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An '''ion''' is an [[atom]] or [[Polyatomic ion|group]] of atoms that normally are electrically neutral and achieve their status as an ion by loss (or addition) of an electron. The simplest ions are the [[proton]] (a hydrogen ion, H<sup>+</sup>, positive charge), and [[alpha particle]] (helium ion, He<sup>2+</sup>, consisting of two protons and two neutrons) . 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''' (pronounced ''an-eye-on''), for it is attracted to [[anode]]s; a positively-charged ion, which has fewer electrons than protons, is known as a '''cation''' (pronounced ''cat-eye-on''), for it is attracted to [[cathode]]s. An ion with a single atom is called a [[monatomic ion]], and an ion with more than one is called a [[polyatomic ion]]. Larger ions containing many atoms are called [[molecular ion]]s. The process of converting into ions and the state of being ionized is called '''[[ionization]]'''. The recombining of ions and electrons to form neutral atoms is called ''recombination''. A [[Polyatomic ion|polyatomic anion]] that contains [[oxygen]] is sometimes known as an '''oxyanion''' .
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Ions are denoted by a superscript with 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>, [[Sulphur|S]][[Oxygen|O]]<sub>4</sub><sup>2−</sup>.
[[User:David E. Volk|David E. Volk]] 13:25, 28 December 2007 (CST)-->
 
An '''ion''' is an [[atom]] or a [[molecule]] that has lost or gained [[electron]]s. If an atom loses one or more electrons, it becomes a positively charged ion called a [[cation]]. If it gains one or more electrons, it becomes a negatively charged ion called an [[anion]].[[Category:Suggestion Bot Tag]]
A collection of non-[[aqueous]] gas-like ions, or even a gas containing a proportion of charged particles, is called a '''[[Plasma (physics)|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 the visible universe [http://science.nasa.gov/newhome/headlines/ast07sep99_1.htm]. The positively charged proton is about 1836 times more massive than the negatively charged electron.
 
== Ionization potential ==
{{main|Ionization potential}}
 
IONIZATION
    Ionization is a process in which a neutral atom splits up into charged particles.  These charged particles are called ions.
    The positively charged particles are called cations, the negatively charged particles are called anions. 
    The grouping up of the charged particles(cation & anion) to form a neutral atom is called recombination of ions.
 
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.
 
==Anion==
In negative ions, anions, the interaction of each electron with the positive nucleus is strongly suppressed; they are very loosely bound systems. Contrary to all other atomic electrons, the extraneous electron in negative ions is initially not bound by the Coulomb interaction, but by polarization of the neutral atom. Due to the short range of this interaction, negative ions have no Rydberg series, but only a few, if any, bound excited states.
 
== 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 loss of such elemental ions from neutral molecules. Many of these processes are acid-bases reactions, as first theorized by German scientist Lauren Gaither. 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.
 
== Other ions ==
A '''dianion''' is a species which has two negative charges on it. For example, the dianion of [[pentalene]] is [[aromatic]]. A [[zwitterion]] is an ion with a net charge of zero, but has both a positive and negative charge on it. [[radical (chemistry)|Radical]] ions are ions that contain an odd number of electrons and are mostly very reactive and unstable.
 
== History ==
 
Ions were first theorized by [[Michael Faraday]] around 1830, to describe the portions of molecules that travel either to an anode or to a cathode. However, the mechanism by which this was achieved was not described until 1884 by [[Svante August Arrhenius]] in his doctoral dissertation to the [[University of Uppsala]]. His theory was initially not accepted but his dissertation won the [[Nobel Prize in Chemistry]] in [[1903 in science|1903]].
 
=== Etymology ===
 
The word ''ion'' is a name given by [[Michael Faraday]], from [[Greek language|Greek]] ''{{polytonic|ἰόν}}'', neutral present participle of ''{{polytonic|ἰέναι}}'', "to go", thus "a goer". So; ''anion'', ''{{polytonic|ἀνιόν}}'', and ''cation'', ''κ{{polytonic|ατιόν}}'', mean "(a thing) going up" and "(a thing) going down", respectively; and ''anode'', ''{{polytonic|ἄνοδος}}'', and ''cathode'', ''κ{{polytonic|άθοδος}}'', mean "a going up" and "a going down", respectively, from ''{{polytonic|ὁδός}}'', "way," or "road."
 
== 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 widespread use.
 
==Common Ion Tables==
{|
|valign="top"|
{|class="wikitable"
|+Common '''Cations'''
|-
!style="text-align: left"|Common Name
!style="text-align: left"|Formula
!style="text-align: left"|Historic Name
|-
|Aluminum||Al<sup>3+</sup>||
|-
|Ammonium||NH<sub>4</sub><sup>+</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
|-
|Helium||He<sup>2+</sup>||(Alpha particle)
|-
|Hydrogen||H<sup>+</sup>||(Proton)
|- 
|Hydronium||H<sub>3</sub>O<sup>+</sup>||
|-
|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(I)||Hg<sub>2</sub><sup>2+</sup>||Mercurous
|-
|Mercury(II)||Hg<sup>2+</sup>||Mercuric
|-
|Nickel(II)||Ni<sup>2+</sup>||Nickelous
|-
|Nickel(III)||Ni<sup>3+</sup>||Nickelic
|-
|Nitronium||NO<sub>2</sub><sup>+</sup>||
|-
|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>||
|}
|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>||
|-
|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
|-
|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>||
|-
|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''
|-
|Hydrogen Sulfide||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>||
|-
|Hydroxide||OH<sup>−</sup>||
|-
|Permanganate||MnO<sub>4</sub><sup>−</sup>||
|-
|}
 
|}
 
==External links==
*[http://www.omcea.be/article-28,91445,Ion,Power.html Ion Power] - article by Graham P. Collins
*[http://www.ed.gov.nl.ca/edu/k12/pub/pg2_periodic_table_ions.pdf Periodic Chart of Ions] - Periodic table with charges for every element
 
[[Category:Ions| ]]
[[Category:Physical chemistry]]
[[Category:Chemistry Workgroup]]

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An ion is an atom or a molecule that has lost or gained electrons. If an atom loses one or more electrons, it becomes a positively charged ion called a cation. If it gains one or more electrons, it becomes a negatively charged ion called an anion.

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