Periodic Debate

  • ChemPubSoc Europe Logo
  • DOI: 10.1002/chemv.201000093
  • Author: David Bradley
  • Published Date: 09 June 2011
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
thumbnail image: Periodic Debate
Complete, But Not Finished


Non-chemists, and perhaps a few chemists, might have assumed that once all the holes in Mendeleev's Periodic Table were filled with modern discoveries and the lanthanides and actinides added, that the Table was forever immutable, a stone tablet to adorn high school chemistry lab walls, textbooks and websites unchanged forever more ...


Well, they'd be very wrong, aside from the recent didacts on atomic masses and isotope ratios wrought on the elements in December 2010 by IUPAC and the official recruitment of elements 114 and 116, there are several issues that have got many chemists in a boiling reflux.


For instance, there are 3D PTs, spirals, circular tables, stepped and even fractal tables (Fig. 1). Eric Scerri, University of California Los Angeles, USA, is developing an alternative approach to that is intuitive and might take us closer to an ultimate version. Scerri's argument for change is based on the fact that the Periodic Table arose from the discovery of triads of atomic weights, but he thinks chemists would be better served if they were to recognize the fundamental importance of triads of atomic number instead. His new Periodic Table could be fundamentally closer to the ideal.


This is perhaps especially pertinent given that atomic mass varies according to isotope ratio (neutron count, in other words), whereas atomic number (proton count) is fixed for each element. In it, listings of electron shells follow an ordered pattern, so that the halogens form the first column on the left, topped by hydrogen, the noble gases are the second column, topped by helium. The alkali metals and the alkaline earth metals follow, then the block of transition metals. The semi-metals and the non-metals then form the final four columns (Fig. 2).

Figure 1.  Some alternative Periodic Table designs.


Positioning Helium


As if this restructuring of the groups were not controversial enough, it is the logical relocation of hydrogen and helium that stirs deep chemical emotions, even though they recreate the atomic number triads of He-Ne-Ar and H-F-Cl invisible in the conventional PT. However, not everyone is convinced by helium's placement. US chemist Henry Bent would prefer to see helium atop beryllium in the otherwise "normal" PT layout. He argues that although helium seems to fit perfectly at the top of the noble gases its presence there breaks several of the rules.


Scerri is quite adamant that there is one true and objective periodic classification but others believe that such an ultimate PT does not exist and that our perspective inevitably distorts reality. Software engineer Melinda Green from Superliminal Software, developed a fractal PT for educational use and believes any arrangement is purely subjective. "Neither the periodicity nor any classification is intrinsic to nature," explains Green.


Atomic number is perhaps the only intrinsic property of the elements, as suggested by Scerri too, but, adds Green, this is only fundamental by our subjective definition of the term "element" rather than it representing something ultimate about the universe as Scerri's reasoning would suggest. "Every description requires a describer," says Green. "Subjectivity is not just an annoyance, it is the source of all meaning."


Art and Function


So, is the menagerie of different PTs, nothing more than an art gallery? Martyn Poliakoff thinks so. Poliakoff is a professor of chemistry at the University of Nottingham, UK, working on supercritical fluids who has gained recent fame for the Periodic Table of Videos project. His is a pragmatic perspective. "I regard the PT as a tool like a hammer and, just like other tools, you have different forms for different purposes (e.g., a claw-hammer and a mallet). There just isn't a "right" and "wrong" form," he told ChemistryViews. He suggests that the different forms can be useful, however. "These weird forms of the PT often serve a purpose by highlighting some aspect of the elements that one might not otherwise have noticed," he adds.


However, Scerri is convinced there is something more fundamental to the ultimate PT. "It concerns me that scientists can express 'relativistic' [aesthetic] views on something as important as the Periodic Table," he says. "It is after all the most profound and deep classification that has ever been discovered." But Poliakoff has the last word: "In the end, I think that one should remember that Mendeleev devised the PT for a textbook to help rationalize the mass of facts in inorganic chemistry," he adds, "For me, the PT remains a tool to help reduce the complexity, not a metaphysical truth that has a correct form yet to be discovered."

Figure 2. Scerri stuff indeed — a new, rearranged Periodic Table.


► Read on:

At Last, A Definitive Periodic Table?, David Bradley

20 July 2011 — ChemViews article and ensuing discussion has spawned a development in this field courtesy of UCLA chemistry professor E. Scerri


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5 Comments

John Martin wrote:

