Rhodium (Rh)


Rhodium is a chemical element with the atomic number 45 in the periodic table. It’s an extremely rare metal that is found in Earth’s crust with an abundance of 0.0002 parts per million. 

Being a member of the platinum group of periodic table elements, this noble metal has three valence electrons and is highly appreciated for its corrosion and oxidation resistance, bright lustrous shine, as well as for its durability as a material. 

Fact Box

Chemical and Physical Properties of Rhodium

The symbol in the periodic table of elements: Rh

Atomic number: 45

Atomic weight (mass): 102.91g.mol-1

Group number: 9 (Platinum group)

Period: 5 (d-block)

Color: A precious silver-white metal

Physical state: Solid at room temperature

Half-life: From 10 milliseconds [>1.5 μs] to 3.742(10) years

Electronegativity according to Pauling: 2.2

Density: 12.4 g.cm-3 at 20°C

Melting point: 1963°C, 3565°F, 2236 K

Boiling point: 3695°C, 6683°F, 3968 K

Van der Waals radius: Unknown

Ionic radius: 75 (3+) pm

Isotopes: 33

Most characteristic isotope: rhodium-103

Electronic shell:  [Kr] 4d8 5s1

The energy of the first ionization: 742 kJ.mol-1

The energy of the second ionization: N/A

Discovery date: In 1803 by William Wollaston

With the periodic table symbol Rh, atomic number 45, atomic mass of 102.91g.mol-1, and electron configuration [Kr] 4d8 5s1, rhodium is a hard, silvery-white precious metal that does not tarnish upon exposure to air. 

It reaches its boiling point at 3695°C, 6683°F, 3968 K, while the melting point is achieved at 1963°C, 3565°F, 2236 K. This member of the platinum family of elements in the periodic table has an electronegativity of 2.2 according to Pauling, whereas the atomic radius according to van der Waals is unknown. 

Classified as a transition metal, rhodium has strong anti-corrosive properties and has the capacity to resist extremely high temperatures. It’s also characterized by a lower density and a higher melting point than platinum.                         

How Was Rhodium Discovered?

Element 45 was discovered in 1804 by the English chemist and physicist William Hyde Wollaston (1766 – 1828). After the French chemist Hippolyte-Victor Collet-Descotils expressed his belief that a sample of platinum ore obtained from South Africa could possibly contain a new metal, he supported his claim by pointing to the presence of the red color of some platinum salts.

This triggered Wollason’s scientific curiosity, so he took a closer look at the platinum sample. First, the English chemist dissolved crude platinum in aqua regia, after which he precipitated platinum metal by dissolving the solution in ammonium chloride. 

The remaining liquid substance was furthermore included in several other chemical reactions, after which Wollaston succeeded in producing a deep red powder, i.e sodium rhodium chloride. In the last step of this series of chemical reactions, the rhodium precipitate was treated with zinc. Finally, the presence of the new element 45 in the platinum ore was evident and confirmed. 

How Did Rhodium Get Its Name?

The name of this chemical element comes from the Greek word ‘rhodon‘, meaning ‘rose colored’. This refers to the characteristic rose-red color of the rhodium salts. 

Where Can You Find Rhodium?

As a member of the platinum group, rhodium mostly occurs in the same mineral ores as the other platinum metals, such as platinum, palladium, nickel, silver, and gold. It can be isolated from the minerals bowieite, rhodite, and rhodplumsite, in which rhodium occurs as a part of a compound. 

Primary rhodium mines are rarely found. Thus, this rare metal is typically obtained as a by-product of platinum and palladium mining or nickel mining. It can also be traced in the native alloys of iridium (at least 11.25 percent) and osmium in iridosmine (at least 4.5 percent in siserskite). 

For commercial purposes, element 45 is mostly isolated as a by-product of the extraction of nickel and copper from their ores. South Africa, South America, Canada, and Russia, are the world’s leading rhodium producers. The price of rhodium is typically high, but also highly variable on the precious metals market. 

