Planck's rule Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy called quanta and the amount of energy is proportional to in. - frequency of radiation. E=hv
whese h is Planck's constant.
Hund s rule According to this rule, electron pair in z will not take place in orbitals of same energy (same sub-shell) until each orbital is first singly filled with parallel spin.
Pauli's exclusion principle An orbital can accommodate maximum of two electrons and these two must have opposite spins.
Aufbau principle In the ground state of an atom, an electron enters the orbitals of lowest energy first and subsequent electrons are fed in the order of increasing energies.