Ion
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225222085
2008-07-12T15:20:15Z
80.200.7.172
Linguistic origin of the words anion & cation.
{{otheruses1|the electrically charged particle}}
[[Image:Nitrate-ion-elpot.png|thumb|right|200px|An [[electric potential|electrostatic potential]] map of the [[nitrate ion]] ([[nitrogen|N]][[oxygen|O]]<sub>3</sub><sup>−</sup>). Areas coloured red are lower in energy than areas colored yellow]]
An '''ion''' is an [[atom]] or [[molecule]] which has lost or gained one or more [[valence electron]]s, giving it a positive or negative electrical charge.
A negatively charged ion, which has more [[electron]]s in its [[electron shell]]s than it has [[proton]]s in its [[atomic nucleus|nuclei]], is known as an '''anion''' (''ana'': Greek 'up') ({{pronEng|ˈænaɪən}}; ''an-eye-on''). Conversely, a positively-charged ion, which has fewer electrons than protons, is known as a '''cation''' (''kata'': Greek 'down') ({{pronEng|ˈkætaɪən}}; ''cat-eye-on'').
An ion consisting of a single atom is called a [[monatomic ion]], but if it consists of two or more atoms, it is a [[polyatomic ion]]. Polyatomic ions containing [[oxygen]], such as [[carbonate]] and [[sulfate]], are called [[oxyanion]]s.
Ions are denoted in the same way as electrically neutral atoms and molecules except for the presence of a superscript indicating the sign of the net electric charge and the number of electrons lost or gained, if more than one. For example: [[Hydrogen|H]]<sup>+</sup> and [[Sulfur|S]][[Oxygen|O]]<sub>4</sub><sup>2−</sup>.
== Formation ==
=== Formation of polyatomic and molecular ions ===
Polyatomic and molecular ions are often formed by the combination of elemental ions such as H<sup>+</sup> with neutral molecules or by the gain of such elemental ions from neutral molecules. A simple example of this is the ammonium ion NH<sub>4</sub><sup>+</sup> which can be formed by ammonia NH<sub>3</sub> accepting a proton, H<sup>+</sup>. Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration but differ in protons. The charge has been added by the addition of a proton (H<sup>+</sup>) not the addition or removal of electrons. The distinction between this and the removal of an electron from the whole molecule is important in large systems because it usually results in much more stable ions with complete electron shells. For example NH<sub>3</sub>'''·'''<sup>+</sup> is not stable because of an incomplete valence shell around nitrogen and is in fact a [[radical (chemistry)|radical]] ion.
=== Ionization potential ===
{{main|Ionization potential}}
The [[energy]] required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ''ionization potential'', or ''ionization energy''. The ''n''th ionization energy of an atom is the energy required to detach its ''n''th electron after the first ''n − 1'' electrons have already been detached.
Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of [[atomic orbital]]s is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, [[sodium]] has one ''[[valence electron]]'', in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na<sup>+</sup>. On the other side of the periodic table, [[chlorine]] has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl<sup>−</sup>. [[Francium]] has the lowest ionization energy of all the elements and [[fluorine]] has the greatest. The ionization energy of [[metals]] is generally much lower than the ionization energy of [[nonmetals]], which is why metals will generally lose electrons to form positively-charged ions while nonmetals will generally gain electrons to form negatively-charged ions.
A neutral atom contains an equal number of Z protons in the nucleus and Z electrons in the electron shell. The electrons' negative charges thus exactly cancel the protons' positive charges. In the simple view of the [[Free electron model]], a passing electron is therefore not attracted to a neutral atom and cannot bind to it. In reality, however, the atomic electrons form a cloud into which the additional electron penetrates, thus being exposed to a net positive charge part of the time. Furthermore, the additional charge displaces the original electrons and all of the Z + 1 electrons rearrange into a new configuration.
==Ions==
*'''Anions''' are negatively charged ions, formed when an atom gains electrons in a reaction. Anions are negatively charged because there are more electrons associated with them than there are protons in their nuclei.
