Fluorine is a non- metallic chemical element, chemical symbol F., and Atomic number 9. Fluorine is one of the halogen elements and belongs to the group A of the periodic system. Fluorine Uses
It is located in the second period in the periodic table. The elemental substance of fluorine is F2, which is a light yellow gas and a highly toxic gas.
Highly corrosive fluorine gas, the chemical properties of extremely active, is one of the most oxidizing species, and even some inert gases under certain conditions, the reaction.
Fluorine is a key element in specialty plastics, rubber and refrigerators ( halothane ). Due to the special chemical properties of fluorine, fluorine chemistry has an important place in the history of chemical development.
Fluorine is a light yellow gas under standard conditions and a yellow liquid when liquefied. It became a colorless liquid at -252°C.
Due to the special chemical properties of fluorine, it is difficult to determine its physical properties. The accuracy of some data is not very high. The following data uses the latest data in the reference material or the data with similar time has more significant digits.
Atomic radius: 71pm (FF), 64pm (FC);
Ionic radius: 133pm;
Density: 1.696g / L (273.15K, 0 ° C);
Melting point: -219.66 ° C
Heat of fusion: 510.36 ± 2.1J · mol -1
Boiling point: -188.12 ℃
Heat of vaporization: 6543.69 ± 12.55J · mol -1 (84.71K, 9.81kPa)
Vapor pressure (s) (kPa):
Solubility: Reacts with water
Critical temperature: 144K]
Critical pressure: 55atm
Thermal conductivity: W / (m · K) 27.7.
Electronic layer arrangement: [He] 2s22p5
Primary oxidation state: F (-I), F (0)
Electronegativity: 3.98 (Bowling scale), 4.10 (Alle-Rocheau scale), 3.91 ( Mullican scale)
Crystal structure: simple cubic; unit cell parameters: a = 550 pm, b = 328 pm, c = 728 pm, α = β = γ = 90°
Chemical bond energy (kJ / mol): FF: 159; FH: 569, FO: 190; FN: 272; FC: 456; FB: 644, F-Al: 582
Affinity: 328.16kJ · mol -1
Ionization energy (kJ / mol): I 1 : 1681.0, I 2 : 3374; I 3 : 6050; I 4 : 8408; I 5 : 11023; I 6 : 15164; I 7 : 17867; I 8 : 92036;: I 9 : 106432;
Elementary dissociation energy: 157.7kJ · mol -1
F – Water and energy: -506.3kJ · mol -1
Standard entropy: F: 158.6J · mol -1 · K -1, F 2: 202.5J · mol -1 · K -1
Fluorine is the most non-metallic element among the known elements, which leaves it without a positive oxidation state. The ground state atomic valence electron layer structure of fluorine is 2s 2 2p 5, and fluorine has a very small atomic radius, so it has a strong tendency to get electrons and has strong oxidizing properties.
Interhalogen compounds of fluorine include ClF, ClF3, BrF3, IF6 and the like.
Reaction with elemental
The reaction of hydrogen and fluorine is extremely violent. Even in a low temperature of -250 ° C, it can explosively combine with hydrogen to generate hydrogen fluoride.
Not only hydrogen, but fluorine can react with elemental elements of all elements except O, N, He, Ne, Ar, and Kr to form the highest-valent fluoride. With the exception of metal fluorides with the highest valence and a few pure perfluorinated organic compounds, almost all compounds can react with fluorine.
Even perfluorinated organic compounds can be burned in fluorine gas if they are contaminated by combustibles. The reaction of most organic compounds with fluorine will explode, and the reaction of carbon or most hydrocarbons with excess fluorine will generate carbon tetrafluoride and a small amount of tetrafluoroethylene or hexafluoropropane.
Due to the strongly oxidizing properties of fluorine, fluorine can even directly react with xenon. Due to different reaction conditions, the products can be XeF2, XeF4, XeF6.
Generally, since nitrogen is inert to fluorine, it can be used as a diluent for gas-phase reactions. Nitrogen and fluorine can be combined into NF3 by a glow discharge method. When fluorine reacts with copper, nickel, or magnesium, a dense fluoride protective film is formed on the metal surface to prevent the reaction, so fluorine gas can be stored in containers made of these materials
Some special properties of F can be explained from the following aspects:
- F has the highest electronegativity.
- Standard electrode potential F 2 / F – maximum.
- The atomic radius of F is small, so the repulsive force of the lone pair of electrons in the fluorine molecule is quite large, and fluorine has no available d orbital, so it cannot form a d-pπ bond, which makes the FF bond energy very small.
- In fluoride, the chemical bond between fluorine and other elements is very strong. Among ionic halides, the fluoride lattice energy U is generally the largest; among covalent halides, the general fluoride △ f G m is the most negative.
The main purpose
- Utilizing the strong oxidizing property of fluorine, UF6 (g) can be prepared. Utilizing the different diffusion rates of 238UF6 and 235UF6 to separate uranium isotopes.
- For the synthesis of coolants such as Freon.
- The system for fluorinating reagents (xenon difluoride) and a metal smelting flux (cryolite), etc.
- ClF 3 and BrF 3 can be used as oxidants for rocket fuel.
- Used to make pesticides and fire extinguishers.
- Fluorinated hydrocarbons can be used as temporary substitutes for blood.
- Fluoride glass (containing ZrF4, BaF2, NaF) is 100 times more transparent than traditional oxide glass, and does not darken even under strong radiation; optical fiber made of fluoride glass fiber is more effective than SiO2 optical fiber A hundred times more effective.
- Fluoroplastics and fluoro rubbers have particularly excellent properties, For fluoride oxygen torch and manufacture of various fluorides.
