Chemistry
Liquid fluorine in a cyrogenic bath

Characteristics and Discovery of Fluorine



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Liquid fluorine in a cyrogenic bath
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"Characteristics and Discovery of Fluorine"
Caption: Liquid fluorine in a cyrogenic bath
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Image by: Prof B. G. Mueller
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Fluorine is the ninth element in the periodic table. It is the most reactive and electronegative of all elements. The lightest of all the halogens, fluorine has a light yellow color, is corrosive and flammable. It is composed of diatomic molecules. This element is extremely reactive so when it is handled it requires care. Fluorine-19 is its only stable isotope.

Discovery

The mineral fluorspar was used in metal refining in the 1500s. Today, this mineral is knows as calcium fluoride. Fluorspar joined with the undesired parts of metal ores, which meant that the metal was able to be collected without impurities. Even though this is not fluorine, both share “fluor” which came from the Latin, “fluere,” which means “to flow”

Many tragic attempts were made to isolate fluorine. Through these attempts, many scientists were blinded or killed.

After correspondence with Andre-Marie Ampere, Humphry Davy was able to announce the discovery of fluorine. The name had been suggested by Ampere.

In 1886, the French chemist Henri Moissan, isolated fluorine, after being poisoned several times in his experimentation. He used electrolysis of dry potassium hydrogen fluoride and anhydrous hydrofluoric acid to finally isolate this element. Final success, with limited corrosion, was accomplished by using a platinum container, fluorite stoppers, and cooling the solution to -23 degrees Fahrenheit. The element was discovered at the positive electrode.

For his work in this field, Henri Moissan received the Nobel Prize in Chemistry in 1906.

Physical properties

The diatomic molecules, which form fluorine, are gaseous when at room temperature. Its very pale yellow color can be seen down the axis of a long tube when it is in its concentrated gaseous form. When seen from the side of a glass tube it appears to be transparent. It also appears this way when allowed to escape into the atmosphere. When concentrations go as low as 20 parts per billion, it possesses a pungent odor.

Fluorine, when it is condensed at -307 degrees Fahrenheit, turns to a bright yellow liquid. It solidifies at -363 degrees Fahrenheit. Its solid structure is a cubic form called beta-fluorine. When it is a solid, it is transparent and soft. At -378 degrees Fahrenheit it turns into alpha-fluorine, a opaque monoclinic structure, with close layers of molecules. When changing to the solid state it requires a great deal of energy which makes the transition so violent it can blow out windows.

Atomic structure

One atom of fluorine has nine protons and nine electrons. The outer electrons are separate so do not protect each other from the nucleus. They have a high effective nuclear charge. Fluorine also has a small covalent radius of less than 60 picometers.

Molecular structure

As a molecule all of fluorine's electrons are paired. This means that elemental fluorine is diamagnetic, it is slightly repelled by magnets. Due to the difficulties in handling fluorine gas and the need to purify it of any paramagnetic oxygen, the magnetic susceptibility was not completed until 1999.

Fluorine molecules have a bond order of exactly one, or exactly single bonded diatomic molecules. The outermost electrons are at the second energy sub-level. At this location there is no d sub-shell.

Due to its flammability and explosiveness, fluorine is always handled with extreme care. Today it can be found in rocket fuel, etching solution, toothpaste, uranium purification and refrigeration fluids






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