Notes On Occurrence of Metals - CBSE Class 12 Chemistry

Most metals are found in nature in a combined state, owing to their high reactivity. Metals found in a combined state in the earth's crust are known as minerals. Only those minerals that have a relatively high concentration of metal and can be extracted in an easy and cost-effective process are called ores.

The only metals found in free (or) native state are gold and platinum. They are usually found along with earthly (or) rocky impurities such as sand and clay in the earth's crust.

The relative abundance of metals varies in the earth's crust.

Relative abundance of some of the metals in the earth's crust by weight:

  Metal          Relative Abundance
         by Weight %
  Al
  Fe
  Ca
  Na
  Mg
  K
  Ti
         8.23
         5.80
         4.15
         2.36
         2.23
         2.09
         0.46












Aluminium and Iron are relatively more abundant than others. Aluminium constitutes about 8%, while iron constitutes 5.8 % by weight of the earth's crust.

Thus, aluminium is the most abundant metal and Iron the second most abundant metal by weight in the earth's crust. Also, aluminium is the 3rd most abundant element and Iron the 4th most abundant element by weight of the earth's crust.

The principal ores of some important metals, and their composition:

     Metal             Ores            Composition
Aluminium (Al) Bauxite,
kaolinite (A Form of Clay)
AlOx(OH)3-2x [Where 0<x<1]
Al2(OH)4Si2O5
Iron (Fe) Haematite
Magnetite
Siderite
Iron pyrites
Fe2O3
Fe3O4
FeCO3
FeS2
Copper (Cu) Copper pyrites
Malachite
Cuprite
Copper glance
CuFeS2
CuCO3.Cu(OH)2
Cu2O
Cu2S
Zinc (Zn) Zinc blende or Sphalerite
Calamine
Zincite
ZnS
ZnCO3
ZnO

Both aluminium and iron are used widely in industrialised nations. Naturally occurring aluminium is a major component of silicates such as mica and clay. Aluminium is extracted mainly from its principal ore bauxite.

Valuable gem stones such as rubies and sapphires contain aluminium oxides along with traces of transition metals as impurities. Rubies are crystalline forms of aluminium oxide, which are red in colour due to the presence of chromium as an impurity. Sapphires are available in various shades owing to the presence of impurities such as nickel, cobalt and titanium.

Iron is mainly extracted from its oxide ores such as haematite and magnetite. The iron extracted from these ores is mostly used in the manufacture of steel an alloy of iron. Iron is also an essential element found in biological systems.

Other metals that are extensively used are copper and zinc.

Summary

Most metals are found in nature in a combined state, owing to their high reactivity. Metals found in a combined state in the earth's crust are known as minerals. Only those minerals that have a relatively high concentration of metal and can be extracted in an easy and cost-effective process are called ores.

The only metals found in free (or) native state are gold and platinum. They are usually found along with earthly (or) rocky impurities such as sand and clay in the earth's crust.

The relative abundance of metals varies in the earth's crust.

Relative abundance of some of the metals in the earth's crust by weight:

  Metal          Relative Abundance
         by Weight %
  Al
  Fe
  Ca
  Na
  Mg
  K
  Ti
         8.23
         5.80
         4.15
         2.36
         2.23
         2.09
         0.46












Aluminium and Iron are relatively more abundant than others. Aluminium constitutes about 8%, while iron constitutes 5.8 % by weight of the earth's crust.

Thus, aluminium is the most abundant metal and Iron the second most abundant metal by weight in the earth's crust. Also, aluminium is the 3rd most abundant element and Iron the 4th most abundant element by weight of the earth's crust.

The principal ores of some important metals, and their composition:

     Metal             Ores            Composition
Aluminium (Al) Bauxite,
kaolinite (A Form of Clay)
AlOx(OH)3-2x [Where 0<x<1]
Al2(OH)4Si2O5
Iron (Fe) Haematite
Magnetite
Siderite
Iron pyrites
Fe2O3
Fe3O4
FeCO3
FeS2
Copper (Cu) Copper pyrites
Malachite
Cuprite
Copper glance
CuFeS2
CuCO3.Cu(OH)2
Cu2O
Cu2S
Zinc (Zn) Zinc blende or Sphalerite
Calamine
Zincite
ZnS
ZnCO3
ZnO

Both aluminium and iron are used widely in industrialised nations. Naturally occurring aluminium is a major component of silicates such as mica and clay. Aluminium is extracted mainly from its principal ore bauxite.

Valuable gem stones such as rubies and sapphires contain aluminium oxides along with traces of transition metals as impurities. Rubies are crystalline forms of aluminium oxide, which are red in colour due to the presence of chromium as an impurity. Sapphires are available in various shades owing to the presence of impurities such as nickel, cobalt and titanium.

Iron is mainly extracted from its oxide ores such as haematite and magnetite. The iron extracted from these ores is mostly used in the manufacture of steel an alloy of iron. Iron is also an essential element found in biological systems.

Other metals that are extensively used are copper and zinc.

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