*'''Cations''' are positively charged ions, formed when an atom loses electrons in a reaction, forming an '[[electron hole]]'. Cations are the opposite of anions, since cations have fewer electrons than protons.
*'''Dianion''': a dianion is a species which has two negative charges on it; for example, the [[aromatic]] dianion [[pentalene]].
*'''[[radical (chemistry)|Radical ions]]''': radical ions are ions that contain an odd number of electrons and are mostly very reactive and unstable.
=== Plasma ===
{{main|Plasma (physics)}}
A collection of non-[[aqueous solution|aqueous]] gas-like ions, or even a gas containing a proportion of charged particles, is called a '''plasma''', often called the ''fourth state of matter'' because its properties are quite different from [[solid]]s, [[liquid]]s, and [[gas]]es. [[Astrophysical plasmas]] containing predominantly a mixture of electrons and protons, may make up as much as 99.9% of visible matter in the universe.<ref>[http://science.nasa.gov/newhome/headlines/ast07sep99_1.htm Plasma, Plasma, Everywere] Science@NASA Headline news, Space Science n° 158, September 7, 1999.</ref>
== Applications ==
Ions are essential to [[life]]. [[Sodium]], [[potassium]], [[calcium]] and other ions play an important role in the [[cell (biology)|cell]]s of living organisms, particularly in [[cell membrane]]s. They have many practical, everyday applications in items such as [[smoke detector]]s, and are also finding use in unconventional technologies such as [[ion engines]]. Inorganic dissolved ions are a component of [[total dissolved solids]], an indicator of [[water quality]] in the world. High levels of atmospheric anions can produce a relaxation effect in animals by decreasing activity in neural and muscular tissue. This atmospheric effect has been reported to reduce anxiety <ref> AJ Giannini, S. Castellani, MC Giannini. Reversal of hyperserotenergic anxiety with generated anions in human subjects. Society for Neuroscience Abstracts.8:76.9,1982</ref> and manic symptoms .<ref> AJ Giannini, JD Giannini, S Melemis, JN Giannini. Treatment of acute mania with ambient air ionization: Variants of climactic heat stress and serotonin syndrome. Psychological Reports.100 :157-163,2007. </ref>
== Negative 'Ions' and Air Ionisers ==
Many manufacturers sell devices that release 'negative ions' into the air, claiming that a higher concentration of negative ions will make a room feel less 'stuffy'. Some also claim health benefits such as relieving [[asthma]] and [[Clinical depression|depression]].
The 'ions' referred to are in fact charged oxygen or nitrogen molecules surrounded by a cluster of water molecules, rather than ions. Scientific studies have shown no particular benefit from a greater concentration of negative ions.<ref>*Niels Jonassen (Mr. Static) "''[http://www.ce-mag.com/archive/02/11/mrstatic.html Are Ions Good for You?]''" Compliance Engineering, November 2002</ref>
Negative air ionization can reduce the concentration of bioaerosols and dust particles in the air by causing them to bond, forming larger particles and thus falling out of the air. This may help reduce infection due to airborne contamination<ref>[http://www.engr.psu.edu/ae/iec/abe/control/neg_ion.asp Negative Air Ionization]</ref>. Ionization was shown to reduce transmission of the Newcastle Disease Virus in an experiment with chickens<ref>[http://links.jstor.org/sici?sici=0005-2086(199410%2F12)38%3A4%3C725%3AEONAIO%3E2.0.CO%3B2-B Effect of Negative Air Ionization on Airborne Transmission of Newcastle Disease Virus]. Bailey W. Mitchell, Daniel J. King. Avian Diseases, Vol. 38, No. 4 (Oct. - Dec., 1994), pp. 725-732.</ref>.
