Question

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

Answer 1

(a) Electrons revolve around the nucleus in imaginary paths called shells or orbits. Shells start from the nucleus to outwards.

Rules: The maximum number of electrons in a shell is given by 2n². Where n is the number of shell i.e. 1st shell can have a maximum of 2 electrons.
2n² = 2(1)² = 2 × 1 = 2
2nd shell can have maximum of 8 electrons
2n² = 2(2)² = 2 × 4 = 8
3rd shell can have maximum of 18 electrons
2n² = 2 (3)² = 2 × 9 = 18 and so on….
(b) Outer most orbit cannot have more than 8 electrons and 18 in penultimate orbit.
(c) A new shell cannot start until previous is filled completely.