What are 'energy levels'?  Explain the arrangement and distribution of electrons in the various shells with reference to an atom in general and t o an atom of potassium '19(atomic number ) and 30(relative atomic mass) of K' with special reference to 2n^2 rule. 

Asked by arti | 30th Dec, 2016, 12:57: PM

Expert Answer:

The electrons revolve rapidly round the nucleus in fixed circular paths called energy levels or shells.

  • According to Bohr’s model, electrons occupy certain stable orbits or shells. Each shell has a definite energy.
  • These orbits or shells are represented by the letters K, L, M, N… or the numbers 1, 2, 3, 4…
  • The maximum number of electrons present in the shell is given by the formula (2n2), where n is the orbit number or shell number.
  • The maximum number of electrons in different shells for potassium is as follows:

Atomic number of potassium = 19

    • The first orbit or K shell will have 2 × 12 = 2 electrons.
    • The second shell will have 2 × 22 = 8 electrons.
    • The third shell will have 2 × 32 = 8 electrons.
    • The fourth shell will have 2 × 42 = 1electron



  • The maximum number of electrons which can be accommodated in the outermost orbit is 8.
  • Electrons are not accommodated in a given shell unless the inner shells are filled.

Answered by Vaibhav Chavan | 30th Dec, 2016, 04:18: PM

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