9. Fluorine: Tyger Tyger, Burning Bright

Just try to tally the body count behind the periodic table’s most reactive element, and learn why you should drink it.

Featured above: Henri Moissan working his apparatus to isolate fluorine in 1886.

Not James Hetfield: It took a long time for anyone to update Pliny’s take on the elements, but after that, it took several more centuries for De Re Metallica to be translated into English. The first person to do so was then-engineer and future U.S. President Herbert Hoover, with assistance from his wife, Lou Henry.

“Halogen,” by the way, is a word that means “salt-former,” because of Group 17 elements’ tendency to, well, form salts. If that doesn’t make a ton of sense right now, it will when we get to sodium.

A Little Goes A Long Way: Our nameless, hapless victim died from a truly small amount of hydrofluoric acid. If you don’t have a solid reference for how much liquid 100ml is, we’re talking about the jar on the right:

It’s Not That Bad, It’s Worse: As acids go, hydrofluoric acid is not a particularly strong one. An acid’s strength is labeled on the pH scale, a measure of how many hydrogen ions it will release when in contact with another substance. This is the “hydro” of hydrochloric and hydrofluoric acids, as well as what the “H” stands for in “pH.” Hydrofluoric acid is no slouch, but there are plenty of other acids that do a better job of donating hydrogen ions. It’s the second half of hydrofluoric acid that makes it so hazardous: that highly reactive fluorine. While acid can cause burns that are highly dangerous, fluorine will go deeper and works on a longer time scale.

It’s Nice They Didn’t Need It: In this episode, I mention briefly the possibility that Neil Armstrong and Buzz Aldrin might not have returned from the Moon. In 1969, this was anything but unthinkable — this was a known and ultimately acceptable risk.

President Nixon’s speechwriter, William Safire, prepared a speech called, “In The Event Of Moon Disaster.” It’s a little surprising that this was eventually made public knowledge, but I think we’re all better for it. Benedict Cumberbatch performed a reading of the speech:

Episode Script

Pliny the Elder’s Naturalis Historia had been a landmark work of research, as we discussed in episode 4, but like all encyclopedias, it needed a little updating. Several volumes of the magnum opus were eclipsed by other authors over the years, but Naturalis Historia remained the definitive work on gems and minerals for a surprisingly long time after its publication in the year 79 AD. It wasn’t until 1556 that Georg Pawer sought to write the new book on mineralogy.

Pawer was a big fan of Pliny. He did more than emulate Pliny’s work, he candidly thanked him in his new book — and he really loved Pliny’s native tongue, Latin. Pawer was part of the New Latin movement, and preferred to go by his Latinized name: Georgius Agricola. He did the same with his book, giving it the frankly excellent name De Re Metallica and writing it entirely in Latin.

It was because of this linguistic choice that when Agricola described a mineral that helps molten metals flow more easily, he gave it the Latinized name fluorspar, directly inspiring the future designation of element 9 as fluorine.

You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.

Today, we’re peering into the eye of the tiger of the elements, fluorine.

Element nine comes by this nickname honestly: It packs a mighty bite. Fluorine is the single most reactive element on the entire periodic table.

If you recall previous episodes, you can probably guess the reason for fluorine’s extreme reactivity: Electrons. Like every element in the halogen group, fluorine is missing only one electron from its outermost valence shell. In the same way that lithium will violently jettison its extra electron to have a full valence shell, fluorine will perform some brutal acts to fill its valence shell to capacity.

Fluorine will rip electrons away from all but the most stable molecules, and does so in spectacular fashion. A stream of cold fluorine gas will cause some surprising substances to burst into flame, like glass, steel, and even asbestos — a supposedly fireproof material.

This behavior makes fluorine a much more powerful oxidizer than oxygen itself, so it’s a good thing that it’s pretty rare on Earth. Most chemists go their entire careers without ever seeing elemental fluorine for themselves, and they’d probably prefer to keep it that way.

In the 1990s, a geologist in Australia spilled fluorine on his lap in the form of hydrofluoric acid. It wasn’t very much, only about 100 milliliters — well under half a cup of liquid. A week later, doctors amputated his leg in a bid to save his life — but eight days after that, the man was dead.1

So you can probably guess why the group of scientists who spent a century searching for element 9 are sometimes referred to as “The Fluorine Martyrs.”

