Define polyatomic | Dictionary and Thesaurus

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« Define polyanthusDefinepolybasic »Go to Dictionary DefinitionGo to User ContributedDictionaryGo to ExtensiveDefinitionDictionary Definitionpolyatomic adj : of or relating to a moleculemade up of more than two atomsUser ContributedDictionaryEnglishAdjective(of a molecule or ion) consisting of three or more atomsTranslationsItalian: poliatomicoSee alsomonatomicdiatomicExtensive DefinitionA polyatomic ion is a charged species (ion) composed of two or more atomscovalentlybonded or of a metalcomplex that can be considered as acting as a single unit inthe context of acid andbasechemistry or in theformation of salts. Theprefix poly- means many in Greek, but even ions of two atoms arecommonly referred to as polyatomic. Note, a polyatomic ion is alsoreferred to in older works as a radical.In current usage the term radical refers to freeradicals which are uncharged species with an unpairedelectron.Hydroxide ions and ammonium ionsA hydroxide ion ismade of one oxygen atom and one hydrogen atom: its chemical formulais ()−. It has a charge of −1.An ammonium ion ismade up of one nitrogen atom and four hydrogen atoms: its chemicalformula is ()+. It has charge of +1.A polyatomic ion can often be considered as theconjugateacid or conjugate base of a neutral molecule. For example thesulfate anion, 2−, isderived from H2SO4 whichcan be regarded as SO3 +H2O.There are two "rules" that can be used for thelearning the nomenclature of polyatomic ions. First, when theprefix bi- is added to a name, a hydrogen is added to the ion'sformula and its charge is increased by 1. It is a consequence ofthe hydrogen ion carrying a +1 charge. An alternate to the bi-prefix is to use the word hydrogen in its place: the anion derivedfrom H+ + CO32−,HCO3− can be calledeither bicarbonate or hydrogen carbonate.Note that many of the common polyatomic anionsare conjugate bases of acids derived from the oxides of non-metallic elements. Forexample the sulfateanion, 2−, is derived from H2SO4 whichcan be regarded as SO3 +H2O.The second rule looks at the number of oxygens inan ion. Consider the chlorine oxoanion family: First, thinkof the -ate ion as being the "base" name, in which case theaddition of a per- prefix adds an oxygen. Changing the -ate suffixto -ite will reduce the oxygens by one, and keeping the suffix -iteand adding the prefix hypo- reduces the number of oxygens by two.In all situations, the charge is not affected.It is important to note that these rules will notwork with all polyatomic ions, but they do work with the mostcommon ones (sulfate, phosphate, nitrate, chlorate).List of polyatomic ionsCaution: chemists classify ions andmolecules even when such species do not exist to any appreciableextent. For example, small ions with high charges are very rare, asillustrated by the fact that oxide, O2-, has not been observed insolution and is not considered as a component in reactionmechanisms. Similarly, orthosilicate, SiO44-enjoys no status as an ion in aqueous solution, except perhapsunder extreme temperatures. In general, ions that have chargesgreater than 2- do not exist in solution unless they areprotonated.See also

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