fluoride fluoride fluoride names iupac name fluoride identifiers cas number 16984-48-8 y 3d model (jsmol) interactive image chebi chebi:17051 chembl chembl1362 y chemspider 26214 y gmelin reference 14905 kegg c00742 y mesh fluoride pubchem cid 28179 unii q80vpu408o y inchi inchi=1s/fh/h1h/p-1 ykey: krhyyfgtrywzrs-uhfffaoysa-m y smiles properties chemical formula f− molar mass 18.998403163 g·mol−1 conjugate acid hydrogen fluoride thermochemistry std molarentropy (s⦵298) 145.58 j/mol k (gaseous) std enthalpy offormation (δfh⦵298) −333 kj mol−1 related compounds other anions chloridebromideiodide except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references this article is about the fluoride ion. for a review of fluorine compounds, see compounds of fluorine. for the fluoride additive used in toothpaste, see fluoride therapy. fluoride (/ˈflʊəraɪd, ˈflɔːr-/) is an inorganic, monatomic anion of fluorine, with the chemical formula f− (also written −), whose salts are typically white or colorless. fluoride salts typically have distinctive bitter tastes, and are odorless. its salts and minerals are important chemical reagents and industrial chemicals, mainly used in the production of hydrogen fluoride for fluorocarbons. fluoride is classified as a weak base since it only partially associates in solution, but concentrated fluoride is corrosive and can attack the skin. fluoride is the simplest fluorine anion. in terms of charge and size, the fluoride ion resembles the hydroxide ion. fluoride ions occur on earth in several minerals, particularly fluorite, but are present only in trace quantities in bodies of water in nature. nomenclature fluorides include compounds that contain ionic fluoride and those in which fluoride does not dissociate. the nomenclature does not distinguish these situations. for example, sulfur hexafluoride and carbon tetrafluoride are not sources of fluoride ions under ordinary conditions. the systematic name fluoride, the valid iupac name, is determined according to the additive nomenclature. however, the name fluoride is also used in compositional iupac nomenclature which does not take the nature of bonding involved into account. fluoride is also used non-systematically, to describe compounds which release fluoride upon dissolving. hydrogen fluoride is itself an example of a non-systematic name of this nature. however, it is also a trivial name, and the preferred iupac name for fluorane. occurrence fluorite crystals fluorine is estimated to be the 13th-most abundant element in earth's crust and is widely dispersed in nature, entirely in the form of fluorides. the vast majority is held in mineral deposits, the most commercially important of which is fluorite (caf2). natural weathering of some kinds of rocks, as well as human activities, releases fluorides into the biosphere through what is sometimes called the fluorine cycle. in water fluoride is naturally present in groundwater, fresh and saltwater sources, as well as in rainwater, particularly in urban areas. seawater fluoride levels are usually in the range of 0.86 to 1.4 mg/l, and average 1.1 mg/l (milligrams per litre). for comparison, chloride concentration in seawater is about 19 g/l. the low concentration of fluoride reflects the insolubility of the alkaline earth fluorides, e.g., caf2. concentrations in fresh water vary more significantly. surface water such as rivers or lakes generally contains between 0.01 and 0.3 mg/l. groundwater (well water) concentrations vary even more, depending on the presence of local fluoride-containing minerals. for example, natural levels of under 0.05 mg/l have been detected in parts of canada but up to 8 mg/l in parts of china; in general levels rarely exceed 10 mg/litre in parts of asia the groundwater can contain dangerously high levels of fluoride, leading to serious health problems. worldwide, 50 million people receive water from water supplies that naturally have close to the "optimal level". in other locations the level of fluoride is very low, sometimes leading to fluoridation of public water supplies to bring the level to around 0.7–1.2 ppm. mining can increase local fluoride levels fluoride can be present in rain, with its concentration increasing significantly upon exposure to volcanic activity or atmospheric pollution derived from burning fossil fuels or other sorts of industry, particularly aluminium smelters. in plants all vegetation contains some fluoride, which is absorbed from soil and water. some plants concentrate fluoride from their environment more than others. all tea leaves contain fluoride; however, mature leaves contain as much as 10 to 20 times the fluoride levels of young leaves from the same plant. chemical properties basicity fluoride