Ionic compound 210000 225824310 2008-07-15T15:57:18Z Starshade17 6018576 [[Image:Sodium-chloride-3D-ionic.png|thumb|200px|The [[crystal]] structure of [[sodium chloride]], NaCl, a typical ionic compound. The purple spheres are [[sodium]] [[cation]]s, Na<sup>+</sup>, and the green spheres are [[chloride]] [[anion]]s, Cl<sup>−</sup>.]] In [[chemistry]], an '''ionic compound''' is a [[chemical compound]] in which [[ion]]s are held together in a lattice structure by [[ionic bond]]s. Usually, the positively charged portion consists of metal [[cation]]s and the negatively charged portion is a [[halogen]] or polyatomic ion. Ions in ionic compounds are held together by the [[electrostatic force]] between oppositely charged bodies. Ionic compounds have a high melting and boiling point, and they have a high hardness and are very brittle. Ions can be single atoms, as in common table salt [[sodium chloride]], or more complex groups such as [[calcium carbonate]]. But to be considered an ion, they must carry a positive or negative charge. Thus, in an ionic bond, one 'bonder' must have a positive charge and the other a negative one. By sticking to each other, they resolve, or partially resolve, their separate charge imbalances. Positive to positive and negative to negative ionic bonds do not occur. (For an easily visible analogy, experiment with a pair of bar [[magnet]]s.) Chemical compounds are rarely strictly ionic or strictly covalent. Except for the most [[electronegative]]/[[electropositive]] pairs such as [[caesium fluoride]], ionic compounds usually exhibit a degree of covalency. Similarly, [[covalent bond|covalent compounds]] often exhibit charge separations. See also [[HSAB theory]]. Physical properties of ionic and molecular compounds: {| class="wikitable" |- ! ! Ionic compounds ! Molecular compounds |- | States (at RTP) | Solid | Can be solid, liquid or gas at room temperature |- | Electrical conductivity | Solid:&nbsp;no<br>Molten:&nbsp;yes | No |- | Boiling point | High | Low |- | Solubility in water | Often high | Variable; usually lower than ionic |- | Thermal conductivity | Low | Low |} ==Characteristics== Ionic compounds have strong [[electrostatic bond]]s between particles. As a result, they generally have high melting and boiling points. They also have good electrical conductivity when molten or in aqueous solution. While ionic [[inorganic compound]]s are solids at room temperature and will usually form crystals, organic [[ionic liquid]]s are of increasing interest. ==Solubility== Following the aphorism, "like dissolves like", ionic compounds dissolve in [[polar solvent]]s, especially those which ionize, such as water and [[ionic liquid]]s. They are usually appreciably soluble in other polar solvents such as [[alcohol]]s, [[acetone]] and [[dimethyl sulfoxide]] as well. Ionic compounds tend not to dissolve in [[nonpolar solvent]]s such as [[diethyl ether]] or [[petrol]] (gasoline). ==Nomenclature== According to the [[IUPAC]], an ionic compound's common name is written using two words. The name of the cation comes first (when using the [[International Union of Pure and Applied Chemistry nomenclature#Stock nomenclature/Classical|Stock system]]) with the [[oxidation number]] written in parenthesis, followed by the name of the anion. For example, Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> is named as iron(III) sulfate. If the Classical naming system is being used, some ionic compounds have special "old" names, such as ferric (iron(III)), ferrous (iron(II)), cupric (copper(II)), and cuprous (copper(I)). ==References== <references/>{{Unreferenced|date=December 2007}} [[Category:Chemical compounds]] [[Category:Ions]] [[it:Composto ionico]] [[he:סריג יוני]] [[pt:Composto iônico]] [[simple:Ionic compound]] [[sv:Jonförening]] [[zh:离子化合物]]