The INTERNET Database of Periodic Tables
There are hundreds of periodic tables in web space, but there is only one comprehensive database of periodic tables & periodic system formulations. If you know of an interesting periodic table that is missing, please contact the database curator: Dr Mark R Leach.
The 8 Periodic Tables most recently added to the database:
Mechanical Engineer's Periodic Table
Avallone EA, Baumeister T & Sadegh AM (eds) 2007, Marks' Standard Handbook for Mechanical Engineers, 11th ed., McGraw-Hill, New York, p. 6-6. Click here for a larger version.
This mech eng PT has a couple of odd features: hydrogen is in Group 17 above fluorine and the lanthanides are split:
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:
Van Spronsen, on p. 157, says:
Jess Tauber adds:
First Ionisation Energy to the Standard Form Periodic Table
There is debate amongst the cognoscenti about the 'best' representation of the periodic table, and how this 'best' formulation can be explained by [rationalized by] quantum mechanics (QM).
Many feel that the Janet PT formulation, the 'Left Step', is the ideal QM PT, but this formulation does not show periodicity very well, and there are issues with the placement of H, He, Be which spill over into questions about their placement in the standard form PT (the periodic table used in classrooms and textbooks around the world).
However, it is possible to get to the conventional standard form PT directly from the first ionisation energy data, where the 1st ionisation energy is the energy required to convert a gas phase atom (M) into its gas phase positive ion plus electron.
The process involves:
Note that a similar logic can be applied to atomic radius and electronegativity data.
However, there are issues about the measurement of atomic radius, because atoms are 'soft at their edges', and gas phase atomic radius is not precisely defined. And, electronegativity is a derived parameter.
Gooch & Walker's Periodic System of The Elements
From a 1905 textbook by Gooch & Walker: Outlines of Inorganic Chemistry (see the Google Books scanned version pp247) comes an early 'right-step' periodic table. The formulation was repoduced in a 1917 textbook (lower image).