can act as a base. it can combine with a proton ( h+): f− + h+ → hf (1) this neutralization reaction forms hydrogen fluoride (hf), the conjugate acid of fluoride. in aqueous solution, fluoride has a pkb value of 10.8. it is therefore a weak base, and tends to remain as the fluoride ion rather than generating a substantial amount of hydrogen fluoride. that is, the following equilibrium favours the left-hand side in water: f− + h2o ↽ − ⇀ hf + ho− (2) however, upon prolonged contact with moisture, soluble fluoride salts will decompose to their respective hydroxides or oxides, as the hydrogen fluoride escapes. fluoride is distinct in this regard among the halides. the identity of the solvent can have a dramatic effect on the equilibrium shifting it to the right-hand side, greatly increasing the rate of decomposition. structure of fluoride salts salts containing fluoride are numerous and adopt myriad structures. typically the fluoride anion is surrounded by four or six cations, as is typical for other halides. sodium fluoride and sodium chloride adopt the same structure. for compounds containing more than one fluoride per cation, the structures often deviate from those of the chlorides, as illustrated by the main fluoride mineral fluorite (caf2) where the ca2+ ions are surrounded by eight f− centers. in cacl2, each ca2+ ion is surrounded by six cl− centers. the difluorides of the transition metals often adopt the rutile structure whereas the dichlorides have cadmium chloride structures. inorganic chemistry upon treatment with a standard acid, fluoride salts convert to hydrogen fluoride and metal salts. with strong acids, it can be doubly protonated to give h2f+. oxidation of fluoride gives fluorine. solutions of inorganic fluorides in water contain f− and bifluoride hf−2. few inorganic fluorides are soluble in water without undergoing significant hydrolysis. in terms of its reactivity, fluoride differs significantly from chloride and other halides, and is more strongly solvated in protic solvents due to its smaller radius/charge ratio. its closest chemical relative is hydroxide, since both have similar geometries. naked fluoride most fluoride salts dissolve to give the bifluoride (hf−2) anion. sources of true f− anions are rare because the highly basic fluoride anion abstracts protons from many, even adventitious, sources. relative unsolvated fluoride, which does exist in aprotic solvents, is called "naked". naked fluoride is a strong lewis base, and a powerful nucleophile. some quaternary ammonium salts of naked fluoride include tetramethylammonium fluoride and tetrabutylammonium fluoride. cobaltocenium fluoride is another example. however, they all lack structural characterization in aprotic solvents. because of their high basicity, many so-called naked fluoride sources are in fact bifluoride salts. in late 2016 imidazolium fluoride was synthesized that is the closest approximation of a thermodynamically stable and structurally characterized example of a "naked" fluoride source in an aprotic solvent (acetonitrile). the sterically demanding imidazolium cation stabilizes the discrete anions and protects them from polymerization. biochemistry at physiological phs, hydrogen fluoride is usually fully ionised to fluoride. in biochemistry, fluoride and hydrogen fluoride are equivalent. fluorine, in the form of fluoride, is considered to be a micronutrient for human health, necessary to prevent dental cavities, and to promote healthy bone growth. the tea plant (camellia sinensis l.) is a known accumulator of fluorine compounds, released upon forming infusions such as the common beverage. the fluorine compounds decompose into products including fluoride ions. fluoride is the most bioavailable form of fluorine, and as such, tea is potentially a vehicle for fluoride dosing. approximately, 50% of absorbed fluoride is excreted renally with a twenty-four-hour period. the remainder can be retained in the oral cavity, and lower digestive tract. fasting dramatically increases the rate of fluoride absorption to near 100%, from a 60% to 80% when taken with food. per a 2013 study, it was found that consumption of one litre of tea a day, can potentially supply the daily recommended intake of 4 mg per day. some lower quality brands can supply up to a 120% of this amount. fasting can increase this to 150%. the study indicates that tea drinking communities are at an increased risk of dental and skeletal fluorosis, in the case where water fluoridation is in effect. fluoride ion in low doses in the mouth reduces tooth decay. for this reason, it is used in toothpaste and water fluoridation. at much higher doses and frequent exposure, fluoride causes health complications and can be toxic. applications