Carl Wilhelm Scheele’s name cropped up when we discussed oxygen, and he’ll probably pop up again in future episodes, too. He was one of the more prominent figures in early chemistry. He was building upon the the work of his predecessors when he deduced that fluorspar, the stone discovered by Agricola, contained a unique, previously unknown acid, which he dubbed fluoric acid (later amended to hydrofluoric acid). His case was compelling, but he couldn’t prove it.2

Other scientists were intrigued enough to keep investigating. Andre-Marie Ampere distilled a sample of hydrofluoric acid and noticed that it behaved similarly to hydrochloric acid. This makes sense, since chlorine occupies the spot directly below fluorine on the periodic table — but Ampere discovered this decades before the first periodic table would be written down. He didn’t make any more progress with the substance, but he wrote about these findings in his correspondence with English chemist Humphry Davy.

Davy carried the torch a little further. He ran an electrical current through hydrofluoric acid, similar to what we did with water in the episodes on hydrogen and oxygen. By this process, he did produce hydrogen gas, but didn’t succeed in isolating fluorine — it had instead immediately reacted with his chemical instruments. He did, however, realize that the mysterious substance “fluorine” was probably an undiscovered element, rather than some kind of compound. He also caused significant injury to his eyes and fingernails — but he was in good company, since Scheele and Ampere had suffered similar wounds.3

Thomas and George Knox were the next to try their hands at isolating fluorine. They never got that far, but they furthered the understanding of hydrofluoric acid, creating a gaseous form of it and cataloging its properties. Like Davy, they too were casualties of their own chemistry. Both suffered hydrogen fluorine poisoning, damaging their eyes, skin, and internal organs, nearly killing them both and confining George to a bed for three years.4

Several other scientists tried and failed in the quest for fluorine, including Paulin Louyet, Jérôme Nicklès, George Gore, and Edmund Fremy, and while all of them brought new insights to the table, none was able to finish the job. Many of them died in the attempt.5

It wasn’t until 1886 that one of Fremy’s students, Henri Moissan, finally succeeded in producing a sample of the elusive elemental fluorine. Fremy bubbled with pride, exclaiming,

A professor is always happy when he sees one of his students proceed farther and higher than himself.”

Clearly, Fremy hadn’t heard of Gilbert Lewis, the jealous genius who was always a nominee, never a Nobel Laureate.

At any rate, Moissan had brought this century-long chase to a close, and was granted his own Nobel Prize for the work. The committee praised his ability, saying, “The whole world has admired the great experimental skill with which you have studied that savage beast among the elements.” But that savage beast wasn’t quite finished wreaking havoc just yet: two months after collecting his prize, Moissan died at the age of 55, becoming the last of the renowned Fluorine Martyrs.6

So who discovered fluorine? Was it Agricola, who first noted the unique properties of fluorspar? Or Scheele, who saw the acidic properties locked within that rock? What about Ampere, who noted its similarity to chlorine, or Davy, who proposed that fluorine must be an element? Or was it only upon Moissan’s successful isolation of elemental fluorine that it could be called “discovered?”

The only honest answer is that all of these scientists helped in the discovery of fluorine, alongside dozens more. Agricola had no idea that his semiprecious stone contained a chemical element that could kill, and Henri Moissan couldn’t have distilled pure fluorine without centuries worth of work that preceded his own.

This isn’t just the case for fluorine. This is how all of science works — and really, all of history. Agricola is often called the “Father of Mineralogy,” and while he was an important scientist, he was mostly just writing down the wisdom of those who surrounded him. Fritz Haber might have fed the world, but if he hadn’t figured out how to fix nitrogen in soil, his colleague Bosch, or someone else entirely, would have gotten there eventually. As we saw at the outset of this series, even the periodic table itself didn’t spring fully formed from Dmitri Mendeleev’s insomniac head.

Telling the tale of history is a necessarily political act. It involves making a series of choices about what to say, how to say it, and what not to say.

