Materials: Metals and Non-Metals
Welcome to HSLC Guru! This page provides complete English-medium study material and question-answer solutions for Class 8 General Science Chapter 3 — Materials: Metals and Non-Metals, prepared strictly according to the latest ASSEB (Assam State School Education Board) syllabus. You will find a clear chapter summary, detailed textbook question answers, additional MCQs, fill-in-the-blanks, true/false statements and a handy glossary, all designed to help you score top marks in your examinations.
Chapter Summary
All matter around us is made up of materials, and these materials are broadly classified into two large groups — metals and non-metals. Metals possess a set of characteristic physical properties that make them easily recognisable. They have a shining surface called metallic lustre; they are malleable, meaning they can be hammered into thin sheets without breaking; they are ductile, meaning they can be drawn into thin wires; they are generally hard (except sodium and potassium which are soft); they are sonorous, producing a ringing sound when struck; and they are excellent conductors of heat and electricity. Most metals also possess high melting and boiling points and have high density. Common examples include iron, copper, aluminium, gold, silver and zinc. Mercury is a special metal because it is liquid at room temperature.
Non-metals, on the other hand, generally show properties that are opposite to those of metals. They are not lustrous (except iodine and graphite), they are brittle in the solid state, they are non-malleable and non-ductile, they are poor conductors of heat and electricity (graphite being a notable exception), they are not sonorous, and they generally have low melting and boiling points. Non-metals can exist in all three physical states — solid (sulphur, carbon, phosphorus, iodine), liquid (bromine) and gas (oxygen, nitrogen, hydrogen, chlorine). Together, metals and non-metals provide the foundation for almost every material we use in daily life.
The chemical properties of metals and non-metals differ sharply. When metals react with oxygen, they form basic oxides (for example, magnesium burns to give MgO which turns red litmus blue), while non-metals form acidic oxides (for example, sulphur burns to give SO₂ which turns blue litmus red). Some metals react with water to liberate hydrogen — sodium and potassium react violently with cold water, calcium reacts slowly, and iron reacts only with steam. Metals generally react with dilute acids to release hydrogen gas and form salts, whereas non-metals usually do not react with acids. Some non-metals react with bases. Displacement reactions are also important: a more reactive metal can displace a less reactive metal from its salt solution. For example, iron displaces copper from copper sulphate solution (Fe + CuSO₄ → FeSO₄ + Cu). The order of metals based on their reactivity is called the reactivity series.
Metals and non-metals have countless uses. Iron (Fe) is used for making machines, vehicles, tools, bridges and buildings. Aluminium (Al) is used for making aircraft bodies, utensils, electric wires and foil for packing food. Copper (Cu) is used in electric wires, hot-water pipes and utensils. Gold (Au) and Silver (Ag) are used in jewellery, coins, medals and electronic devices. Among non-metals, Oxygen (O₂) is essential for respiration and combustion; Nitrogen (N₂) is used in fertilisers and to preserve food packets; Sulphur (S) is used to make sulphuric acid, gunpowder and medicines; Phosphorus (P) is used in matchsticks and fertilisers; Carbon (C) in the form of graphite is used in pencils and electrodes, while diamond is used in cutting tools and ornaments; Chlorine (Cl₂) is used to disinfect drinking water and to make bleaching powder; and Iodine (I₂) is used as a tincture for wounds and in thyroid medicines. Knowing the difference between metals and non-metals helps us choose the right material for the right purpose.
Textbook Questions and Answers
A. Very Short Answer Type Questions (1 Mark)
Q1. What is meant by metallic lustre?
Answer: The shiny appearance of the freshly cut surface of a metal is called metallic lustre.
Q2. Name a metal which is liquid at room temperature.
Answer: Mercury (Hg) is the only metal that is liquid at room temperature.
Q3. Name a non-metal which conducts electricity.
Answer: Graphite, an allotropic form of carbon, conducts electricity.
Q4. What is malleability?
Answer: The property of metals by which they can be hammered into thin sheets without breaking is called malleability.
Q5. Define ductility.
Answer: The property of metals by which they can be drawn into thin wires is called ductility.
Q6. Name two soft metals that can be cut with a knife.
Answer: Sodium (Na) and Potassium (K) are soft metals that can be cut with a knife.
Q7. What type of oxide is formed when sulphur burns in oxygen?
Answer: Sulphur burns in oxygen to form sulphur dioxide (SO₂), which is an acidic oxide.
Q8. Which gas is released when a metal reacts with a dilute acid?
Answer: Hydrogen gas (H₂) is released when a metal reacts with a dilute acid.
Q9. Name a non-metal which is lustrous.
Answer: Iodine is a non-metal that has a shining (lustrous) appearance.
Q10. Which non-metal is used to disinfect drinking water?
Answer: Chlorine (Cl₂) is used to disinfect drinking water.
B. Short Answer Type Questions (2-3 Marks)
Q1. Write any three physical properties of metals.
