitrogen oxides + Rain → Nitric acid (natural fertilizer)

3. Reaction with Bases

Acidic oxides react with bases to form salt and water.

Examples:

CO₂ + 2NaOH → Na₂CO₃ + H₂O SO₂ + 2NaOH → Na₂SO₃ + H₂O

4. Reaction with Acids

Non-metals generally do not react with dilute acids.

However, some react with concentrated acids:

C + 2H₂SO₄(conc.) → CO₂ + 2SO₂ + 2H₂O S + 2H₂SO₄(conc.) → 3SO₂ + 2H₂O P + 5HNO₃(conc.) → H₃PO₄ + 5NO₂ + H₂O

Metalloids (Semi-Metals)

Elements showing properties of both metals and non-metals.

Common Metalloids:

• Silicon (Si)
• Germanium (Ge)
• Arsenic (As)
• Antimony (Sb)
• Tellurium (Te)
• Boron (B)

Properties:

• Metallic luster but brittle
• Intermediate electrical conductivity
• Used as semiconductors in electronics

Example - Silicon:

• Shiny appearance (like metals)
• Brittle (like non-metals)
• Semiconductor properties
• Used in computer chips, solar cells

Metal Reactivity Series

The reactivity series arranges metals in decreasing order of reactivity.

Complete Reactivity Series

MOST REACTIVE ↓ Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Tin (Sn) Lead (Pb) [HYDROGEN] ← Reference point Copper (Cu) Mercury (Hg) Silver (Ag) Gold (Au) Platinum (Pt) ↓ LEAST REACTIVE

Significance of Reactivity Series

1. Reaction with Water:

• Above Ca: React with cold water
• Mg to Fe: React with hot water/steam
• Below Fe: No reaction with water

2. Reaction with Acids:

• Above H: Displace hydrogen from acids
• Below H: Do not react with dilute acids

3. Displacement Reactions:

• More reactive metal displaces less reactive metal from its salt
• Example: Zn + CuSO₄ → ZnSO₄ + Cu

4. Occurrence in Nature:

• Above H: Found as compounds (ores)
• Below H: Can occur in free state (Au, Ag, Pt)

5. Extraction Method:

• Highly reactive: Electrolysis required
• Moderately reactive: Reduction with carbon
• Less reactive: Simple heating may suffice

Displacement Reactions

Reaction where a more reactive metal displaces a less reactive metal from its salt solution.

General Pattern:

More reactive metal + Less reactive metal salt → More reactive metal salt + Less reactive metal

Examples of Displacement Reactions

Example 1: Zinc displaces Copper

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

 (blue) (colorless) (reddish-brown)

• Blue solution turns colorless
• Reddish-brown copper deposits on zinc

Example 2: Magnesium displaces Iron

Mg(s) + FeSO₄(aq) → MgSO₄(aq) + Fe(s)

(green) (colorless) (grey)

Example 3: Iron displaces Copper

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

 (blue) (green) (brown)

Non-Displacement Examples

Example 1: Copper cannot displace Zinc

Cu + ZnSO₄ → NO REACTION

Reason: Cu is less reactive than Zn

Example 2: Silver cannot displace Copper

Ag + CuSO₄ → NO REACTION

Reason: Ag is less reactive than Cu

Ores and Minerals

Minerals

Naturally occurring compounds of metals mixed with earthy impurities (sand, clay, rocks).

• Found beneath Earth's surface
• Chemical ingredients of rocks
• Not all are economically viable

Ores

Minerals from which metals can be extracted profitably and conveniently.

Point:

All ores are minerals, BUT all minerals are NOT ores.

Gangue (Matrix)

Earthy impurities (sand, clay, mud) present in an ore.

Mineral + Gangue = Ore

Common Ores and Their Metals

Occurrence of Metals in Nature

Native or Free State

Metals found in pure form:

• Gold (Au) - Non-reactive, found in river beds
• Platinum (Pt) - Extremely unreactive
• Silver (Ag) - Low reactivity
• Copper (Cu) - Relatively unreactive

Reason: These metals are very less reactive; do not form compounds easily.

