Questions and answers about the construction of
The Earth Scientist's Periodic Table of the Elements and Their Ions

by Bruce Railsback


At heart, what's the philosophical difference between the organization of your new table and that of the conventional periodic table?

The new Earth Scientist's Periodic Table of the Elements and Their Ions differs most fundamentally from the conventional periodic table by showing individual elements multiple times. On the conventional table, each element has one and exactly one place, and that place is dictated by the configuration of electrons in uncharged atoms of that element. In that sense, I would argue that the conventional periodic table is product of Platonist-idealist thought: the elements are considered only in an ideal state, and each element has only one perfect condition/position. This Platonist view ignores the fact that many elements don't exist in nature in this purportedly ideal (uncharged) state, and that many elements exist in multiple charges or states. The new table acknowledges that natural reality deviates from ideality, and that things take different character under different conditions.


Is there a philosophical difference between the purpose of your new table and that of the conventional periodic table? To put it another way, why do we need a new table?

The purpose of the new Earth Scientist's Periodic Table of the Elements and Their Ions is to contextualize trends and occurrences in geochemistry, or the chemistry of the natural (non-laboratory) sciences. To serve that purpose, it has a different form than the conventional table. I'll freely admit that the conventional table is simpler, and perhaps more elegant, than the new table, because the new table tries to explain or contextualize more information.. However, to follow the thinking of William James and John Dewey, an idea is a tool, and the more things an idea can explain, the better tool it is.


You just conceded that the new table doesn't seem very elegant compared to the conventional table - it's much more complicated. Doesn't that bother you?

It's not elegant - but elegance is a criterion more significant to art than science. The Copernican heliocentric model of the solar system, in which planets passed through perfectly circular orbits around the sun, was elegant. Elliptical orbits, the eccentricity of which varies through time, are less elegant - but we now recognize that elliptical orbits of varying eccentricity are a more accurate description of reality. Accuracy of generalization about reality, rather than elegance, is the standard by which scientific concepts are judged.


What's the history of this table?

In retrospect, I now remember that I tried to plot natural occurrences of the elements on a periodic table when I was studying for my Ph.D. comprehensive exams at the University of Illiinois in 1985. It was a disaster - the conventional table just doesn't lend itself to that sort of thing - and I forgot about it until a few months ago. That was just a failed prelude.

The new table had its beginnings in my teaching about aqueous geochemistry at the University of Georgia. My class handouts had a bit of the conventional periodic table with multiple charges and behaviors for some elements - but that wasn't working. One day in the spring of 1999, I found myself discussing aqueous speciation, trying to point out things on the conventional periodic table but with my arms crossed like a contortionist as I tried to bring the far-flung parts of that table together. As I stood there with my arms crossed, I knew there had to be a better way. After class that day I went back to my office to start on a new table, and by the end of the semester had a draft for my students. That table was just a beginning, and over the next few years I episodically added and revised to get to the table in its present state.


This new table shows a structure or geography of chemistry, both with its contours of ionic potential and with the swaths of symbols that coincide with the contours. Are there other trends that are less apparent?

In general, things to the left are the result of oxidation and things to the right are the result of reduction. For example, S6+ in sulfate and N5+ in nitrate are the forms of sulfur and nitrogen at the left side of the table, and S2- and N3- are at the far right. Within the cations, more oxidized forms like Ti4+, Mo6+, and U6+ are in the leftmost block, whereas Ti3+, Mo4+, and U4+ are farther to the right in the intermediate cations. The greater significance within these comparisons is that leftwards becomes "earth-surface - oxidizing" and rightwards becomes "within-the-earth - reducing". That's thinking spatially. In a temporal sense, leftwards becomes "modern to late Proterozoic" and rightwards becomes "pre-solar to Archean to early Proterozoic". Those are huge generalizations with lots of exceptions, but they are useful in understanding some of the geochemistry and cosmochemistry visible from the table.


What's the most insightful comment you've received about the new table?