Magnetic compression as cause of PT structure

The properties of elements can be fully reduced to magnetic compression fractions. Electrons on an atom of each element are divided into those on the inner half wave of each group wave (Ihw) and those on the outer half wave of each group wave (Ohw) for example: 14Si with an electron configuration of 2:4:4:4 has an Ihw configuration of 2:4 and an Ohw configuration of 4:4. 92U with an electron configuration of 2:8:18:32:21:9:2 has an Ihw configuration of 2:8:18:16 and an Ohw configuration of 16:21:9:2, the central 32 being divided equally between Ihw and Ohw. A graph of this division of electrons into Ihw and Ohw shows that Ohw electrons determine the nature of each element and the position of exceptions to Madelung’s law. This eight column table (with one row for each element) is converted into magnetic wave fractions by dividing each value by the total number of protons in an atom of each element, this reveals that magnetic compression is the cause of PT structure, it also shows that magnetic compression is the cause of exceptions to Madelung’s Law. One interesting observation is that the fractions of the innermost col. of Ihw electrons divided by the innermost col. of Ohw electrons produces the atomic number of each element with no margin of error despite the fact that only one third of the total available electrons are being used to produce the atomic numbers; this probably explains why so many electrons are available for molecular bonding in atoms of those elements with a large number of electrons. As Electron Bonding Energies (EBE) is found with neutrons in situ, they can be used to reveal the role of neutrons. Using the Electron Bonding Energies values given in Emsley’s ‘Table of Elements’, divide the nuclear s1 EBE values with the sum of the electron shell EBE values; a graph comparing the result with the number of neutrons in an atom of each element reveals why elements of high atomic number are radioactive. There are only five periodic waves for the six non-nuclear groups shown in the PT; the reason for this is that radioactive elements (Group 7) do not form a magnetic wave. The EBE values divide naturally into six numerical groups dividing the average of each group by the nuclear (s1) values produces approximate fractions of 1/2, 1/3, 1/5, and 1/6 (see note). All elements on the left hand col. of the PT obey the equation ‘the number of Ihw electrons - 1= the number of Ohw electrons’. As H has the (-1) configuration it belongs at the top of the left hand col. above LI. He being the last element of the nuclear wave, belongs at the top of the extreme right hand col. above Ne. Note: Fractions with a numerator of 1 are commonly found in both particle and atomic structure; for example: if the method of finding the atomic number mentioned above is reversed, then the sequence 1/1, 1/2, 1/3, 1/4 etc. appears in place of whole numbers. Extracting 1s values from Table 7.3 Of Molecular Quantum Mechanics (fifth edition) show that (He-H)/H and so on, produces results that when reduced to a single digit numerator are 2/3, 3/5, 3/8, 1/4, 1/5, 1/6, 1/7, 1/8, 1/9, 1/9, 1/11, 1/12, 1/13, 1/14, 1/15, 1/16, and 1/17. The first three equations contain members of the nuclear pair thereafter we have the numerator 1 sequence with a repeat of 1/9 where the second group fills at Ne. The essential point of all this is that Fractional Quantum Hall effect experiments and experiments related to Composite Fermions Theory produce approximate fractions (due to the difficulty of conducting such experiments) whereas analysis of PT structure produces exact fractions that can only be compared to experimental results after they are simplified. Hence PT analysis is best. Attempts to convert 2 dimensional Composite Fermions (CP) theories into 3 dimensional theories were unsuccessful with the best result having a 20% margin of error. Comparing PT actual fractions with FQHE and CP approximate fractions reveals a maximum difference of +2.5% -0.35% and an average difference of +0.5%.

Sun Aug 26 14:35:15 UTC 2012

bryan Sanctuary wrote:

Rearrange of periodic table.

I recall when I was in freshman chemistry I tried writing the Periodic Table like the spiral above. I could not get it to work well. There are some things I am not sure of from the discussion but the comments are useful. I have no objections to shifting the halogens to be the first period, but H is always the odd man out.

Mon Nov 28 21:56:02 UTC 2011

Bernard Schaeffer wrote:

To Jess Tauber

I don't see what you mean by tetrahedral: is it the structure of the atom or the structure of the table? I used a tetrahedral structure to calculate the binding energy of 4He and now I try to extend this model by an NaCl type crystal structure for the nucleus. Concerning the magic numbers in a nucleus, I think that it is a second order effect because the binding energy curve has only small bumps. To Jess Tauber II don't know Janet's reasoning but like him, contrarily to Bohr and Coster, I don't consider the electrons to build the periodic system. Janet table coincides mathematically with the spherical harmonics (http://storage.canalblog.com/58/52/292736/67078483.jpg). On the last line of this figure you see the series 2, 8, 18 32, all even numbers because of the Pauli exclusion principle. The number 2 is used twice; for H and He and for Li and Be. This is because the symmetry is spherical for these elements (it is also true for Na, Mg, K, Ca etc). For B, C, N, O, F, Ne, there is one plane of symmetry. Dividing by 2 to eliminate Pauli principle we obtain 3 values that are the three possibilities of orientation in space. And so we can continue for all elements without any exception. The electrons don't exist in this model: it is entirely based on the de Broglie wave solved by Schrödinger for the hydrogen atom where there is only one electron. In fact the table desribes only the structure of the hydrogen atom. Adding electrons changes the structure because there are electric interactions between them and, therefore, changes the distribution of the electrons a little for light elements and heavily for heavy elements. Now it is always possible to take the electrons into account but it is incompatible in this type of table. It is necessary to use a table like that of Bohr and Coster.

Wed Aug 03 14:06:59 UTC 2011

Eric Scerri wrote:

LAST WORD

Thanks Philip. See you on the new site.

Tue Jul 26 05:46:54 UTC 2011

Philip Stewart wrote:

Last Word

Nothing much left to say on the new site, except that H-- is like a normal ion, so hydrides are a bit like halides, while H+ is not like a normal ion at all, but covalent H is rather like covalent C. Nothing to do with triads though. Anyway, it's nice to have the last word.

Mon Jul 25 06:41:10 UTC 2011

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