CBSE Class 10 Science Metals and Non-metals Notes Set 07

1. Physical properties

Metals are generally hard, lustrous, malleable (beaten into sheets), ductile (drawn into wires), good conductors of heat and electricity, sonorous and have high melting points. Exceptions are mercury (liquid), sodium and potassium (soft, cut with a knife), and lead and mercury (poor conductors of heat). Silver is the best conductor and gold is the most malleable and ductile.

Non-metals are usually brittle, dull and poor conductors, with low melting points. Exceptions are graphite (conducts electricity), diamond (hardest natural substance, very high melting point), iodine (lustrous) and bromine (liquid).

2. Chemical properties of metals

1. With oxygen: metals form basic oxides, for example 2Cu + O₂ → 2CuO. Aluminium and zinc form amphoteric oxides, which react with both acids and bases. Sodium and potassium are kept in kerosene, while magnesium burns with a dazzling white flame.

2. With water: sodium and potassium react violently with cold water, calcium reacts less vigorously, magnesium reacts with hot water, and aluminium, iron and zinc react with steam to form oxide and hydrogen. Example: 2Na + 2H₂O → 2NaOH + H₂. Lead, copper, silver and gold do not react.

3. With dilute acids: metals above hydrogen displace it, for example Mg + 2HCl → MgCl₂ + H₂. Nitric acid is a strong oxidising agent and generally does not release hydrogen. Aqua regia, a 3:1 mixture of concentrated HCl and HNO₃, dissolves gold and platinum.

4. With salt solutions: a more reactive metal displaces a less reactive one, for example Zn + CuSO₄ → ZnSO₄ + Cu.

3. Reactivity series

From most to least reactive: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au. The series is used to predict displacement reactions and to choose the method of extraction.

4. Ionic compounds

A metal atom loses electrons and a non-metal atom gains electrons to reach a stable octet. The oppositely charged ions attract to form an ionic bond. In NaCl, Na gives one electron to Cl, forming Na⁺ and Cl⁻. In MgCl₂, one Mg atom gives one electron to each of two Cl atoms. Ionic compounds are hard crystalline solids, have high melting and boiling points, are soluble in water but not in organic solvents, and conduct electricity in molten or aqueous state.

5. Occurrence and extraction of metals

A mineral is a natural source of a metal, and an ore is a mineral from which the metal can be obtained profitably. Unwanted earthy impurities in an ore are called gangue.

1. Metals high in the series (K, Na, Ca, Mg, Al) are extracted by electrolysis of their molten chlorides or oxides. Example: at the cathode Na⁺ + e⁻ → Na.

2. Metals in the middle (Zn, Fe, Pb) are obtained from oxides. Sulphide ores are roasted: 2ZnS + 3O₂ → 2ZnO + 2SO₂. Carbonate ores are calcined. The oxide is reduced with carbon: ZnO + C → Zn + CO.

3. Metals low in the series (Hg, Cu) can be obtained by heating their sulphides: 2HgS + 3O₂ → 2HgO + 2SO₂, then 2HgO → 2Hg + O₂.

Thermit reaction, Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + heat, gives molten iron used to join railway tracks. Impure copper is refined electrolytically: the impure copper is the anode, pure copper is the cathode and the electrolyte is acidified copper sulphate solution.

6. Corrosion and alloys

Iron rusts in the presence of air and moisture. Rusting is prevented by painting, oiling, galvanisation (coating with zinc), chrome plating and making alloys. An alloy is a homogeneous mixture of a metal with other metals or non-metals. Alloying improves strength and resistance to corrosion. Brass is copper and zinc, bronze is copper and tin, solder is lead and tin, and stainless steel is iron with nickel and chromium.

Worked examples

Example 1. Will iron displace copper from copper sulphate solution?

Iron is above copper in the reactivity series, so yes. Fe + CuSO₄ → FeSO₄ + Cu. The blue solution turns pale green and a reddish brown deposit forms.

Example 2. Show the formation of MgCl₂ using electron transfer.

Mg (2, 8, 2) loses its two outer electrons to become Mg²⁺ (2, 8). Each Cl (2, 8, 7) gains one electron to become Cl⁻ (2, 8, 8), so two chlorine atoms are needed. The ions combine in the ratio 1:2 giving MgCl₂.

Example 3. A metal X is found as a sulphide ore. Outline how it is converted to the metal if it lies in the middle of the series.

The ore is first roasted in excess air to change the sulphide into oxide with release of SO₂. The oxide is then reduced with carbon to give the free metal.

Quick Check Questions

Answer these five questions to test your understanding of the chapter.