So bright and aggressive that everything slips on it

It is not a news agency, although it is known as Efe. The number 9 of the periodic table is the smallest of the family of halogens (yes, those same gases that filled light bulbs), so called because of their extraordinary ability to form salts (halos in Greek). Fluorine was first found in 1670 by the German glassmaker Henry Schwandhard when he worked with a colorful mineral called fluorite. It turns out that when this mineral is acidified with strong acids it releases a yellow-green gas, so ferocious and corrosive with everything that surrounds it, that it went so far as to wear the lenses of its discoverer's glasses when he approached to smell it (we do not know if in that careless attempt also burned his beard or moustache).

It is indeed the same fluoride as toothpastes, but rest assured: this element is not so harmful and dangerous in toothpaste, as it is joined to other elements that placate it and contribute to reducing dental caries and helping the mineralisation of our teeth.

In addition, when some molecules that carry fluoride are illuminated with dim light, they glow in the dark offering magnificent colors. These fluorescent materials, besides shining at all parties when present in T-shirts and sports shoes, are also very useful for detecting fake banknotes. Molecular biologists, for example, use them to differentiate between cells that have been genetically manipulated, or those that carry certain markers labeled with fluorescent antibodies.

The name fluorine is peculiar, since it comes from its ability to "flow" (fluere in Latin), as noble and gentle river... Nothing could be further from the truth, and that is that fluorine, in addition to drilling through glass, gets along very badly with almost all compounds that contain hydrogen: such as water, ammonia and almost all organic compounds, with which it reacts violently and sometimes explosively.

But without a doubt, the most amazing thing about this element, capable of reacting with almost anything, is that, if an organic molecule, called polyethylene has all its hydrogen atoms replaced by fluorine, it turns out to be an impermeable, flexible compound that does not conduct electricity and is practically inert, since it does not react with anything. Literally, this new material, with its low resistance coefficient, seems to be completely slippery. You can heat it up to 270ºC or cool it down to almost absolute zero (-270ºC) and it doesn't even notice. So remember, the next time you stick the omelet in the frying pan, don't think about putting toothpaste in it. It's a slippery Teflon thing...

By José M. Pérez de la Lastra.