- Fluorine is also added to toothpaste as fluoride toothpaste. Sodium fluoride reacts with basic calcium phosphate in the teeth to produce harder and less soluble calcium fluorophosphate.
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Fluorine is the most abundant isotope in nature only 19F. There are 18 known isotopes of fluorine, and only 19F is stable. 18F is a good positron source and is often used in the synthesis of PET tracers for positron emission computed tomography. The most commonly used tracer in clinical practice—fluoro-18-generation deoxyglucose (18F-FDG) is a tracer containing fluorine-18.
|symbol||Proton||neutron||Quality (u)||half life||Nuclear spin||Relative abundance|
|14 F||9||5||14.03506 (43) *||2-*|
|15 F||9||6||15.01801 (14)||410 （60） E-24 s [1.0 (2) MeV]||(1/2 +)|
|16 F||9||7||16.011466 (9)||11 (6) E-21 s [40 (20) keV]||0-|
|17 F||9||8||17.00209524 (27)||64.49 (16) s||5/2 +|
|18 F||9||9||18.0009380 (6)||109.771 （20） min||1+|
|19 F||9||10||18.99840322 (7)||stable||1/2 +||1.0000|
|20 F||9||11||19.99998132 (8)||11.163 (8) s||2+|
|21 F||9||12||20.9999490 (19)||4.158 (20) s||5/2 +|
|22 F||9||13||22.002999 (13)||4.23 (4) s||4+, (3+)|
|23 F||9||14||23.00357 (9)||2.23 (14) s||(3 / 2,5 / 2) +|
|24 F||9||15||24.00812 (8)||400 (50) ms||(1,2,3) +|
|25 F||9||16||25.01210 (11)||50 (6) ms||(5/2 +) *|
|26 F||9||17||26.01962 (18)||9.6 (8) ms||1+|
|27 F||9||18||27.02676 (40)||4.9 (2) ms||5/2 + *|
|28 F||9||19||28.03567 (55) *||<40 ns|
|29 F||9||20||29.04326 (62 *||2.6 (3) ms||5/2 + *|
|30 F||9||twenty one||30.05250 (64) *||<260 ns|
|31 F||9||twenty two||31.06043 (64) *||1 # ms [> 260 ns]||5/2 + *|
* Calculated theoretically, no experimentally proven data.
Safety of fluorine compounds
Fluorine compounds are harmful to the human body. A small amount of fluorine (within 150mg) can cause a series of pain. A large amount of fluoride can cause acute poisoning when it enters the body. Depending on the amount of inhaled, various conditions can occur, such as anorexia, nausea, abdominal pain, stomach ulcers, cramps, bleeding and even death. If the amount of poisoning is insufficient to cause death, the human body can quickly recover from fluorosis.
Especially when using the intravenous or intramuscular injection of calcium gluconate, about 90% of the fluorine can be quickly eliminated, and the remaining fluorine needs time to remove. Frequent exposure to fluoride can easily cause bones to harden, become brittle, and teeth to become brittle and broken. Excessive fluoride in drinking water in some areas can easily lead to fluoride poisoning.
Trace amounts of fluorine are good for preventing dental caries. If the fluorine content in the water is less than 0.5 ppm, the incidence of dental caries will reach 70% to 90%. However, if the fluorine content in drinking water exceeds 1 ppm, the teeth will gradually become spots and become brittle. When the fluorine content in drinking water exceeds 4 ppm, people are susceptible to fluorosis, which causes bone marrow deformities. The method to reduce the fluoride content in drinking water is to boil drinking water.
Insoluble fluoride has low toxicity and no irritation to the skin. However, if a large amount of dust is inhaled, it is easily absorbed by the human body and chronically poisoned. Soluble fluoride can be quickly excreted after being absorbed. It can cause gastrointestinal bleeding and death after swallowing 5-10g.
Acidic fluorides, such as hydrofluoric acid and fluoboric acid, can severely erode the skin, causing swelling and spreading at the contact area, resulting in hard-to-heal ulcers. Elemental fluorine, hydrogen fluoride and other gases have irritation to the eyes and nose. Excessive inhalation can cause severe bronchitis and pulmonary edema, leading to death.
The most serious and dangerous for people working with fluoride is face and skin exposure to fluoride and fluoride. Therefore, when using fluorine and fluoride, the operating procedures must be followed, and reliable safety measures must be taken, including operating utensils, rubber gloves, covered protective masks and gas masks with anti-acid gas. The workplace should have good ventilation facilities, and explosion-proof devices should be provided for items with high reactivity.
When burned by hydrogen fluoride and other fluorides, it is necessary to timely deal with the burned area, and then wash it with a large amount of water, and then coat it with glycerol magnesium oxide. The most appropriate method is to immediately inject calcium gluconate in the affected area to fix the fluorine to insoluble fluoride.
In addition, the use of hexaflurane flushing is a good way to deal with hydrofluoric acid accidents. The principle of hexaflurane is to reduce the number of hydrogen ions and fluoride ions in the human body through neutralization and coordination.
Some organic fluorides are very toxic. Among them, for fluorinated carboxylic acids, the general formula is F(CH2)nCOOH. If n is an odd number, the organic compound is extremely toxic. When n is an even number, the toxicity is very small or non-toxic. . At the end of November 2013, there was a fatal case of express delivery of methyl fluoroacetate, in which the fluoroacetic acid portion of methyl fluoroacetate was n = 1.
The toxicity of fluorine to insects is similar to that of hydrogen fluoride, and the toxicity to plants is similar to that of sulfur dioxide. Fluorine compounds can cause white spots or brown spots on plant leaf ends and veins.