Thursday, October 18, 2012

Turning Over Rocks, Drawing Lines in the Sand

When I flip over a rock in the woods, I'm never quite sure what I'll find. Bugs? Fungi? A gold coin? (maybe someday...).

Turning over rocks in the dense forest of the chemblogosphere gets complicated quickly. My response to this week's chemistry-opposed Washington Post article included a barb near the end: 'correctly' stating the number of elements in the Periodic Table to counter a WaPo assertion:
"...there are 92 naturally-occurring elements, and a total of 118 spots (not all filled!) in the Periodic Table. I didn't have to Google it, because I took middle-school chemistry."
Now, of all the things I've written on this blog, I'd hardly expect this to seem controversial. And yet, within a few minutes, Stu Cantrill had chimed in, favoring 94...then 98. Blog of the Isotopes posted next, saying:
"The question is not at all easy to answer.  It depends what you mean by naturally-occurring.  I think the common meaning is "can be dug up from the ground but didn't come from man-made sources such as weapons fallout."  So, how many is that?"
Although the author didn't commit to a number, he seemed to lean towards the 94-98 that Stu had claimed. Other websites (WiseGeek, Yahoo! Answers) claim anywhere from 88 to 117!

Prof. Per-Ola Norrby weighed in via Twitter; originally favoring 90, he increased his bid to 92, and dug up primordial elements, which geophysicists peg at 84. Most recently, frequent JLC commenter gippgig argued:
"Make that 94 elements, 88 of which occur in significant amounts"
84? 88? 90? 92? 94? 117? That's a lot of different numbers for something we theoretically "know." After a while, I decided to update my original post with a dreaded tilde: the half-baked punctuation mark of the undecided.

Why rehash this rather academic debate? Because it's really important! The conversation illustrates the value of scientific discourse, where individuals find facts, bring them back to the table, and everyone weighs the information. Skeptical eyes inform conclusions - do I think that that "fact" holds water? Sam Arbesman wrote an entire book on this topic, The Half-Life of Facts, showing that research uncovers its share of "inviolable" truths we discover later just aren't so.

So we draw lines in the sand. Include radioactive isotopes? Include stellar chemistry? What's your detection limit? Measurement technique? Where's your cutoff? How many atoms?

An old joke - ask ten organic chemists what "large scale" means, and you'll get ten answers. The 2012 Chemistry Nobel Prize blurred whole fields; where do chemistry and biology divide? Do they? For my part, I'm settled in on 94 'natural' elements for now, but I could be swayed depending on further data.

Perhaps most importantly, I again recommend chemistry class to all Middle Schoolers, painful or no. Thinking through these types of problems really helps you grow, and isn't that what school is for?


  1. So, what was your basis for 94? I can live with it, but I'm curious about your limits. Did you include At, number 85? Do we have more or less of that than of Am, number 95? In any case, we're down to counting single atoms in any sample of ore you could name, but yes, we can detect that they have been there (only by their radiation signature when they are destroyed, so they're no longer there when we detect them...).

  2. See, you scientists can't even agree on the number of naturally occurring elements, so why should we believe what you say about evolution or climate change? ;)

  3. I remember being graded on whether I got the "exact" answer all the time in chemistry: correct yield, correct # of elements, the "correct" answer. Perhaps we should shy away from this whole notion of the "correct" answer. Obviously the number of naturally-occurring elements shouldn't be on the exam!

    (Ok, ok- maybe we could ask for a general answer- no specifics- just be aware of the debate)