Skip to Main Content

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.

+ Open All
- Close All

Summary. 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] β+ to 89Ru 7/2+# N/A 716.96 -
90Rh 89.94287(54)# 15(7) ms [12(+9-4) ms] β+ to 90Ru 0+# N/A 730.63 -
91Rh 90.93655(43)# 1.74(14) s β+ to 91Ru 7/2+# N/A 744.29 -
92Rh 91.93198(43)# 4.3(13) s β+ to 92Ru (6+) N/A 757.03 -
93Rh 92.92574(43)# 11.9(7) s β+ to 93Ru 9/2+# N/A 770.7 -
94Rh 93.92170(48)# 70.6(6) s β+ to 94Ru; β+ + p to 93Tc (2+,4+) N/A 782.5 -
95Rh 94.91590(16) 5.02(10) min β+ to 95Ru (9/2)+ N/A 796.17 -
96Rh 95.914461(14) 9.90(10) min β+ to 96Ru (6+) N/A 805.18 -
97Rh 96.91134(4) 30.7(6) min β+ to 97Ru 9/2+ N/A 816.06 -
98Rh 97.910708(13) 8.72(12) min β+ 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; β- 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; β- to 104Pd 1+ N/A 882.86 -
105Rh 104.905694(4) 35.36(6) h β- to 105Pd 7/2+ 4.45 890.93 -
106Rh 105.907287(8) 29.80(8) s β- to 106Pd 1+ N/A 899.01 -
107Rh 106.906748(13) 21.7(4) min β- to 107Pd 7/2+ N/A 907.09 -
108Rh 107.90873(11) 16.8(5) s β- to 108Pd 1+ N/A 915.17 -
109Rh 108.908737(13) 80(2) s β- to 109Pd 7/2+ N/A 923.25 -
110Rh 109.91114(5) 28.5(15) s β- to 110Pd (>3)(+#) N/A 922.01 -
111Rh 110.91159(3) 11(1) s β- to 111Pd (7/2+) N/A 930.09 -
112Rh 111.91439(6) 3.45(37) s β- to 112Pd 1+ N/A 938.17 -
113Rh 112.91553(5) 2.80(12) s β- to 113Pd (7/2+) N/A 946.25 -
114Rh 113.91881(12) 1.85(5) s β- to 114Pd; β- + n to 113Pd 1+ N/A 954.33 -
115Rh 114.92033(9) 0.99(5) s β- to 115Pd (7/2+)# N/A 953.09 -
116Rh 115.92406(15) 0.68(6) s β- to 116Pd; β- + n to 115Pd 1+ N/A 961.17 -
117Rh 116.92598(54)# 0.44(4) s β- to 117Pd (7/2+)# N/A 969.25 -
118Rh 117.93007(54)# 310(30) ms β- to 118Pd (4-10)(+#) N/A 968.01 -
119Rh 118.93211(64)# 300# ms [>300 ns] β- to 119Pd 7/2+# N/A 976.09 -
120Rh 119.93641(64)# 200# ms [>300 ns] β- to 120Pd N/A N/A 984.17 -
121Rh 120.93872(97)# 100# ms [>300 ns] β- 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

  • Iwona A. Rutkowska, Margaretta D. Koster, Gary J. Blanchard, Pawel J. Kulesza, Enhancement of ethanol oxidation at Pt and PtRu nanoparticles dispersed over hybrid zirconia-rhodium supports, Journal of Power Sources, Volume 272, 25 December 2014
  • Basu D. Panthi, Stephen L. Gipson, Andreas Franken, Structural Studies of Some Rhodium(III) Acyl Complexes Containing Bidentate Phosphines, Inorganica Chimica Acta, Available online 7 October 2014
  • Elizaveta P. Shestakova, Yuri S. Varshavsky, Victor N. Khrustalev, Galina L. Starova, Sergei N. Smirnov, Rhodium(III) cationic methyl complexes containing dimethylformamide ligand, cis-[Rh(β-diket)(PPh3)2(CH3)(DMF)][BPh4] (β-diket = acetylacetonate or benzoylacetonate), in comparison with their acetonitrile analogs, Journal of Organometallic Chemistry, Available online 7 October 2014
  • Stephany García, Jannise J. Buckley, Richard L. Brutchey, Simon M. Humphrey, Effect of microwave heating on the synthesis of rhodium nanoparticles in ionic liquids, Inorganica Chimica Acta, Volume 422, 1 October 2014
  • Arnab Kumar Maity, Manish Bhattacharjee, Sujit Roy, SnCl2 insertion into Ir–Cl and Rh–Cl bonds: Synthesis, characterization and catalytic activity of three-legged piano-stool trichlorostannyl iridium and rhodium complexes, Journal of Organometallic Chemistry, Volume 768, 1 October 2014
  • Song-Il O, Jun-Min Yan, Hong-Li Wang, Zhi-Li Wang, Qing Jiang, Ni/La2O3 catalyst containing low content platinum–rhodium for the dehydrogenation of N2H4·H2O at room temperature, Journal of Power Sources, Volume 262, 15 September 2014
  • Srikanth Cheemalapati, Shen-Ming Chen, M. Ajmal Ali, Fahad M.A. Al-Hemaid, Enhanced electrocatalytic oxidation of isoniazid at electrochemically modified rhodium electrode for biological and pharmaceutical analysis, Colloids and Surfaces B: Biointerfaces, Volume 121, 1 September 2014
  • Mahesh Kalidasan, S.H. Forbes, Yurij Mozharivskyj, Mohan Rao Kollipara, Half-sandwich η6-arene ruthenium and Cp∗ rhodium/iridium compounds comprising with thioether ligands: Synthesis, spectral and molecular studies, Inorganica Chimica Acta, Volume 421, 1 September 2014
  • Hee-Chul Yang, Min-Woo Lee, Ho-Sang Hwang, Jei-Kwon Moon, Dong-Yong Chung, Study of cerium-promoted rhodium alumina catalyst as a steam reforming catalyst for treatment of spent solvents, Journal of Rare Earths, Volume 32, Issue 9, September 2014
  • Sebastian D. Pike, Indrek Pernik, Robin Theron, J. Scott McIndoe, Andrew S. Weller, Relative binding affinities of fluorobenzene ligands in cationic rhodium bisphosphine η6–fluorobenzene complexes probed using collision-induced dissociation, Journal of Organometallic Chemistry, Available online 23 August 2014