What are Elements in chemistry

Updated on Jan. 8, 2021 03:22 PM IST by Lakshmi Arya

Robert Boyle was the first scientist to use the term element in 1661. Antoine L. Lavosier defined an element as basic form of matter that can not be broken down into simpler substances by chemical reactions. Elements contain atoms of only one type. At present,118 elements are known to us.All these have different properties.
Elements can be classified as metals , non metals and metalloids on the basis of their properties.

Properties of Metals:-

  1. Metallic lustre:- Metals have a shining surface in their pure state.
  2. Malleability:- Metals can be hammered or beaten into thin sheets. Gold and silver are the most malleable metals.
  3. Ductility:- Metals can be drawn into thin wires.Gold is the most ductile metal.one gram of gold can be drawn into 2km length of wire.
  4. Metals can conduct heat and electricity. Silver and copper are the best conductors of heat.
  5. Sonorous:- Metals make a sound on striking a hard surface.
  6. Metals are generally hard (solid) but not brittle.Mercury is the only metal that is liquid at room temperature.Gallium and cesium 
  7. become liquid at a temperature slightly above room temperature (303K).
  8. Metals generally have silvery-grey or golden- yellow colour.
  9. Metals in vapour state are monoatomic.
  10. Metallic oxides are basic in nature.
  11. Gold, silver, copper,iron, sodium, potassium etc.are some  examples of metals.  

Properties of Non metals:--

  1. Non metals are not lustrous, sonorous, malleable and ductile.
  2. Metals are poor conductors of heat and electricity.
  3. Metals display a variety of colours.
  4. Non metals are  polyatomic in vapour state. Example- O2  ,O3, N2.
  5. Non metallic oxides are acidic in nature.
  6. Hydrogen, iodine, carbon, bromine, chlorine etc.are some examples of non metals.

CHEMICAL PROPERTIES OF METALS:-

  1. Reaction of metals with Air :-

              Metals combine with oxygen to form metal oxide. Metal + O2 --> Metal oxide
              Examples: (i) 2Cu + O2 --> 2CuO
                                (ii) 4Al +3O2 --> 2Al2O3
              Different metals show different reactivities towards O2.
             a) Na and K react so vigorously that they catch fire if kept in open so they are kept immersed in kerosene oil.
             b) Mg, Al, Zn and Pb react slowly with air. These elements are covered with a thin layer of oxide.
             c) Fe does not burn on heating but iron filings burn vigorously.
             d) Cu does not burn but is coated with black copper oxide.
             e) Ag(Silver) and Au(Gold) do not react with oxygen.

        2. Reaction of metals with water :-
                Metal + Water --> Metal oxide + Hydrogen
                Metal oxide + Water --> Metal hydroxide

                Some Examples -

                1. 2Na + 2H2O --> 2NaOH + H2 + Heat

                2. Mg + 2H2O --> Mg(OH)2 + H2 Examples

                3. 2Al + 3H2O --> Al2O3 + 3H2

Amphoteric Oxides :-

Metal oxides which react with both acids as well as bases to produce salt and water are called Amphoteric Oxides.
Examples : Zinc and Aluminium oxides.

  1. Al2O3 + 6HCl --> 2AlCl3 + H2O
  2. Al2O3 + 2NaOH --> 2NaAlO2 +H2O

 

 

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