Everything Everywhere Daily: History, Science, Geography & More - Fluorine: The Most Reactive Element

Starting point is 00:00:00 There is an element so reactive that it was one of the last to be isolated, and chemists were injured just trying to obtain it. Yet once it was tamed, it became essential to everything from aluminum production and nuclear technology to medicine, batteries, and non-stick coatings. Its compounds have also been at the center of major debates over public health and environmental contamination. Learn more about the extraordinary element, fluorine, on this episode of Everything Everywhere Daily. from Nespresso. Blend wellness into your coffee routine with the coffee plus range, infused with functional benefits. Choose the coffee you love with added B vitamins, like coffee plus B12 to

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Starting point is 00:01:44 elemental fluorine because it is the most reactive element on the periodic table. That being said, almost everyone has encountered fluorine when it's bonded to something else to form a highly stable molecule. But before we get into the uses of fluorine, we should start with the basics of what it is. Fluorine has an atomic number of nine, meaning that there are nine protons in its nucleus, and it has the chemical symbol F. It's a member of the halogens, group 17 on the periodic table, along with chlorine, bromine, iodine, and acetine. At ordinary temperatures, elemental fluorine exists as F2, meaning two fluorine atoms are combined to make a fluorine molecule, and it makes a pale yellow gas. It is the most electronegative element,

Starting point is 00:02:33 and generally regarded as the most chemically reactive element on the periodic table. The reason for fluorine's extraordinary chemistry arises largely from its atomic strong. Fluorine has nine electrons with seven electrons in its outer shell. It needs only one additional electron to complete that shell, and it really wants to complete that shell. Fluorine therefore has an exceptionally strong tendency to attract electrons from other atoms. Its electronegativity on the Pauling scale is 3.98, the highest of any element. Because fluorine is so reactive, essentially no free elemental fluorine exists naturally near

Starting point is 00:03:17 the Earth's surface. It almost immediately combines with some other element. Fluorine is relatively uncommon in the universe. It ranks roughly 24th in cosmic abundance, with only about one fluorine atom for every few hundred million hydrogen atoms. Its scarcity is partly because ordinary stellar fusion does not produce fluorine efficiently. Most cosmic fluorine is thought to form in relatively specialized environments, including certain gas stars and supernovae.

Starting point is 00:03:48 The most important naturally occurring fluorine mineral is fluorite, also known commercially as Florospar. It consists of one calcium atom and two fluorine atoms. Other fluorine-containing minerals include fluoropatite, cryolite, and topaz. Fluorite is overwhelmingly the most important mineral commercially mined specifically as a source of fluorine. Fluorine-based minerals tend to be gorgeous. They can have deep, vibrant colors, and if you're in a mineral collecting, you can even find them relatively cheaply. The name fluorine comes from the Latin flueira, meaning to flow. Miners and metallurgists discovered long before anyone understood fluorine chemistry that fluorospar could be added to ores as a flux.

Starting point is 00:04:36 helping materials melt and flow more easily during smelting. Fluorine has one of the most dramatic discovery stories in all of chemistry. By the 17th and 18th centuries, experimenters knew that fluorite had unusual chemical properties. They discovered that treating fluorite with strong acids produced a substance capable of attacking glass. The Swedish chemist Carl Wilhelm Schill investigated fluorite in the 1770s and produced what we now recognize as hydrofluoric acid. Chemists eventually realized that chemicals produced from fluorite probably contained an unknown element analogous to chlorine.

