2) Chemical properties of metals :i) Reaction with oxygen :Metals react with oxygen to form metal oxides.
When copper is heated it combines with oxygen to form copper oxide.
2Cu + O2
When aluminium is heated it combines with oxygen to form aluminium
oxide. 4Al + 3O2
Some metal oxides are basic oxides because they react with water to
4Na + O2
Na2O + H2O
K + O2
K2O + H2O
Some metal oxides show acidic and basic properties. They are called
amphoteric oxides. Eg :- Aluminium oxide, Zinc oxide etc.
Al2O3 + 6HCl
2AlCl3 + 3H2O
Al2O3 + NaOH
NaAlO2 + H2O
The reactivity of different metals with oxygen is different :-
ii) Reaction with water :Metals react with water to form metal oxides or metal hydroxides and
2Na + 2H2O
2NaOH + H2
2K + H2O
2KOH + H2
Ca + H2O
Ca(OH)2 + H2
2Al + 3H2O
Al2O3 + H2
3Fe + 4H2O
Fe2O3 + 4H2
The reactivity of different metals with water is different :- Sodium and potassium react violently with cold water to form sodium
hydroxide and hydrogen and catches fire.
- Calcium reacts less violently with water to form calcium hydroxide
and water and does not catch fire.
- Magnesium reacts only with hot water to form magnesium hydroxide
- Metals like aluminium, iron and zinc react only with steam to form
the metal oxides and hydrogen.
- Metals like lead, copper, silver and gold do not react with water.
iii) Reaction with acids :Metals react with dilute acids to form salts and hydrogen.
Mg + 2HCl
MgCl 2 + H2
2Al + 6 HCl
2AlCl 3 + 3H2
Zn + 2HCl
ZnCl 2 + H2
Fe + 2HCl
FeCl 2 + H2
The reactivity varies from metal to metal. For the above
metals the decreasing order of reactivity is Mg > Al > Zn > Fe.
Copper, silver and gold do not react with dilute HCl.
Hydrogen gas is not evolved when metals react with
nitric acid (HNO3) because it is a strong oxidising agent and
it oxidises the H2 produced to water and is itself reduced to
oxides of nitrogen.
3Cu + 8HNO3
3Cu(NO3)2 + 4H2O + 2NO2
iv) Reaction of metals with metal salt solutions :A more reactive metal displaces a less reactive metal from its salt
solution. (Displacement reaction)
Magnesium displaces copper from copper sulphate solution.
Mg + CuSO4
MgSO4 + Cu
Zinc displaces copper from copper sulphate solution.
Zn + CuSO4
ZnSO4 + Cu
Iron displaces copper from copper sulphate solution
Fe + CuSO4
FeSO4 + Cu
after 15 – 20 minutes
5a) Formation of sodium chloride molecule – NaCl
AN = 11
EC = 2,8,1
AN = 17
EC = 2,8,7
The atomic number of Na is 11, its electronic
configuration is 2,8,1, it has 1 valence electron, it loses 1
electron to form Na + ion. The atomic number of Cl is 17, its
electronic configuration is 2,8,7, it has 7 valence electrons,
it gains 1 electron to form Cl - ion. Then the attraction
between the Na + ion and Cl - ion results in the formation of
sodium chloride molecule – NaCl.
b) Formation of Magnesium chloride molecule – MgCl2
AN = 12
EC = 2,8,2
Cl + 1e AN = 17
EC = 2,8,7
+ 2e -
The AN of Mg is 12, its EC is 2,8,2, it has 2 valence electrons, it loses
2 electrons to form Mg 2+ . The AN of Cl is 17, its EC is 2,8,7, it has 7
valence electrons, it gains 1 electron to form Cl -. Then the attraction
between Mg 2+ ion and 2 Cl - ions results in the formation of Magnesium
chloride molecule – MgCl .
6) Ionic compounds (Electrovalent compounds) :Ionic compounds are compounds formed by the transfer of
electrons from a metal to a non metal.
Properties of ionic compounds :i) They are formed by the transfer of electrons and are made up of
i) They are crystalline solids.
ii) They have high melting points and boiling points.
iii) They are soluble in water but insoluble in organic solvents (like
petrol, kerosene etc.)
iv) They conduct electricity in molten state or in solution.
7a) Occurence of metals :Some metals like gold, silver, platinum etc are found in the free
state in the earth’s crust because they are least reactive. Most metals
are found as oxides, carbonates, sulphides, halides etc.
Minerals :- are elements or compounds which occur naturally inside
the earth’s crust.
Ore :- is a mineral from which metals can be extracted profitably.