Sometimes these choices are uncontroversial, like saying that Neil Armstrong was the first person to walk on the moon. Every informed person can agree on that fact. But do you mention that Buzz Aldrin was there, too? Michael Collins never set foot on the moon, but if he weren’t piloting the command module in lunar orbit, Neil and Buzz would still be on the moon today. How about the thousands of scientists and engineers in Cape Canaveral and Houston? Or the Soviets who had made so much progress in the space race in the preceding decades?

You can only take in one perspective at a time, even though none of them has an exclusive grip on the truth. That’s the case whether you’re getting your information from a textbook, a professor, or a podcast. It’s often convenient to learn the stories of people who made history, but also worth remembering that none of them achieved greatness on their own.

One of the most famous things Isaac Newton ever said was, “If I have seen further, it is by standing on the shoulders of Giants.” But even that wasn’t an original sentiment — he was simply putting his own spin on an expression that people had already been saying for 500 years. It turns out that none of us is standing on terra firma: it’s Giants all the way down.

Fluorine certainly isn’t the first element we’ve investigated that can be hazardous to your health, but it’s also an element that can be crucial for your

It’s not terribly surprising that fluorine is such a deadly substance. Most of the elements we’ve met so far seem determined to explode, scald, poison, or otherwise kill you in some way, even if you’re not trying very hard. But fluorine is also at the center of one of the most wide-reaching and successful public health initiatives in history.

In 1901, Frederick McKay was a newly minted dentist who had packed up all his things and moved from the East Coast to Colorado Springs to start a new life. He hadn’t been in town very long when he noticed something peculiar about these Coloradans: Most of them had disgusting teeth. And this was in 1901, when most people’s mouths were pretty gross to begin with. His patients’ teeth were often a mottled brown color, sometimes so badly stained that it looked like they were caked with chocolate.7

But strangely, their teeth weren’t undergoing rapid decay. In fact, it actually seemed like the patients with “Colorado Brown Stain,” had fewer cavities than their neighbors with pearly whites.

There was no shortage of theories about the cause of Colorado Brown Stain. Some blamed it on eating too much pork, or drinking bad milk, or maybe some kind of calcium deficiency. The real culprit, as you may have guessed, was abnormally high levels of fluoride in the drinking water. Not just in Colorado Springs, either, but in clusters all around the country. It turned out that industrial aluminum processing plants create a lot of fluoride as a waste byproduct, and it was pretty easily making its way into local water supplies. This might be the only time in history that industrial pollution actually had a positive effect on public health. It didn’t take long for dentists to figure out that if fluoride levels were kept in check, it would prevent cavities — and wouldn’t even cause the unpleasant side effect of Colorado Brown Stain.

This information might be slightly confusing after just hearing about the trail of bodies in the wake of element 9, but this is the crucial difference between fluorine and fluoride. Every element in the halogen group ends in -ine: Fluorine, chlorine, bromine, iodine, astatine, and tennesine. But when those pure elements are ionized, they all take an -ide suffix instead: fluoride, chloride, bromide, et cetera.

Before we go any further, let’s take a moment to see exactly what an ion is.

By this point, we know that atoms with different numbers of protons in their nuclei are different elements. All fluorine atoms have nine protons. Atoms of the same elements with different numbers of neutrons are called isotopes. And we’ve talked a lot about how some elements really want to gain or lose electrons to have a full valence shell. Fluorine is one of these, with an equal number of negative electrons and positive protons, giving it a net electrical charge of zero. But increasing its valence electrons from seven to eight is far more important than maintaining electric neutrality. So when fluorine steals some other atom’s electron to fill its valence shell, it has one more electron than it does protons — giving it a net electrical charge of minus one.

That’s all an ion is: an atom with a positive or negative electrical charge because it has either gained or lost electrons. Negatively charged ions, as we saw before, are given the -ide suffix, but positive ions are just called “ions.” For instance, lithium ions, or potassium ions. It would be nice if the naming convention were a little more consistent, but this is the nature of a patchwork of ideas such as the periodic table.

Once fluorine fills its valence shell and becomes fluoride, it’s done. While it retains the nuclear properties of fluorine, since it still has nine protons, fluoride gains the electrical stability of neon, whose valence shell is naturally filled with eight electrons. The tiger’s bite has been de-fanged, allowing element nine to be piped directly into your home with no fear of becoming the latest in the long canon of fluorine martyrs.