Starting point is 00:05:15 In 1812, the French physicist and chemist, André Marie M. Perre proposed the name fluorine. But actually obtaining the element was another matter. The problem was that whatever apparatus researchers used tended to be attacked by the very substance they were trying to produce. Hydrofluoric acid was itself extremely dangerous, and newly liberated fluorine reacted violently with water, glass, metals, organic matter, and many electrode materials. The breakthrough finally came from the French chemist Henri Moisanne. Moisand dissolved potassium hydrogen fluoride, KHF2, in anhydrous hydrogen fluoride. This produced

Starting point is 00:05:58 an electrolyte through which sufficient electrical current could pass. He constructed specialized equipment using materials able to withstand the chemicals and cooled the apparatus significantly to suppress unwanted reactions. On June 26, 1886, Moisan successfully produced and identified elemental fluorine gas. Moisan received the 1906 Nobel Prize in Chemistry, in significant part for isolating fluorine. The basic electrochemical principle that he developed remained the foundation of industrial fluorine production. While fluorine is very reactive, once it reacts, however, it bonds so strongly that the resulting compound tends to be extremely stable. These seemingly contradictory properties of

Starting point is 00:06:46 fluorine both have industrial and commercial uses. One of the earliest uses of fluorine was in refining aluminum. Producing aluminum metal requires electrolyzing aluminum oxide. Pure aluminum oxide has an extremely high melting point, making direct electrolysis impractical. The Hall-Aru process dissolves alumina in a molten fluoride-based electrolyte, historically cryolite. This dramatically lowers the operating temperature and allows aluminum to be produced economically. One of hydrofluoric acid's most famous properties is its ability to attack glass. Fluoride chemistry can convert silicon-containing materials into fluorosilicate compounds, allowing high-hrulycuitism. hydrofluic acid to etch the surface. This makes hydrofluoric acid valuable for glass treatment,

Starting point is 00:07:37 industrial cleaning, semiconductor processing, and chemical manufacturing. It also happens to make hydrofluoric acid unusually hazardous. Unlike many acids that mainly cause surface burns, hydrofluic acid can penetrate tissue. Fluoride ions combined with calcium and magnesium potentially producing serious toxicity. Significant exposure, can therefore become medical emergencies, even when the initial burn doesn't appear to be catastrophic. One of fluorine's most strategically important applications is uranium enrichment. As I've covered in previous episodes, natural uranium consists primarily of uranium 238 with only about 0.7% uranium 235. Nuclear reactors and nuclear weapons require uranium with a much higher proportion

Starting point is 00:08:27 of uranium 235. Uranium metal itself is unsuitable for many isotope separation methods, but uranium can be converted to uranium hexafluoride. Uranium hexafluoride has the extremely useful property of becoming gaseous at relatively modest temperatures. The gas molecules containing U-235 are ever so slightly lighter than those containing uranium 238. This allows the isotopes to be separated using technologies such as gas,

Starting point is 00:08:59 gaseous diffusion historically, and today primarily gas centrifuges. Demand from the Manhattan Project and the nuclear industry played an important role in expanding industrial fluorine production during and after World War II. One of the best-known fluorinated materials is polytetrophlorophylline, or PTFE. But you probably know it better by its brand name, Teflon. Its repeating structure contains carbon atoms surrounded by fluorine atoms. The carbon fluorine bonds are exceptionally strong, and the fluorine effectively shields the carbon backbone. As a result, the material has low friction, resists many chemicals,

Starting point is 00:09:41 tolerates high temperatures, and doesn't readily react with other materials. PTFE and other related fluoropulomers are used far beyond cookware. They appear in chemical processing equipment, electrical insulation, aerospace systems, seals, tubing, medical devices, semiconductor plants, and countless specialized applications. PTFE and Teflon will be the subject of a future episode as their origins and how they work are really, really interesting. Closely related to PTFEs, but very different are PFS, or polyfluoral alkalpleks substances. They are a large family of synthetic chemicals valued for. resisting heat, water, oil, and chemical breakdown. They have been used in products such as

Starting point is 00:10:29 firefighting foams, stain-resistant fabrics, food packaging, industrial coatings, and some non-stick applications. The controversy is that PFAS breaks down extremely slowly, so they can persist in water, soil, wildlife, and the human body for years, earning the nickname Forever Chemicals. Their incredible stability actually is the problem. Certain P-FAS chemicals have been linked to health concerns, including immune defects, developmental problems, higher cholesterol, and increased risk of some cancers. And this, too, will be the subject of a future episode. Fluorine has also transformed refrigeration during the 20th century.

