Tuesday, January 6, 2015

Periodic table challenge

There was a phenomenal response to my blog post on the periodic table with emphasis graphic (thanks everyone!). While I still hope to uncover more information about the history of the graphic and gain insight into what Sheehan thought about it in his later years, I suspect that Sheehan was always aware that the relative sizes of the different element blocks did not accurately represent the abundance of the elements. For the target audience of pre-college (elementary?) students however, it no doubt succeeded fantastically in generating curiosity about the periodic table and stimulating interest in chemistry. As I hope was clear, my criticism was not directed at Sheehan's pedagogical efforts but rather at the indiscriminate spread of an inaccurate "meme" portrayed as a truism. The Sheehan periodic table appeals to both our aesthetic sensibilities as well as a human desire to simplify the complex. For the same reason it was an effective outreach tool, it became the perfect mechanism to propagate misinformation.

As several have pointed out, this will not be the last time Sheehan's graphic surfaces. We can point of the errors in the graphic every time that it is shared (maybe using my blog post), but a better approach would be to displace it from the zeitgeist. Since I lack the necessary artistic skills, I'm issuing a challenge for someone to create a periodic table that illustrates relative abundance. Sadly, I can't think if anything to offer as a reward, unless there is a sudden uptick in demand for signed reprints of my papers. 

As I cited in the original blog post, several versions of the periodic table showing abundance exist; however, each have shortcomings. The new periodic table with emphasis should meet the following criteria:

1. The periodic table must be visually striking. It should be more aesthetically appealing than Sheehan's graphic. It must encourage sharing and therefore promote education.

2. The periodic table must show all the naturally occurring elements (i.e. at least up to uranium, element 92). Obviously, this the hardest thing to achieve. As we've pointed out, the magnitude of the difference between most abundant and least abundant elements precludes presentation on anything resembling the standard periodic table. The weakness of the existing elemental abundance cartograms and the Google table is that one could conclude that rare elements do not exist. Using Google's periodic table as an example, it is accurate to say that astatine is present at 0 ppm in the Earth's crust, but it is incorrect to say astatine does not exist on earth. If one looked in locations with deposits of radioactive uranium and thorium ores, astatine would be detectable. Google also shows radon at 0 ppm. If radon was nonexistent on earth, radon abatement systems would be relegated to the dustbin of pseudoscience with the QRay bracelet and rhino horn. Radon can be found at approximately parts per trillion in the crust, but concentrated in uranium and thorium ore. 

While the cartograms pass criteria 1, Google's periodic table offers nothing beyond a standard visual. The same lack of artistry applies to all the other abundance tables that I have found.

To get people thinking, I have the skeleton of 2 possible ideas
A) An interactive periodic table that operates like Google Earth. A wide view would show the abundant elements, and the less abundant would come into view as the user zooms in closer. The big difference between Google Earth and this hypothetical periodic table is the amount of zoom required. The transition from a complete map of the continents down to the the standard street level map requires zooming through approximately 6 orders of magnitude. The abundance of elements is a much larger range of values (ca. >20 orders of magnitude).

B) A 2-fold Sheehan-inspired periodic table. The basis for this would be a color coded log scale. Colors would follow the electromagnetic spectrum such that each order of magnitude corresponds to a color (e.g. 10-16 abundance = violet with colors red shifting as the magnitude increases). Within a given color/order of magnitude, the blocks are sized relative to one another similar to Sheehan's graphic and cartograms.

To get you started, here's one possible resource for finding the amount of the elements in the crust or oceans.