Chapter 3 — Metals and Non-metals
Welcome to HSLC Guru! This page provides a complete English-medium guide to Class 10 Science Chapter 3 — Metals and Non-metals based on the ASSEB (Assam State School Education Board) syllabus. You will learn about the physical and chemical properties of metals and non-metals, the reactivity series, the formation of ionic compounds, the occurrence and extraction of metals, corrosion and its prevention, and alloys. This chapter is essential for the HSLC examination, and the questions and answers below are designed to help you score full marks.
Summary
Elements can broadly be classified as metals and non-metals based on their physical and chemical properties. Metals are generally lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity. They have high melting and boiling points, high density, and are usually solid at room temperature (mercury is a liquid). Non-metals, on the other hand, are dull, brittle, non-sonorous, and poor conductors of heat and electricity (graphite is an exception). They may be solid, liquid (bromine), or gas at room temperature. Some elements like silicon, germanium, and arsenic show properties of both metals and non-metals and are called metalloids.
Chemically, metals tend to lose electrons to form positive ions (cations), while non-metals tend to gain electrons to form negative ions (anions). Metals react with oxygen to form basic oxides, with water to release hydrogen gas, and with dilute acids to liberate hydrogen. The reactivity series arranges metals in decreasing order of reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Hg, Ag, Au. A more reactive metal can displace a less reactive metal from its salt solution. When metals and non-metals react, they transfer electrons to form ionic compounds (e.g., NaCl), which have high melting points, are soluble in water, and conduct electricity in molten or aqueous form.
Metals occur in nature either in free state (gold, silver, platinum) or in combined state as minerals and ores. Extraction of metals involves three main steps: (i) concentration of the ore (removal of gangue by hand-picking, washing, magnetic separation, or froth flotation), (ii) conversion to oxide by calcination (heating in limited or no air, used for carbonate ores) or roasting (heating in excess air, used for sulphide ores), and (iii) reduction of the oxide to metal using carbon, aluminium (thermite reaction), or electrolysis. Highly reactive metals (K, Na, Ca, Mg, Al) are extracted by electrolytic reduction, moderately reactive metals (Zn, Fe, Pb) by reduction with carbon, and less reactive metals (Cu, Hg) by simple heating in air. Refining is often done by electrolytic refining.
Corrosion is the gradual deterioration of metals due to reaction with air, moisture, or chemicals (e.g., rusting of iron, tarnishing of silver, formation of green coating on copper). Iron rusts to form hydrated iron(III) oxide. Corrosion can be prevented by painting, oiling, greasing, galvanising (coating with zinc), tin-plating, chrome-plating, or alloying. Alloys are homogeneous mixtures of two or more metals (or a metal and a non-metal) prepared to improve properties such as hardness, resistance to corrosion, or appearance. Common examples are brass (Cu + Zn), bronze (Cu + Sn), steel (Fe + C), stainless steel (Fe + Cr + Ni), and amalgam (any metal + Hg).
Textbook Question & Answer
1-Mark Questions
Q1. Name the only metal that is liquid at room temperature.
Answer: Mercury (Hg).
Q2. Name the only non-metal that is liquid at room temperature.
Answer: Bromine (Br2).
Q3. Which non-metal is a good conductor of electricity?
Answer: Graphite (an allotrope of carbon).
Q4. Name the most malleable and ductile metal.
Answer: Gold (Au) is the most malleable and ductile metal.
Q5. What is an ore?
Answer: A mineral from which a metal can be extracted profitably is called an ore.
Q6. Name the process of heating a sulphide ore in excess air.
Answer: Roasting.
Q7. What is the chemical formula of rust?
Answer: Fe2O3·xH2O (hydrated iron(III) oxide).
Q8. Name an alloy of copper and zinc.
Answer: Brass.
Q9. What is amalgam?
Answer: An alloy in which one of the metals is mercury is called an amalgam.
Q10. Which metal is used in galvanisation?
Answer: Zinc (Zn).
2-3 Mark Questions
Q1. Distinguish between metals and non-metals on the basis of physical properties.
Answer: (i) Metals are lustrous; non-metals are dull (except iodine and graphite). (ii) Metals are malleable and ductile; non-metals are brittle. (iii) Metals are good conductors of heat and electricity; non-metals are poor conductors (except graphite). (iv) Metals are sonorous; non-metals are non-sonorous. (v) Metals usually have high melting and boiling points; non-metals generally have low melting and boiling points.
Q2. What is the reactivity series? Write the order of metals in decreasing order of reactivity.
Answer: The arrangement of metals in the decreasing order of their chemical reactivity is called the reactivity series. Order: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au. Potassium is most reactive and gold is least reactive among common metals.
Q3. What is the difference between calcination and roasting?
