Editing Transition metal (section)

===Oxidation states===
A characteristic of transition metals is that they exhibit two or more [[oxidation state]]s, usually differing by one. For example, compounds of [[vanadium]] are known in all oxidation states between −1, such as {{chem|[V(CO)|6|]|-}}, and +5, such as {{chem|VO|4|3-}}.

[[File:Transition metal oxidation states.svg|frame|center|Oxidation states of the transition metals. The solid dots show common oxidation states, and the hollow dots show possible but unlikely states.]]

[[Main-group element]]s in groups 13 to 18 also exhibit multiple oxidation states. The "common" oxidation states of these elements typically differ by two instead of one. For example, compounds of [[gallium]] in oxidation states +1 and +3 exist in which there is a single gallium atom. Compounds of Ga(II) would have an unpaired electron and would behave as a [[free radical]] and generally be destroyed rapidly, but some stable radicals of Ga(II) are known.<ref>{{cite journal|last1=Protchenko|first1=Andrey V.|last2=Dange|first2=Deepak|last3=Harmer|first3=Jeffrey R.|last4=Tang|first4=Christina Y.|last5=Schwarz|first5=Andrew D.|last6=Kelly|first6=Michael J.|last7=Phillips|first7=Nicholas|last8=Tirfoin|first8=Remi|last9=Birjkumar|first9=Krishna Hassomal|last10=Jones|first10=Cameron|last11=Kaltsoyannis|first11=Nikolas|last12=Mountford|first12=Philip|last13=Aldridge|first13=Simon|title=Stable GaX<sub>2</sub>, InX<sub>2</sub> and TlX<sub>2</sub> radicals|journal=Nature Chemistry|date=16 February 2014|volume=6|issue=4|pages=315–319|doi=10.1038/nchem.1870|pmid=24651198|bibcode = 2014NatCh...6..315P }}</ref> Gallium also has a formal oxidation state of +2 in dimeric compounds, such as {{chem|[Ga|2|Cl|6|]|2-}}, which contain a Ga-Ga bond formed from the unpaired electron on each Ga atom.<ref>{{Greenwood&Earnshaw}} p. 240</ref> Thus the main difference in oxidation states, between transition elements and other elements is that oxidation states are known in which there is a single atom of the element and one or more unpaired electrons.

The maximum oxidation state in the first row transition metals is equal to the number of valence electrons from [[titanium]] (+4) up to [[manganese]] (+7), but decreases in the later elements. In the second row, the maximum occurs with [[ruthenium]] (+8), and in the third row, the maximum occurs with [[iridium]] (+9). In compounds such as {{chem|[MnO|4|]|-}} and {{chem|OsO|4}}, the elements achieve a stable configuration by [[covalent bonding]].

The lowest oxidation states are exhibited in [[metal carbonyl]] complexes such as {{chem|Cr(CO)|6}} (oxidation state zero) and {{chem|[Fe(CO)|4|]|2-}} (oxidation state −2) in which the [[18-electron rule]] is obeyed. These complexes are also covalent.

Ionic compounds are mostly formed with oxidation states +2 and +3. In aqueous solution, the ions are hydrated by (usually) six water molecules arranged octahedrally.
<!-- [[Image:Transition metal oxidation states 3.png|center|frame|This table shows some of the oxidation states found in compounds of the transition-metal elements.<br> A solid circle represents a common oxidation state, and a ring represents a less common oxidation state.]] -->