The Sequence in Which Electrons Fill Atomic Orbitals

Understanding the sequence in which electrons fill atomic orbitals is fundamental to comprehending electronic configurations and the behavior of elements in the periodic table. This process follows specific rules based on the nl values of the orbitals, where the electromagnetic forces and Pauli exclusion principle guide the distribution of electrons.

Determining Orbital Filling Order Using nl Values

The primary rule governing the filling order of atomic orbitals involves the calculation of the nl values. The n value represents the principal quantum number, which indicates the energy level or shell, while the l value, the azimuthal quantum number, specifies the subshell (s, p, d, f, etc.).

First, compare the nl values to determine the order in which subshells are filled. Between two subshells, the one with the smaller nl value is filled first. For instance, comparing the 3d subshell (32, nl 5) and the 4s subshell (40, nl 4), the 4s subshell is filled before the 3d subshell.

Next, if the nl values are equal, the subshell with the lower n value is filled first. This is evident in the comparison between 3d (32, nl 5) and 4p (41, nl 5). Since 3

Based on these principles, the sequence in which orbitals are filled is as follows:

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s 5g 6f 7d 8p 9s

Note that the heaviest atom now known, oganesson (Og, Z 118), has not filled orbitals higher than 9s.

Quantum Numbers and Orbital Filling

Electrons fill orbitals by obeying the Pauli exclusion principle, a quantum mechanical rule that states no two electrons in the same atom can have the same set of quantum numbers (n, l, m, s). These quantum numbers specify the quantum states of the electron:

n - principal quantum number, determining the energy level and orbital radius. l - azimuthal quantum number, determining the orbital shape (0 for s, 1 for p, 2 for d, 3 for f, etc.). m - magnetic quantum number, determining the orientation of the orbital in space. s - spin quantum number, determining the spin direction (either 1/2 or -1/2).

By considering these rules, we can visualize the filling of orbitals with increasing n and l values. This process not only helps in predicting the electronic structure of atoms but also in understanding their chemical properties.