Answer: Calcination is the process of heating a carbonate ore strongly in the absence or limited supply of air to convert it into oxide. Example: ZnCO3 → ZnO + CO2. Roasting is the process of heating a sulphide ore strongly in the presence of excess air to convert it into oxide. Example: 2ZnS + 3O2 → 2ZnO + 2SO2.
Q4. Why do ionic compounds have high melting points?
Answer: Ionic compounds are made up of positive and negative ions held together by strong electrostatic forces of attraction (ionic bonds). A large amount of heat energy is required to overcome these strong forces and break the crystal lattice. Therefore, ionic compounds have high melting and boiling points.
Q5. What is corrosion? Give two examples.
Answer: Corrosion is the gradual eating away of metals due to their reaction with air, moisture, acids, or other chemicals present in the surroundings. Examples: (i) Rusting of iron — formation of a reddish-brown layer of hydrated iron(III) oxide on iron. (ii) Tarnishing of silver — formation of a black coating of silver sulphide (Ag2S) when silver reacts with sulphur compounds in air. (iii) Copper develops a green coating of basic copper carbonate.
Q6. Why is sodium kept immersed in kerosene oil?
Answer: Sodium is a highly reactive metal. It reacts vigorously with oxygen and moisture present in the air, catching fire spontaneously. To prevent this reaction and accidental fires, sodium is stored under kerosene oil, which keeps it isolated from air and moisture.
5-6 Mark Questions
Q1. Describe the steps involved in the extraction of metals from their ores.
Answer: The extraction of metals from their ores generally involves the following steps: (i) Mining — the ore is dug out from the earth’s crust. (ii) Concentration / enrichment — unwanted impurities (gangue) are removed by methods such as hand-picking, washing, magnetic separation, or froth flotation. (iii) Conversion of ore to metal oxide — carbonate ores are converted to oxide by calcination (heating in limited air); sulphide ores are converted to oxide by roasting (heating in excess air). (iv) Reduction of oxide to metal — metal oxide is reduced to metal using a suitable reducing agent. For metals of medium reactivity (Zn, Fe, Pb), carbon is used. For highly reactive metals (Na, K, Ca, Mg, Al), electrolytic reduction is carried out. Highly unreactive metals such as mercury and copper are obtained simply by heating their ores in air. (v) Refining / purification — the impure metal is purified, usually by electrolytic refining, in which the impure metal is made the anode and a thin strip of pure metal acts as the cathode in an electrolyte solution of the metal salt.
Q2. Explain rusting of iron and methods to prevent it.
Answer: When an iron object is exposed to moist air, a reddish-brown flaky layer of hydrated iron(III) oxide (Fe2O3·xH2O) is formed on its surface. This is called rusting. Both oxygen and water are necessary for rusting. Rusting causes huge economic loss as it weakens iron structures. Methods of prevention: (i) Painting / oiling / greasing — forms a protective layer that prevents contact with air and moisture. (ii) Galvanisation — coating iron with a thin layer of zinc; even if the coating is broken, zinc being more reactive corrodes first and protects iron. (iii) Tin-plating and chromium-plating — using electrolysis to coat iron with tin or chromium. (iv) Alloying — making stainless steel by mixing iron with chromium and nickel, which does not rust. (v) Sacrificial protection — connecting iron with a more reactive metal such as magnesium.
Q3. What are alloys? Why are alloys made? Give the composition and uses of any three common alloys.
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, in fixed proportions. Reasons for making alloys: (i) to increase hardness and strength, (ii) to lower melting point, (iii) to improve resistance to corrosion, (iv) to modify colour and appearance, (v) to reduce electrical conductivity in some cases. Examples: (a) Brass — Cu (70%) + Zn (30%); used for utensils, decorative items, electrical fittings. (b) Bronze — Cu (90%) + Sn (10%); used for making statues, medals, coins. (c) Stainless steel — Fe + Cr (18%) + Ni (8%) + C; used for cutlery, kitchenware, surgical instruments because it does not rust. (d) Solder — Pb + Sn; used for joining electrical wires.
Q4. Explain the reactions of metals with water, oxygen, and dilute acids with suitable examples.
Answer: (a) With oxygen: Metals react with oxygen to form basic oxides. Example: 2Mg + O2 → 2MgO; 4Na + O2 → 2Na2O. Some metal oxides like Al2O3, ZnO are amphoteric. (b) With water: Reactive metals like sodium and potassium react vigorously with cold water to liberate hydrogen and form hydroxide; example 2Na + 2H2O → 2NaOH + H2. Magnesium reacts with hot water; iron reacts only with steam: 3Fe + 4H2O → Fe3O4 + 4H2. Cu, Ag, Au do not react with water. (c) With dilute acids: Metals above hydrogen in the reactivity series displace hydrogen from dilute acids. Example: Zn + 2HCl → ZnCl2 + H2↑; Fe + H2SO4 → FeSO4 + H2↑. Copper, silver, and gold do not react with dilute acids.