Combined State

Most metals occur as compounds:

• Highly reactive metals form stable compounds
• Found as:
  • Oxides
  • Sulphides
  • Carbonates
  • Sulphates
  • Silicates

Relative Abundance in Earth's Crust:

Metallurgy: Extraction of Metals

Metallurgy is the science and process of extracting pure metals from their ores.

Factors Affecting Extraction

1. Type of ore being used
2. Nature of impurities present
3. Degree of reactivity of the metal

Steps in Metallurgical Process

Step 1: Concentration of Ore (Ore Dressing)

Removal of gangue (earthy impurities) from ore.

Purpose:

• Increase metal concentration
• Make extraction easier
• Reduce waste

Methods of Concentration

a) Hydraulic Washing (Gravity Separation)

• Based on difference in density of ore and gangue
• Used for: Tin, Lead ores
• Process:
  • Crushed ore is placed in large tanks
  • Water current washes away lighter gangue
  • Heavier ore particles settle at bottom

b) Froth Flotation

• Based on difference in wettability with oil and water
• Used for: Sulphide ores (Cu, Pb, Zn)
• Process:
  • Crushed ore mixed with water and pine oil
  • Air is blown through the mixture
  • Ore particles stick to oil froth
  • Froth is skimmed off; gangue settles

c) Magnetic Separation

• Based on magnetic properties
• Used for: Iron ore, Nickel, Manganese
• Process:
  • Ore is placed on moving belt
  • Magnetic roller attracts ore particles
  • Non-magnetic gangue falls separately

Step 2: Conversion to Metal Oxide

Concentrated ore is converted to metal oxide by:

a) Roasting

Heating concentrated ore in excess air at high temperature.

Used for: Sulphide ores

Purpose:

• Removes water
• Removes volatile impurities (arsenic, phosphorus)
• Converts ore to oxide
• Makes ore porous

Examples:

2ZnS + 3O₂ --roasting→ 2ZnO + 2SO₂ 2Cu₂S + 3O₂ --roasting→ 2Cu₂O + 2SO₂ 2PbS + 3O₂ --roasting→ 2PbO + 2SO₂ 4FeS + 7O₂ --roasting→ 2Fe₂O₃ + 4SO₂

b) Calcination

Strongly heating concentrated ore in absence/limited air below its melting point.

Used for: Carbonate ores

Purpose:

• Removes moisture
• Removes volatile impurities (CO₂)
• Converts carbonates to oxides
• Makes ore porous

Examples:

CuCO₃ --calcination→ CuO + CO₂ ZnCO₃ --calcination→ ZnO + CO₂ PbCO₃ --calcination→ PbO + CO₂ CaCO₃ --calcination→ CaO + CO₂

Step 3: Reduction of Metal Oxide (Smelting)

Removal of oxygen from metal oxide to obtain pure metal.

Three Methods:

a) Reduction by Carbon/Carbon Monoxide

Used for: Moderately reactive metals (Zn, Fe, Pb, Cu)

Examples:

ZnO + C → Zn + CO PbO + C → Pb + CO Fe₂O₃ + 3CO → 2Fe + 3CO₂ CuO + CO → Cu + CO₂

b) Reduction by Electrolysis

Used for: Highly reactive metals (Na, K, Ca, Mg, Al)

Reason: Cannot be reduced by carbon (too reactive)

Example - Extraction of Aluminium:

2Al₂O₃ --electrolysis→ 4Al + 3O₂

c) Reduction by Thermal Decomposition

Used for: Least reactive metals (Hg, Ag)

Process: Simply heating above 300°C

Example:

2HgO --heat→ 2Hg + O₂ 2Ag₂O --heat→ 4Ag + O₂

Step 4: Refining of Impure Metal

Removing remaining physical and chemical impurities from extracted metal.

