Ion

For the television network, see Ion Television.

An ion is an electrically charged atom or molecule (group of atoms). It is "charged" so it will move near electricity. Atoms are made from positively charged protons, negatively charged electrons, and uncharged neutrons. Ions are charged because they have an unequal number of protons and electrons.

Making an ion from an atom or molecule is called ionization. Two or more ions can combine to make a chemical compound. The link between the ions is called an ionic bond.

The charge on a proton is chosen as +1 (positively charged). The charge on an electron is opposite to the charge on the proton. The charge on the electron is -1 (negatively charged). An atom that is ionized makes two parts, one positive, and one negatively charged. For example, a neutral hydrogen atom has one proton and one electron. Ionizing the atom breaks it into two parts: (1) a positively charged hydrogen ion, H+ (2) a negatively charged electron.

A liquid with ions is called an electrolyte. A gas with lots of ions is called a plasma. When ions move, it is called electricity. For example, in a wire, the metal ions do not move, but the electrons move as electricity. A positive ion and a negative ion will move together. Two ions of the same charge will move apart. When ions move they also make magnetic fields.

Many ions are colourless. Elements in the main groups in the Periodic Table form colourless ions. Some ions are coloured. The transition metals usually form coloured ions.

Chemistry

In physics, atomic nuclei that have been completely ionized are called charged particles. These are ones in alpha radiation.

Ionization happens by giving atoms high energy. This is done using electrical voltage or by high-energy ionizing radiation or high temperature.

A simple ion is formed from a single atom.

Polyatomic ions are formed from a number of atoms. Polyatomic ions usually consist of all non-metal atoms. But sometimes the polyatomic ion can have a metallic atom too.

Positive ions are called cations. They are attracted to cathodes (negatively charged electrodes). (Cation is pronounced "cat eye on", not "kay shun".) All simple metal ions are cations.

Negative ions are called anions. They are attracted to anodes (positively charged electrodes). All simple non-metal ions (except H⁺, which is a proton) are anions.

Transition metals can form more than one simple cation with different charges.

Most ions have a charge of less than 4, but some can have higher charges.

Michael Faraday was the first person to write a theory about ions, in 1830. In his theory, he said what the portions of molecules were like that moved to anions or cations. Svante August Arrhenius showed how this happened. He wrote this in his doctoral dissertation in 1884 (University of Uppsala). The university did not accept his theory at first (he only just passed his degree). But in 1903, he won the Nobel Prize in Chemistry for the same idea.

In Greek ion is like the word "go". "Anion" and "cation" mean "up-goer" and "down-goer". "Anode" and "cathode" are "way up" and "way down".

Common ions

Common cations Common name Formula Historic name Simple cations Aluminium Al3+ Barium Ba2+ Beryllium Be2+ Calcium Ca2+ Chromium(III) Cr3+ Copper(I) Cu+ cuprous Copper(II) Cu2+ cupric Hydrogen H+ Iron(II) Fe2+ ferrous Iron(III) Fe3+ ferric Lead(II) Pb2+ plumbous Lead(IV) Pb4+ plumbic Lithium Li+ Magnesium Mg2+ Manganese(II) Mn2+ Mercury(II) Hg2+ mercuric Potassium K+ kalic Silver Ag+ argentous Sodium Na+ natric Strontium Sr2+ Tin(II) Sn2+ stannous Tin(IV) Sn4+ stannic Zinc Zn2+ Polyatomic cations Ammonium NH+ 4 Hydronium H3O+ Mercury(I) Hg2+ 2 mercurous

Common anions Formal name Formula Alt. name Simple anions Azide N− 3 Bromide Br− Chloride Cl− Fluoride F− Hydride H− Iodide I− Nitride N3− Oxide O2− Sulfide S2− Oxoanions Carbonate CO2− 3 Chlorate ClO− 3 Chromate CrO2− 4 Dichromate Cr2O2− 7 Dihydrogen phosphate H2PO− 4 Hydrogen carbonate HCO− 3 bicarbonate Hydrogen sulfate HSO− 4 bisulfate Hydrogen sulfite HSO− 3 bisulfite Hydroxide OH− Hypochlorite ClO− Monohydrogen phosphate HPO2− 4 Nitrate NO− 3 Nitrite NO− 2 Perchlorate ClO− 4 Permanganate MnO− 4 Peroxide O2− 2 Phosphate PO3− 4 Sulfate SO2− 4 Sulfite SO2− 3 Superoxide O− 2 Thiosulfate S2O2− 3 Silicate SiO4− 4 Metasilicate SiO2− 3 Aluminium silicate AlSiO− 4 Anions from organic acids Acetate CH3COO− ethanoate Formate HCOO− methanoate Oxalate C2O2− 4 ethanedioate Cyanide CN−

Ion Media

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  Electron transfer between lithium (Li) and fluorine (F). Forming an ionic bond, Li and F become Li⁺ and F⁻ ions.

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  Hydrogen atom (center) contains a single proton and a single electron. Removal of the electron gives a cation (left), whereas the addition of an electron gives an anion (right).

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  Schematic of an ion chamber, showing drift of ions. Electrons drift faster than positive ions due to their much smaller mass.

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  Avalanche effect between two electrodes. The original ionization event liberates one electron, and each subsequent collision liberates a further electron, so two electrons emerge from each collision: the ionizing electron and the liberated electron.

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  Equivalent notations for an iron atom (Fe) that lost two electrons, referred to as ferrous.

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  Mixed Roman numerals and charge notations for the uranyl ion. The oxidation state of the metal is shown as superscripted Roman numerals, whereas the charge of the entire complex is shown by the angle symbol together with the magnitude and sign of the net charge.

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  An electrostatic potential map of the nitrate ion (2NO−
  3). The 3-dimensional shell represents a single arbitrary isopotential.