- Elements can be classified as metals and non-metals on the basis of their properties.
- Examples of some metals are: Iron (Fe), Aluminium (Al), Silver (Ag), Copper (Cu)
- Examples of some non-metals are: Hydrogen (H), Nitrogen (N), Sulphur (S), Oxygen (O)
PHYSICAL PROPERTIES
CHEMICAL PROPERTIES OF METALS
REACTION OF METALS WITH AIR
- Metals combine with oxygen to form metal oxide.
- Metal + O2 → Metal oxide
Examples:
(i) 2Cu + O2 → 2CuO Copper oxide (black) (ii) 4Al + 3O2 → 2Al2O3 Aluminium oxide (iii) 2Mg + O 2 → 2MgO - The reactivity of different metals are different with O2.
- Na and K react so vigorously that they catch fire if kept in open so they are kept immersed in kerosene.
- Surfaces of Mg, Al, Zn, Pb are covered with a thin layer of oxide which prevent them from further oxidation.
- Fe does not burn on heating but iron fillings burn vigorously.
- Cu does not burn but is coated with black copper oxide.
- Au and Ag does not react with oxygen.
AMPHOTERIC OXIDES
- Metal oxides which react with both acids as well as bases to produce salts and water are called amphoteric oxides.
- Examples:
(i) Al2O3 + 6HCl → 2AlCl3 + H2O
(ii) Al2O3 + 2NaOH → 2NaAlO2 + H2O Sodium Aluminate
REACTION OF METALS WITH WATER
- Metal + Water → Metal oxide + Hydrogen
- Metal oxide + Water → Metal hydroxide
- Examples:
(i) 2Na + 2H2O → 2NaOH + H2 + Heat
(ii) Ca + 2H2O → Ca(OH)2 + H2
(iii) Mg + 2H2O → Mg(OH)2 + H2
(iv) 2Al + 3H2O → Al2O3 + 3H2
(v) 3Fe + 4H2O → Fe3O4 + 4H2
REACTION OF METALS WITH ACIDS(DILUTE)
- Metal + Dilute acid → Salt + H2
- Cu, Ag, Hg do not react with dil. acids.
- Examples:
(i) Fe + 2HCl → FeCl2 + H2
(ii) Mg + 2HCl → MgCl2+ H2
(iii) Zn + 2HCl → ZnCl2 + H2
(iv) 2Al + 6HCl → 2AlCl3 + 3H2
REACTION OF METALS WITH SOLUTIONS OF OTHER METAL SALTS
- Metal A + Salt solution B
- Salt solution A + Metal B
- Reactive metals can displace less reactive metals from their compounds in solution form.
- Fe + CuSO4→ FeSO4 + Cu
REACTIVITY SERIES
REACTION OF METALS WITH NON-METALS
- Reactivity of elements is the tendency to attain a completely filled valence shell.
- Atoms of the metals lose electrons from their valence shell to form cation. Atom of the non-metals gain electrons in the valence shell to form anion.
- E.g.: Formation of NaCl
Sodium cation Na → Na+ + e- 2, 8, 1 2, 8
Chloride anion Cl + e- → Cl- 2, 8, 7 2, 8, 8
IONIC COMPOUNDS
FORMATION OF IONIC COMPOUNDS
(i) Physical nature: They are solid and hard, generally brittle.
(ii) Melting and Boiling Point: They have high melting and boiling point.
(iii) Solubility : Generally soluble in water and insoluble in solvents such as kerosene, petrol etc.
(iv) Conduction of electricity : Ionic compounds conduct electricity in molten and solution form but not in solid state.
OCCURENCE OF METALS
(i) Minerals: The elements or compounds which occur naturally in the earth’s crust are called minerals.
(ii) Ores: Minerals that contain very high percentage of particular metal and the metal can be profitably extracted from it, such minerals are called ores.
EXTRACTION OF METALS FROM ORES
- Step 1. Enrichment of ores.
- Step 2. Extraction of metals.
- Step 3. Refining of metals.
- Steps Involved in Extraction of Metals from Ores
Gangue → Roasting → Calcination → Reduction
IMPORTANT TERMS
(a) Gangue : Ores are usually contaminated with large amount of impurities such as soil, sand etc. called gangue.
(b) Roasting : The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is called roasting.
2ZnS + 3O2 →(Heast) 2ZnO + 2SO2
(c) Calcination : The carbonate ores are changed into oxides by heating strongly in limited air. This process is called calcination.
ZnCO3 →(Heat) ZnO + CO2
(d) Reduction : Metal oxides are reduced to corresponding metals by using reducing agent like carbon.
ZnO + C → Zn + CO
REFINING OF METALS
- The most widely used method for refining impure metal is electrolytic refining.
(i) Anode : Impure copper
(ii) Cathode : Strip of pure copper
(iii) Electrolyte : Solution of acidified copper sulphate - On passing the current through the electrolyte, the impure metal from anode dissolves into the electrolyte.
- An equivalent amount of pure metal from the electrolyte is deposited at the cathode.
- The insoluble impurities settle down at the bottom of the anode and is called anode mud.
CORROSION
- The surface of some metals get corroded when they are exposed to moist air for a long period of time. This is called corrosion.
- Examples: (i) Silver becomes black when exposed to air as it reacts with air to form a coating of silver sulphide. (ii) Copper reacts with moist carbon dioxide in the air and gains a green coat of copper carbonate. (iii) Iron when exposed to moist air acquires a coating of a brown flaky substance called rust.
PREVENTION OF CORROSION
- The rusting of iron can be prevented by painting, oiling, greasing, galvanizing, chrome plating, anodizing or making alloys.
- Galvanization : It is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
- Alloy : An alloy is a homogeneous mixture of two or more metals or a metal and a non- metal.
- Examples of alloy:
(i) Iron : Mixed with small amount of carbon becomes hard and strong.
(ii) Steel : Iron + Nickel and chromium
(iii) Brass : Copper + Zinc
(iv) Bronze : Copper + Tin (Sn)
(v) Solder : Lead + tin
(vi) Amalgam : If one of the metal is mercury (Hg).