Impurities May Include:

• Other metals (pure or impure)
• Non-metals
• Dissolved gases

Methods of Refining

a) Distillation

• Used for low melting metals (Zn, Hg)

b) Liquefaction

• Selective melting and separation

c) Oxidation

• Impurities oxidized and removed

d) Electro-refining (Best Method)

• Gives 99-99.9% pure metal
• Used for: Cu, Zn, Sn, Al, Ni, Cr, Ag, Au

Electro-refining Process:

1. Anode: Impure metal
2. Cathode: Pure metal strip
3. Electrolyte: Metal salt solution

Process:

• Impure metal dissolves from anode
• Pure metal deposits on cathode
• Impurities settle as anode mud

Flux and Slag

Flux

Substance added to ore to remove impurities during reduction.

Purpose:

• Lowers melting point
• Reacts chemically with impurities
• Forms fusible slag

Common Fluxes:

• Limestone (CaCO₃) - for acidic impurities
• Silica (SiO₂) - for basic impurities

Slag

Fusible compound formed by reaction of flux with impurities.

Flux + Impurities → Slag

Properties:

• Lighter than molten metal
• Floats on top
• Easily removed

Example:

CaCO₃ → CaO + CO₂ CaO + SiO₂ → CaSiO₃ (slag) (flux) (impurity) (removed)

Thermite Reaction

Reduction of certain metal oxides using aluminium as reducing agent.

General Equation:

Metal Oxide + Al → Metal + Al₂O₃ + Heat

Examples:

3MnO₂ + 4Al → 3Mn + 2Al₂O₃ Fe₂O₃ + 2Al → 2Fe + Al₂O₃ Cr₂O₃ + 2Al → 2Cr + Al₂O₃

Uses:

• Welding railway tracks
• Repairing broken machine parts
• Joining heavy metal pieces

Uses of Common Metals

Copper (Cu)

Properties:

• Reddish-brown color
• Highly ductile
• Excellent heat and electricity conductor

Uses:

1. Electric wires and cables
2. Cooking utensils
3. Water pipes
4. Electronic devices
5. Coins (in alloys - brass, bronze)
6. Electroplating operations

Why not silver for wiring?

Though silver is the best conductor, copper is used because:

• Silver is costly
• Copper is chemically more stable
• Copper is sufficiently conductive

Iron (Fe)

Three Varieties:

1. Pig Iron (Cast Iron)
   • Highest carbon content (~4%)
   • Most impure form
   • Uses: Radiators, pipes, drain covers
2. Wrought Iron
   • Lowest carbon content (~0.1%)
   • Purest form
   • Uses: Chains, wires, bolts, nails, gates
3. Steel
   • Moderate carbon content (0.5-1.5%)
   • Most widely used
   • Uses: Bridges, buildings, ships, automobiles, utensils

Why steel is most useful:

• Stronger than pure iron
• Does not rust easily
• Can be molded easily
• Cost-effective

Aluminium (Al)

Properties:

• Silvery-white color
• Light and strong
• Malleable and ductile
• Excellent conductor
• Corrosion-resistant (forms protective oxide layer)

Uses:

1. Cooking utensils
2. Aircraft bodies (duralumin alloy)
3. Automobile parts
4. Electrical wires
5. Window frames
6. Aluminium foil (food packaging)
7. Paints (aluminium powder)
8. Mirrors (reflective coating)

Why aluminium doesn't corrode?

Forms a thin, protective Al₂O₃ layer that prevents further corrosion.

Zinc (Zn)

Uses:

1. Galvanization: Coating iron to prevent rusting
2. Dry cells and batteries
3. Brass and bronze (alloys)
4. Extraction of gold and silver (from ores)
5. Die-casting
6. Protective coatings

Lead (Pb)

Uses:

1. Pipes and sanitary fittings
2. Bullets
3. Roofing material
4. Storage batteries
5. Paint pigments (lead compounds)
6. X-ray shielding
7. Solder (lead-tin alloy)

Magnesium (Mg)

Uses:

1. Fireworks and flares (burns with dazzling light)
2. Alloys - duralumin, magnalium (for aircraft)
3. Flash photography
4. Fuse wire
5. Nuclear reactors (neutron absorption)

Gold (Au)

Properties:

• Does not tarnish
• Excellent conductor
• Most malleable and ductile metal

Uses:

