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Classification of Elements, Minerals and Ores- Chemistry Guide for Class 8

Classification of Elements

Information about Classification of Elements

Title

Classification of Elements, Minerals and Ores

Class

Class 8

Subject

Class 8 Chemistry

Topics Covered

  • Classification of Elements
  • Occurence of Elements
  • Minerals and Ores

  • Materials, made up of same kind of particles, are known as pure substances.
  • A sample, of a given element, or a given compound, is a 'pure substance'. This is because a given element (/compound) is made up of atoms (/molecules) of the same kind.
  • Different elements/compounds differ from each other in their physical and chemical properties as they are made up of atoms/molecules of different kind. 

Classification of Elements

  • There are about 118 elements known at present. It is difficult to study and describe all the properties of all these elements separately. Hence, elements, showing similar properties, are grouped together and their general characteristics are studied. Such 'grouping' of elements is called classification of elements.
  • The elements have been broadly classified into two categories: metals and non-metals; this classification is based on the differences in their physical and chemical properties.

Occurrence of Elements

  • Metals exist in abundance in the earth's crust. Aluminium is the most abundant metal; it is followed by iron.
  • Highly reactive metals, like sodium, potassium, aluminium and zinc, are found in nature in the form of their compounds (like oxides, sulphides and carbonates).
  • Less reactive metals, like gold, silver and platinum, occur in nature in their elemental, or native state. 
  • Many non-metals are found in their free state in the atmosphere. Oxygen and nitrogen are two well known examples of such non-metals.
  • Several non-metals exist in nature in the form of their compounds (like oxides and nitrates).
  • Sulphur exists in the free state as well as in the combined state (as sulphides and sulphates).
  • Carbon exists in its native state as diamond, graphite and fullerene; it also exists in the form of its compounds like carbon dioxide, carbonates and bicarbonates.

Minerals and Ores 

  • A mineral is a naturally occuring inorganic substance found deep under the surface of the earth.
  • An ore is a mineral from which one or more metals can be extracted profitably.
    For example, aluminium is extracted from its bauxite ore and iron from its haematite ore.
  • The sequence of processes, used to extract a metal, in its pure form from its ore, is called metallurgy.
The extraction of a metal, from its ore, generally involves the following steps: 
  1. Concentration of ore: It is the process of removal of impurities from the ore. 
  2. Reduction: It is the process of 'treating the metal ore' to get the metal in its free state. 
  3. Refining of metal: The metal, obtained by reduction, is generally impure. Refining is the process of purification of this impure metal.

Some Important Terms

  • Alloy: A homogenous mixture of two or more metals, or a metal and a non-metal.
  • Conductivity: The ability of a material to transfer heat energy, or electrical current, from one point to another.
  • Ductility: The property of metals due to which they can be drawn into thin wires.
  • Malleability: The property of metals due to which they can be hammered into thin sheets.
  • Metalloid: Elements which show (some) properties of metals as well as non-metals
  • Metallurgy: The sequence of processes used to extract a metal from its ore in its pure form.
  • Mineral: A natural occuring inorganic substance found deep under the surface of earth.
  • Noble metals: Those metals which are least reactive and so are not chemically affected by the substances around them. 
  • Ore: It is a mineral from which one, or more, metals can be extracted.
  • Reactivity: The tendency of an element to react with other substances to form compounds.
  • Reactivity series: The series of metals arranged in the order of their decreasing reactivity.
  • Sonorosity: The property of metals to produce sound when struck with something hard.
  • Tensile strength: The property, due to which a substance can bear a lot of strain, without breaking.

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