Metals and Non-Metals — AP Board Class 8 Physical Science
1. Introduction
'Matter around us can be classified into METALS and NON-METALS based on their properties.' About 118 elements are known today. Of these, roughly 90 are metals, 20 are non-metals, and a few are metalloids (having properties of both).
AP Board Context
'Andhra Pradesh is RICH in mineral resources.' The state has significant deposits of:
- Copper — Guntur district
- Barytes — Mangampeta (YSR Kadapa district) — ONE OF THE LARGEST barytes deposits IN THE WORLD
- Limestone — widely used in cement plants across AP
- Manganese — Srikakulam and Vizianagaram districts
- Iron ore — parts of the Eastern Ghats
2. Physical Properties — Metals vs Non-Metals
| Property | Metals | Non-Metals |
|---|---|---|
| State at room temperature | Solid (except mercury — liquid) | Solid, liquid (bromine), or gas |
| Lustre (shine) | HIGH lustre — shiny | Dull (except diamond and iodine) |
| Hardness | Generally HARD (can be beaten) | Generally SOFT (brittle in solid form) |
| Malleability | YES — can be hammered into thin sheets | NO — break when hammered |
| Ductility | YES — can be drawn into wires | NO — are brittle |
| Conduction of heat | GOOD conductors (heat flows easily) | POOR conductors (insulators) |
| Conduction of electricity | GOOD conductors | POOR conductors (except graphite) |
| Sonority | SONOROUS — produce a ringing sound | NOT sonorous |
| Density | Generally HIGH | Generally LOW |
| Melting/boiling point | Generally HIGH | Generally LOW |
Key Definitions
- Malleability: 'The property of metals that allows them to be HAMMERED into thin sheets.' Gold is the MOST malleable metal — 1 gram can be beaten into a sheet of 1 m².
- Ductility: 'The property of metals that allows them to be DRAWN into thin wires.'
- Sonority: 'The property of producing a RINGING sound when struck.'
3. Chemical Properties — Reactions of Metals
3.1 Reaction with Oxygen
Metal + Oxygen → Metal Oxide
[ 4\text{Na} + \text{O}_2 \rightarrow 2\text{Na}_2\text{O} \quad (\text{Sodium oxide}) ]
[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \quad (\text{Magnesium oxide}) ]
- Metal oxides are generally BASIC in nature — they turn red litmus BLUE.
- Some metal oxides are amphoteric (show both acidic and basic properties) — e.g., aluminium oxide (Al₂O₃).
3.2 Reaction with Water
| Metal | Reaction with Water | Product |
|---|---|---|
| Sodium (Na) | Violent reaction — catches fire | Sodium hydroxide + Hydrogen |
| Calcium (Ca) | Less violent — bubbles of H₂ gas | Calcium hydroxide + Hydrogen |
| Magnesium (Mg) | Reacts with HOT water only | Magnesium hydroxide + Hydrogen |
| Iron (Fe) | Reacts with STEAM only | Iron oxide + Hydrogen |
| Gold (Au), Silver (Ag) | Do NOT react with water | — |
[ 2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2 \uparrow ]
'NOTE: Sodium and potassium are so reactive that they are stored under KEROSENE to prevent contact with air and moisture.'
3.3 Reaction with Acids
Metal + Acid → Salt + Hydrogen gas
[ \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \uparrow ]
[ \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \uparrow ]
- The presence of hydrogen gas can be tested by bringing a BURNING matchstick near the test tube — it burns with a 'POP' sound.
- Metals like gold, silver, and copper do NOT react with dilute acids — they are below hydrogen in the reactivity series.
3.4 Reaction with Bases
Some metals react with strong bases to produce hydrogen gas.
[ 2\text{Al} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow 2\text{NaAlO}_2 + 3\text{H}_2 \uparrow ]
[ \text{Zn} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \uparrow ]
'Not all metals react with bases. Aluminium and zinc are the most common examples that do.'
4. Reactivity Series of Metals (Introduction)
Metals can be arranged in DECREASING order of their reactivity. This arrangement is the Reactivity Series.
| Reactivity | Metal | Symbol |
|---|---|---|
| MOST reactive | Potassium | K |
| ↓ | Sodium | Na |
| ↓ | Calcium | Ca |
| ↓ | Magnesium | Mg |
| ↓ | Aluminium | Al |
| ↓ | Zinc | Zn |
| ↓ | Iron | Fe |
| ↓ | Tin | Sn |
| ↓ | Lead | Pb |
| ↓ | (Hydrogen) | H |
| ↓ | Copper | Cu |
| ↓ | Silver | Ag |
| LEAST reactive | Gold | Au |
'A more reactive metal can DISPLACE a less reactive metal from its compound. This is the basis of DISPLACEMENT REACTIONS.'
Displacement Reactions
[ \text{Fe} + \text{CuSO}_4 \rightarrow \text{FeSO}_4 + \text{Cu} ]
Iron (more reactive) displaces copper (less reactive) from copper sulphate solution. The blue colour of copper sulphate FADES and a reddish-brown layer of copper is deposited.