1. Jewelry (22-carat gold)
2. Electronic devices
3. Coins
4. Dental fillings (gold amalgam)
5. Gold plating
6. Space equipment (reflects radiation)

Purity Measurement:

• 24-carat = 100% pure gold
• 22-carat = 91.6% gold
• 18-carat = 75% gold

Silver (Ag)

Properties:

• Best conductor of electricity
• Most ductile after gold
• Lustrous

Uses:

1. Jewelry
2. Dental amalgam
3. Photography (AgBr, AgNO₃)
4. Water purification
5. Electrodes
6. Cloud seeding (AgI for artificial rain)
7. Electroplating

Mercury (Hg)

Properties:

• Only liquid metal at room temperature
• Does not wet glass
• Expands uniformly with temperature

Uses:

1. Thermometers
2. Barometers
3. Dental amalgam
4. Scientific instruments
5. Mercury vapor lamps

Platinum (Pt)

Uses:

1. Jewelry and watches
2. Electrodes in electrolytic cells
3. Catalysts in chemical reactions
4. Laboratory equipment

Uses of Common Non-Metals

Oxygen (O₂)

Uses:

1. Respiration (breathing)
2. Combustion (burning)
3. Welding and metal cutting
4. Steel manufacturing
5. Medical use (carbogen: 95% O₂ + 5% CO₂)
6. Rocket fuel (liquid oxygen - LOX)
7. Explosives
8. Deep sea diving, mountaineering

Nitrogen (N₂)

Properties:

• Slightly lighter than air
• Neither combustible nor supports combustion
• Essential component of proteins

Uses:

1. Controls combustion rate (dilutes oxygen)
2. Ammonia production
3. Fertilizers (ammonium salts, urea)
4. Explosives (TNT)
5. Food preservation (prevents bacterial growth)
6. Protein formation in plants

Natural Nitrogen Cycle: During thunderstorms:

N₂ + O₂ --lightning→ nitrogen oxides Nitrogen oxides + rain → nitric acid (fertilizes soil)

Chlorine (Cl₂)

Uses:

1. Bleaching agent (paper, textiles)
2. Water purification (kills bacteria)
3. Swimming pool disinfectant
4. Manufacturing HCl
5. Pesticides (DDT, BHC)
6. Bleaching powder (disinfectant)

Sulphur (S)

Properties:

• Yellow solid
• Brittle
• Found in garlic, onion, eggs, hair

Uses:

1. Sulphuric acid production
2. Gunpowder
3. Matches and fireworks
4. Dyes
5. Fungicides and insecticides
6. Skin ointments (fungicide)
7. Blood purification
8. Medicines (homeopathy, ayurveda)

Phosphorus (P)

Occurrence:

• Bones and teeth (calcium phosphate)
• Brain cells

Uses:

1. Match boxes (phosphorus sulphide on sides)
2. Fertilizers
3. Detergents
4. Ceramics and chinaware
5. Rat poison (white phosphorus)
6. Fireworks

Silicon (Si)

Properties:

• Does not occur free in nature
• Second most abundant element (as SiO₂ - sand)

Uses:

1. Microchips and transistors
2. Solar cells
3. Computer components
4. Silicon carbide (grinding agent - hardest man-made substance)
5. Concrete, bricks, cement
6. Glass manufacturing
7. Pottery and enamel
8. Steel production (as alloy)

Iodine (I₂)

Uses:

1. Iodized salt (prevents goiter)
2. Tincture of iodine (antiseptic)
3. Photography
4. Iodex (pain reliever)

Fluorine (F₂)

Uses:

1. Toothpaste (stannous fluoride - prevents decay)
2. Teflon plastic (non-stick coating)
3. Refrigerants
4. Water fluoridation

Alloys

Homogeneous mixture of two or more metals, or a metal and a non-metal.

Why Make Alloys?

