Editing Rhodium (section)

== Characteristics ==
{| class="wikitable" style="float: right; margin: 0; margin-left: 1em;"
|-
![[Atomic number|Z]] !! [[Chemical element|Element]] !! [[Electron shell|No. of electrons/shell]]
|-
| 27 || cobalt || 2, 8, 15, 2
|-
| 45 || rhodium || 2, 8, 18, 16, 1
|-
| 77 || iridium || 2, 8, 18, 32, 15, 2
|-
| 109 || meitnerium || 2, 8, 18, 32, 32, 15, 2 (predicted)
|}

Rhodium is a hard, silvery, durable metal that has a high [[reflectance]]. Rhodium metal does not normally form an [[oxide]], even when heated.<ref name="ASM13B">{{cite book|editor-last = Cramer|editor-first = Stephen D.|editor2-last = Covino |editor2-first=Bernard S. Jr.|title = ASM handbook|year = 1990|publisher = ASM International|location = Materials Park, OH|isbn=978-0-87170-707-9|pages = 393–396|url = https://books.google.com/books?id=QV0sWU2qF5oC&pg=PA396}}</ref> [[Oxygen]] is absorbed from the [[atmosphere]] only at the [[melting point]] of rhodium, but is released on solidification.<ref>{{cite book|last = Emsley|first = John|title = Nature's Building Blocks|edition = (Hardcover, First Edition)|publisher = [[Oxford University Press]]|year = 2001|page = [https://archive.org/details/naturesbuildingb0000emsl/page/363 363]|isbn = 978-0-19-850340-8|url = https://archive.org/details/naturesbuildingb0000emsl/page/363}}</ref> Rhodium has both a higher melting point and lower [[density]] than [[platinum]]. It is not attacked by most [[acid]]s: it is completely insoluble in [[nitric acid]] and dissolves slightly in [[aqua regia]].

Rhodium belongs to [[group 9 element|group 9]] of the periodic table, but exhibits an atypical [[ground state]] [[valence electron]] configuration for that group.  Like neighboring elements [[niobium]] (41), [[ruthenium]] (44), and [[palladium]] (46), it only has one electron in its outermost [[s orbital|''s'' orbital]].

===Chemical properties===
[[Image:Wilkinson's-catalyst-2D.png|thumb|left|upright|Structure of [[Wilkinson's catalyst]] (Ph = [[phenyl]] = C<sub>6</sub>H<sub>5</sub>).]]

{|class="wikitable" style="float: right; margin: 0; margin-left: 1em;"
|-
! colspan=2|Oxidation states<br />of rhodium
|-
| +0 ||{{chem|Rh|4|(||CO)|12|}}
|-
| +1 ||{{chem|RhCl||(PH|3|)|2|}}
|-
| +2 ||{{chem|Rh|2|(O|2|CCH|3|)|4}}
|-
| '''+3''' ||{{chem|RhCl|3|, Rh|2|O|3|}}
|-
| +4 ||{{chem|RhO|2}}
|-
| +5 ||{{chem|RhF|5|, Sr|3|LiRhO|6}}
|-
| +6 ||{{chem|RhF|6}}
|}

The common [[oxidation state]]s of rhodium are +3 and +1. Oxidation states 0, +2, and +4 are also well known.<ref name="Holl">{{cite book|publisher = Walter de Gruyter|year = 1985|edition = 91–100|pages = 1056–1057|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman|author2 = Wiberg, Egon|author3 = Wiberg, Nils}}</ref> A few complexes at still higher oxidation states are known.<ref>{{cite journal |doi=10.1002/anie.202207688 |title=The Highest Oxidation State of Rhodium: Rhodium(VII) in &#91;RhO<sub>3</sub>&#93;<sup>+</sup> |date=2022 |last1=Da Silva Santos |first1=Mayara |last2=Stüker |first2=Tony |last3=Flach |first3=Max |last4=Ablyasova |first4=Olesya S. |last5=Timm |first5=Martin |last6=von Issendorff |first6=Bernd |last7=Hirsch |first7=Konstantin |last8=Zamudio-Bayer |first8=Vicente |last9=Riedel |first9=Sebastian |last10=Lau |first10=J. Tobias |journal=Angewandte Chemie International Edition |volume=61 |issue=38 |pages=e202207688 |pmid=35818987 |pmc=9544489 }}</ref>

