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Explain distribution of electrons in different shells with examples.

Asked by singhaivk05 27th January 2015, 6:59 PM
Answered by Expert

Electrons tend to arrange themselves around nuclei so that they have the lowest possible energy. They would all like to get into the lowest energy level, sometimes called the K-shell, but are prevented from doing so by some rules that pop up in quantum mechanics. You can see how electrons are arranged in a particular atom by taking a look at our Periodic Table of Elements.

Example: The electronic configuration of Oxygen is 1s22s22p4


Thus, there are four shells in an atom namely K, L, M, N. In these shells, electrons are added in a systematical manner with the formula 2N2.

Energy Level


    Number of Electrons

1 (K-shell)



2 (L-shell)

   s, p

     8 (2 in s, 6 in p)

3 (M-shell)

   s, p, d

     18 (2 in s, 6 in p, 10 in d)

4 (N-shell)

   s, p, d, f

     32 (2 in s, 6 in p, 10 in d, 14 in f)

The rules of placing electrons within shells is known as the Aufbau principle. These rules are:

  1. Electrons are placed in the lowest energetically available subshell.
  2. An orbital can hold at most 2 electrons.
  3. If two or more energetically equivalent orbitals are available (example, p and d) then electrons should be spread out before they are paired up (Hund’s rule).
Answered by Expert 28th January 2015, 11:28 AM
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