1. Increase strength
2. Improve corrosion resistance
3. Lower melting point
4. Enhance appearance
5. Modify electrical properties

Common Alloys

Enhanced Study Notes

Quick Revision Points

Metals:

• ✓ Lustrous, hard, malleable, ductile
• ✓ Good conductors of heat and electricity
• ✓ High melting points (except Na, K)
• ✓ Form basic oxides
• ✓ React with acids to give H₂ gas

Non-Metals:

• ✓ Dull, soft, brittle
• ✓ Poor conductors (except graphite)
• ✓ Low melting points (except C, Si)
• ✓ Form acidic oxides
• ✓ Do not react with dilute acids

Metalloids:

• ✓ Properties of both metals and non-metals
• ✓ Semiconductors
• ✓ Examples: Si, Ge, As

Memory Tricks & Mnemonics

1. Reactivity Series: "Please Send Charlies Monkeys And Zebras In Trunk Like Happy Children Making Silver Golden Pancakes"

K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, [H], Cu, Hg, Ag, Au, Pt

2. Properties of Metals: "Most Dogs Love Salty Chicken Meals Twice Daily"

Metallic luster, Ductile, Lustrous, Sonorous, Conductive, Malleable, Tensile strength, Dense

3. Metallurgy Steps: "Cats Can Run Really Fast"

Concentration, Conversion, Reduction, Refining

4. Concentration Methods: "Happy Fish Move"

Hydraulic washing, Froth flotation, Magnetic separation

5. Noble Metals:"Good Silver Platinum"

Gold, Silver, Platinum (do not react with oxygen)

Summary Table for Quick Revision

Solved Examples

Example 1: Conceptual

Q: Why is sodium kept immersed in kerosene oil?

Solution:

Sodium is a highly reactive metal. It reacts vigorously with:

• Oxygen in air to form Na₂O
• Moisture in air to form NaOH

Reaction:

4Na + O₂ → 2Na₂O 2Na + 2H₂O → 2NaOH + H₂↑ + Heat

The reaction is so vigorous that it can catch fire.

Answer: To prevent contact with oxygen and moisture in air, sodium is stored in kerosene oil.

Example 2: Identification

Q: A greenish layer forms on copper vessels left in moist air. What is this layer? Why does it form?

Solution:

Observation: Greenish layer on copper

Reason: Copper reacts with moist air containing:

• Oxygen (O₂)
• Water vapor (H₂O)
• Carbon dioxide (CO₂)

Reaction:

2Cu + O₂ + H₂O + CO₂ → Cu(OH)₂·CuCO₃ (basic copper carbonate - green)

Answer: The greenish layer is basic copper carbonate [Cu(OH)₂·CuCO₃]. It forms due to corrosion of copper by moist air.

Example 3: Comparison

Q: Compare the malleability of: (a) Gold (b) Sulphur

Solution:

(a) Gold:

• Most malleable metal
• 1 gram can be beaten into 0.5 m² sheet
• Used in gold foils for decorating sweets

(b) Sulphur:

• Non-metal, hence non-malleable
• Brittle in nature
• Breaks into powder when hammered

Answer: Gold is highly malleable; sulphur is non-malleable and brittle.

Example 4: Reaction Prediction

Q: What happens when zinc granules are added to copper sulphate solution? Write the equation.

Solution:

Given: Zn + CuSO₄ solution

Reactivity: Zn is more reactive than Cu

Observation:

• Blue color of CuSO₄ fades
• Colorless ZnSO₄ solution forms
• Reddish-brown Cu deposits on Zn

Equation:

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s) (blue) (colorless) (brown)

Answer: Zinc displaces copper from copper sulphate. Blue solution becomes colorless and copper metal is deposited.

Example 5: Property-Based

Q: Why are electrical wires made of copper and not silver, even though silver is the best conductor?

Solution:

Comparison:

Conclusion: Though silver has higher conductivity, copper is preferred because:

1. Much cheaper
2. More readily available
3. Sufficiently good conductor
4. More chemically stable for long-term use

Answer: Copper is used instead of silver due to cost-effectiveness and sufficient conductivity.

Example 6: Differentiation

Q: Differentiate between roasting and calcination.

Solution:

Answer: Roasting uses excess air for sulphide ores; calcination uses limited air for carbonate ores.

Example 7: Application-Based

Q: Why is aluminium used for making cooking utensils?

