Apr 18, 2008
Rebuilding the Periodic Table
The Periodic Table of the elements is a fascinating icon of science. It is incredibly useful and has been exploited and sexploited too in the form of a periodic table of yoga and a sexy PT. It has also been hacked apart, cut and paste into different formats, created as illuminated wall cases, woodworked into furniture, spiralled, spherized, and generally rebuilt in almost every imaginable way ever since Mendeleev first dreamed of laying out his elemental cards according to the periodicity of elemental properties.
Now, in an effort to inspire chemists to reconsider the foundations of the periodic table, chemical philosopher Eric Scerri of the University of California, Los Angeles, is building a new way to classify the chemical elements one step at a time.
Writing in the latest issue of the Journal of Chemical Education (PDF 2008, 85, 585-589), Scerri explains how the periodic table initially arose from the discovery of atomic weight triads but he now suggests that chemists should recognize the fundamental importance of atomic number triads.
This sea change in elemental attitude might enhance the periodic table by classifying the elements at a fundamental level as basic substances. As such, he and his colleagues have developed a new version of the “left-step” periodic table, which looks very different from the conventional PT. In the new layout, with its step-like pattern actinides and lanthanides are no longer relegated to a standalone box, but form the first step of the PT.
Climbing right to the transition metals (Fe, Mn, Ir, Sg et al) on the next step and then to the non- and semi-metals, such as boron carbon, oxygen, silicon etc and finally a step in which the halogens (fluorine, chlorine…), noble gases (neon, xenon…), alkali metals (potassium, sodium…) and alkaline earth metals (beryllium, calcium…) form the final highest step on the right. Hydrogen tops the halogen column and helium crowns the noble gases rather than acting as the outer beacons as with the conventional layout. (Click the graphic for a clearer, full-size view).
“The left step table has been around for some time,” Scerri told me, “but I am modifying it to accommodate two atomic number triads which would otherwise be absent. They are He, Ne, Ar which ceases to exist as a triad in the usually encountered left-step table and H, F, Cl which does not exist either in the conventional medium-long form table or the usually encountered left-step table.”
In the grander scheme of things, whatever form the Periodic Table takes in the future matters not to those of us who sing, so we end with a song, the periodic table song from Tom Lehrer (who was 80 on April 9, 2008 and gets a mention in the Official Google Blog this week), known simply as The Elements.
Hi Melinda.
We may be talking at cross purposes. I am not discussing the best model for a particular purpose such as teaching this or that aspect of electronic configurations.
I am claiming that elements belong in particular groups and that the task of science is to discover the closest thing to the truth regarding the grouping of elements.
As I see it H and He belong in one particular group. It is not dependent on what properties one happens to focus on or at least it should not depend on this. If it does it means that the criteria that are being used are not good enough, not essential to the elements.
My suggestion for the essential criterion for ordering AND ALSO group membership is atomic number. The first is commonplace. The second is more radical and based on what I have written about atomic number triads in Journal of Chemical Education and the Jan-Feb issue of American Scientist. I would go as far as to say that atomic number triads are a better criterion for group membership that electronic configuration.
This is the case with Sc, Y, Lu and Lr for example as opposed to Sc, Y, La, Ac.
Published periodic tables seem to be divided. Atomic number triads argues for the first grouping and against the second one.
There is other physical evidence in favor of the first grouping.
Finally, can you send me a copy of your spiral representation at my UCLA chem department address please. See my website for detail.
regards,
eric scerri
@Melinda – point taken re the sequential nature of the elemental list.
@Eric – I tried to relate this point, that the elements exist independently from any particular graphical representation we may overlay on the world. However, isn’t there still controversy in where specifically elements H and He should fit. The general periodicity may be intrinsic to nature, but I thought the specifics were open to re-interpretation depending on which properties you consider most important with regards to H and He…
db
I half agree with you in that I believe that one of the grid form tables may be best for cribsheet use, however I think that’s only most useful for someone who already understands what it represents. I would argue that for explaining chemistry basics to beginners that my spiral form may be close to ideal. That’s because the first thing that a beginner needs to understand is the linear sequence of atomic number represented by a thick line in my diagram, and the second thing they need to grasp is how the elements fall into families, represented by the thin radial lines. The standard grid captures only the second concept very well, and even then only with difficulty. The self-similar nature of my diagram at different scales causes beginners to wonder what’s up with those bifurcations.
Again, the “best” model depends completely upon your need. As an introduction, I’d use mine but if I were going to cheat on a Chemistry test, I’d probably sneak in a left-step table.
Thanks melinda but you raise a point on which I have strong views and would like to respond briefly.
The idea that all forms of the periodic tables are just representations and that there is no ultimate best table.
My belief is that there is one true and objective periodic classification even if we have not yet arrived at it. It concerns me that scientists can express such ‘relativistic’ views on something as important as the periodic table.
It is after all THE most basic, profound and deep classification that has ever been discovered.
Elements are natural kinds. They are not just a contingent way in which the world is carved up for our convenience. Similarly the pattern they fall into is objective and not decided by us.
Please see the final chapter of my book for a fuller discussion of this issue.
Just to be clear I am not talking about the shape of a periodic table or whether groups are arranged vertically, horizontally or in a 3D pattern. What I am getting at is the placement of elements in groups. I believe that H and He belong to specific groups and that the compromises that one sees in some tables are just avoiding the issue.
Responses welcome.
eric scerri
Actually, Melinda, it’s pretty cool. But, my problem with all these novel formats whether they’re 3D, 2D, spirals, fractals whatever is that for grasping the basics and have a cribsheet that’s easy to print, nothing yet beats a 2D grid. Obviously, for non-beginners, something more advanced is needed and I accept that might need to be in the form of a 3D spiral or whatever.
db