The properties of fluorine and its compounds

Fluorine is the second periodic element of Group VIIA in the p-region of the chemical periodic table. And fluorine is synthesized during the star explosion and the supernova explosion. The cosmic abundance is 843, which ranks 24th: The crustal abundance is 950, which ranks 13th. In 1670, H.Schwanhardt mixedsulfuric acid with fluorite to obtain impure hydrofluoric acid. In 1771, C. W. Scheele obtained relatively pure hydrofluoric acid. In 1886, H. Moissam electrolyzed the mixture of potassium hydrofluoride and anhydrous hydrogen fluoride to obtain fluorine at low temperature. Because of the development of fluorochemicals, fluorides such as XeF2, XeF4, XeF6, and XeOF2 were found and one new branch of chemistry emerged:Noble-gas chemistry.


The atomic radius (covalent radius) of fluorine is 64pm, radius of F- is 136pm. Atomic weight: 18.99984; Atomic volume: 17.1 cm3/mol; Density: 1.696 g/dm3; Specific heat capacity: 824 J/(kg·k); Melting point -219.62°C; Boiling point: -188.14°C. The heat of vaporization is 169.452kJ/kg and the heat of fusion is 41.84kJ/kg. Fluorine is diatomic molecule, is yellow in color, and have a strong pungent odor. And fluorine is molecular crystal, which is diamagnetic and non-superconducting.


The valence electron configuration of fluorine is 2s22p5, electronegativity is 4.0, the first electron affinity is 322.31kJ/mol, the first ionization energy is 1680kJ/mol, the standard electrode potential is 2.870V, oxidation number is -1, valence is -1. Fluorine is the most active non-metal elements, which can directly interact with all metal elements at low temperatures. Even gold can burn in fluorine gas after it is heated. Fluorine can also directly combined with rare gas elements, and even directly displace the oxygen in the water. Fluorine is only soluble in common alkalis, and it does not react with strong bases and triacids. And fluorine can form anaerobic acid salts with all metals. Fluorine compounds mainly include fluorite (CaF2), cryolite (3NaF·AlF3), fluoroapatite [CaF2(PO4)6], topaz [Al2(F9OH)2SiO4], and frost crystallite (NaCaAlF6·H2O). Fluorine can be used to produce the king of plastics PTFE, hydrofluoric acid, rocket oxidants, superacids, and it can also used for water fluorination and metal smelting. The fluorine gas can be obtained by electrolyisis and pyrolysis of fluoride.


After inhalation of fluoride (greater than 150mg) will cause a series of pain and bleeding and even death. If it is a non-lethal dose of fluoride, the recovery is extremely rapid especially with  the intravenous injection of calcium gluconate, about 90% of fluoride in the body will be eliminated, while the remaining 10% will takes a long time to remove. It must be treated immediately after being burned with fluoride. Magnesium glycerine can be coated on the burn site and then injected with calcium gluconate. In this method, fluorine will be fixed as insoluble fluoride.


Hydrogen fluoride (chemical formula: HF) is a very strong corrosive agent and is highly toxic. It is a colorless gas, but it will produce a pungent taste if it exceeds 3ppm in the air. Hydrofluoric acid can be absorbed through the skin, mucous membranes, respiratory tract and gastrointestinal tract. Hydrofluoric acid reacts with calcium ions and magnesium ions in the human body. So if people exposure to hydrofluoric acid, the symptoms may not appear until hydrofluoric acid reacts with calcium in the bones after a few hours. High concentrations of hydrofluoric acid solution can cause acute hypocalcemia, resulting in cardiac arrest and death.

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