Question

: State the order of filling atomic orbitals following Auf- bau principle.

Answer 1

To answer this question, you must recall the Aufbau principle. The Aufbau principle depicts the order in which electrons are filled in the orbitals of an atom in its ground state. According to the principle, in the ground state of any atom or ion, the electrons fill the atomic orbitals in increasing order of their energies, that is, filling the lower available energy levels first before the higher levels.

Complete step by step solution:
We can understand the Aufbau principle in few points as:
It says that the electrons occupy those orbitals first whose energy is the lowest. In other words, the orbitals having higher energies are filled only after the orbitals with lower energies are completely filled.
The order of the energy of orbitals can be found out with the help of the $\left( {n + l} \right)$ rule, which says that the sum of the principal quantum number and azimuthal quantum number depicts the energy level of the orbitals.
Lower $\left( {n + l} \right)$ values correspond to lower energy of the orbitals, i.e., the orbitals with a lower value of $\left( {n + l} \right)$ are filled first.
If the $\left( {n + l} \right)$ values for two orbitals are equal, then the orbital with a lower value of the principal quantum number will be filled first
Thus, according to the Aufbau principle, the order of filling of electrons is in the order
${\text{1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s}}........$

Note:
However, some elements like chromium, copper, rhodium, silver and ruthenium do not follow the Aufbau principle. This is because of extra stability of half- filled and full filled orbitals. For lower elements, the difference between the energy levels of different orbitals is larger and exceptions are not commonly observed.