The rhodium oxides include {{chem|link=Rhodium(III) oxide|Rh|2|O|3}}, {{chem|link=Rhodium(IV) oxide|RhO|2}}, {{chem|RhO|2|·''x''H|2|O}}, {{chem|Na|2|RhO|3}}, {{chem|Sr|3|LiRhO|6}} and {{chem|Sr|3|NaRhO|6}}.<ref>{{cite journal|first = B. A.|last = Reisner|author2=Stacy, A. M. |title={{chem|Sr|3|ARhO|6}} (A = Li, Na): Crystallization of a Rhodium(V) Oxide from Molten Hydroxide|doi = 10.1021/ja974231q|volume = 120|issue = 37|date = 1998|pages = 9682–9989|journal =Journal of the American Chemical Society }}</ref>  None are of technological significance.

All the Rh(III) halides are known but the hydrated trichloride is most frequently encountered. It is also available in an anhydrous form, which is somewhat refractory.  Other rhodium(III) chlorides include sodium hexachlororhodate, {{chem2|Na3RhCl6}}, and [[pentaamminechlororhodium dichloride]], {{chem2|[Rh(NH3)5Cl]Cl2}}.  They are used in the recycling and purification of this very expensive metal.  Heating a methanolic solution of hydrated rhodium trichloride with [[sodium acetate]] give the blue-green [[rhodium(II) acetate]], {{chem2|Rh2(O2CCH3)4}}, which features a Rh-Rh bond.  This complex and related [[rhodium(II) trifluoroacetate]] have attracted attention as catalysts for [[cyclopropanation]] reactions. Hydrated rhodium trichloride is reduced by [[carbon monoxide]], [[ethylene]], and [[trifluorophosphine]] to give rhodium(I) complexes {{chem2|Rh2Cl2L4}} (L = CO, {{chem2|C2H4, PF3}}).  When treated with [[triphenylphosphine]], hydrated rhodium trichloride converts to the maroon-colored {{chem2|RhCl(P(C6H5)3)3}}, which is known as [[Wilkinson's catalyst]]. Reduction of [[rhodium carbonyl chloride]] gives [[hexarhodium hexadecacarbonyl]], {{chem2|Rh6(CO)16}}, and [[tetrarhodium dodecacarbonyl]], {{chem2|Rh4(CO)12}}, the two most common Rh(0) complexes.

As for other metals, rhodium forms high oxidation state [[binary phase|binary fluoride]]s.  These include [[rhodium pentafluoride]], a tetrameric complex with the true formula {{chem2|Rh4F20}}) and [[rhodium hexafluoride]].<ref>{{cite book|author=Griffith, W. P.|title=The Rarer Platinum Metals|publisher=John Wiley and Sons|location=New York|year=1976}}</ref>

=== Isotopes ===
{{Main|Isotopes of rhodium}}

Naturally occurring rhodium is composed of only one [[isotope]], <sup>103</sup>Rh. The most stable [[radioisotope]]s are <sup>101</sup>Rh with a [[half-life]] of 3.3 years, <sup>102</sup>Rh with a half-life of 207 days, <sup>102m</sup>Rh with a half-life of 2.9 years, and <sup>99</sup>Rh with a half-life of 16.1 days. Twenty other radioisotopes have been characterized with [[atomic weight]]s ranging from 92.926 [[atomic mass unit|u]] (<sup>93</sup>Rh) to 116.925 u (<sup>117</sup>Rh). Most of these have half-lives shorter than an hour, except <sup>100</sup>Rh (20.8 hours) and <sup>105</sup>Rh (35.36 hours). Rhodium has numerous [[meta state]]s, the most stable being <sup>102m</sup>Rh (0.141&nbsp;MeV) with a half-life of about 2.9 years and <sup>101m</sup>Rh (0.157&nbsp;MeV) with a half-life of 4.34 days (see [[isotopes of rhodium]]).<ref name="nubase">{{NUBASE 2003}}</ref>

In isotopes weighing less than 103 (the stable isotope), the primary [[decay mode]] is [[electron capture]] and the primary [[decay product]] is [[ruthenium]]. In isotopes greater than 103, the primary decay mode is [[beta emission]] and the primary product is [[palladium]].<ref>David R. Lide (ed.), Norman E. Holden in ''CRC Handbook of Chemistry and Physics, 85th Edition'' CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.</ref>