Answer: Three physical properties of metals are:
- Metals possess a shining surface known as metallic lustre.
- Metals are malleable and can be beaten into thin sheets.
- Metals are ductile and can be drawn into thin wires.
Q2. How does magnesium react with oxygen? Write the chemical equation.
Answer: When a magnesium ribbon is burnt in air, it reacts with oxygen with a dazzling white flame and forms magnesium oxide (MgO), which is a white powder.
2Mg + O₂ → 2MgO
Magnesium oxide dissolves in water to form magnesium hydroxide, which is a basic solution and turns red litmus blue.
Q3. What is a displacement reaction? Give an example.
Answer: A reaction in which a more reactive metal displaces a less reactive metal from its salt solution is called a displacement reaction. For example, when an iron nail is placed in copper sulphate solution, the blue colour of the solution fades and a reddish-brown layer of copper is deposited on the nail.
Fe + CuSO₄ → FeSO₄ + Cu
Q4. Why is aluminium used for making aircraft bodies?
Answer: Aluminium is used for making aircraft bodies because it is light in weight, strong, resistant to corrosion (due to a protective oxide layer), and a good conductor of heat. These properties make it ideal for aircraft, which need to be light and durable.
Q5. How does sodium react with water?
Answer: Sodium reacts violently with cold water. It floats on the water surface, melts due to the heat produced, and gives off hydrogen gas, which often catches fire. The solution formed is sodium hydroxide, which is strongly basic.
2Na + 2H₂O → 2NaOH + H₂↑
Q6. Mention two important uses of nitrogen and two uses of sulphur.
Answer:
- Uses of Nitrogen: (i) It is used in the manufacture of nitrogenous fertilisers like urea and ammonium sulphate. (ii) It is used to fill packets of chips and food items to prevent spoilage.
- Uses of Sulphur: (i) It is used in the manufacture of sulphuric acid (H₂SO₄). (ii) It is used in the preparation of gunpowder, matches and certain medicines.
C. Long Answer Type Questions (5-6 Marks)
Q1. Compare the physical properties of metals and non-metals using a table.
Answer: The physical properties of metals and non-metals can be compared as follows:
| Property | Metals | Non-Metals |
|---|---|---|
| Lustre | Possess metallic lustre | Generally non-lustrous (except iodine, graphite) |
| Malleability | Malleable — can be hammered into sheets | Non-malleable — break when hammered |
| Ductility | Ductile — can be drawn into wires | Non-ductile |
| Hardness | Generally hard (except Na, K) | Generally soft (except diamond) |
| Sonority | Sonorous — produce ringing sound | Not sonorous |
| Conductivity | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Melting/Boiling Point | Generally high | Generally low |
| Physical State | All solids except mercury | Found in solid, liquid and gaseous states |
Q2. Describe the chemical reactions of metals with (a) oxygen, (b) water and (c) dilute acid with examples.
Answer:
(a) Reaction with Oxygen: Most metals react with oxygen to form basic oxides. For example, magnesium burns brightly in air to give magnesium oxide.
2Mg + O₂ → 2MgO
Iron reacts slowly with the oxygen and moisture in the air to form rust (iron oxide).
(b) Reaction with Water: Different metals react with water differently. Sodium and potassium react violently with cold water. Calcium reacts slowly with cold water. Magnesium reacts only with hot water. Iron reacts with steam to form iron oxide and hydrogen.
2Na + 2H₂O → 2NaOH + H₂↑
3Fe + 4H₂O → Fe₃O₄ + 4H₂↑
(c) Reaction with Dilute Acid: Metals react with dilute acids to form salt and release hydrogen gas. For example,
Zn + 2HCl → ZnCl₂ + H₂↑
Mg + H₂SO₄ → MgSO₄ + H₂↑
However, copper, silver and gold do not react with dilute acids.
Q3. Write the important uses of iron, copper, gold and silver.
Answer:
- Iron (Fe): Used for making machinery, vehicles, agricultural tools, railway tracks, bridges, buildings, water pipes, and (in the form of steel) cutlery and surgical instruments.
- Copper (Cu): Used for making electrical wires and cables, hot-water tanks and pipes, cooking utensils, and various alloys such as brass and bronze.
- Gold (Au): Used for making jewellery, coins, medals, in dental work, and in electronic components like connectors because it does not corrode.
- Silver (Ag): Used for making jewellery, ornaments, silverware, mirrors, photographic films, and in some medicines and electronic components.
Q4. Distinguish between metals and non-metals on the basis of their chemical properties.
Answer:
| Chemical Property | Metals | Non-Metals |
|---|---|---|
| Reaction with oxygen | Form basic oxides (e.g., MgO, CaO) | Form acidic oxides (e.g., SO₂, CO₂) |
| Reaction with water | Many react to release hydrogen and form hydroxides | Generally do not react with water |
| Reaction with dilute acid | React to release hydrogen gas and form salts | Generally do not react with dilute acids |
| Reaction with bases | Most do not react; a few like Al, Zn react | Many react with bases to form salts |
| Nature in compounds | Form positive ions (cations) | Form negative ions (anions) |
| Displacement | More reactive metals displace less reactive ones | Show similar displacement among themselves |
Q5. Describe any five important uses of non-metals in our daily life.
