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About Rhodium

Rhodium Bohr

Platinum first came to Europe as platina, grey metallic crumbs that were unusable to metalworkers in their native form. Initially, few people could convert platina to workable platinum, and the process involved was a carefully guarded secret. The problem with early platina processing had been that the final material produced did not seem to have consistent properties--a problem solved when it was recognized that platina actually included several different metals. William Hyde Wollaston, an English chemist, was the first to isolate rhodium from platina samples, and named the element based on the rose-red color of one of its compounds.

Rhodium is a hard durable metal with a shiny silver appearance and high resistance to corrosion. It is one of the rarest metals in the Earth’s crust, a factor that along with its value for many applications ensures its extremely high cost. The majority of new rhodium produced is used to produce three-way catalytic converters, where it is more efficient than other platinum group elements at reducing nitrogen oxides. Additionally, rhodium-based catalysts are widely used in industrial processes and other organic chemistry applications.

The remaining rhodium is used as an alloying agent that improves the corrosion resistance and increases the hardness of platinum and palladium, or used ornamentally. Rhodium-containing alloys are used in spark plugs, advanced laboratory equipment, and in thermocouples. In jewelry making, extremely thin layers of the precious metal are electroplated onto white gold or platinum to give a reflective white surface, a process known as “rhodium flashing”.

Like other platinum group metals, rhodium is typically obtained for commercial use as a byproduct from nickel and copper mining and processing, but can also be obtained from ores rich in platinum and from alluvial deposits. Along with ruthenium and palladium, rhodium is a decomposition product of uranium and could theoretically be recovered from spent nuclear fuel, but the problems inherent in working with radioactive materials make this an impractical source for the rare element.

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Rhodium is alloyed with platinum and palladium in electrodes for spark plugs, advanced laboratory equipment and in thermocouples. Rhodium compounds also have catalytic uses in automotive catalytic converters. High Purity (99.999%) Rhodium Oxide (Rh2O3) PowderRhodium is used as a plating metal in jewelry production to enhance the whiteness of white gold. Rhodium is available as metal and in compound forms with purities ranging from 99% to 99.999% (ACS grade to ultra-high purity). High Purity (99.999%) Rhodium (Rh) Sputtering TargetElemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. Rhodium nanoparticles and nanopowders provide ultra-high surface area.Rhodium oxides is an insoluble rhodium source available in powder and dense pellet form for such uses as optical coating and thin film applications Rhodium fluoride is another insoluble form of for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Rhodium is also available in soluble forms including chlorides, nitrates and acetates. These compounds can be manufactured as solutions at specified stoichiometries.

Rhodium Properties

Rhodium(Rh) atomic and molecular weight, atomic number and elemental symbolRhodium is a Block D, Group 9, Period 5 element. Rhodium Bohr ModelThe number of electrons in each of Rhodium's shells is 2, 8, 18, 16, 1 and its electron configuration is [Kr] 4d8 5s1. The rhodium atom has a radius of and its Van der Waals radius is In its elemental form, CAS 7440-16-6, rhodium has a silvery white metallic appearance. Rhodium is a member of the platinum group of metals. It has a higher melting point than platinum, but a lower density. Elemental Rhodium Rhodium is found in ores mixed with other precious metals such as palladium, silver, platinum, and gold. Rhodium was first discovered by William Wollaston in 1803. The name rhodium originates from the Greek word 'Rhodon,' which means rose.