I was describing the new table to Celeste Condit, a very smart person trained in everything from classical rhetoric to genetics, in my usual terms - talking about cations and their coordination in minerals, about cations' behavior or speciation in solution, and about the properties of the minerals that the these cations form. After all my talk about cations, she responded in her typical quick style, "So it's all about oxygen". Indeed, most of the table is about O2-: how cations bond (or don't) to oxygen, how they coordinate in solution with oxygen (plus or minus the hydrogen ions of water and hydroxide), how stable or strong oxide phases are, and so on. Celeste's "It's all about oxygen" is a good way to summarize most of the mineralogy and geochemistry of phases at or near the earth surface.


This new table is synthetic document. How does that play in the reductionist world of science?

The reductionist response has been something between indulgence and dismissal: indulgence of a desire to generalize, and dismissal of anything not reporting new data. The best example of that response came when, after a friendly discussion of the table, a new acquaintance at a well-known institution cordially changed the subject by asking "So, what's your day job?". I instantly knew what he meant: "This table is cute, but what is your real research?".

A second thing I've come to appreciate is that it's less embarrassing to be a reductionist than a synthecizer. If a reductionist specializing in a system studied by no one else makes a mistake, no one knows about it for years. If a synthecizer attempting to generalize the knowledge of other scientists makes a mistake, those other scientists will be howling immediately. It therefore takes a thick skin to be a synthecizer. The flip side is that, so long as one is willing to suffer embarrassment, being a synthecizer is safer, in that one doesn't impede science because one's mistakes are immediately exposed and corrected, whereas a reductionist's mistakes may misinform science for years before they are recognized.


Have different kinds of people responded differently to the new table?

Yes, largely by age. Many (but certainly not all) older people don't like new synthetic theories, but perhaps that's because because they don't need them. Some of the harshest criticism of the table has come from senior scientists who said not that the table is wrong but that it only contextualizes information they already knew. I can't argue with that - if someone has already memorized lists and tables, that person may not need a tool that makes sense of those lists for them. It's a newcomer, or person seeking a deeper understanding of why the lists and tables are as they are, who appreciates something like the new table. I suspect old timers who knew the locations of volcanoes and earthquakes didn't think the newfangled theory of plate tectonics told them much - but to those learning geology and to those wanting to know why earthquakes and volcanoes occur where they do, it was an invaluable framework. The new table may not be quite as invaluable, but I think the analogy holds.


Your table, its insets, and its accompanying figures use ionic potential as a not-very-quantitative explanation of mineral stability. Why worry about all this business about ionic potential with regard to stability of minerals - isn't all dictated by thermodynamics?

I know many chemists and geochemists view thermodynamics as the explanation of all aspects of the stability and behavior of substances, or - as you put it - that thermodynamics dictates stability and behavior of substances. I agree that thermodynamics is a powerful tool to predict phenomena if one knows the values to insert for the variables - but I'm not sure it really explains or dictates anything.

Let me use an analogy to explain that heretical statement. Accounting is a powerful tool to explain how a business works - it shows whether a company is making or losing money (the analog of ΔG), it shows from where the company's revenues come, it shows where the company's expenditures go, and it predicts losses or earnings with different levels of production and sales. However, it doesn't show why a company's products are purchased, or not purchased, by consumers - it has absolutely no power to tell us why revenues are high or low. Thus, accounting can tell management whether the company is making money or losing money, but it can't tell management the ultimate controls on the company's performance - it can't tell management that the perfectly functional, cost-effective, and attractively packaged kitchen widgets that the company offers for sale smell like rotten eggs and repulse buyers. Before you can tell management that, you need to know something about the intrinsic nature of these widgets.

I think thermodynamics is much the same. We can measure the thermodynamic properties of substances and plug the resulting parameters into equations to get results predicting the stability of those substances under different conditions. That's very powerful. However, thermodynamics doesn't tell us why those parameters are what they are, whereas an understanding of concepts like ionic potential helps explain why.


