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Home › Grade8 › Grade 8 CBSE › Chemistry › Materials: Metals and Non-Metals › Materials: Metals and Non-Metals Notes › Elements

Elements

ELEMENTS

  • There are about 118 chemical elements known at present of which only 98 elements are known to occur naturally on earth.
  • Based upon their properties elements are classified into two main groups :

      1.  Metals

      2. Nonmetals

 

Physical properties of metals:

  1. Malleability:
  • Metals can be beaten into thin sheets with a hammer.

For example: 

  • Gold, Silver, Aluminum, Copper etc are malleable metals and they can be beaten into thin sheets.
  • Silver foil is used for decorating sweets, Aluminium foil is used for wrapping food.

  1. Ductility:
  • Metals can be drawn into thin wires.

For example:

  • Gold, Silver, Copper, Aluminium etc. can be drawn into thin wires.

  1. Electrical conductivity:
  • Metals are good conductors of electricity because they contain, free electrons and these electrons conduct the electricity.
 
  1. Thermal conductivity:
  • Metals are good conductors of heat and are therefore used for making cooking utensils.
 
  1. Metals are sonorous:
  • Metals produce ringing sound when struck with an object.
  • Metals are solids at room temperature. (Except Hg which is liquid at room temperature)
 
  1. Hardness:
  • Metals are hard with and have high Melting and Boiling point.

For example:

  • M.P. of Aluminium is 660º C, Gold  1063º C, Copper 1083º C

Exceptions:

  •  Sodium (Na) and Potassium (K) are soft and can be cut with Knife.
  •  The metal with the lowest melting point is mercury - the only metallic element with a melting point (–40º C) below room temperature (20º C) .
  • Gallium melts at 86º F (30º C) which would be liquid on a warm day or in your hand.
 
  1. Metals have high densities.

 

Physical properties of non metals:

Proprieties of nonmetals are exactly opposite to the properties of metals:

  1. Non metals are brittle: They break into pieces when hammered with an object.

Graphite

  1. Non metals are non-ductile: Non metals cannot be drawn into thin wires.
  2. Non metals are bad conductors of heat and electricity: Except carbon (graphite)
  3. Non metals are not sonorous, they are non lustrous.
  4. Non metals may be solid, liquid and gases at room temperature.

 

Examples:

  • Chlorine, Oxygen, Nitrogen, Hydrogen