Symbol: Rh
Atomic Number: 45
Atomic Weight: 102.9055
Element Category: transition metal
Group, Period, Block: 9, 5, d
Color: silvery white metallic/ silvery-white
Other Names: Rodio, Ródio
Melting Point: 1964 °C, 3567 °F, 2237 K
Boiling Point: 3695 °C, 6683 °F, 3968 K
Density: 12.41 g·cm3
Liquid Density @ Melting Point: 10.7 g·cm3
Density @ 20°C: 12.4 g/cm3
Density of Solid: 12450 kg·m3
Specific Heat: 0.24 (kJ/kg K)
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: N/A
Heat of Fusion (kJ·mol-1): 21.55
Heat of Vaporization (kJ·mol-1): 494.34
Heat of Atomization (kJ·mol-1): 555.59
Thermal Conductivity: 150 W·m-1·K-1
Thermal Expansion: (25 °C) 8.2 µm·m-1·K-1
Electrical Resistivity: (0 °C) 43.3 nΩ·m
Tensile Strength: N/A
Molar Heat Capacity: 24.98 J·mol-1·K-1
Young's Modulus: 380 GPa
Shear Modulus: 150 GPa
Bulk Modulus: 275 GPa
Poisson Ratio: 0.26
Mohs Hardness: 6
Vickers Hardness: 1246 MPa
Brinell Hardness: 1100 MPa
Speed of Sound: (20 °C) 4700 m·s-1
Pauling Electronegativity: 2.28
Sanderson Electronegativity: N/A
Allred Rochow Electronegativity: 1.45
Mulliken-Jaffe Electronegativity: N/A
Allen Electronegativity: N/A
Pauling Electropositivity: 1.72
Reflectivity (%): 84
Refractive Index: N/A
Electrons: 45
Protons: 45
Neutrons: 58
Electron Configuration: [Kr] 4d8 5s1
Atomic Radius: 134 pm
Atomic Radius,
non-bonded (Å):
Covalent Radius: 142±7 pm
Covalent Radius (Å): 1.34
Van der Waals Radius: 200 pm
Oxidation States: 6, 5, 4, 3, 2, 1, -1 (amphoteric oxide)
Phase: Solid
Crystal Structure: face-centered cubic
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) 109.665
1st Ionization Energy: 719.68 kJ·mol-1
2nd Ionization Energy: 1744.47 kJ·mol-1
3rd Ionization Energy: 2996.86 kJ·mol-1
CAS Number: 7440-16-6
EC Number: 231-125-0
MDL Number: MFCD00011201
Beilstein Number: N/A
SMILES Identifier: [Rh]
InChI Identifier: InChI=1S/Rh
PubChem CID: 23948
ChemSpider ID: 22389
Earth - Total: 252 ppb 
Mercury - Total: 194 ppb
Venus - Total: 265 ppb
Earth - Seawater (Oceans), ppb by weight: N/A
Earth - Seawater (Oceans), ppb by atoms: N/A
Earth -  Crust (Crustal Rocks), ppb by weight: 0.7
Earth -  Crust (Crustal Rocks), ppb by atoms: 0.1
Sun - Total, ppb by weight: 2
Sun - Total, ppb by atoms: 0.02
Stream, ppb by weight: N/A
Stream, ppb by atoms: N/A
Meterorite (Carbonaceous), ppb by weight: 180
Meterorite (Carbonaceous), ppb by atoms: 40
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: 0.6
Universe, ppb by atom: 0.007
Discovered By: William Hyde Wollaston
Discovery Date: 1804
First Isolation: William Hyde Wollaston (1804)

Health, Safety & Transportation Information for Rhodium

Rhodium is not toxic in its elemental form; however, safety data for Rhodium and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental (metallic) Rhodium.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H228
Hazard Codes N/A
Risk Codes N/A
Safety Precautions N/A
RTECS Number VI9069000
Transport Information N/A
WGK Germany 3
Globally Harmonized System of
Classification and Labelling (GHS)