Gangue :- is the impurities present in the ore like rock particles,
sand particles, clay particles etc.
b) Extraction of metals from their ores :Metals are extracted from their ores in three main steps. They are :i) Concentration of the ore (Enrichment of the ore).
ii) Reduction to the metal.
iii) Refining (Purification of the metal).
Concentration of the ore :- is the removal of gangue (impurities)
from the ore by different methods.
8) Steps involved in the extraction of metals from their ores :Ore
Oxide of metal
Reduction to metal
i) Extraction of metals low in the activity series :Metals which are low in the activity series can be
reduced to the metals by heating in the presence of oxygen
Eg :- Mercury is obtained from its ore Cinnabar (HgS) by
heating in the presence of oxygen. When it is heated in the
presence of oxygen it is first converted into mercuric oxide
(HgO) and on further heating it is reduced to mercury.
2HgS + 3O2
2HgO + 2O 2
2Hg + O 2
Copper is obtained from its sulphide ore (CuS) by
heating in the presence of oxygen.
2CuS + 3O2
2Cu2O + 2SO2
2Cu2O + Cu2S
6Cu + SO 2
ii) Extraction of metals in the middle of the activity series :
Metals in the middle of the activity series like Zn, Fe, Pb, are found as
oxide, sulphide or carbonate ores.
It is easier to obtain metals from their oxides than from their
sulphides or carbonates. So non oxide ores are converted into oxide
form before reduction. Non oxide ores can be converted into oxide form
by roasting or calcination.
Roasting :- is heating of an ore in the presence of oxygen. It is used to
convert suphide ores into oxide form.
Eg :- 2 ZnS + 3O2
2 ZnO + 2SO2
Calcination :- is heating of an ore in the absence of oxygen. It is used to
convert sulphide ores into oxide form.
Eg :- ZnCO3
ZnO + CO2
The oxide ore is then reduced to the metal by heating with a reducing
agent. The most common reducing agent is coke (carbon).
Eg :- ZnO + C
Zn + CO
iii) Extraction of metals at the top of the activity series :Metals at the top of the activity series like K, Na, Ca, Al etc. cannot
be obtained from their ores by simple heating or by heating with
reducing agents. They are obtained by electrolytic reduction of their
Eg :- When electric current is passed through molten sodium
chloride, sodium metal is deposited at the cathode and chlorine gas is
deposited at the anode.
At cathode :- Na + + e At anode :-
Na (Sodium metal)
Cl2 + 2e - (Chlorine gas)
9) Refining of metals :The removal of impurities from the metal to obtain the pure metal is
called refining of metals. The most common method for refining of
metals is electrolytic refining.
In this method a block of the impure metal is made the anode and a
thin sheet of the pure metal is made the cathode. The electrolyte is a salt
solution of the metal to be purified.
Eg :- In the electrolytic refining of copper, a block of impure copper is
made the anode and a thin sheet of pure copper is made the cathode.
The electrolyte is acidified copper sulphate solution. When electric
current is passed through the electrolyte, pure copper from the anode is
deposited at the cathode and the impurities settle down as anode mud.
10a) Corrosion :Corrosion is the damage caused to metals due to the reaction of metals
with oxygen, moisture, carbon dioxide etc.
Eg :- Formation of brown coating of rust over iron.
Formation of green coating of basic copper carbonate over copper.
Formation of black coating of silver sulphide over silver.
To show that air and moisture are necessary for the rusting of iron :Take three test tubes marked 1,2,3 and put iron nails in each of them. Put some
anhydrous calcium chloride in test tube 1 to absorb moisture. Pour some boiled distilled
water in test tube 2 and pour some oil over it to prevent air into the test tube. Pour some
water in test tube 3. Cork the test tubes and leave them for a few days. The nails in test
tube 1 does not get rusted because it had only air and no water. The nails in test tube 2
does not rust because it had only water and no air. The nails in test tube 3 gets rusted
because it had air and water.
b) Prevention of corrosion :Corrosion of metals can be prevented by :i) Applying oil or grease.
ii) Applying paint.
iii) By galvanisation. (Coating with zinc)
iv) By tinning. (Coating with tin)
v) By electroplating. (Coating a less reactive metal like chromium)
vi) By alloying. (Making alloys)
c) Alloy :An alloy is a homogeneous mixture of a metal with other metals or
Eg :- Steel – iron, carbon
Stainless steel – iron, carbon, cobalt, nickel
Brass – copper, zinc
Bronze – copper, tin
Solder – Lead, tin (used for welding electrical wires together)
If one of the metals in an alloy is mercury, it is called an amalgam.