Question

Electrons in an orbital are filled according to which rule?

Answer 1

Aufbau principle: electrons fill atomic orbitals of the lowest available energy levels in the ground state of an atom or ion before occupying higher levels.

• The order in which the energy of orbitals increases can be determined with the help of the (n+l) rule, where the sum of the principal and azimuthal quantum numbers determines the energy level of the orbital.
• Lower (n+l) values correspond to lower orbital energies. If two orbitals share equal (n+l) values, the orbital with the lower n value is said to have lower energy associated with it.
• The order in which the orbitals are filled with electrons is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, and so on.
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Hence electrons in an orbital are filled according to $(\mathrm{n}+\mathrm{l})$ rule., where n is the principal quantum number and l is the azimuthal quantum number.