Page 6 - classification of elements

Aufbau’s principle: It states that,”In ground state of an atom the

electrons fill atomic orbitals of lowest available energy levels before

occupying higher energy levels.”

For electronic configuration the sequence of the

sub-shell according to increasing level of energy

must be as-

1s 2s 2p 3s 3p 4s 3d 4p 5s …………...

Here,

sub-shell
shell 1s 1 No. of electrons

The electronic configuration of first 30 elements in terms of sub-

shells are here