Question

What is the Aufbau principle for filling up orbitals with electrons?

Answer 1

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, the lower energy levels will be occupied first before occupying the higher energy levels.

Order of filling of atomic orbitals:

• The order of filling of atomic orbitals is shown below in the image.

According to the Aufbau principle, the filling up of orbitals with electrons is done as follows-

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}4f^{14}5d^{10}6p^{6}7s^{2}5f^{14}6d^{10}7p^6$.