Rhodium Element Properties
Complete reference for Rhodium (Rh, element 45): atomic data, electron configuration, isotopes, physical constants, and unit converter.
Rhodium
Transition Metal (Platinum Group) — Period 5, Group 9
Atomic Identity
Periodic Table Locator — Period 5 Neighborhood (d-block)
Rhodium (Z=45) sits between ruthenium (Z=44) and palladium (Z=46) in Period 5. It is directly below cobalt (Z=27) and above iridium (Z=77) in Group 9. All six platinum group metals occupy the central d-block of Periods 5 and 6.
Electron Configuration
2 unpaired d electrons — anomalous 5s¹ configuration
Key Isotopes of Rhodium
| Isotope | Symbol | Protons | Neutrons | Mass (u) | Natural Abundance | Stability |
|---|---|---|---|---|---|---|
| Rhodium-103 | ¹⁰³Rh | 45 | 58 | 102.905504 | 100% | Stable |
| Rhodium-101 | ¹⁰¹Rh | 45 | 56 | 100.906164 | Radioactive |
Unstable
EC, t½ = 3.3 yr |
| Rhodium-102 | ¹⁰²Rh | 45 | 57 | 101.906843 | Radioactive |
Unstable
EC + β⁺/β⁻, t½ = 207 d |
| Rhodium-104 | ¹⁰⁴Rh | 45 | 59 | 103.906655 | Radioactive |
Unstable
β⁻ decay, t½ = 42.3 s |
| Rhodium-105 | ¹⁰⁵Rh | 45 | 60 | 104.905695 | Radioactive |
Unstable
β⁻ decay, t½ = 35.4 h |
| Rhodium-99 | ⁹⁹Rh | 45 | 54 | 98.908132 | Radioactive |
Unstable
EC + β⁺, t½ = 16.1 d |
| Rhodium-106 | ¹⁰⁶Rh | 45 | 61 | 105.907285 | Radioactive |
Unstable
β⁻ decay, t½ = 29.8 s |
Rhodium-103 is the only stable isotope, making rhodium a monoisotopic element — all natural rhodium has atomic mass 102.905504 u. Rh-105 is a fission product and used in targeted radionuclide therapy research. The long-lived Rh-101 is produced in nuclear reactors.
Physical Properties
Chemical Properties
Ground State Quantum Numbers
Notable Emission Lines
Rhodium produces characteristic emission lines used in inductively coupled plasma (ICP) spectroscopy for trace analysis. The 343.49 nm line is frequently chosen as the primary analytical wavelength due to minimal spectral interference. Flame tests show a faint blue-green color distinct from other PGMs.
Property Unit Converter
Convert common Rhodium property values between units. Enter a value and select the conversion.
Common Rhodium Compounds
| Compound | Formula | Common Name | Key Uses |
|---|---|---|---|
| Rhodium(III) chloride | RhCl₃ | Rhodium trichloride | Precursor for rhodium catalysts, electroplating solution, synthesis of Wilkinson's catalyst |
| Rhodium(III) oxide | Rh₂O₃ | Rhodia | Catalyst support, thin-film electrodes, substrate for ceramic coatings |
| Rhodium sulfate | Rh₂(SO₄)₃ | Rhodium sulfate | Electroplating bath for decorative and technical rhodium coatings on jewelry and optical components |
| Wilkinson's catalyst | RhCl(PPh₃)₃ | Chlorotris(triphenylphosphine)rhodium(I) | Landmark homogeneous catalyst for alkene hydrogenation, isomerization, hydroformylation |
| Rhodium nitrate | Rh(NO₃)₃ | Rhodium(III) nitrate | Preparation of rhodium oxide catalysts; used in three-way catalytic converter manufacturing |
| Rhodium carbonyl | Rh₄(CO)₁₂ | Tetrarhodium dodecacarbonyl | Hydroformylation catalyst (oxo process), carbonylation reactions, organometallic synthesis |
| Cisplatin analog (Rh) | [Rh(en)₂Cl₂]⁺ | Rhodium(III) ethylenediamine | Research into antitumor activity; model complex for bioinorganic chemistry studies |
| Rhodium acetate | Rh₂(OAc)₄ | Dirhodium tetraacetate | Carbene and nitrene insertion catalyst; cyclopropanation reactions in synthetic organic chemistry |
Key Facts About Rhodium
Catalytic Converter Champion
Rhodium is the critical component in three-way automotive catalytic converters responsible for reducing nitrogen oxides (NOx) into harmless nitrogen and oxygen. No other metal approaches its performance for this reaction under real-world exhaust conditions. Approximately 80% of global rhodium demand comes from this single application, making automotive production cycles the primary driver of rhodium price volatility.