Rhodium in Everyday Life

Rhodium is a noble metal praised for its superb anti-corrosive properties, as well as for its thermal and oxidation resistance. The practical uses of this rare chemical with a high price can be observed in the following instances:

  • Car industries use rhodium with internal combustion engines fueled by either gasoline or diesel for reduction of the toxic exhaust gases; 
  • Allows made with rhodium are used in the manufacturing of high-temperature thermocouple and resistance wires, pen nibs, phonograph needles, electrodes for aircraft spark plugs, bearings, and electrical contacts;
  • Rhodium is commonly electroplated onto metal objects; when it’s polished, it gives high shine to jewelry. Similarly, rhodium metal is used metal for creating reflecting surfaces for optical instruments;
  • When added to platinum, rhodium adds both hardness and lightness to the alloys which are further used in the production of laboratory furnace crucibles, as well as catalysts in very hot chemical environments (including automobile catalytic converters), thermocouple elements, and headlight reflectors. Rhodium’s presence in cars supports the transformation of harmful unburned hydrocarbons, carbon monoxide, and nitrogen oxide exhaust emissions into less noxious gases;
  • The chemical industry also uses this noble metal in the production of nitric acid, acetic acid, and hydrogenation reactions;
  • The rhodium-platinum alloy is used in the production of heart pacemakers; 
  • Rhodium plating of white gold gives the shiny silvery-white finish to the jewelry;
  • Rhodium’s resistance to tarnishing and its bright shine are employed in the making of searchlights and mirrors.

How Dangerous Is Rhodium?

The rhodium salts are extremely toxic substances, while rhodium is suspected to be a carcinogen element. On the other hand, rhodium metal is a confirmed hypoallergenic, which makes it suitable to be used as a protective coating of white gold jewelry with some allergy-triggering nickel in it.

Environmental Effects of Rhodium

Since rhodium is one of the rarest elements found in the earth’s crust, the environmental effects of this chemical cannot be considered. However, the improper waste disposal of the industries that include rhodium in their production could potentially pollute the environment.  

Isotopes of Rhodium

There are 33 isotopes of rhodium observed, with atomic mass ranging from rhodium-89 to rhodium-122. Naturally occurring rhodium consists of only one stable isotope – 103Rh. The primary decay mode before this stable form of element 45 is electron capture, while the primary decay mode after it is beta emission.


[n 1]

Z N Isotopic mass (Da)

[n 2][n 3]


[n 4]



[n 5]



[n 6]

Spin and


[n 7][n 4]

Natural abundance (mole fraction)
Excitation energy[n 4] Normal proportion Range of variation
89Rh 45 44 88.94884(48)# 10# ms

[>1.5 μs]

β+ 89Ru 7/2+#
90Rh 45 45 89.94287(54)# 15(7) ms

[12(+9−4) ms]

β+ 90Ru 0+#
91Rh 45 46 90.93655(43)# 1.74(14) s β+ 91Ru 7/2+#
92Rh 45 47 91.93198(43)# 4.3(13) s β+ 92Ru (6+)
93Rh 45 48 92.92574(43)# 11.9(7) s β+ 93Ru 9/2+#
94Rh 45 49 93.92170(48)# 70.6(6) s β+ (98.2%) 94Ru (2+, 4+)
β+, p (1.79%) 93Tc
95Rh 45 50 94.91590(16) 5.02(10) min β+ 95Ru (9/2)+
96Rh 45 51 95.914461(14) 9.90(10) min β+ 96Ru (6+)
97Rh 45 52 96.91134(4) 30.7(6) min β+ 97Ru 9/2+
98Rh 45 53 97.910708(13) 8.72(12) min β+ 98Ru (2)+
99Rh 45 54 98.908132(8) 16.1(2) d β+ 99Ru 1/2−
100Rh 45 55 99.908122(20) 20.8(1) h β+ 100Ru 1−
101Rh 45 56 100.906164(18) 3.3(3) y EC 101Ru 1/2−
102Rh 45 57 101.906843(5) 207.0(15) d β+ (80%) 102Ru (1−, 2−)
β (20%) 102Pd
103Rh[n 8] 45 58 102.905504(3) Stable 1/2− 1.0000
104Rh 45 59 103.906656(3) 42.3(4) s β (99.55%) 104Pd 1+
β+ (.449%) 104Ru
105Rh[n 8] 45 60 104.905694(4) 35.36(6) h β 105Pd 7/2+
106Rh 45 61 105.907287(8) 29.80(8) s β 106Pd 1+
107Rh 45 62 106.906748(13) 21.7(4) min β 107Pd 7/2+
108Rh 45 63 107.90873(11) 16.8(5) s β 108Pd 1+
109Rh 45 64 108.908737(13) 80(2) s β 109Pd 7/2+
110Rh 45 65 109.91114(5) 28.5(15) s β 110Pd (>3)(+#)
111Rh 45 66 110.91159(3) 11(1) s β 111Pd (7/2+)
112Rh 45 67 111.91439(6) 3.45(37) s β 112Pd 1+
113Rh 45 68 112.91553(5) 2.80(12) s β 113Pd (7/2+)
114Rh 45 69 113.91881(12) 1.85(5) s β (>99.9%) 114Pd 1+
β, n (<.1%) 113Pd
115Rh 45 70 114.92033(9) 0.99(5) s β 115Pd (7/2+)#
116Rh 45 71 115.92406(15) 0.68(6) s β (>99.9%) 116Pd 1+
β, n (<.1%) 115Pd
117Rh 45 72 116.92598(54)# 0.44(4) s β 117Pd (7/2+)#
118Rh 45 73 117.93007(54)# 310(30) ms β 118Pd (4−10)(+#)
119Rh 45 74 118.93211(64)# 300# ms

