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| What is the Periodic Table Showing? | Periodicity |
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. The database holds information on periodic tables, the discovery of the elements, the elucidation of atomic weights and the discovery of atomic structure (and much, much more).
Periodic Tables from the year 1950:
| Year: 1950 | PT id = 14, Type = formulation |
The modern periodic table is based on quantum numbers and blocks, here.
A periodic table can be constructed by listing the elements by n and l quantum number:
The problem with this mapping is that the generated sequence is not continuous with respect to atomic number atomic number, Z: Check out the sequence Ar to K, 18 to 19.
Named after a French chemist who first published in the formulation in 1929, the Janet or Left-Step Periodic Table uses a slightly different mapping:
While the Janet periodic table is very logical and clear it does not separate metals from non-metals as well as the Mendeleev version, and helium is a problem chemically.
However, it is a simple mapping to go from the Janet or Left-Step periodic table to a modern formulation of Mendeleev's periodic table:
On this page web, "full" f-block included periodic tables are shown wherever possible, as above.
However, the periodic table is usually exhibited in book and on posters in a compressed form with the f-block "rare earths" separated away from the s-block, p-block and d-block elements:
However, the compression used introduces the well known problem known as a "fence post error".
The effect is that:
La and Ac: move from f-block to d-block
Lu and Lr: move from p-block to f-blockChemically, the elements can be fitted in and classified either way. Many thanks to JD for pointing the situation with the periodic table is a fence post error.
Mark Winter's Web Elements project, here, uses the formulation shown below:
Interestingly, the IUPAC periodic table separates out 15 lanthanides, La-Lu, and 15 actinides, Ac-Lr by leaving gaps in period 3 under Sc & Y:
This corresponds to:
By Mark Leach
| Year: 1950 | PT id = 153, Type = formulation spiral |
Clark's Updated Periodic Table
John D Clark's 1950 chart. It looks as though the experience of producing the 1949 version for Life Magazine caused him to have a radical rethink. John D. Clark, A modern periodic chart of chemical elements. Science,111, 661-663 (1950). Information supplied by Philip Stewart.
| Year: 1950 | PT id = 287, Type = formulation spiral |
Scheele's System
Scheele's system of 1950 (from van Spronsen):
| Year: 1950 | PT id = 475, Type = formulation element |
Elements Known in the Year 1950
Elements known in the year 1950, taken from this Wikipedia page:
| Year: 1950 | PT id = 878, Type = element |
Discovery of Californium
Cf 
Californium, atomic number 98, has a mass of 251 au.
Synthetic radioactive element.
Californium was first observed in 1950 by S. G. Thompson, K. Street, Jr., A. Ghiorso and G. T. Seaborg.
| Year: 1950 | PT id = 1080, Type = formulation |
Sidgwick's Periodic Classification (Mendeleeff)
From N.V. Sidgwick, Chemical Elements and Their Compounds, vol. 1, Oxford University, London, p. xxviii (1950).
René Vernon writes:
"In this curious table the Lanthanides are located in group IIIA while the Actinides have been fragmented.
Instead:
• Ac, Th, and Pa are located in groups IIIA, IVA and VA under Lu, Hf, and Ta, respectively
• The uranides, U, Np, Pu, Am, and Cm, are located in group VIA, under W."
Sidgwick writes:
"This subgroup (VIA) consists of Cr, Mo, W, and U, to which the 'uranide' elements, Np, Pu, Am, and Cm (which might be assigned to any Group from III to VI) must now be added." (p. 998)
"...the trans-uranium elements 93–6... for the first time give clear evidence of the opening of the 'second rare earth series', the 'uranides', through the expansion of the fifth quantum group from 18 towards 32." (p. 1069)
"The question whether the fifth quantum group of electrons which is completed up to 18 in gold begins to expand towards 32, as the fourth does in cerium, has now been settled by the chemical properties of these newly discovered elements. In the Ln the beginning of the expansion is marked by the main valency becoming and remaining 3. With these later elements of the seventh period there is scarcely any sign of valencies other than those of the group until we come to uranium... Up to and including uranium, the group valency is always the stablest, but beyond this no further rise of valency occurs, such as we find in rhenium and osmium. Hence the point of departure of the new series of structures (corresponding to lanthanum in the first series) is obviously uranium, and the series should be called the uranides. (p. 1092):
| Year: 1950 | PT id = 1119, Type = formulation 3D |
McCutchon's Simplified Periodic Classification of the Elements
McCutchon KB, A simplified periodic classification of the elements, Journal of Chemical Education, vol. 27, no. 1, pp. 17–19 (1950)
This 3-dimensional table has two double-sided flaps attached. The top flap is the f bock. Under that is the d block.
The superscripts denote the number of d electrons an element has. Thus, La1 is shown as being an f1 element. But it has a 1 superscript, meaning that the f electron count is reduced by 1 and the d electron count is 1.
René Vernon writes:
"On group 3, McCutchon cryptically says: The proposed arrangement brings out certain known facts about the tertiary elements which are rarely shown by other arrangements. For example, it suggests, correctly, that the resemblance between yttrium and lutecium is greater than that between yttrium and lanthanum. It classifies lanthanum but not lutecium as a rare earth, in accordance with their chemical properties (which also contradict spectrographic evidence at this point). It also demonstrates the tetravalence of both cerium and thorium, and that thorium and protactinium show a resemblance in chemical properties to zirconium and niobium, as well as to hafnium and tantalum."
I say "cryptically" because McCutchon presents no further evidence in support of his assertion that the resemblance between Y and Lu is greater than between Y and La. He may have had in mind the fact that Lu is more often found in ores of Y than is the case for La... and I don't understand his reference to spectrographic evidence.
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| What is the Periodic Table Showing? | Periodicity |
© Mark R. Leach Ph.D. 1999 –
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