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| In ], '''iron(II)''' refers to the ] ] in its +2 ]. In ] (salts), such an atom may occur as a separate ] (positive ion) denoted by '''Fe<sup>2+</sup>'''. | |||
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| The adjective '''ferrous''' or the prefix '''ferro'''- is often used to specify such compounds — as in "ferrous chloride" for ], {{chem2|FeCl2}}. The adjective "ferric" is used instead for ] salts, containing the cation or Fe<sup>3+</sup>. The word ferrous is derived from the ] word ''ferrum'' for iron. | |||
| Iron(II) atoms may also occur as ]es, such as the polymer ] ], {{chem2|''n''}} or {{chem2|\{2\}''n''}}; and ]s, such as the neutral molecule ], {{chem2|Fe(C2H5)2}} or {{chem2|2}}. | |||
| Iron is almost always encountered in the oxidation states 0 (as in the metal), +2, or +3. Solid iron(II) salts are relatively stable in air, but in the presence of air and water they tend to ] to iron(III) salts that include ] ({{chem2|HO(-)}}) or ] ({{chem2|O(2-)}} anions. | |||
| ==Iron(II) and life== | |||
| All known forms of life require iron. Many ]s in living beings contain bound iron ions; those are an important subclass of the ]s. Examples include ], ], and the ]s. | |||
| These proteins perform their vital functions thanks to the relatively easy switching of the iron atom between the +2 and +3 states. ] for example, carries ] in the blood by binding one molecule {{chem2|O2}} to the iron atom, forming ]. In the process, the iron(II) core of hemoglobin loses an electron to become iron(III), while the oxygen molecule is turned into the ] anion {{chem2|O2(-)}}.<ref>{{cite book |author=Berg, Jeremy Mark |author2=Lippard, Stephen J. |title=Principles of bioinorganic chemistry |publisher=University Science Books |location=Sausalito, Calif |year=1994 |isbn=0-935702-73-3 }}</ref> | |||
| Insufficient iron in the human diet causes ]. Animals and humans can obtain the necessary iron from foods that contain it in assimilable form, such as meat. Other organisms must obtain their iron from the environment. However, iron tends to form highly insoluble iron(III) oxides/hydroxides in aerobic (]ated) environment, especially in ]s. Plants (except ]) solve that problem by encouraging the growth around their roots of certain ] that ] iron(III) to soluble iron(II). (Bacteria and grasses instead secrete compounds called ]s that form soluble complexes with iron(III).)<ref name=weiss/><ref name=marsch94/><ref name=koba2012/> | |||
| For the same reason, iron is very scarce in seawater, and is often the limiting factor to the growth of the microscopic plants (]) that are the basis of the marine food web. This fact was dramatically demonstrated by an experiment where a large area of the ocean surface was sprayed with soluble iron(II) salts, specifically ]. After several days, the phytoplankton within the treated area bloomed to such an extent that the effect was visible from outer space. This fertilizing process has been proposed as a means to mitigate the ] content of the atmosphere.<ref>{{cite journal |vauthors=Boyd PW, Watson AJ, Law CS |title=A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization |journal=Nature |volume=407 |issue=6805 |pages=695–702 |date=October 2000 |pmid=11048709 |doi=10.1038/35037500 |display-authors=etal|bibcode=2000Natur.407..695B }}</ref> | |||
| ] of aqueous iron]] | |||
| ==Iron(II) in solution== | |||
| Many iron(II) salts are soluble in water, such as ] {{chem2|FeCl2}} and ] {{chem2|FeSO4}}. Unlike their iron(III) counterparts, these salts dissolve in pure water without significant hydrolysis, and without affecting the ] | |||
| <ref name=earn/> <!--Discuss {{chem2|Fe(OH)2}} solubility and the absence of oxide-hydroxide.--> | |||
| When metallic iron (oxidation state 0) is placed in a solution of ], iron(II) chloride is formed,with release of ] gas, by the reaction | |||
| : {{chem2|Fe^{0} + 2 H(+) -> Fe(2+) + H2}} | |||
| Iron metal is more ] than ], and therefore will displace it from its salts: | |||
| : {{chem2|Fe^{0} + Cu(2+) -> Fe(2+) +Cu^{0} }} | |||
| When iron metal is exposed to air and water, usually it turns into ], a mixure of oxides and oxide-hydroxides. However, in some environments the metal forms a mixed iron(II) and iron(III) salt with hydroxide and other anions, called ]. | |||
| ==Complexes== | |||
| Iron(II) is a d<sup>6</sup> center, meaning that the atom has six "valence" electrons in the 3d orbital shell. These orbitals can accept a great variety of ]s to form coordination complexes and organometallic compounds.<!-- More... --> | |||
| ==See also== | |||
| ==References== | |||
| <references> | |||
| <ref name=earn>{{cite book |author=Earnshaw, A. |author2=Greenwood, N. N. |title=Chemistry of the elements |publisher=Butterworth-Heinemann |location=Oxford |year=1997 |pages= |isbn=0-7506-3365-4 |edition=2nd}}</ref> | |||
| <ref name=weiss>Johanna V. Weiss, David Emerson, Stephanie M. Backer, and J. Patrick Megonigal (2003): "Enumeration of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the root zone of wetland plants: Implications for a rhizosphere iron cycle". ''Biogeochemistry'', volume 64, issue 1, pages 77–96. {{doi|10.1023/A:102495302}}</ref> | |||
| <ref name=marsch94>H. Marschner and V. Römheld (1994): "Strategies of plants for acquisition of iron". ''Plant and Soil'', volume 165, issue 2, pages 261–274. {{doi|10.1007/BF00008069}}</ref> | |||
| <ref name=koba2012>Takanori Kobayashi and Naoko K. Nishizawa (2012): "Iron Uptake, Translocation, and Regulation in Higher Plants". ''Annual Review of Plant Biology'', volume 63, pages 131-152. {{doi|10.1146/annurev-arplant-042811-105522}}</ref> | |||
| </references> | |||
| {{reflist}} | |||
| {{chem-stub}} | |||
| ] | |||
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