Ionic potential is a tool that Viktor Goldschmidt employed, and his distinction between lithophile, chalcophile, siderophile, and atmophile elements is much like the groupings on your table. If Goldschmidt had it all right, why bother with this complicated new table?

Goldschmidt did indeed make great strides, and I hope he would look on the The Earth Scientist's Periodic Table of the Elements and Their Ions favorably. However, Goldschmidt was classifying elements. For example, his plot of charge and radius (and thus ionic potential) didn't even show Fe, seemingly because he couldn't bring himself to show one element mutliple times there. Thinking about ions, rather than elements, leads one to treat elements in their multiple ionic guises and so opens the way for a more reasonable understanding of geo chemistry. It also lets one realize that some elements can be both lithophile (e.g., Mo6+ and U6+) and siderophile (Mo4+ and U4+).

That leads to a larger philosophical issue. Any attempt at classification leads one to have to put an entity (here, a chemical element) into exactly one of some number of categorical boxes. In Goldschmidt's classification, for example, Fe had to be siderophile and so couldn't be lithophile, even though it's very abundant with other lithophiles in common rock-forming minerals. A more realistic approach is to let things be what they are, and if they occur in two clusters, so be it. That's much more the spirit of the The Earth Scientist's Periodic Table of the Elements and Their Ions, where the ions are arranged in order of charge and then the symbols for natural occurrence were added as demanded by natural occurrence. It's not as simple, but it's a lot more realistic.


You call this new table an "Earth Scientist's Table". Does it have any implications for study of planets other than Earth?

I've certainly designed the table for the science of the Earth - to show natural occurrences on Earth, and to explain mineralogy, which is essentially the study of crystalline solids that occur naturally on Earth. However, the concepts can be extended with little trouble. For example, the red-and-brown swath of ions that make oxide minerals and that are retained in soils would expand on a drier and/or cooler planet and would shrink on a hotter or more pervasively wet planet.

A good example is CO2 on Mars. On a warmer planet like Earth, CO2 isn't a mineral because it melts and/or sublimates at ambient Earth temeratures. On Mars, the colder ambient temperatures are low enough to sustain CO2 as a mineral - a naturally occrring crystalline solid. Thus the "Martian Scientist's Period Table of the Elements and Their Ions" would have a red diamond indicating an oxide mineral in the rectangle for C4+ - the field of red-and-brown symbols would expand for the Martian table.


Your table seems to organize and contextualize a lot of information that now "fits" together well. Is there anything that doesn't fit?

Grananite is at least one good example. Grananite is a bismuth fluoride mineral (BiF3) and so requires a blue diamond for simple fluoride minerals in the Bi3+ cell of the table. All the other such symbols fall in the cells of hard cations of low ionic potential (for example, Li+, Na+, Mg2+, K+, Ca2+, and Ba2+). Fluocerite, a fluoride of La3+ and Ce3+, is the closest analog of grananite, but even La3+ and Ce3+ are essentially hard cations, whereas Bi3+ is a soft cation, so that grananite's blue diamond sits by itself in the table. It's a good reminder that anomalies, and probably more than a few, remain to be explained, or to be reconciled into systems in which they're no longer anomalies.


Your table organizes and contextualize a lot of information, but it doesn't provide any new data. It may be an educational tool, but what good is it to the progress of science?

The new table provokes some questions or hypotheses. For example, geochemists commonly list Sr among the refractory elements, the elements that form high-temperature minerals. On the new table, Sr2+ falls in with the large non-refractory ions. It prompts one to ask if we've miscategorized Sr. As another example, the literature on nutrients lists Cr3+ as a critical nutrient in human nutrition, but Cr3+ appears in the table as such an insoluble ion that one wonders how it could be a nutrient (and in fact the same literatue concedes that biological absorption of Cr3+ is very slight). It prompts one to ask, at least, if we're correct either about the valence state of the Cr that acts as a nutrient or if Cr is really a nutrient in any of its valence states. The development of questions like these is the value of the table to scientists, regardless whether they want or need the table to organize their understanding of geochemistry.



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