Aufbau PrincipleAccording to this principle in the ground state of the atoms the orbital’s are filled in order of their increasing energies means electrons enter higher energy orbital’s so order in which orbital’s are filled is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
Pauli Exclusion Principle
· given by W. Pauli (1926).
· Two electrons in an atoms can’t have same set of 4-quantum no.
· Only two electrons may exist in same orbital and these electrons must have opposite spin.
Hund’s Rule of Maximum Multiplicity
· According to this rule pairing of electron in the orbital’s belonging to the same sub-shell (p, d or f)· Does not take place until each orbital belonging to that sub-shell has got one electron each i.e. it is singly occupied.