Solution:

Properties of Aluminium favorable for cooking:

1. Good heat conductor - cooks food evenly
2. Light weight - easy to handle
3. Does not rust - forms protective Al₂O₃ layer
4. Non-toxic - safe for food contact
5. Malleable - can be shaped easily
6. Does not react with food acids in normal conditions

Answer: Aluminium's conductivity, lightness, corrosion resistance, and non-toxicity make it ideal for utensils.

Example 8: Assertion-Reason

Q: Assertion (A): Sodium and potassium are stored in kerosene. Reason (R): They are highly reactive and react with oxygen and moisture in air.

Options:

(a) Both A and R are true, R is correct explanation of A

(b) Both A and R are true, R is not correct explanation of A

(c) A is true, R is false

(d) A is false, R is true

Solution:

Assertion: TRUE

• Na and K are indeed stored in kerosene

Reason: TRUE

• They react vigorously:

2Na + O₂ → 2Na₂O 2Na + 2H₂O → 2NaOH + H₂ + Heat

Relation: Reason correctly explains why they are stored in kerosene (to prevent contact with air and moisture)

Answer: (a) Both A and R are true, R is correct explanation of A

Example 9: Prediction

Q: Predict whether the following reactions will occur. Give reasons. (a) Cu + ZnSO₄ → ? (b) Mg + FeSO₄ → ?

Solution:

(a) Cu + ZnSO₄ → ?

Reactivity: Cu < Zn (from reactivity series)

Conclusion: Cu cannot displace Zn

Answer: NO REACTION occurs

(b) Mg + FeSO₄ → ?

Reactivity: Mg > Fe (from reactivity series)

Conclusion: Mg can displace Fe

Equation:

Mg + FeSO₄ → MgSO₄ + Fe

Answer: REACTION OCCURS; magnesium displaces iron.

Example 10: Numerical

Q: If 1 gram of gold can be drawn into a wire of 2 km length, calculate the length of wire from 10 grams of gold.

Solution:

Given:

• 1 g gold = 2 km wire

To find: Length from 10 g gold

Method: Since gold is perfectly ductile, the relationship is directly proportional:

Length ∝ Mass Length = 2 km/g × Mass

Calculation:

Length = 2 km/g × 10 g Length = 20 km

Answer: 10 grams of gold can be drawn into 20 km of wire.

Example 11: Identification

Q: A student added a few pieces of aluminium metal to two test tubes A and B containing aqueous solutions of iron sulphate and copper sulphate. In the second part of the experiment, she added iron metal to another two test tubes C and D containing aqueous solutions of aluminium sulphate and copper sulphate. In which test tube(s) will a metal deposition occur?

Solution:

Test Tube A: Al + FeSO₄

• Reactivity: Al > Fe
• Reaction occurs: Al displaces Fe
• Metal deposition: Iron metal deposited

Test Tube B: Al + CuSO₄

• Reactivity: Al > Cu
• Reaction occurs: Al displaces Cu
• Metal deposition: Copper metal deposited

Test Tube C: Fe + Al₂(SO₄)₃

• Reactivity: Al > Fe
• No reaction: Fe cannot displace Al
• No deposition

Test Tube D: Fe + CuSO₄

• Reactivity: Fe > Cu
• Reaction occurs: Fe displaces Cu
• Metal deposition: Copper metal deposited

Answer: Metal deposition occurs in test tubes A, B, and D.

Example 12: Process-Based

Q: Name the process used for:

(a) Removing gangue from iron ore

(b) Extracting zinc from zinc oxide

Solution:

(a) Removing gangue from iron ore

Ore: Haematite (Fe₂O₃) or Magnetite (Fe₃O₄)

Method:Magnetic separation

Reason: Iron ore has magnetic properties; gangue does not

Process:

• Crushed ore on moving belt
• Magnetic roller attracts ore particles
• Non-magnetic gangue falls separately

(b) Extracting zinc from zinc oxide

Method:Reduction by carbon

Equation:

ZnO + C → Zn + CO

Reason: Zn is moderately reactive; can be reduced by carbon

Answer: (a) Magnetic separation (b) Reduction by carbon

Example 13: Anomaly Explanation

Q:Explain why:

