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Polyatomic Ion
2011-01-20
An electrostatic potential map of the nitrate ion (NO3). Areas coloured red are lower in energy than areas coloured yellow
A polyatomic ion, also known as a molecular ion, is a charged species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix poly- means many in Greek, but even ions of two atoms are commonly referred to as polyatomic. In older literature, a polyatomic ion is also referred to as a radical, and less commonly, as a radical group. In contemporary usage, the term radical refers to free radicals which are uncharged species with an unpaired electron.
ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its chemical formula is butterfly valve (NH4)+. It has charge of +1.
A polyatomic ion, also known as a molecular ion, is a charged species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix poly- means many in Greek, but even ions of two atoms are commonly referred to as polyatomic. In older literature, a polyatomic ion is also referred to as a radical, and less commonly, as a radical group. In contemporary usage, the term radical refers to free radicals which are uncharged species with an unpaired electron.
ammonium ion is made up of one nitrogen atom and four hydrogen atoms: its chemical formula is butterfly valve (NH4)+. It has charge of +1.
A polyatomic ion can often be considered as the conjugate acid or
conjugate base of a neutral molecule. For example the sulfate anion,
SO42, is derived from H2SO4 which can be regarded as SO3 + H2O.
There are two "rules" that can be used for the learning the nomenclature of polyatomic ions. First, when the prefix bi- is added to a name, a hydrogen is added to the ion's formula and its charge is increased by 1, the latter being a consequence of the hydrogen ion carrying a +1 charge. An alternate to the bi- prefix is to use the word hydrogen in its place: the anion derived from H+ + CO32, HCO3 can be called either bicarbonate or hydrogen carbonate.
Note that many of the common polyatomic anions are conjugate bases of acids derived from the oxides of non-metallic elements.
There are two "rules" that can be used for the learning the nomenclature of polyatomic ions. First, when the prefix bi- is added to a name, a hydrogen is added to the ion's formula and its charge is increased by 1, the latter being a consequence of the hydrogen ion carrying a +1 charge. An alternate to the bi- prefix is to use the word hydrogen in its place: the anion derived from H+ + CO32, HCO3 can be called either bicarbonate or hydrogen carbonate.
Note that many of the common polyatomic anions are conjugate bases of acids derived from the oxides of non-metallic elements.
