CBSE Class 10 Chemistry Metals and Non-metals Notes Set 22

Ionic Compounds

When a metal atom gives electrons to a non-metal atom, the two become oppositely charged ions held by electrostatic attraction. This is an ionic (electrovalent) bond. In NaCl, Na gives one electron to Cl, forming \( \ce{Na+} \) and \( \ce{Cl-} \).

1. Ionic compounds are hard, brittle solids with high melting and boiling points because the attraction between ions is strong.
2. They dissolve in water but not in organic solvents.
3. They conduct electricity when molten or dissolved because ions are free to move, but not as solids.

Occurrence and Extraction of Metals

1. A mineral is a natural compound of a metal. An ore is a mineral from which the metal can be extracted economically. Impurities such as sand and clay are called gangue.
2. Enrichment (concentration) removes gangue. Gravity separation (levigation), froth flotation (for sulphide ores) and magnetic separation are used.
3. Roasting heats a sulphide ore in air to give the oxide, and calcination heats a carbonate ore in limited air.
4. Reduction of the oxide: moderately reactive metals (Zn, Fe, Pb) by carbon. Highly reactive metals (Na, Mg, Ca, Al) by electrolysis of the molten compound. Metals low in the series such as mercury by heating the sulphide in air.
5. Refining: the impure metal is made the anode and pure metal the cathode in a suitable salt solution. Copper is refined this way.
6. Thermite reaction: aluminium reduces iron oxide and the hot molten iron is used to weld railway tracks. \( \ce{Fe2O3 + 2Al -> Al2O3 + 2Fe} \).

Corrosion and Alloys

1. Rusting needs both air and moisture. Rust is hydrated iron(III) oxide, \( \ce{Fe2O3.xH2O} \). Prevention includes painting, oiling, galvanising (zinc coating) and alloying.
2. Aluminium forms a protective oxide layer that stops further corrosion.
3. An alloy is a homogeneous mixture of a metal with other metals or non-metals. Brass is copper and zinc, bronze is copper and tin, and stainless steel is iron with chromium, nickel and carbon.
4. Alloys are usually harder and more resistant to corrosion than the pure metal.