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In chemistry, a fluoroanion or fluorometallate anion is a polyatomic anion that contains one or more fluorine atoms. The ions and salts form from them are also known as complex fluorides. They can occur in salts, or in solution, but seldom as pure acids. Fluoroanions often contain elements in higher oxidation states. They mostly can be ...
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.
There may also be energy changes associated with breaking of existing bonds or the addition of more than one electron to form anions. However, the action of the anion's accepting the cation's valence electrons and the subsequent attraction of the ions to each other releases (lattice) energy and, thus, lowers the overall energy of the system.
A cation is a positively charged ion with fewer electrons than protons [2] (e.g. K + (potassium ion)) while an anion is a negatively charged ion with more electrons than protons. [ 3 ] (e.g. Cl − (chloride ion) and OH − (hydroxide ion)).
The fluorine–fluorine bond of the difluorine molecule is relatively weak when compared to the bonds of heavier dihalogen molecules. The bond energy is significantly weaker than those of Cl 2 or Br 2 molecules and similar to the easily cleaved oxygen–oxygen bonds of peroxides or nitrogen–nitrogen bonds of hydrazines. [8]
Despite the low reactivity of the tetrafluoroborate anion in general, BF − 4 serves as a fluorine source to deliver an equivalent of fluoride. [2] The Balz–Schiemann reaction for the synthesis of aryl fluorides is the best known example of such a reaction. [3]
In calcium fluoride, the calcium cations are surrounded by fluorine anions that occupy the tetrahedral sites, with an 8:4 coordination number, fluorine to calcium. This ratio is consistent with the stoichiometry of the compound, where the ratio of fluorine to calcium is 2:1.
The bifluoride ion has a linear, centrosymmetric structure (D ∞h symmetry), with an F−H bond length of 114 pm. [1] The bond strength is estimated to be greater than 155 kJ/mol. [2] In molecular orbital theory, the atoms are modeled to be held together by a 3-center 4-electron bond (symmetrical hydrogen bond), [3] in a sort of hybrid between a hydrogen bond and a covalent bond.