(a) Platinum is more expensive than gold

(b) Diamond is hard but graphite is soft (both are carbon)

Solution:

(a) Platinum more expensive than gold

Reasons:

1. Rarity: Platinum is 30 times rarer than gold
2. Extraction difficulty: Harder to extract and purify
3. Industrial demand: Used in catalytic converters, lab equipment
4. Higher density: More platinum needed for same volume
5. Higher melting point: More energy for processing

(b) Diamond hard, graphite soft

Structure explains properties:

Diamond:

• Each C atom bonded to 4 others
• 3D tetrahedral network
• Very strong covalent bonds
• Hardest natural substance

Graphite:

• Each C atom bonded to 3 others
• 2D layered structure
• Weak forces between layers
• Layers slide easily
• Soft and slippery

Answer: (a) Rarity, extraction difficulty, higher demand (b) Different structural arrangements of carbon atoms

Example 14: Observation-Based

Q: A shiny brown coloured element X on heating in air becomes black in colour. Name the element X and the black compound formed.

Solution:

Clue Analysis:

• Shiny brown metal → Copper
• Turns black on heating → Formation of black oxide

Element X: Copper (Cu)

Reaction:

2Cu(s) + O₂(g) --heat→ 2CuO(s) (brown) (black)

Black compound: Copper oxide (CuO)

Confirmation:

• Copper is the only common brown metal
• CuO is black in color
• Reaction occurs readily on heating copper

Answer: Element X is copper (Cu); black compound is copper oxide (CuO).

Example 15: Case-Based Question

Q: A jeweler claims to sell pure gold (24-carat). When tested, it was found to be 22-carat gold.

(a) What does 22-carat mean?

(b) Why is jewelry not made from 24-carat gold?

(c) What are the common metals mixed with gold to make jewelry?

Solution:

(a) 22-carat meaning:

Carat system: Measures gold purity out of 24 parts

22-carat gold:

Purity = 22/24 × 100 = 91.67% gold

Remaining 2 parts: Other metals (Cu, Ag)

(b) Why not 24-carat jewelry?

24-carat gold issues:

1. Too soft - easily bends and scratches
2. Loses shape - cannot hold intricate designs
3. Not durable for daily wear
4. Difficult to work with for making jewelry
5. Pure gold color is too yellow (not preferred by all)

(c) Common metals mixed:

Main additions:

• Copper (Cu): Adds hardness, reddish tinge
• Silver (Ag): Adds strength, whitish tone
• Zinc (Zn): Improves workability

Common jewelry gold:

• 22-carat: 91.6% Au + 8.4% Cu/Ag (Indian standard)
• 18-carat: 75% Au + 25% Cu/Ag (Western standard)

Answer: (a) 91.67% pure gold (b) Pure gold is too soft and loses shape (c) Copper, silver, zinc

Example 16: Equation Writing

Q: Complete and balance the following equations: (a) Al + Fe₂O₃ → (b) Zn + H₂SO₄(dil) → (c) CaCO₃ --heat→

Solution:

(a) Thermite reaction:

2Al + Fe₂O₃ → Al₂O₃ + 2Fe + Heat

(Aluminium reduces iron oxide)

(b) Metal-acid reaction:

Zn + H₂SO₄(dil) → ZnSO₄ + H₂↑

(Zinc displaces hydrogen)

(c) Calcination:

CaCO₃ --heat→ CaO + CO₂↑

(Calcium carbonate decomposes)

Answer: See balanced equations above.

Example 17: Critical Thinking

Q: An element A reacts with water to form a compound B which is used in white washing. Identify A and B. Write the reactions involved.

Solution:

Clue analysis:

"Used in white washing" → Calcium hydroxide [Ca(OH)₂] - commonly called slaked lime

Working backwards:

• B = Ca(OH)₂
• A must give Ca(OH)₂ with water
• A = Calcium (Ca)

Reaction 1: Calcium with water

Ca + 2H₂O → Ca(OH)₂ + H₂↑ (compound B)

Reaction 2: Ca(OH)₂ with air (during whitewashing)

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (white layer)

Answer:

• Element A: Calcium (Ca)
• Compound B: Calcium hydroxide [Ca(OH)₂]

Example 18: Assertion-Reason (Type 2)

Q: Assertion (A): Aluminium is a highly reactive metal, yet it is used for making cooking utensils. Reason (R): Aluminium forms a thin protective layer of aluminium oxide on its surface.

