METALS
Physical properties:
- Lustre
- Hardness
- Malleability
- Ductility
- Good conductor of heat and electricity
Chemical properties:
- When metals are burnt in air: Metals combine with oxygen to form metal oxides.
- When metals react with water: Metals react with water to form metal oxide and hydrogen.
- When metals react with acids: Metals react with acids to form salt and hydrogen.
- When metals react with other metal salts: Reactive metals can displace less reactive metals from their compounds in solution form.
Reactivity Series:
The reactivity series of metals is as follows. Reactivity decreases as the series progresses:
K Potassium
Na Sodium
Ca Calcium
Mg Magnesium
Al Aluminium
Zn Zinc
Fe Iron
Pb Lead
H Hydrogen
Cu Copper
Hg Mercury
Ag Silver
Au Gold
REACTION OF METALS AND NON-METALS
Metals and non-metals react to form compounds like ionic compounds.
Ionic compounds: The compounds formed by transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds. The properties of ionic compounds are:
- Physical nature: Ionic compounds are solid, hard and brittle.
- Melting and boiling points: Ionic compounds have high melting and boiling points.
- Solubility: Ionic compounds are generally soluble in water and insoluble in other solvents like kerosene, etc.
- Conduction of electricity: Ionic compounds do not conduct electricity in solid state but in molten state they are good conductors of electricity.
OCCURRENCE OF METALS
Extraction of metals: Metals are extracted from their ore. To extract metals which are low in the reactivity series, their oxides are reduced to metals by heating alone. The metals which are in the middle of the reactivity series are usually found in the form of sulphides and carbonates. These are converted into oxides first and then are extracted from the oxides. The highly reactive metals that are on the top of the reactivity series are obtained by electrolytic reduction.
Enrichment of ores: Ores usually contain large amount of impurities. They have to be enriched first before extracting the metal.
Refining of metals: The metals obtained by various reduction processes are not very pure and have to be further refined to remove the fine impurities. The most widely used method for refining impure metals is electrolytic refining.
Electrolytic refining: in this process, the impure metal is made the anode and pure metal is made the cathode. A solution of the metal salt id used as an electrolyte. When current is passed through the electrolyte, the pure metal from the anode dissolves into the electrolyte and an equivalent amount of pure metal from the electrolyte is deposited on the cathode.
CORROSION
Corrosion is the deterioration of a metal due to its reaction with its surroundings. For e.g. Rusting of iron when it comes in contact with the water vapour in the air.
Prevention of corrosion: There are a number of methods to prevent corrosion. Some of them are:
- Painting
- Oiling
- Greasing
- Galvanising
- Chrome plating
- Alloying