The Formidable Element Fluorine

fluoride toothpaste

The Element Fluorine

Everyone is familiar with the element fluorine– maybe because it is found in household items, such as toothpaste, or maybe just because fluorine is an amazingly dangerous element. This halogen element is the lightest of its group and is the 13th most abundant element in the Earth’s crust.

At room temperature, this nonmetal element exists as a gas and possesses the ability to form diatomic molecules. While fluorine’s pale, yellow-green color is interesting to look at, it is important to stay away from this violently reactive gas. Let’s learn more about this terrorizing element. 

Cool Facts About Fluorine

  1. The main mining areas of fluorite are China, Mexico, and Western Europe. 
  2. Fluorine was not commercially produced until World War II, when it was used to make atom bombs.
  3. The Heinz Maier Leibnitz Research Neutron Source is a powerful neutron source. Using this, the structure of solid fluorine has been discovered. This is a great breakthrough because of the many failed attempts in trying to unveil the crystalline structure of the solid. When trying to use X-rays to accomplish this in 1968, it ended in an explosion.
  4. This gaseous element only presents itself as a solid at a temperature of -220˚C.  
  5. If you ever find yourself caught in a fluorine fire, do not waste time by running for water or your fire extinguisher. These will only dramatize the fire. Make sure to extinguish the source of fluorine, as this is the only effective way to fight the fire. 
  6. The name is derived form the Latin ‘fluere’, meaning to flow, because the mineral fluorspa, CaF2, was used as a flux.

Fluorine in the Periodic Table

The element fluorine has an atomic symbol of F, and atomic number 9. It sits at the top of the halogen group, group 17, to the right of oxygen and the left of the element neon. Fluorine is above chlorine on the periodic table, and is the lightest, most dangerous, and most reactive of all the halogens.

The fluorine atom has an electron configuration of [He] 2s22p5, or 1s22s22p5 and it the most electronegative element on the periodic table, with an electronegativity of 3.98. It will violently rip an electron off almost any other atom and is very difficult to isolate.

Fluorine has 7 valence electrons. It needs only 1 more electron to complete its second shell, which is why it is so reactive and electronegative.

Acid or Not?  

There are numerous compounds that fluorine exists in, including hydrofluoric acid (HF). After learning about periodic trends, it is reasonable to assume that HF would be a strong acid. Another reason to assume its strong acidity is the behavior of fluorine and hydrogen atoms’ orbitals, as they overlap each other.

However, HF is surprisingly a weak acid with a pKa of 3.1.This is simply due to fluorine’s small F ion. Therefore, all of its negative charges are concentrated to the center. When put in water, HF will initially dissociate to about completion. After dissociation, HF will start to undergo other reactions with itself and the water. The more water there is, the weaker HF becomes. The hydronium cation and F come together to form H3O+, which will decrease HF’s acidity. 

Even though HF is a weak acid, it is highly corrosive, even towards glass. Therefore, it is safer to store it in a plastic container. Furthermore, HF will numb your nerves, so if the chemist is unaware of its toxicity, he or she may not know to seek help if in contact with it. 

Danger! Danger!

Fluorine gas occurs in very low concentrations in the environment. Additionally, it is almost never in its pure elemental state, due to its high reactivity. The element exists in many different compounds that vary in toxicity. However, a general rule is that as the solubility of the compound increases, the more toxic it is to humans, because of how it can easily be absorbed. Short-term exposure to this gas will cause irritation to the eyes, skin, and lungs. At higher concentrations, the gas will impair your breathing and can eventually lead to death. 

Fluorine is one of the most corrosive elements, making it an element to beware of. In its gas form, it is extremely toxic because of how violently reactive it is. Furthermore, the element is difficult to isolate without risking an explosion.

How to Protect Yourself

Now that we have scared ourselves from ever wanting to get in close proximity with this element, I am going to tell you how you can protect yourself from it. Just make sure you are wearing a self-contained breathing apparatus and that it is covering your entire face. Additionally, when working with fluorine, make sure the space is in pressure-demand or positive pressure mode. Easy, right? 

Fluorine’s Applications in Today’s World

How can an element seemingly as aggressive as fluorine have any use? Let’s find out. 

Fluorine is a great nuclear material and an excellent electrical insulator. This makes it ideal for the production of nuclear power plants and electrical towers. Additionally, fluorine is in the manufacturing of semiconductor devices- electronic components that utilize semiconductor material. Both molecular and atomic fluorine fulfills this role and is used for plasma etching and flat panel display production. 

One of the most important and common applications of fluorine gas is for uranium enrichment, which involves the metal being in its gas state. The gas state is achieved by producing the easily sublimable uranium hexafluoride. Through centrifugation, this vapor is enriched, meaning it increases in the concentration of the uranium isotope U235. The uranium oxide that gets made is selectively converted to uranium hexafluoride because fluorine has only one naturally-occurring isotope. Therefore uranium hexafluoride will not affect the weight of the final product. Another benefit of uranium hexafluoride remains in its gas state at the operating temperature. 

Due to its high reactivity, fluorine can be used for rocket fuel. Liquid chemical rockets generally use fuel and oxidizer as a propellant. Common fuels are kerosene, alcohol, and liquid hydrogen, while common oxidizers obviously include fluorine. What makes fluorine such a great oxidizer? As discussed briefly, fluorine is a gas at room temperature and is one of few elements that is liquid at low temperatures. This, however, can make fluorine both difficult and dangerous to work with, especially when you also think about how corrosive and toxic it is. 

