present in any subshell. For example, subshell s comprises one orbital and thus the maximum number of electrons present in s subshell can be two, in p and d subshells, the maximum number of electrons can be and and so on. This can be summed up as : the maximum number of electrons in the shell with principal quantum number n is equal to n . Hund’s Rule of Maximum Multiplicity This rule deals with the filling of electrons into the orbitals belonging to the same subshell (that is, orbitals of equal energy, called degenerate orbitals).
It states : pairing of Fig. . Order of filling of orbitals electrons in the orbitals belonging to the same subshell ( p , d or f ) does not take place until each orbital belonging to that subshell has got one electron each i.e., it is singly occupied. Since there are three p , five d and seven f orbitals, therefore, the pairing of electrons will start in the p , d and f orbitals with the entry of 4th, 6th and 8th electron, respectively.
It has been observed that half filled and fully filled degenerate set of orbitals acquire extra stability due to their symmetry (see Section, . . ). .
. Electronic Configuration of Atoms The distribution of electrons into orbitals of an atom is called its electronic configuration . If one keeps in mind the basic rules which govern the filling of different atomic orbitals, the electronic configurations of different atoms can be written very easily. The electronic configuration of different atoms can be represented in two ways.
For example : (i) s a p b d c ...... notation (ii) Orbital diagram s p d In the first notation, the subshell is represented by the respective letter symbol and the number of electrons present in the subshell is depicted, as the super script, like a, b, c, ... etc. The similar subshell represented for different shells is differentiated by writing the principal quantum number before the respective subshell.
In the second notation each orbital of the