5. Uses of Metals
| Metal | Property Exploited | Use |
|---|---|---|
| Gold (Au) | Lustre, non-reactive, malleable | Jewellery, coins, electronic connectors |
| Silver (Ag) | Best conductor of electricity AND heat | Electrical contacts, mirrors, jewellery |
| Copper (Cu) | Good conductor of electricity, ductile | Electrical wires, cooking vessels, coins |
| Aluminium (Al) | Lightweight, good conductor, malleable | Aeroplanes, window frames, foil, cans |
| Iron (Fe) | Strong, magnetic | Construction (buildings, bridges), tools |
| Zinc (Zn) | Protective coating | Galvanisation of iron (to prevent rusting) |
| Mercury (Hg) | Liquid at room temperature | Thermometers, barometers |
6. Uses of Non-Metals
| Non-Metal | Property Exploited | Use |
|---|---|---|
| Oxygen (O₂) | Supports combustion, essential for respiration | Breathing, medical oxygen cylinders, welding |
| Carbon (C) | Allotropes: diamond (hardest), graphite (conducts) | Diamond — cutting tools, jewellery; Graphite — pencil lead, lubricant |
| Nitrogen (N₂) | Unreactive (inert) | Food packaging (preserves food by excluding oxygen) |
| Sulphur (S) | Yellow solid, burns with blue flame | Gunpowder, matches, vulcanisation of rubber |
| Chlorine (Cl₂) | Kills bacteria | Water purification, bleaching, disinfectants |
| Iodine (I₂) | Essential for thyroid function | Antiseptic (tincture of iodine) |
7. Alloys — Why Pure Metals Are Not Always Best
'An ALLOY is a mixture of a metal with other metals or non-metals.' Pure metals often have limitations — they may be too soft, too reactive, or too heavy. Alloys solve these problems.
| Alloy | Composition | Uses |
|---|---|---|
| Steel | Iron + Carbon + (other elements) | Construction, tools, vehicles |
| Stainless Steel | Iron + Chromium + Nickel | Kitchenware, medical instruments |
| Brass | Copper + Zinc | Decorative items, musical instruments |
| Bronze | Copper + Tin | Statues, coins, bells |
| Solder | Lead + Tin | Joining electrical wires |
8. Common Mistakes and Fixes
| Mistake | Why It's Wrong | Correction |
|---|---|---|
| "All metals are solid at room temperature" | Mercury is a LIQUID at room temperature | Exception: mercury |
| "Non-metals do not conduct electricity at all" | Graphite (a form of carbon) conducts electricity | Graphite is an EXCEPTION |
| "All metals react with acids" | Gold, silver, and copper do NOT react with dilute acids | Only metals ABOVE hydrogen in the reactivity series react |
| "Metal oxides are always basic" | Aluminium oxide is AMPHOTERIC — it reacts with both acids and bases | Some metal oxides show dual behaviour |
| "Gold is the most expensive metal" | Platinum and rhodium are MORE expensive | Price varies; gold is one of several precious metals |
9. AP Exam Focus and Marks Distribution
| Topic | Likely Marks | Question Type |
|---|---|---|
| Physical properties (comparison table) | 3 | Short answer / Table |
| Reactions with oxygen, water, acids | 4 | Short answer / Equations |
| Reactivity series and displacement | 3 | Short answer / Problem |
| Uses of metals and non-metals | 2 | Very short answer |
| Alloys — composition and uses | 2 | Short answer |
| Total | 14 marks |
10. Quick Self-Test
Q1: Give TWO differences between metals and non-metals based on physical properties.
Q2: Why is sodium stored under kerosene?
Q3: Write the equation for the reaction of zinc with hydrochloric acid. How can you test for the gas produced?
Q4: What is an alloy? Give one example.
Q5: Why is graphite used in pencil leads even though carbon is a non-metal?
Q6: A blue solution of copper sulphate is taken in a beaker. An iron nail is placed in it. What will you observe after 30 minutes? Why?
Q7: Why are aluminium foils used for packing food?
Q8: What is the reactivity series? Which is the most reactive and least reactive metal?
Answers
A1: (i) Metals are MALLEABLE (can be hammered into sheets); non-metals are NOT malleable (break when hammered). (ii) Metals are SONOROUS (produce ringing sound); non-metals are NOT sonorous.
A2: Sodium is EXTREMELY REACTIVE. It reacts violently with oxygen and moisture in the air (can even catch fire). Storing it under kerosene ISOLATES it from air and moisture, preventing accidental reaction.
A3: Zn + 2HCl → ZnCl₂ + H₂↑. The gas produced is HYDROGEN. Test: Bring a BURNING matchstick near the mouth of the test tube. Hydrogen burns with a 'POP' sound.
A4: An alloy is a HOMOGENEOUS MIXTURE of a metal with other metals or non-metals. Example: BRASS = copper + zinc. Alloys are made to improve properties like strength, hardness, or corrosion resistance.
A5: Graphite is an ALLOTROPE of carbon. Unlike other non-metals, graphite can conduct electricity because of its unique structure — carbon atoms are arranged in layers with free electrons that can move. Also, graphite is soft and leaves a mark on paper.
A6: The blue colour of copper sulphate solution FADES, and a REDDISH-BROWN layer of copper metal is deposited on the iron nail. This is because IRON is MORE reactive than copper and DISPLACES copper from copper sulphate solution: Fe + CuSO₄ → FeSO₄ + Cu.
A7: Aluminium is used for food packing because: (i) it is MALLEABLE — can be rolled into thin sheets, (ii) it is NON-TOXIC, (iii) it does not react with food (a thin layer of aluminium oxide protects it), (iv) it is LIGHTWEIGHT, and (v) it forms a barrier against light, air, and moisture.
A8: The reactivity series is a list of metals arranged in DECREASING order of their reactivity. The MOST reactive metal is POTASSIUM (K). The LEAST reactive metal is GOLD (Au).