==Common ions==
{{Cleanup-section|date=April 2008}}
{|
|valign="top"|
{|class="wikitable"
|+Common '''Cations'''
|-
!style="text-align: left"|Common Name
!style="text-align: left"|Formula
!style="text-align: left"|Historic Name
|-
!colspan="3" style="background-color: aliceblue"|''Simple Cations''
|-
|Aluminium||Al<sup>3+</sup>||
|-
|Barium||Ba<sup>2+</sup>||
|-
|Beryllium||Be<sup>2+</sup>||
|-
|Caesium||Cs<sup>+</sup>||
|-
|Calcium||Ca<sup>2+</sup>||
|-
|Chromium(II)||Cr<sup>2+</sup>||Chromous
|-
|Chromium(III)||Cr<sup>3+</sup>||Chromic
|-
|Chromium(VI)||Cr<sup>6+</sup>||Chromyl
|-
|Cobalt(II)||Co<sup>2+</sup>||Cobaltous
|-
|Cobalt(III)||Co<sup>3+</sup>||Cobaltic
|-
|Copper(I)||Cu<sup>+</sup>||Cuprous
|-
|Copper(II)||Cu<sup>2+</sup>||Cupric
|-
|Copper(III)||Cu<sup>3+<sup/>||
|-
|Gallium ||Ga<sup>3+</sup>||
|-
|Helium||He<sup>2+</sup>||(Alpha particle)
|-
|Hydrogen||H<sup>+</sup>||(Proton)
|-
|Iron(II)||Fe<sup>2+</sup>||Ferrous
|-
|Iron(III)||Fe<sup>3+</sup>||Ferric
|-
|Lead(II)||Pb<sup>2+</sup>||Plumbous
|-
|Lead(IV)||Pb<sup>4+</sup>||Plumbic
|-
|Lithium||Li<sup>+</sup>||
|-
|Magnesium||Mg<sup>2+</sup>||
|-
|Manganese(II)||Mn<sup>2+</sup>||Manganous
|-
|Manganese(III)||Mn<sup>3+</sup>||Manganic
|-
|Manganese(IV)||Mn<sup>4+</sup>||Manganyl
|-
|Manganese(VII)||Mn<sup>7+</sup>||
|-
|Mercury(II)||Hg<sup>2+</sup>||Mercuric
|-
|Nickel(II)||Ni<sup>2+</sup>||Nickelous
|-
|Nickel(III)||Ni<sup>3+</sup>||Nickelic
|-
|Potassium ||K<sup>+</sup>||
|-
|Silver||Ag<sup>+</sup>||
|-
|Sodium||Na<sup>+</sup>||
|-
|Strontium||Sr<sup>2+</sup>||
|-
|Tin(II)||Sn<sup>2+</sup>||Stannous
|-
|Tin(IV)||Sn<sup>4+</sup>||Stannic
|-
|Zinc||Zn<sup>2+</sup>||
|-
!colspan="3" style="background-color: aliceblue"|''Polyatomic Cations''
|-
|Ammonium||NH<sub>4</sub><sup>+</sup>||
|-
|Hydronium||H<sub>3</sub>O<sup>+</sup>||
|-
|Nitronium||NO<sub>2</sub><sup>+</sup>||
|-
|Uranyl||UO<sub>2</sub><sup>2+</sup>||
|-
|Mercury(I)||Hg<sub>2</sub><sup>2+</sup>||Mercurous
|}
|valign="top"|
{|class="wikitable"
|+Common '''Anions'''
|-
!style="text-align: left"|Formal Name
!style="text-align: left"|Formula
!style="text-align: left"|Alt. Name
|-
!colspan="3" style="background-color: aliceblue"|''Simple Anions''
|-
|Arsenide||As<sup>3−</sup>||
|-
|Azide||N<sub>3</sub><sup>−</sup>||
|-
|Bromide||Br<sup>−</sup>||
|-
|Chloride||Cl<sup>−</sup>||
|-
|Fluoride||F<sup>−</sup>||
|-
|Hydride||H<sup>−</sup>||
|-
|Iodide||I<sup>−</sup>||
|-
|Nitride||N<sup>3−</sup>||
|-
|Oxide||O<sup>2−</sup>||
|-
|Phosphide||P<sup>3−</sup>||
|-
