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The INTERNET Database of Periodic Tables

There are thousands of periodic tables in web space, but this is the only comprehensive database of periodic tables & periodic system formulations. If you know of an interesting periodic table that is missing, please contact the database curator: Mark R. Leach Ph.D.

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 Year:  1936 PT id = 777

Orbital Filling With Electrons

Students of chemistry are often confused why the orbitals fill with electrons: 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6... etc., because the 3d10 seems to be 'out of sequence'.

This 'out of sequence' difficulity is nicely explained if the orbitals are arranged in a slightly different way:

The aufbau principle states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. For example, the 1s shell is filled before the 2s subshell is occupied. In this way, the electrons of an atom or ion form the most stable electron configuration possible.

The order in which these orbitals are filled is given by the n + rule, also known as the Madelung rule (after Erwin Madelung), the Janet rule or the diagonal rule.

Orbitals with a lower n + value are filled before those with higher n + values. In this context, n represents the principal quantum number and ? the azimuthal quantum number. The values = 0, 1, 2, 3 correspond to the s, p, d and f orbital lables.

Julio Gutiérrez Samanez writes:

"I send you the diagram below that reconciles quantum mechanics (diagram for filling the electronic cells) with the Janet table or LSPT. Explaining the duplication of periods with the duplication of the quantum number n, and the introduction of Tao (T) spin of the level or spin of the period, which explains the parity of the symmetric periods."

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© Mark R. Leach Ph.D. 1999 –

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