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Question
State the order of filling atomic orbitals following Aufbau principle.
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Solution
Aufbau principle:
- The Aufbau principle gives the sequence in which various orbitals are filled with electrons.
- In the ground state of an atom, the orbitals are filled with electrons based on the increasing order of energies of orbitals, Pauli’s exclusion principle, and Hund’s rule of maximum multiplicity.
- Increasing order of energies of orbitals:
a. Orbitals are filled in order of increasing value of (n + 1)
b. In cases where the two orbitals have the same value of (n + 1), the orbital with a lower value of n is filled first. - The increasing order of energy of different orbitals in a multi-electron atom is:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s and so on.

Increasing order of orbital energy
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