State the suggestions made by Bohr and Bury with regard to distribution of electrons in different energy levels in the atoms of elements.
Or
Explain the arrangement of electrons outside the nucleus.
(i) Electrons are revolving around the nucleus in different orbits or shells. These energy shells are represented by numbers 1, 2, 3, 4 or K, L, M, N.
(ii) The maximum number of electrons in any shell cannot exceed 2n2 , where n is the number of that energy level. Thus for
K-shell, n = 1, no. of electrons = 2x12 =2
L-shell, n = 2, no. of electrons = 2x22 =8
M-shell, n = 3, no. of electrons = 2x32 =18
N-shell, n = 4, no. of electrons = 2x42 = 32.
(iii) The outermost orbit of an atom cannot have more than 8 electrons and the next to the outermost shell (penultimate shell) can have at the most 18 electrons.
(iv) It is not necessary that an orbit has its full quota of electrons before starting to fill the next higher orbit.
