“Cuddle a chemist and see the reaction.” That’s a little chemistry joke that has been around for longer than I have. For chemistry is all about chemical reactions. We mix two or more substances together (we call these reactants), and they react to give new substances called products.
Reactants and products are often distinctly different in appearance, and this is how we know a chemical reaction has taken place. For example, if you mix vinegar and baking soda, it is immediately apparent something is happening: the mixture bubbles like mad as the bicarbonate in the solid baking soda is converted to gaseous carbon dioxide in a chemical reaction.
However, merely mixing two or more substances is no guarantee of a chemical reaction. Although we are surrounded by an atmosphere containing 78% nitrogen and 21% oxygen, these gases, fortunately for us, do not react with each other at ambient temperature, despite the fact oxygen is considered a very reactive species.
For an observable chemical reaction to occur, we require (in very simple terms) that the energy of the products is lower than the energy of the reactants, and that the energy barrier to the chemical reaction (there is always an energy barrier) is relatively low.
These conditions are almost always met in reactions of one element of the periodic table: fluorine.
Fluorine is the most reactive element on the periodic table. It reacts, often violently, with every other element, except helium and neon, and with essentially all chemical compounds. Sane chemists shun it. As it is so reactive, it must be stored in special steel or nickel cylinders, the insides of which are rendered unreactive by (careful) prior treatment with fluorine.
A colleague once told me the story of an unfortunate worker who managed (inadvertently, of course) to get his thumb in a stream of fluorine gas and was aghast to see the thumb catch fire. It really is that nasty.
And this makes it all the more surprising that German chemists last month reported the first discovery of elemental fluorine in nature. The fact is it so incredibly reactive means it is incredibly difficult to make, and it has long been thought there is no natural (i.e. non-laboratory) process that can produce fluorine.
However, it now appears this is not the case. Florian Kraus and co-workers have been studying the mineral “antozonite”, which is found in Bavaria and other parts of the world. This mineral, which is composed predominantly of calcium fluoride, is well known to emit a peculiar smell when crushed, and the source of this smell has been the subject of speculation since 1914.
Using several modern techniques, as well as his (or, more likely, his student’s) own nose, Kraus has now shown with certainty that small amounts of elemental fluorine are contained in antozonite, and are responsible for this smell.
In addition, he has proposed the fluorine is most probably formed from reaction of the calcium fluoride with particles given off in highly energetic radioactive processes, as the antozonite sample also contains small amounts of uranium.
This is quite a remarkable discovery that goes against many of our intuitive ideas about chemistry, and will result in the rewriting of more than a few textbook pages.
It should be emphasised there is a big difference between elemental fluorine and fluoride.
The latter is the reaction product of the former, and because of the way chemistry works, the more reactive a reactant, the less reactive is its product. So please, no letters about the fluorination of our water supply, OK?