Starting point is 00:11:11 Early refrigeration systems sometimes use dangerous substances such as ammonia, sulfur dioxide, or methyl chloride. Chemists developed chloro-fluorocarbons, or CFCs, which appeared nearly ideal. They were stable, relatively non-flammable, and useful as refrigerants, aerosol propellants, and solvents. But, once again, their chemical stability became an environmental problem. CFC molecules survive long enough to reach the stratosphere, where ultraviolet radiation breaks them apart. Importantly, it's primarily the chlorine in the molecule, rather than the fluorine released from CFCs, that destroys stratospheric ozone. When CFCs were phased out, the replacement,

Starting point is 00:11:53 still relied on fluorine. HCFCs, or hydrochloral floral floral carbons, replace CFCs, but they still contain chlorine, so they've also been phased out. HFCs, or hydrofluoral carbons, replace them. They contain hydrogen, fluorine, and carbon, but no chlorine, so they do not significantly deplete the ozone layer. However, many HFCs are powerful greenhouse gases, so they too are being phased out. Fluorine plays an essential role in powering modern consumer electronics, as today's lithium-ion batteries regularly rely on fluorine chemistry. Lithium hexaflrophosphate serves as one of the most widely used electrolyte salts. When dissolved in organic solvents, this compound facilitates the

Starting point is 00:12:40 transport of lithium ions between battery electrodes. Fluorinated electrolyte additives and fluorinated electrode materials are also becoming increasingly important in battery research because chemists can use fluorine to alter voltage stability, conductivity, surface chemistry, and resistance to degradation. While fluorine has many uses, you probably thought of one immediately when you saw this episode title. Dental products. Fluoride, which is just a negative fluorine ion, can become incorporated into tooth minerals, making enamel more resistant to acid attack. It can also promote remineralization of early tooth decay. Fluoride can be found in almost all toothpaste, and many communities also adjust fluoride levels in drinking water. The current U.S. Public Health

Starting point is 00:13:31 Service recommendation is approximately 0.7 milligrams per liter, or 0.7 parts per million. The Centers for Disease Control states that fluoridation at recommended levels reduces tooth decay and sites in approximate 25% reduction in cavities among children and adults. Water fluoridation began in the United States in 1945 after observation showed that communities with certain naturally occurring fluoride levels had lower rates of dental cavities. For decades, major dental and public health organizations have strongly supported fluoridation because of its effect on tooth decay. However, the decision to fluoridate water has been controversial, as fluoride is toxic at high levels.

Starting point is 00:14:14 Excessive fluoride exposure, while children's permanent teeth are developing, can cause dental fluorosis, in which a nabble develops white streaks. Of all the uses for fluorine that I've covered, the benefits and drawbacks both pretty much stem from the exact same thing. Fluorine forms incredibly strong chemical bonds that do not break easily. Fluorine's reactivity allows it to, etch glass, processed metals, produce uranium hexafluoride, and modify surfaces. The strength of fluorinated compounds gives us chemically resistant plastics, durable coatings, powerful pharmaceuticals,

Starting point is 00:14:52 stable refrigerants, and batteries. In nature, it can form beautiful minerals and gemstones. But that same chemical stability created CFCs that survived long enough to reach the ozone layer, HFCs that are powerful greenhouse gases, and PFS compounds that can persist in the environment, environment for decades or even longer. Fluorine is not inherently a technological blessing or an environmental curse. It is an unusually powerful chemical tool that requires careful consideration of how it should be used. The executive producer of Everything Everywhere Daily is Charles Daniel.

Starting point is 00:15:32 The associate producers are Austin Otkin and Cameron Kiefer. My big thanks go to everyone who supports the show over on Patreon. Your support helps make this podcast. possible. And I also want to remind everyone about the community groups on Facebook and Discord. That's where everything happens that's outside the podcast. And links to those are available in the show notes. As always, if you leave a review on any major podcast app or in the above community groups, you too can have it read in the show.

Everything Everywhere Daily: History, Science, Geography & More - Fluorine: The Most Reactive Element

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