More Practical Applications

Compounds of fluorine have some more practical applications. Many fluorine compound-containing items are probably in your own homes:

From a young age, we are taught to not put anything dangerous in our mouths. However, if you want whiter teeth, you may have to. Fluoride toothpaste contains fluoride as an active ingredient.

Fluoride is a compound that comes from elemental fluorine salts combined with soil or rock minerals. It is naturally in human bones and teeth, so using fluoride toothpaste is safe and will definitely not explode in your mouth. Fluoride toothpaste is popular because it makes tooth enamel stronger and fights cavities effectively. The bacteria-containing plaque on teeth produces acidic saliva when feeding on sugar in the mouth. This weakens tooth enamel. Fluoride can help to protect against acidic saliva. Moreover, fluoride bonds with the calcium and phosphate ions in your enamel, forming fluorapatite, which hardens the teeth. Fluoride is even added to water to protect against tooth decay. Water fluoridation involves adding very low levels of fluoride to water to provide consistent teeth protection.

Sulfur hexafluoride, SF6, is a colorless, man-made, greenhouse gas. Direct contact with this gas causes frostbite, so make sure to avoid exposure. Otherwise, SF6 is non-flammable and non-reactive (at room temperature). Its chemical stability makes it a great electrical insulator and cooling medium. It is found in refrigerators, air-conditioners, and fire extinguishers. 

History of Fluorine 

fluorine element history periodic table

Fluorine Reactions

Fluorine is both the most chemically reactive and electronegative element. It has an electronegativity value of 3.98, which tells us about fluorine’s small atomic size and its high electron affinity. Fluorine will rapidly attack any metal that it encounters. Instead of naming all the elements that fluorine will react with, it will be much faster to just name the ones that do not react: argon, helium, and neon. Fluorine is a Lewis acid in weak acids, which as we learned, makes it an electron acceptor. Moreover, this is a strong oxidizing agent that contains seven negatively charged valence electrons, which very strongly bind to other positive protons to form F anions. 

Certain metals, such as nickel, copper, and aluminum, react poorly with fluorine. Storing fluorine can be difficult because of how corrosive it is. However, when nickel comes in contact with fluorine, it instantaneously covers itself with a fluoride layer, which we call a nickel (II) fluoride (NiF2) passivation layer. This layer protects the nickel from any further attack. Copper and aluminum will not react with fluorine at room temperature, and will only have a reaction at high temperatures. However, fluorine reacts very violently with all organic matter. 

Isolation of Fluorine

Elemental fluorine is pretty dangerous, as we have learned. However, through the electrolysis of potassium hydrogen difluoride solution in anhydrous hydrofluoric acid, fluorine can “easily” be obtained. The reason pure hydrofluoric acid is not used is because it is not an electrical conductor. This would then result in the hydroxide ions turning into oxygen ions. Mixing potassium hydrogen difluoride and hydrogen fluoride together ensures low operating temperatures of 86.85˚C and therefore reduces the need for great cell insulation. The electrode cell contains an anode made of hard, corrosive-resistant carbon, while the cathodes are made of strong steel. When the electrolysis process is finished, fluoride gas is formed. 

Fluorine Chemistry & Compounds

Oxidation States 

Fluorine has a very strong affinity for electrons, and fluorine always has a -1 oxidation state. when it forms compounds.

Hydrofluoric Acid

One of the most well known compounds of fluorine is hydrofluoric acid, a solution of hydrogen fluoride, with formula HF. It is a highly corrosive and dangerous acid. Hydrofluoric acid is also technically a weak acid, which means its Ka is not large. It can be formed by combining calcium fluoride and sulfuric acid. It is very dangerous, readily burns and penetrates the skin, and can kill you. Calcium hydroxide is a great way to neutralize it.

Uranium Hexafluoride

Uranium hexafluoride, UF6, is a white crystalline solid, and one of the most important fluorine compounds, because it is used to separate isotopes of uranium – U-235 from U-238. It’s molecule is a beautiful octahedral shape. At 56.5C it sublimes directly into a dense, toxic gas. It produces hydrofluoric acid upon contact with water, which caused 2 fatalities in 1944. There are 686,000 tons of depleted uranium hexafluoride, a mind-boggling quantity, stored in steel cylinders in Kentucky, Ohio and Tennessee that will need to be dealt with during the 21st century.

Toxicity of the fluoride ion

In very tiny amounts, the fluoride ion, or the bifluoride ion HF2, can pass through the human body, with no long term effects. This is why it is used in toothpaste. However, once you start getting over 100mg, the fluoride and bifluoride ions are dangerous, and just a few grams can be lethal.

Physical Properties of Fluorine Element

  • Fluorine symbol: F
  • Melting point: 53.48 K; −219.67°C; −363.41°F
  • Boiling point: 85.04 K; −188.11°C; −306.6°F
  • Density: 0.001553 g/cm3
  • Atomic weight: 18.998
  • Atomic number: 9
  • Electronegativity: 3.98
  • Classification: Halogen
  • Natural abundance in the Earth’s crust
  • Electron shell configuration: [He] 2s22p5
  • Isotopes: 19F is the only stable and naturally occurring isotope
  • Found naturally in the minerals: 0.054%
  • Toxicity: Toxic and reactive

Where can I buy this? 

Fluorine gas is extremely toxic and you likely do not want it in your home. 

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