[>300 ns]

β 119Pd 7/2+#
120Rh 45 75 119.93641(64)# 200# ms

[>300 ns]

β 120Pd
121Rh 45 76 120.93872(97)# 100# ms

[>300 ns]

β 121Pd 7/2+#
122Rh 45 77 121.94321(75)# 50# ms

[>300 ns]

Source: Wikipedia

List of Rhodium Compounds

In compounds, rhodium mostly adopts the +1 and +3 oxidation states. It’s not affected by acids – rhodium cannot be dissolved by hot concentrated nitric or hydrochloric acids, or even by aqua regia. Rhodium does not react with oxygen either, which makes this chemical resistant to tarnishing in the air.

The list of most commonly prepared  rhodium compounds includes:


  • Dichlorotetrakis(pyridine)rhodium(III) chloride
  • Hydridotetrakis(triphenylphosphine)rhodium(I)
  • Pentaamminechlororhodium dichloride
  • Rhodium acetylacetonate
  • Rhodium hexafluoride
  • Rhodium pentafluoride
  • Rhodium trifluoride
  • Rhodium-platinum oxide
  • Rhodium(II) acetate
  • Rhodium(III) bromide
  • Rhodium(III) chloride
  • Rhodium(III) iodide
  • Rhodium(III) nitrate
  • Rhodium(III) oxide
  • Rhodium(III) perchlorate
  • Rhodium(III) sulfate
  • Rhodium(III) sulfide
  • Rhodium(IV) fluoride
  • Rhodium(IV) oxide
  • Tris(triphenylphosphine)rhodium carbonyl hydride
  • Uranium rhodium germanium
  • Wilkinson’s catalyst
  • Xenon hexafluororhodate
  • Ytterbium dirhodium disilicide

5 Interesting Facts and Explanations

  1. William Wollaston discovered not one, but two new elements in the same year – the chemicals rhodium and palladium.
  2. In 1976, Volvo introduced rhodium as a catalytic converter in the automobile fuel industry. Since then, this chemical element is widely used as an agent that reduces toxic gases and pollutants in exhaust fumes. 
  3. The platinum group metals (PGM) incorporate the elements platinum, palladium, rhodium, osmium, iridium, and ruthenium.
  4. Platinum-group elements are referred to as precious metals, because of their stable electron configuration and strong corrosion and oxidation resistance. They are also very durable and resistant materials, which makes them even more valuable.
  5. Rhodium is considered one of the rarest substances that have ever been detected on our planet. 

Chemical Property and physical property of element Rhodium

Symbol of Rhodium: Rh
Name: Rhodium
Atomic Number of Rhodium: 45
Atomic Mass of Rhodium: 102.9055
Uses of Rhodium: Used as a coating to prevent wear on high quality science equipment and with platinum to make thermocouples.
Description of Rhodium: Soft, malleable, ductile, silvery-white metal.
Melting Point of Rhodium:
Boiling Point of Rhodium:
Group of Rhodium: Transition Metal
Shells of Rhodium: 2,8,18,16,1
Orbitals of Rhodium: [Kr] 4d8 5s1
Valence of Rhodium: 2,3,4,5,6
Crystal Structure of Rhodium: Cubic: Face centered
Electro Negativity of Rhodium: 2.28
Covalent Radius of Rhodium: 1.25 Å
Ionic Radius of Rhodium: .67 (+3) Å
Atomic Radius of Rhodium: 1.83 Å
Atomic Volume of Rhodium: 08.3 cm³/mol
Name Origin of Rhodium: Greek: rhodon (rose). Its salts give a rosy solution.
Discovered of Rhodium By: William Wollaston
Year: 1803
Location: England
Pronounced of Rhodium: RO-di-em
Oxydation States of Rhodium: 2,(3),4
Density of Rhodium: 12.4 g/cm³