Explain Aufbau principle.
The word aufbau in German means building up. The building up of orbitals means the filling up of orbitals with electrons. The principle states that in the ground state of the atoms, the orbitals are filled in order. of their increasing energies. In other words, electrons first occupy the lowest energy orbital available to them and: enter into higher energy orbitals only after the lower energy orbitals are filled. The order in which the energies of the orbitals increase and hence the order in which the orbitals are filled is as follows:
.1s,.2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s…
The order may be remembered by using the method given in Fig Starting from the top, the direction of the arrows ‘.gives the order of filling of orbitals, that is starting from right top to bottom left.