Options:

(a) Both A and R true, R explains A

(b) Both A and R true, R doesn't explain A

(c) A true, R false

(d) A false, R true

Solution:

Assertion: TRUE

• Al is highly reactive (above Zn in reactivity series)
• Yet widely used for utensils

Reason: TRUE

• Al reacts with O₂ to form Al₂O₃ layer

4Al + 3O₂ → 2Al₂O₃ (thin protective layer)

Relation:

• R explains WHY highly reactive Al can be used
• The oxide layer prevents further reaction
• Makes Al resistant to corrosion

Answer: (a) Both A and R true, R correctly explains A

Example 19: Practical Application

Q: During the extraction of metals, limestone (CaCO₃) is often added. Explain why.

Solution:

Purpose: Limestone acts as flux

What happens:

Step 1: Limestone decomposes

CaCO₃ --heat→ CaO + CO₂

Step 2: CaO reacts with sandy impurities (SiO₂)

CaO + SiO₂ → CaSiO₃ (flux) (impurity) (slag)

Benefits:

1. Removes impurities: Converts sand (gangue) to slag
2. Lowers melting point: Makes extraction easier
3. Slag floats: Being lighter, easily separated
4. Improves purity: Metal obtained is cleaner

Analogy: Like soap removing dirt by converting it to easily removable foam

Answer: Limestone acts as flux to remove silica impurities by forming calcium silicate slag.

Example 20: Multi-Step Problem

Q: Explain the complete metallurgical process for extracting iron from haematite ore. Include all steps with equations.

Solution:

Ore: Haematite (Fe₂O₃)

STEP 1: CONCENTRATION

Method: Hydraulic washing + Magnetic separation

Process: Removes sand, clay impurities

STEP 2: CALCINATION/ROASTING

Process: Heating to remove moisture and volatile impurities

2Fe₂O₃ + Heat → Concentrated ore (no chemical change in this case)

STEP 3: REDUCTION (in Blast Furnace)

Reducing agent: Carbon (coke) and carbon monoxide

Temperature: 1200°C

Reactions:

(a) Coke burns to form CO:

2C + O₂ → 2CO

(b) CO reduces Fe₂O₃:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

(c) Direct reduction also occurs:

Fe₂O₃ + 3C → 2Fe + 3CO

STEP 4: FLUX AND SLAG FORMATION

Flux used: Limestone (CaCO₃)

Reactions:

CaCO₃ → CaO + CO₂ CaO + SiO₂ → CaSiO₃ (slag) (impurity)

Slag removal: Floats on top; tapped separately

STEP 5: REFINING

Method: Re-melting and removing remaining impurities

Alternatively: Electrolytic refining for pure iron

Final product:

• Pig iron (93% Fe, 4% C) for general use
• Further refined to make steel or wrought iron

Answer: Complete process involves concentration → calcination → reduction by CO → slag removal → refining.

Conclusion

Understanding metals and non-metals is fundamental to chemistry. This chapter covers:

Physical properties - conductivity, malleability, ductility
Chemical properties - reactions with oxygen, water, acids
Reactivity series - predicting reactions and displacement
Metallurgy - extraction of metals from ores
Uses - applications in daily life and industry

Exam Focus Areas:

• Properties comparison table
• Reactivity series
• Chemical equations
• Displacement reactions
• Extraction processes
• Alloys and their uses

Practice Tips:

• Write chemical equations daily
• Make flashcards for reactivity series
• Solve previous year questions
• Understand concepts, don't just memorize
• Relate to real-life examples

About This Revision Note: This comprehensive guide covers all aspects of Metals and Non-Metals for Class 8 students, designed to aid both learning and exam preparation. For doubts and queries, consult your subject teacher or refer to NCERT textbooks.