Rhodium Isotopes

Naturally occurring rhodium (Rh) has one stable isotope: 103Rh.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
89Rh 88.94884(48)# 10# ms [>1.5 µs] ß+ to 89Ru 7/2+# N/A 716.96 -
90Rh 89.94287(54)# 15(7) ms [12(+9-4) ms] ß+ to 90Ru 0+# N/A 730.63 -
91Rh 90.93655(43)# 1.74(14) s ß+ to 91Ru 7/2+# N/A 744.29 -
92Rh 91.93198(43)# 4.3(13) s ß+ to 92Ru (6+) N/A 757.03 -
93Rh 92.92574(43)# 11.9(7) s ß+ to 93Ru 9/2+# N/A 770.7 -
94Rh 93.92170(48)# 70.6(6) s ß+ to 94Ru; ß+ + p to 93Tc (2+,4+) N/A 782.5 -
95Rh 94.91590(16) 5.02(10) min ß+ to 95Ru (9/2)+ N/A 796.17 -
96Rh 95.914461(14) 9.90(10) min ß+ to 96Ru (6+) N/A 805.18 -
97Rh 96.91134(4) 30.7(6) min ß+ to 97Ru 9/2+ N/A 816.06 -
98Rh 97.910708(13) 8.72(12) min ß+ to 98Ru (2)+ N/A 825.07 -
99Rh 98.908132(8) 16.1(2) d EC to 99Ru 1/2- N/A 835.01 -
100Rh 99.908122(20) 20.8(1) h EC to 100Ru 1- N/A 843.09 -
101Rh 100.906164(18) 3.3(3) y EC to 101Ru; IT 1/2- N/A 858.62 -
102Rh 101.906843(5) 207.0(15) d EC to 102Ru; ß- to 102Pd (1-,2-) 4.04 866.7 -
103Rh 102.905504(3) Observationally Stable - 1/2- -0.0884 874.78 100
104Rh 103.906656(3) 42.3(4) s EC to 104Ru; ß- to 104Pd 1+ N/A 882.86 -
105Rh 104.905694(4) 35.36(6) h ß- to 105Pd 7/2+ 4.45 890.93 -
106Rh 105.907287(8) 29.80(8) s ß- to 106Pd 1+ N/A 899.01 -
107Rh 106.906748(13) 21.7(4) min ß- to 107Pd 7/2+ N/A 907.09 -
108Rh 107.90873(11) 16.8(5) s ß- to 108Pd 1+ N/A 915.17 -
109Rh 108.908737(13) 80(2) s ß- to 109Pd 7/2+ N/A 923.25 -
110Rh 109.91114(5) 28.5(15) s ß- to 110Pd (>3)(+#) N/A 922.01 -
111Rh 110.91159(3) 11(1) s ß- to 111Pd (7/2+) N/A 930.09 -
112Rh 111.91439(6) 3.45(37) s ß- to 112Pd 1+ N/A 938.17 -
113Rh 112.91553(5) 2.80(12) s ß- to 113Pd (7/2+) N/A 946.25 -
114Rh 113.91881(12) 1.85(5) s ß- to 114Pd; ß- + n to 113Pd 1+ N/A 954.33 -
115Rh 114.92033(9) 0.99(5) s ß- to 115Pd (7/2+)# N/A 953.09 -
116Rh 115.92406(15) 0.68(6) s ß- to 116Pd; ß- + n to 115Pd 1+ N/A 961.17 -
117Rh 116.92598(54)# 0.44(4) s ß- to 117Pd (7/2+)# N/A 969.25 -
118Rh 117.93007(54)# 310(30) ms ß- to 118Pd (4-10)(+#) N/A 968.01 -
119Rh 118.93211(64)# 300# ms [>300 ns] ß- to 119Pd 7/2+# N/A 976.09 -
120Rh 119.93641(64)# 200# ms [>300 ns] ß- to 120Pd N/A N/A 984.17 -
121Rh 120.93872(97)# 100# ms [>300 ns] ß- to 121Pd 7/2+# N/A 992.24 -
122Rh 121.94321(75)# 50# ms [>300 ns] Unknwon N/A N/A 991.01 -
Rhodium Elemental Symbol

