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CBSE-IX-Science

11: 2-Structure of the Atom

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  • #6
    Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
    Ans : The following rules are followed for writing the number of electrons in different energy levels or shells:

    (i) The maximum number of electrons present in a shell is given by the formula, where ‘n’ is the orbit number or energy level index, 1,2,3,... Hence the maximum number of electrons in different shells are as follows:

    first orbit or K-shell will be,

    second orbit or L-shell will be,

    third orbit or M-shell will be,

    fourth orbit or N-shell will be, and so on.

    (ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.

    (iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.