|Sulfide||S<sup>2−</sup>||
|-
|Peroxide||O<sub>2</sub><sup>2−</sup>||
|-
!colspan="3" style="background-color: aliceblue"|''Oxoanions''
|-
|Arsenate||AsO<sub>4</sub><sup>3−</sup>||
|-
|Arsenite||AsO<sub>3</sub><sup>3−</sup>||
|-
|Borate||BO<sub>3</sub><sup>3−</sup>||
|-
|Bromate||BrO<sub>3</sub><sup>−</sup>||
|-
|Hypobromite||BrO<sup>−</sup>||
|-
|Carbonate||CO<sub>3</sub><sup>2−</sup>||
|-
|Hydrogen carbonate||HCO<sub>3</sub><sup>−</sup>||Bicarbonate
|-
|Hydroxide||OH<sup>−</sup>||
|-
|Chlorate||ClO<sub>3</sub><sup>−</sup>||
|-
|Perchlorate||ClO<sub>4</sub><sup>−</sup>||
|-
|Chlorite||ClO<sub>2</sub><sup>−</sup>||
|-
|Hypochlorite||ClO<sup>−</sup>||
|-
|Chromate||CrO<sub>4</sub><sup>2−</sup>||
|-
|Dichromate||Cr<sub>2</sub>O<sub>7</sub><sup>2−</sup>||
|-
|Iodate||IO<sub>3</sub><sup>−</sup>||
|-
|Nitrate||NO<sub>3</sub><sup>−</sup>||
|-
|Nitrite||NO<sub>2</sub><sup>−</sup>||
|-
|Phosphate||PO<sub>4</sub><sup>3−</sup>||
|-
|Hydrogen phosphate||HPO<sub>4</sub><sup>2−</sup>||
|-
|Dihydrogen phosphate||H<sub>2</sub>PO<sub>4</sub><sup>−</sup>||
|-
|Permanganate||MnO<sub>4</sub><sup>−</sup>||
|-
|Phosphite||PO<sub>3</sub><sup>3−</sup>||
|-
|Sulfate||SO<sub>4</sub><sup>2−</sup>||
|-
|Thiosulfate||S<sub>2</sub>O<sub>3</sub><sup>2−</sup>||
|-
|Hydrogen sulfate||HSO<sub>4</sub><sup>−</sup>||Bisulfate
|-
|Sulfite||SO<sub>3</sub><sup>2−</sup>||
|-
|Hydrogen sulfite||HSO<sub>3</sub><sup>−</sup>||Bisulfite
|-
!colspan="3" style="background-color: aliceblue"|''Anions from Organic Acids''
|-
|Acetate||C<sub>2</sub>H<sub>3</sub>O<sub>2</sub><sup>−</sup>||
|-
|Formate||HCO<sub>2</sub><sup>−</sup>||
|-
|Oxalate||C<sub>2</sub>O<sub>4</sub><sup>2−</sup>||
|-
|Hydrogen oxalate||HC<sub>2</sub>O<sub>4</sub><sup>−</sup>||Bioxalate
|-
!colspan="3" style="background-color: aliceblue"|''Other Anions''
|-
|hydrosulfide||HS<sup>−</sup>||Bisulfide
|-
|Telluride||Te<sup>2−</sup>||
|-
|Amide||NH<sub>2</sub><sup>−</sup>||
|-
|Cyanate||OCN<sup>−</sup>||
|-
|Thiocyanate||SCN<sup>−</sup>||
|-
|Cyanide||CN<sup>−</sup>||
|-
|}
|}
==References==
{{Refimprove|date=December 2007}}
<references/>
==External links==
*Department of Education, Newfoundland and Labrador-Canada "''{{PDFlink|[http://www.ed.gov.nl.ca/edu/k12/pub/pg2_periodic_table_ions.pdf Periodic Chart of Ions]|70.9 [[Kibibyte|KiB]]<!-- application/pdf, 72685 bytes -->}}''". A Periodic table reporting ionic charges for every chemical element.
[[Category:Ions| ]]
[[Category:Physical chemistry]]
{{Link FA|lmo}}
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