Just because it’s in your water supply does not make that a good source of fluorine for your element collection, unfortunately. There’s only about one ion of fluorine present for every million molecules of water that flow through your faucet, which means you’d have to somehow extract all the fluoride from a thousand liters of water just to get a gram of the stuff.

Once again, the pharmaceutical route is a pretty viable way to acquire the element we’re searching for: Fluorine can really fine-tune a molecule’s behavior, so it winds up in about 20% of all prescription drugs. You can even order tablets of relatively pure fluoride, marketed to people who drink well water or some other supply that’s not fluoridated.

Because of fluorine’s ability to form incredibly strong bonds, it finds its way into consumer products that require a high degree of strength or inertness. Polytetrafluoroethyle is probably the most prevalent example, a chemical coating that practically nothing on earth can adhere to. It’s more commonly known as Teflon, and it might already be present on cookware in your home.

It might appear that the discerning collector is out of luck this week, unless they have a death wish. We’ve seen precisely what hunting for elemental fluorine can do to a person, and indeed, I would certainly not recommend anyone try to synthesize concentrated fluorine from hydrofluoric acid.

Even if you could conduct the experiment without killing yourself, you’d have a new problem on your hands: Fluorine is practically impossible to store. It will chew its way out of practically any vessel you could store it in, and usually pretty quickly. But there is a safe, easy way you can ensure that you always have a pure sample of element nine in your collection — provided you’re willing to look really, really closely.

Antozonite is a specific variety of calcium fluoride that’s local to a mine in Wolsendorf, Germany. It contains trace amounts of radioactive uranium, which causes some interesting things to happen: As uranium embedded within the stone ejects radioactive particles, they collide with the calcium fluoride, occasionally breaking apart a molecule here or there. The calcium atoms clump together, leaving the fluorine to exist as pure, elemental F2 gas, trapped on all sides by nonreactive calcium fluoride molecules.8

These few and far between atoms of pure fluorine will find some way to escape the stone, given enough time. But by then, another alpha particle will have knocked loose another few atoms of fluorine.

For an element collector, it’s awfully considerate of nature to pack one of its most dangerous chemicals inside a self-sealing container.

Thanks for listening to the Episodic Table of Elements.

Music is by Kai Engel. To learn about Agricola’s surprising connection to an American president,.visit episodic table dot com slash fluorine.

Next time, we’ll bask in the soft glow of neon.

This is T. R. Appleton, reminding you that so many times, it happens too fast // You trade your passion for glory // Don’t lose your grip on the dreams of the past // You must fight just to keep them alive


  1. Fatality Due To Acute HF Exposure. Joseph Kwan, Director, Health, Safety and Environment Office, University of Vermont. Backed up on this site for archival purposes.
  2. The Royal Society of Chemistry, Fluorine, An Obsession With A Tragic Past. Richard Toon, September 2011.
  3. Humphry Davy: Poet And Philosopher, p. 174. Sir Thomas Edward Thorpe, 1896.
  4. Science History Institute, Not-So-Great Momens In Chemical Safety. Mark Michalovic, Summer 2008.
  5. The Story Of Chemistry, Anne Rooney.
  6. Lateral Science, The Tiger Of Chemistry.
  7. CDC, Achievements In Public Health, 1900-1999: Fluoridation Of Drinking Water To Prevent Dental Caries.
  8. Chemistry World, Fluorine Finally Found In Nature. Neil Withers, July 11, 2012.

4 Replies to “9. Fluorine: Tyger Tyger, Burning Bright”

  1. I love your podcast. I might be writing you more later about it. Right now I just want to comment that my iPad and phone say that the website is not secure. Does that have any implications for me? Thank you!

    1. Hi Leynia, thank you for both listening and commenting! I’m sorry for the rather alarming error message you’re receiving. Fortunately, it doesn’t mean anything bad for you or your devices! It sounds like I might need to make sure everything on the website’s back-end is up to date. I’ll take a look — thank you again!

  2. I just started listening so my comment is from two years ago. The music in the flooring chapter interferes with your with the ability to understand what you are saying. If you use music of a tone lower than the picture of your speech it would interfere less with what you are saying.

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