Answer: Non-metals play a crucial role in our day-to-day life. Five important uses are:
- Oxygen (O₂): It is essential for the respiration of all living beings. It is also necessary for the burning of fuels, used in hospitals for patients having breathing problems, and in welding torches.
- Nitrogen (N₂): It is used to manufacture fertilisers like urea and ammonium nitrate. It is also used to preserve food packets and in the manufacture of explosives.
- Carbon (C): Graphite is used in pencils, electrodes and as a lubricant. Diamond, the hardest natural substance, is used in cutting tools and as a precious gem.
- Sulphur (S): It is used to manufacture sulphuric acid (the king of chemicals), gunpowder, matches, and many drugs and ointments.
- Chlorine (Cl₂): It is used to disinfect drinking water in water-supply plants, to make bleaching powder for the textile and paper industries, and to manufacture plastics like PVC.
Additional Multiple Choice Questions (MCQs)
Q1. Which of the following is a non-metal?
(a) Iron (b) Copper (c) Sulphur (d) Aluminium
Answer: (c) Sulphur
Q2. The metal that is liquid at room temperature is:
(a) Sodium (b) Mercury (c) Bromine (d) Gallium
Answer: (b) Mercury
Q3. Which non-metal is a good conductor of electricity?
(a) Sulphur (b) Phosphorus (c) Graphite (d) Iodine
Answer: (c) Graphite
Q4. When a metal reacts with a dilute acid, the gas evolved is:
(a) Oxygen (b) Hydrogen (c) Carbon dioxide (d) Nitrogen
Answer: (b) Hydrogen
Q5. The oxide formed by the burning of sulphur is:
(a) Basic (b) Acidic (c) Neutral (d) Amphoteric
Answer: (b) Acidic
Q6. Which of these metals reacts most violently with cold water?
(a) Iron (b) Copper (c) Sodium (d) Magnesium
Answer: (c) Sodium
Q7. The non-metal used to disinfect drinking water is:
(a) Oxygen (b) Nitrogen (c) Chlorine (d) Sulphur
Answer: (c) Chlorine
Q8. The hardest naturally occurring substance is:
(a) Iron (b) Graphite (c) Diamond (d) Quartz
Answer: (c) Diamond
Q9. Which metal is used for making electric wires due to its high conductivity?
(a) Iron (b) Lead (c) Copper (d) Tin
Answer: (c) Copper
Q10. Which of these is NOT a property of non-metals?
(a) Brittle (b) Non-sonorous (c) Malleable (d) Poor conductor
Answer: (c) Malleable
Fill in the Blanks
Q1. Metals are generally good conductors of heat and __________.
Answer: electricity
Q2. The oxide of a metal is __________ in nature.
Answer: basic
Q3. The property by which metals can be drawn into wires is called __________.
Answer: ductility
Q4. __________ is the only non-metal which is liquid at room temperature.
Answer: Bromine
Q5. When iron is placed in copper sulphate solution, __________ is deposited on the iron surface.
Answer: copper
True or False
Q1. All metals are solid at room temperature.
Answer: False (Mercury is a liquid metal at room temperature.)
Q2. Non-metals form acidic oxides when burnt in oxygen.
Answer: True
Q3. Gold and silver react with dilute hydrochloric acid.
Answer: False (Gold and silver are unreactive metals and do not react with dilute acids.)
Q4. Graphite is a non-metal that conducts electricity.
Answer: True
Q5. Sodium is a hard metal that cannot be cut with a knife.
Answer: False (Sodium is a soft metal and can easily be cut with a knife.)
Glossary
| Term | Meaning |
|---|---|
| Metal | An element that is generally hard, lustrous, malleable, ductile and a good conductor of heat and electricity. |
| Non-Metal | An element that is generally brittle, dull, non-malleable, non-ductile and a poor conductor of heat and electricity. |
| Lustre | The shining property of the surface of metals. |
| Malleability | The property of being beaten into thin sheets without breaking. |
| Ductility | The property of being drawn into thin wires. |
| Sonority | The property of producing a ringing sound when struck. |
| Basic Oxide | An oxide that reacts with acid and turns red litmus blue (formed by metals). |
| Acidic Oxide | An oxide that reacts with bases and turns blue litmus red (formed by non-metals). |
| Displacement Reaction | A reaction in which a more reactive metal displaces a less reactive metal from its salt. |
| Reactivity Series | The arrangement of metals in the descending order of their reactivity. |
| Corrosion | The slow eating away of a metal due to its reaction with air, moisture or chemicals. |
| Alloy | A homogeneous mixture of two or more metals (or a metal and a non-metal) made to improve properties. |
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