State how electrons are distributed in an atom. Explain in brief the rules which govern their distribution.

Electrons revolve around the nucleus in imaginary paths called orbits or shells. Different Orbits are K shell [first shell, n=1], L shell [second shell, n=2] M, N…… etc.

Rules governing the distribution of electrons are summarized below:

1. The maximum number of electrons in each shell or orbit is determined by the formula 2n², where n is the number of shell.
   K shell, n=1, no. of electrons = 2 x 1² = 2
   L shell, n=2, no. of electrons = 2 x 2² = 8
   M shell, n=3, no. of electrons = 2 x 3² = 18
2. Electrons are not accommodated in a given shell, unless the inner shells are filled. Shells are filled in step-wise manner.
3. The atom's outermost shell needs 2 electrons for stability (duplet rule) if it has only one shell. If it has multiple shells, it requires 8 electrons (octet rule) in the outermost shell for stability.