Recent Research & Development for Rhodium

  • Rhodium-Catalyzed 1,4-Addition of Arylboronic Acids to 3-Benzylidene-1H-pyrrolo[2,3-b]pyridin-2(3H)-one Derivatives. Croix C, Prié G, Chaulet C, Viaud-Massuard MC. J Org Chem. 2015 Mar 2.
  • Rhodium-catalyzed dehydrogenative coupling of phenylheteroarenes with alkynes or alkenes. Iitsuka T, Hirano K, Satoh T, Miura M. J Org Chem. 2015 Mar 6
  • Rhodium Catalyzed Arylation of Diazo Compounds with Aryl Boronic Acids. Ghorai J, Anbarasan P. J Org Chem. 2015 Mar 11.
  • Rhodium-Catalyzed Asymmetric Arylation of Allyl Sulfones under the Conditions of Isomerization into Alkenyl Sulfones. Lim KM, Hayashi T. J Am Chem Soc. 2015 Mar 11
  • Rhodium-Catalyzed [(3+2)+2] Carbocyclization of Alkynylidenecyclopropanes with Substituted Allenes: Stereoselective Construction of Tri- and Tetrasubstituted Exocyclic Olefins. Evans PA, Negru DE, Shang D. Angew Chem Int Ed Engl. 2015 Feb 27.
  • Rhodium(I)-Catalyzed Asymmetric Carbene Insertion into B-H Bonds: Highly Enantioselective Access to Functionalized Organoboranes. Chen D, Zhang X, Qi WY, Xu B, Xu MH. J Am Chem Soc. 2015 Mar 4.
  • Rhodium/Chiral Diene Complexes in the Catalytic Asymmetric Arylation of β-Pyrazol-1-yl Acrylates. Gopula B, Tsai YF, Kuo TS, Wu PY, Henschke JP, Wu HL. Org Lett. 2015 Mar 6
  • Rhodium(I)-Catalyzed Regiospecific Dimerization of Aromatic Acids: Two Direct C?H Bond Activations in Water. Gong H, Zeng H, Zhou F, Li CJ. Angew Chem Int Ed Engl. 2015 Mar 12.
  • Access to Coumarins by Rhodium-Catalyzed Oxidative Annulation of Aryl Thiocarbamates with Internal Alkynes. Zhao Y, Han F, Yang L, Xia C. Org Lett. 2015 Mar 11.
  • Transfer of Chirality in the Rhodium-Catalyzed Intramolecular Formal Hetero-[5 + 2] Cycloaddition of Vinyl Aziridines and Alkynes: Stereoselective Synthesis of Fused Azepine Derivatives. Feng JJ, Lin TY, Wu HH, Zhang J. J Am Chem Soc. 2015 Mar 16.
  • Rhodium Catalyzed C2-Selective Cyanation of Indoles and Pyrroles. Chaitanya M, Anbarasan P. J Org Chem. 2015 Mar 12.
  • Pyridine versus acetonitrile coordination in rhodium-N-heterocyclic carbene square-planar complexes. Palacios L, Di Giuseppe A, Castarlenas R, Lahoz FJ, Pérez-Torrente JJ, Oro LA. Dalton Trans. 2015 Mar 10
  • Control and utilization of ruthenium and rhodium metal complex excited states for photoactivated cancer therapy. Knoll JD, Turro C. Coord Chem Rev. 2015 Jan 1
  • Rhodium(II) Metallopeptide Catalyst Design Enables Fine-Control in Selective Functionalization of Natural SH3 Domains. Vohidov F, Coughlin JM, Ball ZT. Angew Chem Int Ed Engl. 2015 Feb 16.
  • Synthesis of Dibenzo[c,e]oxepin-5(7H)-ones from Benzyl Thioethers and Carboxylic Acids: Rhodium-Catalyzed Double C?H Activation Controlled by Different Directing Groups. Zhang XS, Zhang YF, Li ZW, Luo FX, Shi ZJ. Angew Chem Int Ed Engl. 2015 Mar 10.
  • Chiral Pyrrolidines and Piperidines from Enantioselective Rhodium-Catalyzed Cascade Arylative Cyclization. Serpier F, Flamme B, Brayer JL, Folléas B, Darses S. Org Lett. 2015 Mar 12.
  • Enantioselective Synthesis of cis-Fused Cyclooctanoids via Rhodium(I)-Catalyzed [4 + 2 + 2] Cycloadditions. Lainhart BC, Alexanian EJ. Org Lett. 2015 Mar 6
  • Correction: Pyridine synthesis from oximes and alkynes via rhodium(iii) catalysis: Cp and Cpt provide complementary selectivity. Hyster TK, Rovis T. Chem Commun (Camb). 2015 Mar 9.
  • A novel rhodium-catalyzed domino-hydroformylation-reaction for the synthesis of sulphonamides. Dong K, Fang X, Jackstell R, Beller M. Chem Commun (Camb). 2015 Mar 10
  • Rhodium-Catalyzed Cyclopropanation of Fluorinated Olefins: A Straightforward Route to Highly Functionalized Fluorocyclopropanes. Pons A, Beucher H, Ivashkin P, Lemonnier G, Poisson T, Charette AB, Jubault P, Pannecoucke X. Org Lett. 2015 Mar 13.