Element of the month: Cool as helium


This month’s ‘in your element’ article (subscription required) is also a winning entry from last year’s competition. Christine Herman, known on Twitter at @CTHerman, a PhD student at the Department of Chemistry, University of Illinois at Urbana-Champaign, who also likes to write about science — for example she contributes to C&En’s Just Another Electron Pusher — shares why she loves helium.

In 1868, astronomers Jules Janssen and Norman Lockyer — who was about to found a certain Nature journal — both noticed (independently) a bright yellow line in the spectrum of the Sun that could not be accounted for by known elements. The suggestion that this line might come from an element present in the Universe but so far undiscovered on Earth seemed bizarre at first, but was to be later unambiguously backed up. Luigi Palmieri detected this element in 1882 in Mt Vesuvius’ lava, and William Ramsey managed to isolate it in 1895 by treating a sample of the uranium mineral (cleveite) with sulfuric acid, liberating helium that had been produced by the radioactive decay of uranium.

It’s perhaps no wonder that this noble gas wasn’t noticed earlier — it is, after all, colourless, odourless, tasteless, non-toxic, and escapes easily from the Earth’s atmosphere so that its concentration is only about 0.0005% by volume. It does however get trapped under the surface, usually with natural gas, and this is where we get the helium we need.

And need it we do, not just for balloons and squeaky voices at parties. You already know this if you’re, among other things, a paleontologist, a deep-sea diver or an arc welder; read Herman’s article to find out more.

She does make a fair point — helium is cool. So much so that many scientists in many fields (for example physics and medicine but also nuclear energy applications) use it as a cryogen. And if you go down to temperatures below 2 K, helium becomes downright bizarre and very intriguing: it adopts a superfluidic state that has no viscosity but a very high thermal conductivity. It is also enticing to chemists who, undeterred by its inertness, keep trying to combine it with various elements. Some of these — excited dimers rather than actual compounds — went on to find a use in lasers.

And, as if helium wasn’t exciting enough in its own right, antihelium observed last year made for the heaviest anti-particles produced so far. All in all, colourless, odourless, tasteless, non-toxic element 2 is very far from dull.

Anne

Anne Pichon (Associate Editor, Nature Chemistry)