Rarest and Most Expensive PGM
Rhodium is produced at roughly 30 tonnes per year worldwide, mostly as a byproduct of platinum and nickel mining in South Africa. This extreme scarcity means its price can exceed that of gold by a factor of 10 or more. In 2021, rhodium reached a historic high above $29,000 per troy ounce. Its price swing between $640 (2016) and $29,000 (2021) represents the highest percentage price range of any precious metal.
Wilkinson's Catalyst — Nobel Prize Chemistry
The discovery of chlorotris(triphenylphosphine)rhodium(I) — Wilkinson's catalyst — by Geoffrey Wilkinson and his team in 1965 transformed synthetic chemistry. It enabled selective, mild hydrogenation of alkenes without affecting other functional groups, and earned Wilkinson the 1973 Nobel Prize in Chemistry (shared with Ernst Otto Fischer). It remains a cornerstone of industrial and academic organic synthesis.
Named for Rose-Colored Salts
When William Hyde Wollaston dissolved platinum ore residue in aqua regia in 1803 and added sodium chloride, a distinctive rose-red precipitate formed — sodium chlororhodate. He named the new element after the Greek word "rhodon" (rose). This rose color from dilute rhodium(III) salts in acidic solution contrasts sharply with the bright silver luster of the bulk metal.
Exceptional Reflectivity
Rhodium has one of the highest reflectivities of any metal (~80% in visible light) and surpasses silver and aluminum in the ultraviolet range. Combined with its resistance to tarnish and oxidation, this makes rhodium the preferred electroplating material for optical reflectors, scientific instruments, searchlights, and jewelry. A thin rhodium layer only a few microns thick protects silver jewelry from tarnishing indefinitely.
Monoisotopic Element
Natural rhodium consists entirely of one stable isotope: Rh-103. This makes rhodium a monoisotopic element — every atom of natural rhodium has the same mass. Only about 20 elements are monoisotopic. This property makes rhodium uniquely useful as an internal standard in mass spectrometry and as a neutron flux monitor in nuclear reactors, where Rh-103 captures a neutron to form the short-lived Rh-104.
Summary
Complete reference for Rhodium (Rh, element 45): atomic data, electron configuration, isotopes, physical constants, and unit converter.
How it works
- Browse the atomic identity section for symbol, atomic number, and standard atomic weight.
- Check the electron configuration panel for orbital notation and quantum numbers.
- Review the isotopes table for stable and notable radioactive isotopes with natural abundances.
- Consult the physical and chemical properties panels for melting point, density, ionization energies, and more.
- Use the interactive unit converter to convert rhodium property values between common units.
- Explore the mini periodic table locator to visualize where rhodium sits among neighboring elements.
Use cases
- Look up rhodium constants for chemistry homework or exams.
- Verify atomic data when writing lab reports or research papers.
- Reference isotope data for nuclear chemistry or radiochemistry studies.
- Convert melting and boiling points between Celsius, Fahrenheit, and Kelvin.
- Teach or learn platinum group metal properties using rhodium as an example.
- Confirm electron configuration before writing molecular orbital diagrams.
- Research rhodium compounds for catalysis, automotive, or materials science work.
- Quick-reference ionization energies for electrochemistry or spectroscopy calculations.