Q5. Describe the formation of an ionic compound such as sodium chloride (NaCl) and list the properties of ionic compounds.
Answer: Sodium (2,8,1) has one electron in its outermost shell, while chlorine (2,8,7) needs one electron to complete its octet. The sodium atom transfers its outermost electron to the chlorine atom, forming Na+ (2,8) and Cl– (2,8,8). The two oppositely charged ions are held together by strong electrostatic forces, forming ionic compound NaCl. Properties of ionic compounds: (i) They are solids at room temperature and are usually hard and brittle. (ii) They have high melting and boiling points due to strong ionic bonds. (iii) They are generally soluble in water and insoluble in organic solvents like kerosene and petrol. (iv) They do not conduct electricity in the solid state but do conduct in molten state and in aqueous solution because the ions become free to move. (v) They form crystalline structures.
Additional MCQs
Q1. Which of the following is the most reactive metal?
(a) Iron (b) Copper (c) Potassium (d) Zinc
Answer: (c) Potassium.
Q2. Which gas is evolved when a metal reacts with a dilute acid?
(a) Oxygen (b) Hydrogen (c) Carbon dioxide (d) Chlorine
Answer: (b) Hydrogen.
Q3. Which of the following is an amphoteric oxide?
(a) Na2O (b) MgO (c) Al2O3 (d) CaO
Answer: (c) Al2O3.
Q4. The process of coating iron with zinc is called:
(a) Galvanisation (b) Roasting (c) Calcination (d) Electroplating
Answer: (a) Galvanisation.
Q5. Which one of the following is a non-metal but conducts electricity?
(a) Diamond (b) Graphite (c) Sulphur (d) Phosphorus
Answer: (b) Graphite.
Q6. Which of the following metals is extracted by electrolytic reduction?
(a) Iron (b) Copper (c) Aluminium (d) Zinc
Answer: (c) Aluminium.
Q7. Stainless steel is an alloy of iron with:
(a) Cu and Zn (b) Cr and Ni (c) Sn and Pb (d) Al and Mg
Answer: (b) Cr and Ni.
Q8. Heating a sulphide ore in excess of air is called:
(a) Calcination (b) Roasting (c) Smelting (d) Refining
Answer: (b) Roasting.
Q9. Which is the most malleable metal?
(a) Silver (b) Aluminium (c) Gold (d) Copper
Answer: (c) Gold.
Q10. Which metal does NOT react with dilute hydrochloric acid?
(a) Zn (b) Fe (c) Mg (d) Cu
Answer: (d) Cu.
Fill in the Blanks
Q1. The most abundant metal in the earth’s crust is __________.
Answer: Aluminium.
Q2. Metals are __________ conductors of heat and electricity.
Answer: Good.
Q3. An alloy of mercury with another metal is called __________.
Answer: Amalgam.
Q4. The chemical formula of bauxite is __________.
Answer: Al2O3·2H2O.
Q5. Rusting of iron requires both __________ and __________.
Answer: Air (oxygen) and water (moisture).
True or False
Q1. All metals are solid at room temperature.
Answer: False (Mercury is a liquid at room temperature).
Q2. Gold and silver occur in nature in the free state.
Answer: True.
Q3. Ionic compounds conduct electricity in the solid state.
Answer: False (They conduct only in molten or aqueous form).
Q4. Calcination is carried out for sulphide ores.
Answer: False (Calcination is for carbonate ores; roasting is for sulphide ores).
Q5. Bronze is an alloy of copper and tin.
Answer: True.
Glossary
| Term | Meaning |
|---|---|
| Metal | Element that loses electrons to form positive ions; usually lustrous, malleable, ductile, and a good conductor. |
| Non-metal | Element that gains electrons to form negative ions; generally dull and a poor conductor. |
| Metalloid | Element showing properties of both metals and non-metals (e.g., silicon, germanium). |
| Mineral | Naturally occurring substance containing a metal in combined form. |
| Ore | Mineral from which a metal can be extracted profitably. |
| Gangue | Unwanted impurities (sand, rocky matter) present in an ore. |
| Calcination | Heating a carbonate ore strongly in limited air to convert it into oxide. |
| Roasting | Heating a sulphide ore strongly in excess air to convert it into oxide. |
| Reduction | Process of converting metal oxide into metal by removing oxygen. |
| Reactivity Series | Arrangement of metals in decreasing order of reactivity. |
| Ionic Compound | Compound formed by transfer of electrons between a metal and a non-metal. |
| Corrosion | Slow eating away of metals due to reaction with air, moisture, or chemicals. |
| Galvanisation | Coating iron with a layer of zinc to prevent rusting. |
| Alloy | Homogeneous mixture of two or more metals or a metal and a non-metal. |
| Amalgam | An alloy in which one of the metals is mercury. |
| Electrolytic Refining | Purification of metals by electrolysis using an impure metal anode and a pure metal cathode. |