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Electron arrangement in atom

Atoms Molecules Ions Chemical Equations On-line practice

 

 

  1. Electrons are arranged around the nucleus in shells.
  2. Each shell is numbered 1, 2, 3 and so on, going outwards from the nucleus.
  3. Each shell can hold a certain maximum number of electrons.
  4. For the first 20 elements, the max. no. of electrons that can go into the first shell is 2, the second shell is 8 and the third shell is also 8.
  5. For atoms more than 20 electrons, the third shell can take up to 18 electrons. 

              On Period 1 (2 elements only)

           On Period 2 ........ (3 of the 8 elements)

           On Period 3 ....   (3 of the 8 elements)

                 On Period 4 ===> Kr [2.8.18.8],

 

Finding electron arrangement ] Outer electrons ]