DatabaseThere are hundreds of periodic tables in web space, but
there is . only one comprehensive database of periodic tables & periodic system formulationsIf you know of an interesting periodic table that is missing, please contact the database curator: Dr Mark R Leach.
From elsewhere in Mark Leach's Chemogenesis webbook: Madelung's Rule tells us that the orbitals fill in the order Electronic structure can be illustrated adding electrons to boxes (to represent orbitals). This representation shows the Pauli exclusion principle, the aufbau principle and Hund's rule in action. There are some subtle effects with the d block elements chromium, Cr, and copper, Cu. Hund's rule of maximum multiplicity lowers the energy of the 3d orbital below that of the the 4s orbital, due to the stabilisation achieved with a complete and spherically symmetric set of five 3d orbitals containing five or ten electrons. Thus, - Chromium has the formulation: [Ar] 3d
^{5}4s^{1}and not: [Ar] 3d^{4}4s^{2} - Copper has the formulation: [Ar] 3d
^{10}4s^{1}and not: [Ar] 3d^{9}4s^{2}
© Mark R. Leach 1999-
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